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During the 1920s and 1930s, the British surgeon Geoffrey Keynes (1887-1982) treated breast cancer with radium instead of the hegemonic radical mastectomy, while vehemently attacking the "radicalists" for mutilating women. Keynes was also a leading bibliographer of literary figures from Sir Thomas Browne to William Blake through Jane Austen. This article argues that these endeavors did not inhabit separate worlds, but rather his bibliographic methods of collecting and sorting were deeply interwoven with his therapeutic practices and medical ways of knowing. The article also examines the profound influence his engagement with the works of William Blake had on his battle against the reigning medical orthodoxy and on the humanity of his relationship with his patients. It concludes that Keynes' story sheds light on a now distant medico-cultural world where literary studies, often centered on book collecting and critique, were not only highly valued, but were influential in guiding the vision and behavior of a number of physicians.

This study demonstrates the feasibility of using a novel 2D spectrum ultrasonic tissue characterization (UTC) technique for prostate-cancer diagnosis. Normalized 2D spectra are computed by performing Fourier transforms along the range (beam) and the cross-range directions of the digital radio-frequency echo data, then dividing by a reference spectrum. This 2D spectrum method provides axial and lateral information of tissue microstructures, an improvement over the current 1D spectrum analysis which only provides axial information. A pilot study was conducted on four prostate-cancer patients who underwent radical prostatectomies. Cancerous and noncancerous regions of interest, identified through histology, were compared using four 2D spectral parameters: peak value and 3 dB width of the radially integrated spectral power (RISP), slope and intercept of the angularly integrated spectral power (AISP). For noncancerous and cancerous prostatic tissues, respectively, our investigation yielded 23 +/- 1 and 26 +/- 1 dB for peak value of RISP, 7.8 +/- 0.5 degrees and 7.6 +/- 0.6 degrees for 3 dB of RISP, -2.1 +/- 0.2 and -2.7 +/- 0.4 dB/MHz for slope of AISP, and 92 +/- 5 and 112 +/- 6 dB for intercept of AISP. Preliminary results indicated that 2D spectral UTC has the potential for identifying tumor-bearing regions within the prostate gland.

The goal of this study was to implement and validate a noninvasive, quantitative ultrasonic technique for accurate and reproducible measurement of normal-tissue toxicity in radiation therapy. The authors adapted an existing ultrasonic tissue characterization (UTC) technique that used a calibrated 1D spectrum based on region-of-interest analysis. They modified the calibration procedure by using a reference phantom instead of a planar reflector. This UTC method utilized ultrasonic radio-frequency echo signals to generate spectral parameters related to the physical properties (e.g., size, shape, and relative acoustic impedance) of tissue microstructures. Three spectral parameters were investigated for quantification of normal-tissue injury: Spectral slope, intercept, and midband fit. They conducted a tissue-mimicking phantom study to verify the reproducibility of UTC measurements and initiated a clinical study of radiation-induced breast-tissue toxicity. Spectral parameter values from measurements on two phantoms were reproducible within 1% of each other. Eleven postradiation breast-cancer patients were studied and significant differences between the irradiated and untreated (contralateral) breasts were observed for spectral intercept (p=0.003) and midband fit (p

Purpose To integrate imaging performance characteristics, specifically sensitivity and specificity, of magnetic resonance angiography (MRA) and digital subtraction angiography (DSA) into arteriovenous malformation (AVM) radiosurgery planning and evaluation. Methods and Materials Images of 10 patients with AVMs located in critical brain areas were analyzed in this retrospective planning study. The image findings were first used to estimate the sensitivity and specificity of MRA and DSA. Instead of accepting the imaging observation as a binary (yes or no) mapping of AVM location, our alternative is to translate the image into an AVM probability distribution map by incorporating imagers' sensitivity and specificity, and to use this map as a basis for planning and evaluation. Three sets of radiosurgery plans, targeting the MRA and DSA positive overlap, MRA positive, and DSA positive were optimized for best conformality. The AVM obliteration rate (ORAVM) and brain complication rate served as endpoints for plan comparison. Results In our 10-patient study, the specificities and sensitivities of MRA and DSA were estimated to be (0.95, 0.74) and (0.71, 0.95), respectively. The positive overlap of MRA and DSA accounted for 67.8% ± 4.9% of the estimated true AVM volume. Compared with plans targeting MRA and DSA–positive overlap, plans targeting MRA-positive or DSA-positive improved ORAVM by 4.1% ± 1.9% and 15.7% ± 8.3%, while also increasing the complication rate by 1.0% ± 0.8% and 4.4% ± 2.3%, respectively. Conclusions The impact of imagers' quality should be quantified and incorporated in AVM radiosurgery planning and evaluation to facilitate clinical decision making.

A theoretical model is described for application in ultrasonic tissue characterization using a calibrated 2-D spectrum analysis method. This model relates 2-D spectra computed from ultrasonic backscatter signals to intrinsic physical properties of tissue microstructures, e.g., size, shape, and acoustic impedance. The model is applicable to most clinical diagnostic ultrasound systems. Two experiments employing two types of tissue architectures, spherical and cylindrical scatterers, are conducted using ultrasound with center frequencies of 10 and 40 MHz, respectively. Measurements of a tissue-mimicking phantom with an internal suspension of microscopic glass beads are used to validate the theoretical model. Results from in vitro muscle fibers are presented to further elucidate the utility of 2-D spectrum analysis in ultrasonic tissue characterization.

Purpose: To investigate how the performance characteristics of ultrasound tissue typing (UTT) affect the design of a population-based prostate dose-painting protocol. Methods and Materials: The performance of UTT is evaluated using the receiver operating characteristic curve. As the imager's sensitivity increases, more tumors are detected, but the specificity worsens, causing more false-positive results. The UTT tumor map, obtained with a specific sensitivity and specificity setup, was used with the patient's CT image to guide intensity-modulated radiotherapy (IMRT) planning. The optimal escalation dose to the UTT positive region, as well as the safe dose to the negative background, was obtained by maximizing the uncomplicated control ( i.e. , a combination of tumor control probability and weighted normal tissue complication probability). For high- and low-risk tumors, IMRT plans guided by conventional ultrasound or UTT with a one-dimensional or two-dimensional spectrum analysis technique were compared with an IMRT plan in which the whole prostate was dose escalated. Results: For all imaging modalities, the specificity of 0.9 was chosen to reduce complications resulting from high false-positive results. If the primary tumors were low risk, the IMRT plans guided by all imaging modalities achieved high tumor control probability and reduced the normal tissue complication probability significantly compared with the plan with whole gland dose escalation. However, if the primary tumors were high risk, the accuracy of the imaging modality was critical to maintain the tumor control probability and normal tissue complication probability at acceptable levels. Conclusion: The performance characteristics of an imager have important implications in dose painting and should be considered in the design of dose-painting protocols.

