Search

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

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.

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.

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.

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.

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.

Purpose: To investigate whether it is necessary to adjust the prescription dose to compensate for Cobaltsource decay of Gamma Knife radiosurgery (GKRS) for trigeminal neuralgia. Methods and Materials: A radiobiological model for GKRS was utilized to estimate the radiation response of the braintissue to the radiosurgerydose distributions expressed in the form of dose volume histogram (DVH). For each bin of the DVH, a linear‐quadratic equation was constructed to calculate the Extrapolated Response Dose (ERD) given the specific dose rate and dose. The relationship between ERD and clinical outcome, i.e., pain relief of trigeminal neuralgia, was evaluated using the data from 343 patients who received trigeminal neuralgia GKRS during a period of 6 years. This model is validated by published clinical data. Necessary dose adjustment to compensate for source decay was obtained during a period of 10 years (two half‐lives). Results: Between the first (5/98–5/99) and last (11/01–11/03) quartile of the patients, complete or nearly complete (⩾90%) pain relief rate was 54.2% verse 50.6%, respectively, at the 12 month follow‐up. Dose rate was not a factor influencing pain relief (p=0.755). Meanwhile, our model predicts that pain relief rate drops 3%, and the necessary dose adjustment for the trigeminal neuralgia GKRS should increase 3–5% for the typical prescription dose of 70–90Gy at the end of two half‐lives. The model also suggests that when the radiosurgery prescription dose is low (e.g. cases such as acoustic neuroma or brain metastases) dose adjustment is not necessary because the change of ERD is negligible. Conclusions: Prolonged treatment due to radiationsource decay has little effect on clinical outcome for trigeminal neuralgia GKRS with up to 10 years of service.

Purpose: To develop a new lungIMRT planning algorithm that shapes dose distributions to the probability distribution of the tumor over the breathing cycle in order to compensate for respiratory motion, thereby enabling tumor dose escalation. Method and Materials: We implemented a new optimization algorithm on an in‐house IMRT planning system on an Eclipse (r) workstation (Varian, Palo Alto). Our new dose shaping algorithm makes the dose of each voxel on the 3‐D dataset proportional to its probability of being inside the tumor over the respiratory cycle. The maximum dose is set to be the prescription dose multiplied by the ratio of the volume encompassed by the extreme positions of the tumor to the tumor volume. We also implemented two other popular approaches: (1) an optimal margin method in which the margin is generated based on the extreme positions of the tumor; and (2) a convolution method that performs 4‐D dose calculations using a modeled tumor motion probability density function. A simulated 4‐D CT dataset, which was generated by superimposing the patient's respiratory motion pattern onto one's 3‐D CT dataset, was used to evaluate the performance of these three approaches via DVH comparison for the inhale phase of the breathing. Results: Five‐field 6MV beams were used for all plans delivering a total dose of 63Gy in 35 fractions. Comparing to the IMRT plan with optimal margin, the convolution method reduced the mean dose to the ipsilateral lung by 5% while maintaining the same tumor coverage. Compared to the convolution method, our dose shaping method achieved the same lung sparing, but is much faster and has the extra ability to escalate tumor dose: 95% tumor received more than 72Gy. Conclusion: Dose shaping method is able to spare the healthy lungtissue, and has the capacity to further facilitate dose escalation.

Purpose: To investigate a novel combination of two non‐invasive techniques, spectrophotometry and ultrasoundtissue characterization (UTC) imaging, to quantitatively evaluate breast tissue toxicity in radiation treatment.Method and Materials:Skin and soft tissue injury are the most common toxicities of breast cancerradiation therapy. There is currently no objective means of measuring breast tissue injury in the clinic. We investigated the combination of Spectrophotometry and UTC imaging to examine radiation toxicity. A spectrophotometer (Mexameter® MX) was used to measure the radiation damage to the skin surface and an ultrasound scanner (Ultrasonix® with 14‐MHz probe) was utilized to measure the soft tissue changes. Six imaging parameters were computed to quantitatively measure toxicity: melanin, erythema, skin thickness, UTC slope, intercept and midband value. Subjective clinical assessment of toxicity was done by a radiation oncologist. Statistical analysis was performed to correlate spectrophotometer and UTC findings with clinical assessments (RTOG clinical toxicity scale). To date, twelve breast cancer patients were enrolled. All patients received a standard course of radiation: the whole breast received 50–50.4 Gy followed by an electron boost of 10–16 Gy at the lumpectomy site. Each patient received a series of spectrophotometer and ultrasound scans prior to, during and post radiation treatment.Results: Twenty‐eight spectrophotometer and ultrasound scans were performed. The contra‐lateral (untreated) breast scans showed good accuracy and reproducibility. Our spectrophotometer and UTC evaluations were consistent with the clinical breast toxicity assessments. We observed significant patient variations. During six‐week radiation treatment, patient melanin increases were between 5 to 20%, erythema increases varied from 0% to 100%. Conclusion: The combination of spectrophotometer and UTC provides effective means of assessing radiation damage to the skin and the underlying breast tissue respectively. This tool becomes increasingly valuable as we evaluate new strategies for breast cancerradiation therapy, such as partial breast IMRT and MammoSite.