To effectively deliver radiation dose to lung tumors, respiratory motion has to be considered in treatment planning. In this paper we first present a new lung IMRT planning algorithm, referred as the dose shaping (DS) method, that shapes the dose distribution according to the probability distribution of the tumor over the breathing cycle to account for respiratory motion. In IMRT planning a dose-based convolution method was generally adopted to compensate for random organ motion by performing 4-D dose calculations using a tumor motion probability density function. We modified the CON-DOSE method to a dose volume histogram based convolution method (CON-DVH) that allows nonuniform dose distribution to account for respiratory motion. We implemented the two new planning algorithms on an in-house IMRT planning system that uses the Eclipse (Varian, Palo Alto, CA) planning workstation as the dose calculation engine. The new algorithms were compared with (1) the conventional margin extension approach in which margin is generated based on the extreme positions of the tumor, (2) the dose-based convolution method, and (3) gating with 3 mm residual motion. Dose volume histogram, tumor control probability, normal tissue complication probability, and mean lung dose were calculated and used to evaluate the relative performance of these approaches at the end-exhale phase of the respiratory cycle. We recruited six patients in our treatment planning study. The study demonstrated that the two new methods could significantly reduce the ipsilateral normal lung dose and outperformed the margin extension method and the dose-based convolution method. Compared with the gated approach that has the best performance in the low dose region, the two methods we proposed have similar potential to escalate tumor dose, but could be more efficient because dose is delivered continuously.

Studies suggest that clinical outcomes are improved in repeat trigeminal neuralgia (TN) Gamma Knife radiosurgery if a different part of the nerve from the previous radiosurgery is treated. The MR images taken in the first and repeat radiosurgery need to be coregistered to map the first radiosurgery volume onto the second treatment planning image. We propose a fully automatic and robust three-dimensional (3-D) mutual information- (MI-) based registration method engineered by a simulated annealing (SA) optimization technique. Commonly, Powell's method and Downhill simplex (DS) method are most popular in optimizing the MI objective function in medical image registration applications. However, due to the nonconvex property of the MI function, robustness of those two methods is questionable, especially for our cases, where only 28 slices of MR T1 images were utilized. Our SA method obtained successful registration results for all the 41 patients recruited in this study. On the other hand, Powell's method and the DS method failed to provide satisfactory registration for 11 patients and 9 patients, respectively. The overlapping volume ratio (OVR) is defined to quantify the degree of the partial volume overlap between the first and second MR scan. Statistical results from a logistic regression procedure demonstrated thatmore » the probability of a success of Powell's method tends to decrease as OVR decreases. The rigid registration with Powell's or the DS method is not suitable for the TN radiosurgery application, where OVR is likely to be low. In summary, our experimental results demonstrated that the MI-based registration method with the SA optimization technique is a robust and reliable option when the number of slices in the imaging study is limited.« less

We are investigating the utility of a new ultrasonic tissue characterization technique, specifically two-dimensional (2-D) spectrum analysis of radio-frequency backscatter signals, which promises to provide quantitative measures of the physical properties of tissue microstructures. Previously successful 1-D spectrum analysis is expanded to 2-D to more fully characterize diagnostically significant features of biological tissue. Two new spectral functions, radially integrated spectral power (RISP) and angularly integrated spectral power (AISP), are defined to quantitatively characterize tissue properties. This new approach is applied to the diagnosis of in vivo ocular melanomas. Our initial results indicate that 2-D spectrum analysis can provide significant new information on tissue anisotropy that are not apparent in 1-D spectra. Acoustic scattering models are applied to relate the 2-D spectral parameters to the physical properties (e.g., size and shape) of biological tissues.

Background and purpose : To assess the effect of internal organ motion on the dose distributions and biological indices for the target and non-target organs for three different conformal prostate treatment techniques. Materials and methods : We examined three types of treatment plans in 20 patients: (1) a six field plan, with a prescribed dose of 75.6 Gy; (2) the same six field plan to 72 Gy followed by a boost to 81 Gy; and (3) a five field plan with intensity modulated beams delivering 81 Gy. Treatment plans were designed using an initial CT data set (planning) and applied to three subsequent CT scans (treatment). The treatment CT contours were used to represent patient specific organ displacement; in addition, the dose distribution was convolved with a Gaussian distribution to model random setup error. Dose–volume histograms were calculated using an organ deformation model in which the movement between scans of individual points interior to the organs was tracked and the dose accumulated. The tumor control probability (TCP) for the prostate and proximal half of seminal vesicles (clinical target volume, CTV), normal tissue complication probability (NTCP) for the rectum and the percent volume of bladder wall receiving at least 75 Gy were calculated. Results : The patient averaged increase in the planned TCP between plan types 2 and 1 and types 3 and 1 was 9.8% (range 4.9–12.5%) for both, whereas the corresponding increases in treatment TCP were 9.0% (1.3–16%) and 8.1% (−1.3–13.8%). In all patients, plans 2 and 3 (81 Gy) exhibited equal or higher treatment TCP than plan 1 (75.6 Gy). The maximum treatment NTCP for rectum never exceeded the planning constraint and percent volume of bladder wall receiving at least 75 Gy was similar in the planning and treatment scans for all three plans. Conclusion : For plans that deliver a uniform prescribed dose to the planning target volume (PTV) (plan 1), current margins are adequate. In plans that further escalate the dose to part of the PTV (plans 2 and 3), in a fraction of the cases the CTV dose increase is less than planned, yet in all cases the TCP values are higher relative to the uniform dose PTV (plan 1). Doses to critical organs remain within the planning criteria.

Purpose and Objective: Late rectal bleeding is a potentially dose limiting complication of three-dimensional conformal radiotherapy (3D-CRT) for prostate cancer. The frequency of late rectal bleeding has been shown to increase as the prescription dose rises above 70 Gy. The purpose of this study is to identify features of the cumulative dose–volume histogram (DVH) for the rectal wall that correlate with late rectal bleeding after 3D-CRT for prostate cancer. Methods and Materials: Follow-up information on rectal bleeding is available for 261 and 315 patients treated using 3D-CRT at Memorial Sloan-Kettering Cancer Center for Stage T1c-T3 prostate cancer with minimum target doses of 70.2 and 75.6 Gy, respectively. All patients in this study were treated with a coplanar 6-field technique (2 lateral and 4 oblique fields). Patients were classified as having rectal bleeding if they bled (≥ Grade 2) before 30 months, and nonbleeding (⩽ Grade 1) if they were without bleeding at 30 months, using the RTOG morbidity scale. Rectal bleeding was observed in 13 and 38 of the patients treated at 70.2 and 75.6 Gy, respectively. Treatment plans were analyzed for 39 nonbleeding and 13 bleeding patients receiving 70.2 Gy, and 83 nonbleeding and 36 bleeding patients receiving 75.6 Gy. Dose–volume histograms (DVHs) for the anatomic rectal wall were calculated. Average DVHs of the bleeding and nonbleeding patients were generated, and a permutation test was used to assess the significance of differences between them, for each dose group. The confounding effect of total rectal wall volume (VRW) was removed by calculating the average differences in DVHs between all combinations of bleeding and nonbleeding patients with similar VRWs. Finally, multivariate analysis using logistic regression was performed to test the significance of the DVH variables in the presence of anatomic, geometric, and medical variables previously found to correlate with rectal bleeding in a companion analysis of the same patients. Results: The area under the average percent volume DVH for the rectal wall of patients with bleeding was significantly higher than those of patients without bleeding in both dose groups (p = 0.02, 70.2 Gy; p < 0.0001, 75.6 Gy). However, small VRWs were associated with rectal bleeding (p = 0.06, 70.2 Gy; p < 0.01, 75.6 Gy), resulting in an increase in average percent volumes exposed to all doses for patients with rectal bleeding. For patients with similar VRWs, rectal bleeding was significantly correlated with the volumes exposed to 46 Gy in both dose groups (p = 0.02, 70.2 Gy; p = 0.005, 75.6 Gy, tolerance in VRW: 5 ccs). For the 75.6 Gy dose group, the percent volume receiving 77 Gy was significantly correlated with rectal bleeding (p < 0.005). Bivariate analysis using logistic regression, including VRW together with a single DVH variable, showed good agreement with the above analysis. Multivariate analysis revealed a borderline significant correlation of the percent volume receiving 71 Gy in the 70.2 Gy dose group. It also showed that the DVH variables were highly correlated with geometric and dosimetric variables previously found to correlate with rectal bleeding in multivariate analysis. Conclusion: Significant volume effects were found in the probability of late rectal bleeding for patients undergoing 3D-CRT for prostate cancer with prescription doses of 70.2 and 75.6 Gy. The percent volumes exposed to 71 and 77 Gy in the 70.2 and 75.6 Gy dose groups respectively were significantly correlated with rectal bleeding. The independent correlation of small VRW with rectal bleeding may indicate the existence of a functional reserve for the rectum. The independent association with larger percent volumes exposed to intermediate doses (∼ 46 Gy) seen in both dose groups may indicate that a large surrounding region of intermediate dose may interfere with the ability to repair the effects of a central high dose region.

Salivary gland scintigraphy (SGS) is used to depict salivary gland dysfunction after radiotherapy (RT). The aim of this study was to investigate the utility of SGS combined with single photon emission computed tomography (SPECT). Twenty-one patients with a carcinoma of head and neck underwent SGS before and 1 month after RT. After injection of 370 MBq 99Tcm-pertechnetate, a biplanar dynamic acquisition (12 x 1 min) was started, followed by a SPECT acquisition during 4 min. Carbachol was then injected and a second dynamic study (16 x 1 min) was performed, again followed by a SPECT acquisition. The salivary excretion fraction (SEF) was calculated both from the geometric mean planar image for each parotid and from the SPECT data for each transverse plane through the parotids. The RT-induced changes in the SEF (dSEF) were correlated with the mean radiation dose calculated using tomography-based dosimetry. The mean radiation dose to the parotids was 44 Gy (range 4.4-68.1 Gy). The mean range of the variation in radiation dose to the transverse slices within the parotids of a patient was 24 Gy (range 6.2-51.9 Gy). Considering all transverse planes through the parotids in all patients, a linear correlation was found between the dSEF calculated using SGS-SPECT and the radiation dose (r=0.45, P=0.0001). Thirteen patients had a variation in radiation dose within the parotids of more than 20 Gy. In nine of these a significant intra-individual correlation between radiation dose and the dSEF of the transverse parotid slices was found (r range 0.55-0.97; P value range 0.037-0.0001). In conclusion, SGS-SPECT can be used for monitoring radiation-induced parotid gland dysfunction. It offers the unique possibility for the assessment of intra-individual dose-dysfunction curves in patients with large variations in the radiation dose within the parotids.

Purpose : To evaluate the differences in palliative radiotherapy for painful bone metastases amongst different Western European countries. Materials and methods : A questionnaire was sent to 565 radiotherapy centres in 19 Western European countries, based on the 1997 ESTRO directory. In this questionnaire the current local palliative radiotherapy practice for bone metastases was assessed in terms of total dose, fractionation, treatment complexity (use of shielding blocks, frequency of isodose calculations, field set-up) and type of machine used. The differences were analyzed according to the country and to the type and size of radiotherapy centre. Results : A total of 205 centres (36%) returned the questionnaire, of which 198 could be further analyzed. The most frequently used antalgic fractionation schedule is 30 Gy in ten daily fractions of 3 Gy (50%), single fractions and conventional 2 Gy fractions being used in a minority of the centres (respectively, 11 and 9%). Most antalgic treatments are performed on a linear accelerator (67% of the centres uses linear accelerators) and 64% of the centres predominantly uses a two-field set-up. The majority of the centres uses shielding blocks and performs isodose calculations in less than 50% of the patients, (respectively, 88 and 81%). There is a correlation between the centre size and the palliative irradiation practice, the largest centres using more hypofractionation ( χ 2 : P =0.001; logit: P =0.0003) and a less complex treatment set up as expressed by the use of isodose calculations ( χ 2 : P =0.027; logit: P =0.0161). There is also a tendency to use less shielding blocks ( P =0.177). The same goes for university centres as compared with private centres: university centres use shorter fractionation schedules ( χ 2 : P =0.008; logit: P =0.0094), less isodoses ( χ 2 : P =0.010; logit: P =0.0115) and somewhat less shielding blocks ( P =0.151). Amongst the analyzed countries different tendencies in fractionation ( P =0.001) and treatment complexity are observed (use of isodoses: P =0.014, use of shielding blocks: P =0.001). Conclusion : These data suggest that beside work-load and clinical evidence, country-related factors such as tradition and habits, past teaching, the national organization of health care and reimbursement criteria may influence the local practice.

Background and purpose : Due to the complexity of the treatment preparation in radiotherapy, a number of errors go undetected until after the first treatment session. Some of these errors could easily have been noticed before treatment if an objective filter existed in addition to human supervision. With this in mind, a conceptually novel extension to conventional quality assurance procedures was explored to create a global platform monitoring treatment preparation by comparison with the existing local standards. Materials and methods : The feasibility of developing such a platform was evaluated for a test case on a cohort of 202 patients having received breast irradiation. By statistical analysis of the treatment parameters, mean values and tolerance levels could be defined for most parameters based on the observed standard deviations. Useful correlations were traced providing us with a means to automatically track errors, the detection of which would otherwise solely depend upon the alertness of the supervisor. Results and conclusions : Apart from its possibilities as a mere quality control tool, the platform, developed in the framework of EQUART (European Quality Assurance Program in Radiotherapy by Monitoring Treatment Preparation), can be incorporated in the treatment preparation chain, providing standard setup values for the simulation. A crucial achievement of EQUART lies in the fact that filtering out of errors occurs prior to treatment initiation.