Purpose: To spare the normal lung we developed a novel lungIMRT plan optimization algorithm that incorporates both biological model and respiratory motion. Method and Materials: We implemented a novel IMRToptimization algorithm on an in‐house IMRT planning system that interfaces with an Eclipse® workstation (Varian, Palo Alto, CA). The IMRT objective function is a combination of the normal lungtissue complication probability (NTCP), the equivalent uniform dose (EUD), and a penalty on tumor dose in‐homogeneity. A series of 4‐D CT scans were taken at different breath phases and a deformable registration was applied to trace voxel‐to‐voxel correspondence at each snapshot. The time averaged (4‐D) dose was utilized to calculate the NTCP and EUD in the optimization process. The proposed method was compared with the gated IMRT approach, which allowed a residual respiratory motion of 3mm and used a PTV defined as the union of the tumors at different phases within the gating window. The performance of the two approaches was evaluated via comparison of DVH at the exhale phase of the breathing cycle and quantitative parameters such as V20, V10, and the mean lung dose. Results: Five‐field 6MV IMRT beams were setup to deliver a total dose of 63Gy in 35 fractions. Each plan was renormalized such that the prescribed dose covers 95% of the tumor volume. Comparing with the gated IMRT plan, our proposed method resulted in a reduction of 4.3%, 4.4%, 2.2Gy and 11.2%, in terms of V10, V20, the mean dose and NTCP, respectively. Meanwhile, the EUD obtained by our method was 65.6Gy, slightly higher than 64.5Gy obtained by the gated IMRT approach. Conclusion: Compared with the gated lungIMRT approach, the proposed biological model‐based 4‐D lungIMRT plan optimization algorithm is able to further spare the healthy lungtissue while maintaining relatively homogeneous tumor coverage.

Purpose: There is much interest in using biological and functional imaging to provide guidance in IMRT dose painting. Yet, it is important to incorporate the performance characteristics of these modalities. In this study an example of UltrasoundTissue Typing (UTT) was utilized to investigate the implications of the imager's performance on the design of a population based prostate dose painting protocol. Method and Materials: The performance of an imaging modality can be evaluated via the receiver operating characteristic curve, which is a plot of the imaging modality's sensitivity versus false‐positive ratio (1‐specificity). As sensitivity increases, more tumors are detected, although specificity worsens, causing more false negatives. The UTT tumor map obtained with a specific sensitivity and specificity setup is fused with the patient's CTimage to guide IMRT planning. The optimal escalation dose to the tumor positive region identified by UTT, as well as the safe dose to the identified tumor negative background was obtained by maximizing uncomplicated control, which is a combination of tumor control probability (TCP), and weighted normal tissue complication probability (NTCP). Results: A practical dose escalation protocol requires a high specificity imager setup to reduce complications. For tumors at the high‐risk stage, with sensitivity at 0.6 and specificity at 0.9, optimal dose to the positive and negative regions are 88.2Gy and 83.6Gy respectively, which resulted in a 25% NTCP reduction compared to that the whole prostate is dose escalated to the same TCP. If the imager becomes more accurate, i.e., sensitivity improves to 0.9 when specificity remains at 0.9, the optimal plan would have a further 10% NTCP decrease with a 2% TCP increase. Conclusion: Performance characteristics of an imager as described by sensitivity and specificity has important implications in prostate dose painting, and should be considered in the future design of dose painting protocols.