Purpose : 18 F-fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET) combined with computer tomography (PET-CT) is superior to CT alone in mediastinal lymph node (LN) staging in non-small cell lung cancer (NSCLC). We studied the potential impact of this non-invasive LN staging procedure on the radiation treatment plan of patients with NSCLC. Patients and methods : The imaging and surgical pathology data from 105 patients included in two previously published prospective LN staging protocols form the basis for the present analysis. For 73 of these patients, with positive LN's on CT and/or on PET, a theoretical study was performed in which for each patient the gross tumour volume (GTV) was defined based on CT and on PET-CT data. For each GTV, the completeness of tumour coverage was assessed, using the available surgical pathology data as gold standard. A more detailed analysis was done for the first ten consecutive patients in whom the PET-CT-GTV was smaller than the CT-GTV. Theoretical radiation treatment plans were constructed based on both CT-GTV and PET-CT-GTV. Dose-volume histograms for the planning target volume (PTV), for the total lung volume and the lung volume receiving more than 20 Gy ( V lung(20) ), were calculated. Results : Data from 988 assessed LN stations were available. In the subgroup of 73 patients with CT or PET positive LN's, tumour coverage improved from 75% when the CT-GTV was used to 89% with the PET-CT-GTV ( P =0.005). In 45 patients (62%) the information obtained from PET would have led to a change of the treatment volumes. For the ten patients in the dosimetry study, the use of PET-CT to define the GTV, resulted in an average reduction of the PTV by 29±18% (±1 SD) ( P =0.002) and of the V lung(20) of 27±18% (±1 SD) ( P =0.001). Conclusion : In patients with NSCLC considered for curative radiation treatment, assessment of locoregional LN tumour extension by PET will improve tumour coverage, and in selected patients, will reduce the volume of normal tissues irradiated, and thus toxicity. This subgroup of patients could then become candidates for treatment intensification.

Purpose/Objective: This study evaluates the dosimetric benefits and feasibility of a deep inspiration breath-hold (DIBH) technique in the treatment of lung tumors. The technique has two distinct features—deep inspiration, which reduces lung density, and breath-hold, which immobilizes lung tumors, thereby allowing for reduced margins. Both of these properties can potentially reduce the amount of normal lung tissue in the high-dose region, thus reducing morbidity and improving the possibility of dose escalation. Methods and Materials: Five patients treated for non-small cell lung carcinoma (Stage IIA-IIIB) received computed tomography (CT) scans under 4 respiration conditions: free-breathing, DIBH, shallow inspiration breath-hold, and shallow expiration breath-hold. The free-breathing and DIBH scans were used to generate 3-dimensional conformal treatment plans for comparison, while the shallow inspiration and expiration scans determined the extent of tumor motion under free-breathing conditions. To acquire the breath-hold scans, the patients are brought to reproducible respiration levels using spirometry, and for DIBH, modified slow vital capacity maneuvers. Planning target volumes (PTVs) for free-breathing plans included a margin for setup error (0.75 cm) plus a margin equal to the extent of tumor motion due to respiration (1–2 cm). Planning target volumes for DIBH plans included the same margin for setup error, with a reduced margin for residual uncertainty in tumor position (0.2–0.5 cm) as determined from repeat fluoroscopic movies. To simulate the effects of respiration-gated treatments and estimate the role of target immobilization alone (i.e., without the benefit of reduced lung density), a third plan is generated from the free-breathing scan using a PTV with the same margins as for DIBH plans. Results: The treatment plan comparison suggests that, on average, the DIBH technique can reduce the volume of lung receiving more than 25 Gy by 30% compared to free-breathing plans, while respiration gating can reduce the volume by 18%. The DIBH maneuver was found to be highly reproducible, with intra breath-hold reproducibility of 1.0 (± 0.9) mm and inter breath-hold reproducibility of 2.5 (± 1.6) mm, as determined from diaphragm position. Patients were able to perform 10–13 breath-holds in one session, with a comfortable breath-hold duration of 12–16 s. Conclusion: Patients tolerate DIBH maneuvers well and can perform them in a highly reproducible fashion. Compared to conventional free-breathing treatment, the DIBH technique benefits from reduced margins, as a result of the suppressed target motion, as well as a decreased lung density; both contribute to moving normal lung tissue out of the high-dose region. Because less normal lung tissue is irradiated to high dose, the possibility for dose escalation is significantly improved.

To determine the extent and predictors for prostatic motion in a large number of patients evaluated with multiple CT scans during radiotherapy, and evaluate the implications of these data on the design of appropriate treatment margins for patients receiving high-dose three-dimensional conformal radiotherapy.Fifty patients underwent four serial computerized tomography (CT) scans, consisting of an initial planning scan and subsequent scans at the beginning, middle, and end of the treatment course. Each scan was performed with the patient in the prone treatment position within an immobilization device used during therapy. Contours of the prostate and seminal vesicles were drawn on the axial CT slices of each scan, and the scans were matched by alignment of the pelvic bones with a chamfer matching algorithm. Using the contour information, distributions of the displacement of the organ center of mass and organ border from the planning position were determined separately for the prostate and seminal vesicles in each of the three principle directions: anterior-posterior (AP), superior-inferior (SI) and left-right (LR). Each distribution was fitted to a normal (Gaussian) distribution to determine confidence limits in the center of mass and border displacements and thereby evaluate for the optimal margins needed to contain target motion.The most common directions of displacement of the prostate center of mass (COM) were in the AP and SI directions and were significantly larger than any LR movement. The mean prostate COM displacement (+/- 1 standard deviation, SD) for the entire population was -1.2 +/- 2.9 mm, -0.5 +/- 3.3 mm and -0.6 +/- 0.8 mm in the, AP and SI and LR directions respectively (negative values indicate posterior, inferior or left displacement). The mean (+/- 1 SD) seminal vesicle COM displacement for the entire population was - 1.4 +/- 4.9 mm, 1.3 +/- 5.5 mm and -0.8 +/- 3.1 mm in the AP and SI and LR directions, respectively. The data indicate a tendency for the population towards posterior displacements of the prostate from the planning position and both posterior and superior displacements of the seminal vesicles. AP movement of both the prostate and seminal vesicles were correlated with changes in rectal volume (P = 0.0014 and0.0001, respectively) more than with changes in bladder volume (P = 0.030 for seminal vesicles and 0.19 for prostate). A logistic regression analysis identified the combination of rectal volume60 cm3 and bladder volumes40 cm3 as the only predictor of large (3 mm) systematic deviations for the prostate and seminal vesicles (P = 0.05) defined for each patient as the difference between organ position in the planning scan and mean position as calculated from the three subsequent scans.Prostatic displacement during a course of radiotherapy is more pronounced among patients with initial planning scans with large rectal and bladder volumes. Such patients may require more generous margins around the CTV to assure its enclosure within the prescription dose region. Identification and correction of patients with large systematic errors will minimize the extent of the margin required and decrease the volume of normal tissue exposed to higher radiation doses.

In recent years, the sophistication and complexity of clinical treatment planning and treatment planning systems has increased significantly, particularly including three-dimensional (3D) treatment planning systems, and the use of conformal treatment planning and delivery techniques. This has led to the need for a comprehensive set of quality assurance (QA) guidelines that can be applied to clinical treatment planning. This document is the report of Task Group 53 of the Radiation Therapy Committee of the American Association of Physicists in Medicine. The purpose of this report is to guide and assist the clinical medical physicist in developing and implementing a comprehensive but viable program of quality assurance for modern radiotherapy treatment planning. The scope of the QA needs for treatment planning is quite broad, encompassing image-based definition of patient anatomy, 3D beam descriptions for complex beams including multileaf collimator apertures, 3D dose calculation algorithms, and complex plan evaluation tools including dose volume histograms. The Task Group recommends an organizational framework for the task of creating a QA program which is individualized to the needs of each institution and addresses the issues of acceptance testing, commissioning the planning system and planning process, routine quality assurance, and ongoing QA of the planning process. This report, while not prescribing specific QA tests, provides the framework and guidance to allow radiation oncology physicists to design comprehensive and practical treatment planning QA programs for their clinics.

We have assessed radiation therapy physics quality assurance (QA) elements in the United States and compared the results with the Patterns of Care Study (PCS) Consensus Guidelines for Treatment Planning and the American College of Radiology (ACR) Standard for Radiation Oncology Physics for External Beam Therapy. Data were obtained during PCS site visits to 73 facilities randomly selected from the 1,321 radiation therapy facilities in the United States: 21 academic, 26 hospital, and 26 freestanding. The following is a representative sample of results. The estimated national averages for facilities having QA programs for treatment planning systems, simulators, accelerators, film processors, and blocking systems are 44%, 79%, 94%, 62%, and 55%, respectively. Only 63% of facilities obtain an independent check of their accelerator calibrations from a source outside the facility. Twenty-six percent of facilities surveyed did not have in vivo dosimetry capability. These results and others in the study were compared with PCS consensus guidelines and ACR standards. This is the first such study performed in the United States, and the results establish a baseline for future studies. A recommendation for a comprehensive national physics QA study is based on deficiencies found in this study and the implementation of new technologies in radiation therapy.

Purpose: To prospectively assess the effect of supine vs. prone treatment position on the dose to normal tissues in prostate cancer patients treated with the three-dimensional conformal technique. Methods and Materials: Twenty-six patients underwent three-dimensional treatment planning in both the supine and prone treatment positions. The planning target volume and normal tissue structures were outlined on each CAT scan slice, and treatment plans were compared to assess the effect of treatment position on the volume of rectum, bladder, and bowel exposed to the high doses of irradiation. Results: The average dose to the rectal wall and the V95 (volume of rectal wall receiving at least 95% of the prescription dose) for the prone position were 64 and 24% of the prescription dose, respectively, compared to 72 and 29%, respectively, for the supine position (p < 0.05). When the average rectal wall dose was used as an endpoint, 14 of the 26 patients (54%) had an advantage for the prone position compared to 1 (4%) who demonstrated and advantage for the supine position (p < 0.0002). Similarly, when V95 of the rectal wall was used as a measure of comparison, 15 patients (58%) had an advantage for the prone position compared to 1 (4%) who demonstrated an advantage for the supine position (p < 0.0002). In 13 patients (50%), a change from spine to the prone position was associated with reduction of the V95 to levels < 30% of the prescription dose compared to 3 patients (11%) in whom such an advantage resulted from change of the prone to the supine position (p < 0.005). The effect of treatment position on the rectal wall dose was most pronounced in the region of the seminal vesicles. An increased volume of bowel was also noted in the supine position. The treatment position, however, had no significant impact on the dose to the bladder wall. Conclusions: Three-dimensional conformal radiotherapy for prostate cancer in the prone position is associated with significant reduction of the dose to the rectum and bowel resulting in an improvement in the therapeutic ratio.

The 1989 Patterns of Care Study included treatment planning for early breast cancer. A Consensus Committee of radiation physicists and oncologists determined current guidelines and developed questionnaires to determine treatment planning and delivery processes used by the participating institutions (e.g., use of portal films). This article presents and analyzes the results of that survey.The survey included 449 respondents, distributed as follows: 136 (30%) from Strata I (academic facilities); 169 (38%) from Strata II (hospital based facilities); and 144 (32%) from Strata III (freestanding facilities). The treatment planning procedures surveyed included: whether individualized tissue compensators are used, whether inhomogeneity corrections are used in dose calculations, the use of computerized tomography, whether isodose distributions for external beam tangents and interstitial implants are generated, the use of lymphoscintigraphy, immobilization devices, simulations, portal films, etc.The survey results demonstrated that out of 305 patients from Strata I and II institutions, 237 (78%) had simulated tangential fields. Consistent with this finding is that 76% of patients from Strata I and II institutions were immobilized, while only 51% of Strata III patients were. Moreover, only 18 out of the 449 (4%) of cases did not have any type of external beam dose distribution calculated--presumably, in these cases missing tissue compensation would be unlikely. On the other hand, 41% of the Strata II, 27% of Strata III, but only 19% of Strata I (p0.0002) cases received CT. Surprisingly, 19% of the Strata I, 35% of the Strata II, and 25% of the Strata III (p = 0.0011) patients received lymphoscintigraphy, perhaps reflecting the use of wide tangents to encompass the internal mammary nodes in these patients. In terms of optimizing treatments, 74% of Strata I, 70% of Strata II, and 78% of Strata III patients had wedges used on both tangential fields, although in 5, 12, and 14%, respectively, no beam modification of any sort was used. Furthermore, it should be noted that in 7% of the Strata I, 23% of Strata II, and 37% of Strata III cases there was no attempt to reduce the divergence of the tangential fields into the lung. On the other hand, if one considers the 135 (of 449) patients where matching of the tangential and supraclavicular fields was applicable, 41% of Strata I, 22% of Strata II and 46% of Strata III patients had those fields matched in a vertical plane, which would involve sophisticated alignment procedures. Quality control of treatment delivery was high: 97% of all surveyed received portal films at least once. The use of thermoluminescent dosimetry (TLD) to measure the dose to the contralateral breast was of little interest: only 4 of the 305 Strata I and II patients received in vivo measurements.This national survey has established the patterns of treatment planning for early breast cancer. It shows a generally consistent approach-although a number of statistically significant variations have been identified.

Purpose : We describe a method of incorporating organ motion into three-dimensional (3D) conformal treatment plans, which predict the effect of organ motion on the calculated dose to both the clinical target volume (CTV) and nontarget organs. Methods and Materials : The method is based on measurements of organ motion by means of multiple computed tomography (CT) scans from a group of “reference” patients, in which the data consist of previously drawn contours of the target and nontarget organs. A computer program records the differences in contour position and shape that occurs between scans in the reference data, and according to those differences adjusts the contours and dose calculation points of a study” patient currently being planned, thus simulating organ motion. Dose-volume histograms (DVHs) are accumulated, and the process is repeated over the set of reference patient scans, resulting in a set of treatment plans that are ranked according to a dose-based endpoint. Two plans are selected corresponding to specified lower and upper confidence limits in the endpoint, and the DVHs from these plans are displayed for comparison with the DVHs from the nominal plan in the absence of motion. Results | As an example of the method's use, it is applied to a 6-field conformal treatment plan for prostate cancer. Confidence limit DVHs of the CTV and rectal wall (in which the plans were ranked by probabilities for tumor control and normal tissue complication, respectively) are presented and compared to those from the nominal plan. Conclusion : The method provides a means of estimating the uncertainty in dose delivered by a treatment plan when organ motion is present. It is generally applicable to any treatment site for which data in the form of multiple CT scans are available, and can be extended to include other treatment uncertainties such as variation in patient positioning.

As advances in radiotherapy technology enable higher precision treatment, it becomes increasingly important to understand the factors that contribute to treatment uncertainty. The recent developments in imaging modalities and computer algorithms have made possible quantitative measurements of treatment uncertainties on statistically significant numbers of patients, which has led to new strategies for reducing as well as incorporating them into the treatment planning process. This article reviews the current literature on two sources of uncertainties deemed important in photon therapy, namely, patient localization (setup) errors and organ motion. In the area of patient localization there has been increasing work on protocols using electronic portal imaging devices to correct setup errors. These protocols are derived from probability analyses based on knowledge of setup errors for a population of patients in combination with defined clinical endpoints. Measurements of organ motion and methods to correct or control it have been more limited, due partly to the larger difficulties in imaging and motion characteriation. We also review two paradigms for accounting for uncertainties in treatment plans: the conventional approach, which adds a margin around the tumor volume, and an alternative one, which includes uncertainties directly in the dose distributions of the tumor volume and nearby normal organs.

Acute morbidity, late complications and tumor response were evaluated in 324 prostate cancer patients treated with 3-dimensional conformal radiation therapy in a phase I dose-escalation study. This radiotherapy technique targeted the prostate and seminal vesicles but effectively excluded the surrounding normal tissues. The minimum tumor dose was 64.8 to 66.6Gy. in 87 patients, 70.2Gy. in 138, 75.6Gy. in 69 and 81.0Gy. in 30. The treatment was well tolerated with minimal acute morbidity, observed in 15% of the patients who required medication for relief of rectal symptoms and in 34% for urinary symptoms. Two patients (0.6%) to date have had grades 3 and 4 late complications (Radiation Therapy Oncology Group morbidity grading system). The 3-year actuarial probability of survival with a normal serum prostate specific antigen level was 97% for patients with stages T1c and T2a, 86% with stage T2b, 60% with stage T2c and 43% with stage T3 disease. A multivariate analysis demonstrated that initial prosta...

The objective of the work presented in this paper is to explore the scope of the applicability of the inverse radiotherapy technique for designing optimized intensity distributions to achieve a desired dose distribution. A specified desired uniform dose to the target volume is inverted, subject to constraints on the surrounding normal tissue dose, to produce optimum intensity distributions in a set of beams arranged around the target volume. We employed the inverse technique and software developed by Bortfeld and evaluated results both qualitatively and quantitatively using dose distribution displays, dose-volume histograms and biological indices including tumor control probability and normal tissue complication probabilities. So far we have applied this methodology to prostate and lung treatment plans. For prostate the inverse technique produces satisfactory approximations of the desired dose distributions. However, for lung its performance is considerably inferior. Our investigations point to a number of factors for this difference, the primary ones being differences in the tolerance doses of neighboring normal tissues, magnitudes of volume effect, tissue architectures, and the achievability of the specified desired dose distributions. We conclude that, for certain clinical situations, it is not sufficient to specify the objectives of optimization purely in terms of the desired pattern of the dose. The objectives must also include dose-volume effects and biological indices. Furthermore, the mathematics of optimization must be able to incorporate these factors into the process. We find that the inverse technique is not suitable for situations where dose-volume considerations and biological indices are important and that other methods of optimization of intensity distributions should be explored.

Purpose : To analyze the effect that immobilization devices used in conjunction with beam modifiers may have on the dose to the skin and build-up region. Methods and Materials : Central axis depth dose measurements were made in a polystyrene phantom in the build-up regions using the 6 and 15 MV photon beams, at two different source-to-phantom distances, and various field sizes. The effects of acrylic blocking trays, lead wedges, and cerrobend blocks were assessed in conjunction with the enhancement of dose in the build-up region due to immobilizing devices using plaster and thermoplastic casting materials of different thicknesses. Results : For the 6 MV photons, solid (3 mm) thermoplastic casting material was found to have the greatest effect on surface dose: for a 12 × 12 cm field we measured 79% of maximum dose when treating through the material versus 22% of maximum dose when no beam modifiers or immobilization devices are used. Measurements were also made to evaluate the effect of the immobilization of patients receiving three-dimensional conformal treatments using a 15 MV photon beam. Conclusions : The relevance of these results to treatments in the pelvis, breast, and head and neck regions is discussed. For 6 MV beams, special consideration should be given if the need arises to treat through the immobilization device, as unacceptable skin reactions may result.

Background. Radiation, including radiation therapy (RT) for a variety of conditions, is known to be a lung carcinogen. Methods. Data from the Surveillance, Epidemiology, and End Results program of the National Cancer Institute for 1973-1986 were utilized to investigate whether RT for breast cancer affects the risk of subsequent lung cancer. The relative risk was calculated by comparing the incidence rate in patients with irradiated breast cancer with that in those with nonirradiated breast cancer. Results. It was found that the risk of lung cancer overall was increased in women who underwent irradiation compared with those who were not irradiated 10 years after the initial breast cancer diagnosis with a relative risk of 2.0 (95% confidence interval, 1.0-4.3). In addition, the risk of lung cancer was in the ipsilateral lung compared with the contralateral lung for irradiated women. This increase was observed after 10 years for lung cancer overall and for the three major histologic subgroups (small cell, squamous cell, and adenocarcinoma). Specific information on RT doses and treatment plans and cigarette smoking were not available. Conclusions. It was concluded that RT for breast cancer may increase the risk of lung cancer after a latency period of 10 years.

We investigate the use of a multi-leaf collimator for conformal radiation therapy of carcinomas of the prostate and of the nasopharynx. Following verification of dose calculation algorithms for multi-leaf collimated fields using film dosimetry, we compute dose distributions for multi-field conformal treatment using fields shaped with either the multi-leaf collimator or conventional cerrobend blocks. We compare the two sets of treatment plans using graphical isodose displays, tissue specific dose volume histograms, tumor control probabilities, and normal tissue complication probabilities. We also incorporate setup errors into the calculated dose distributions to assess the effect of treatment uncertainties on the various criteria. Based on these comparisons, we conclude that for multi-field conformal radiotherapy for these two disease sites, the use of multi-leaf collimation is equivalent to that of conventional cerrobend blocks.

This study demonstrates the feasibility of using a novel 2D spectrum ultrasonic tissue characterization (UTC) technique for prostate-cancer diagnosis. Normalized 2D spectra are computed by performing Fourier transforms along the range (beam) and the cross-range directions of the digital radio-frequency echo data, then dividing by a reference spectrum. This 2D spectrum method provides axial and lateral information of tissue microstructures, an improvement over the current 1D spectrum analysis which only provides axial information. A pilot study was conducted on four prostate-cancer patients who underwent radical prostatectomies. Cancerous and noncancerous regions of interest, identified through histology, were compared using four 2D spectral parameters: peak value and 3 dB width of the radially integrated spectral power (RISP), slope and intercept of the angularly integrated spectral power (AISP). For noncancerous and cancerous prostatic tissues, respectively, our investigation yielded 23 +/- 1 and 26 +/- 1 dB for peak value of RISP, 7.8 +/- 0.5 degrees and 7.6 +/- 0.6 degrees for 3 dB of RISP, -2.1 +/- 0.2 and -2.7 +/- 0.4 dB/MHz for slope of AISP, and 92 +/- 5 and 112 +/- 6 dB for intercept of AISP. Preliminary results indicated that 2D spectral UTC has the potential for identifying tumor-bearing regions within the prostate gland.

The goal of this study was to implement and validate a noninvasive, quantitative ultrasonic technique for accurate and reproducible measurement of normal-tissue toxicity in radiation therapy. The authors adapted an existing ultrasonic tissue characterization (UTC) technique that used a calibrated 1D spectrum based on region-of-interest analysis. They modified the calibration procedure by using a reference phantom instead of a planar reflector. This UTC method utilized ultrasonic radiofrequency echo signals to generate spectral parameters related to the physical properties (e.g., size, shape, and relative acoustic impedance) of tissue microstructures. Three spectral parameters were investigated for quantification of normal-tissue injury: Spectral slope, intercept, and midband fit. They conducted a tissue-mimicking phantom study to verify the reproducibility of UTC measurements and initiated a clinical study of radiation-induced breast-tissue toxicity. Spectral parameter values from measurements on two phantoms were reproducible within 1% of each other. Eleven postradiation breast-cancer patients were studied and significant differences between the irradiated and untreated (contralateral) breasts were observed for spectral intercept (p = 0.003) and midband fit (p0.001) but not for slope (p = 0.14). In comparison to the untreated breast, the average difference in the spectral intercept was 2.99 +/- 0.75 dB and the average difference in the midband fit was 3.99 +/- 0.65 dB. The preliminary clinical study demonstrated the feasibility of using the quantitative ultrasonic method to evaluate normal-tissue toxicity in radiation therapy.

The recent introduction of new computer technology for treatment planning and computer-driven treatment delivery systems, such as multi-leaf collimators and on-line verification systems, has accelerated the development of 3-dimensional (3-D) radiation therapy as a modality for curative cancer treatment. The goal of 3-D treatment planning is to conform the spatial distribution of the high radiation dose to the shape of the tumor contour while concomitantly decreasing the volume of the surrounding normal tissues receiving high radiation doses. The improved precision of tumor coverage and the exclusion of normal tissues should permit tumor dose escalation and may enhance local tumor control. It has been suggested that any survival gains derived from improvements in local control may be offset by the subsequent appearance of distant metastases arising from micrometastases already present at the time of initial diagnosis. However, clinical and laboratory studies indicate that failure to control the primary tumor at the time of initial treatment significantly increases the incidence of metastatic dissemination. This phenomenon is consistent with the hypothesis that the enhanced mitotic activity associated with the re-growth process of locally recurring primary tumors promotes the multi-step transformation of non-metastatic tumor cells into clonogens with metastatic potential, leading to increased overall rates of metastatic disease. These biologic considerations provide support for the need to focus attention on the identification of more effective therapeutic strategies designed to eradicate the primary local tumor completely at the time of initial therapy and serve as the rationale for clinical studies using 3-D conformal radiation therapy.

This study was designed to demonstrate the feasibility of 3-dimensional (3D) treatment planning in patients with carcinoma of the nasopharynx, and to explore its potential therapeutic advantage over the traditional 2-dimensional (2D) approach in this disease. Qualitative and quantitative comparisons between the two techniques were made for the boost portion of the treatment (19.8 Gy of a total 70.2 Gy treatment schedule) in 10 previously untreated patients and for the entire treatment in 5 patients with locally recurrent disease. The 2D and 3D plans were compared in each patient using dose-volume histograms (DVH's), tumor control probabilities (TCP's), normal tissue complication probabilities (NTCP's), and a new biologic figure of merit that describes the probability of uncomplicated control. Although there was no attempt to optimize the 313 treatment approach by using this method throughout the total treatment course (rather than for the boost only), it was still found that for each of the endpoints examined the 3D approach resulted in improved plans. An average of 22% of the target volume was underdosed at the 95% isodose level with the 2D plans compared to 7% with the 3D plans. The improved treatment planning by 3D increased the mean dose to the tumor volume by an average of 13% over 2D planning. The dose to normal structures such as the mandible and parotid glands was reduced with the 3D plans while the brain stem and spinal cord remained within tolerance limits. The probability of uncomplicated tumor control was increased by an average of 15% with 3D treatment planning compared to the 2D approach. Our findings demonstrate the potential of 3D planning for improving the treatment of carcinoma of the nasopharynx, but prospective studies are required to define the true clinical advantages of this methodology.

Presented here is a method of designing compensators for a single beam or one or more pairs of beams, not necessarily parallel opposed. The objective is to produce a flat distribution in a plane that may be perpendicular to the central ray or may be an arbitrarily oriented plane, for example, a plane that bisects the hinge angle between two beams. The method takes into account not only surface irregularities but also tissue inhomogeneities, hinge angles between beams, distance from the source, and even ‘‘horns’’ in the beam. The design process employs convolution of Monte Carlo generated pencil beams with photon fluence distributions, appropriately modified for the presence of beam modifiers (blocks and compensators), to compute dose in a flat homogeneous phantom. Corrections for inhomogeneities and surface curvature are applied by using computerized tomography information to determine the effective path length through tissue. Multiple interations are used to arrive at a compensator that properly incorporates changes in radiation transport, and therefore dose distribution, resulting from the presence of beam‐shaping devices. In each iteration it is assumed that the required reduction in dose at a point can be achieved by reducing the fluence along the ray joining the source to computation point proportionately. The compensator design is represented as a finely spaced matrix of thickness values which is entered into a prorammable milling maching for fabrication. Dose measurements in phantom exposed to 6‐MV x rays with and without compensation are presented.

This paper presents a technique for producing uniform dose distributions within the target volume with noncoplanar field arrangements. The method is based upon the principle used for producing homogeneous dose distributions for a pair of fields in two dimensions, namely, that if the isodose distributions for the fields are made parallel to one another, the combined dose distribution will be uniform. For the three-dimensional non-coplanar case, homogeneous target dose distributions are obtained by designing field modifiers which produce a uniform dose distribution on the perpendicular bisector plane for each pair of fields. It is demonstrated that for three noncoplanar fields irradiating a spherical phantom with spherical target volumes, the target dose distribution will be homogeneous for any arbitrary non-coplanar field arrangement. Furthermore, this technique can be extended to any number of fields. Therefore, target dose distributions for non-coplanar plans can be as homogeneous as the coplanar case. An example of the application of the method to the treatment of rectal carcinoma with non-coplanar fields is given. Furthermore, it is demonstrated that the therapeutic ratio is improved over traditional methods for this clinical example.

Skin injury is a common side effect of breast- cancer radiation therapy. Although physicians often observe skin toxicity, quantifying its severity remains a challenge. We present a novel quantitative ultrasonic technique to evaluate skin changes associated with radiotherapy. An in vivo study with twelve breast- cancer patients was conducted. All patients received a standard course of post-surgery radiation therapy. Each patient received ultrasound scans to the irradiated breast and the untreated (contra-lateral) breast. Radio-frequency (RF) backscatter signals and B-mode images were acquired simultaneously. To quantify the severity of skin injury, two metrics were calculated from the RF signals: skin thickness and Pearson correlation coefficient of the subcutaneous layer. Comparing to the non-irradiated skin, the average thickness of the irradiated skin increased by 40% (p=0.005) and the average correlation coefficient of the irradiated hypodermis decreased by 35% (p=0.02). This study demonstrates the feasibility of using a non-invasive ultrasonic technique to detect and quantify radiation-induced skin changes.

A theoretical model is described for application in ultrasonic tissue characterization using a calibrated 2-D spectrum analysis method. This model relates 2-D spectra computed from ultrasonic backscatter signals to intrinsic physical properties of tissue microstructures, e.g., size, shape, and acoustic impedance. The model is applicable to most clinical diagnostic ultrasound systems. Two experiments employing two types of tissue architectures, spherical and cylindrical scatterers, are conducted using ultrasound with center frequencies of 10 and 40 MHz, respectively. Measurements of a tissue-mimicking phantom with an internal suspension of microscopic glass beads are used to validate the theoretical model. Results from in vitro muscle fibers are presented to further elucidate the utility of 2-D spectrum analysis in ultrasonic tissue characterization.

Our research is aimed at ultrasonically characterizing cancerous prostate tissue so that we can imaging it effectively and thereby provide improved means of detecting, treating, and monitoring prostate cancer. We base our characterization methods on spectrum analysis of RF echo signals combined with clinical variables such as prostate-specific antigen (PSA). These parameters are classified using artificial neural networks (ANNs), and classification efficacy is measured using relative-operating-characteristic (ROC) methods. These methods produced ROC-curve areas of 0.80 compared to 0.64 for conventional methods. We then used our optimal classifiers to generate lookup tables (LUTs) that translate spectral parameters and clinical variables to pixel values in tissue-type images (TTIs). TTIs show cancerous regions in 2D or 3D, and may prove to be particularly useful clinically in combination with other ultrasonic and non-ultrasonic methods, e.g., magnetic-resonance methods.

Our objective is to develop imaging methods that can distinguish viable cancerous tissue from other prostate tissues in order to improve biopsy guidance and treatment targeting. To do this, we acquired ultrasonic RF echo-signal data and clinical variables, e.g., PSA, for over 3,000 biopsies, and computed spectral-parameter values for each biopsied region. Using a neural network trained with these data, we generated a lookup table that translated parameter values at each pixel location into a local score for cancer likelihood. Images displaying the map of local scores are called tissue-type images (TTIs). ROC-curve areas were greater for neural-network classification than for classification using conventional B-mode-based methods, and predicted a sensitivity improvement of more than 20% over conventional, ultrasound-guided biopsies. We are initiating studies of prostate tissue characterization using magnetic resonance spectroscopy (MRS), and are investigating the feasibility of combining information from ultrasound and MRS for improved imaging of prostate cancer. TTIs applied in real time may markedly improve cancer-detection by directing biopsies to cancerous regions. TTI data combined with MRS parameters potentially can provide a powerful new hybrid 3-D imaging method for detecting, evaluating, and treating prostate cancer.

Colon cancer is the second leading cause of cancer-related death in the United States. Earlier detection and removal of polyps can dramatically reduce the chance of developing malignant tumor. Due to some limitations of optical colonoscopy used in clinic, many researchers have developed virtual colonoscopy as an alternative technique, in which accurate colon segmentation is crucial. However, partial volume effect and existence of residue make it very challenging. The electronic colon cleaning technique proposed by Chen et al is a very attractive method, which is also kind of hard segmentation method. As mentioned in their paper, some artifacts were produced, which might affect the accurate colon reconstruction. In our paper, instead of labeling each voxel with a unique label or tissue type, the percentage of different tissues within each voxel, which we call a mixture, was considered in establishing a maximum a posterior probability (MAP) image-segmentation framework. A Markov random field (MRF) model was developed to reflect the spatial information for the tissue mixtures. The spatial information based on hard segmentation was used to determine which tissue types are in the specific voxel. Parameters of each tissue class were estimated by the expectation-maximization (EM) algorithm during the MAP tissue-mixture segmentation. Real CT experimental results demonstrated that the partial volume effects between four tissue types have been precisely detected. Meanwhile, the residue has been electronically removed and very smooth and clean interface along the colon wall has been obtained.

We have conducted a general study that relates calibrated 2-D ultrasonic spectral parameters to the physical properties of sub-resolution tissue scatterers. Our 2-D spectra are computed form digital radio-frequency echo data obtained as the transducer linearly scans along the cross-range (scan direction) with increments smaller than the half beam width. Acquired data are Fourier transformed with respect to range (beam) and cross-range (scan) directions. To quantitatively measure and classify the physical properties of tissues, we have defined two spectral functions and four spectral parameters. The 2-D spectral functions are: radially integrated spectral power (RISP) and angularly integrated spectral power (AISP). The summary parameters are: peak value and 3-dB width of the RISP, slope and intercept of the AISP. These parameter are understood in terms of the beam properties, transducer parameters and the physical properties of the tissue microstructures including size, shape, orientation, concentration and acoustic impedance. Our theoretical model indicates that 1) the 3-dB width of the RISP is predominantly determined by the scatterer size along the beam direction; 2) the slope of the linear fit of the AISP is predominantly determined by the scatterer size along range direction; 3) the concentration and the relative acoustic impedance fluctuation of the scatterers change the overall spectrum magnitude. The predictions of the theoretical model have been verified using beef muscle fibers examined with 40 MHz center frequency.

Background and purpose : Quality assurance (QA) in intensity modulated treatments is a complex and time-consuming process. In spite of intensive quality control procedures some types of errors still can go undetected through the course of a treatment. This study aims to develop an objective QA filter for fast, automatic detection of errors, based on the creation of a global platform monitoring treatment parameters by comparison with existing local standards. Since such a conceptually new type of QA has already proven successful for conventional treatments, we aim to extend it to intensity modulated radiotherapy (IMRT) treatments. Material and methods : The feasibility of developing such a QA platform was evaluated on 12 prostate treatment plans. Apart from the classical treatment parameters, the optimised fluence distributions were compared and screened for repetitive patterns. This screening was performed by calculating specific parameters, defined to characterise the fluence maps. Results : Repetitive patterns were found in the beam shapes as well as in the intensity distributions, and useful parameters could be defined to quantify typical field patterns. By statistical analysis of these parameters, mean values and tolerance levels were derived, providing a means to automatically filter out unprobable or erroneous intensity modulated treatment fields during the treatment preparation stage. Conclusion : It is possible to identify parameters quantifying the characteristic patterns found in fluence distributions of intensity modulated fields of a specific treatment, allowing the development of a platform for automatic pre-treatment quality control.