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Purpose: In accurate proton spot-scanning therapy, continuous target tracking by fluoroscopic x ray during irradiation is beneficial not only for respiratory moving tumors of lung and liver but also for relatively stationary tumors of prostate. Implanted gold markers have been used with great effect for positioning the target volume by a fluoroscopy, especially for the cases of liver and prostate with the targets surrounded by water-equivalent tissues. However, recent studies have revealed that gold markers can cause a significant underdose in proton therapy. This paper focuses on prostate cancer and explores the possibility that multiple-field irradiation improves the underdose effect by markers on tumor-control probability (TCP)., Methods: A Monte Carlo simulation was performed to evaluate the dose distortion effect. A spherical gold marker was placed at several characteristic points in a water phantom. The markers were with two different diameters of 2 and 1.5 mm, both visible on fluoroscopy. Three beam arrangements of single-field uniform dose (SFUD) were examined: one lateral field, two opposite lateral fields, and three fields (two opposite lateral fields + anterior field). The relative biological effectiveness (RBE) was set to 1.1 and a dose of 74 Gy (RBE) was delivered to the target of a typical prostate size in 37 fractions. The ratios of TCP to that without the marker (TCP(r)) were compared with the parameters of the marker sizes, number of fields, and marker positions. To take into account the dependence of biological parameters in TCP model, α∕β values of 1.5, 3, and 10 Gy (RBE) were considered., Results: It was found that the marker of 1.5 mm diameter does not affect the TCPs with all α∕β values when two or more fields are used. On the other hand, if the marker diameter is 2 mm, more than two irradiation fields are required to suppress the decrease in TCP from TCP(r) by less than 3%. This is especially true when multiple (two or three) markers are used for alignment of a patient., Conclusions: It is recommended that 1.5-mm markers be used to avoid the reduction of TCP as well as to spare the surrounding critical organs, as long as the markers are visible on x-ray fluoroscopy. When 2-mm markers are implanted, more than two fields should be used and the markers should not be placed close to the distal edge of any of the beams.

Purpose: The Medical Physics Working Group of the Radiation Therapy Study Group at the Japan Clinical Oncology Group is currently developing a virtual audit system for intensity‐modulated radiation therapy dosimetry credentialing. The target dosimeters include films and array detectors, such as ArcCHECK (Sun Nuclear Corporation, Melbourne, Florida, USA) and Delta4 (ScandiDos, Uppsala, Sweden). This pilot study investigated the feasibility of our virtual audit system using previously acquired data. Methods: We analyzed 46 films (32 and 14 in the axial and coronal planes, respectively) from 29 institutions. Global gamma analysis between measured and planned dose distributions used the following settings: 3%/3 mm criteria (the dose denominator was 2 Gy), 30% threshold dose, no scaling of the datasets, and 90% tolerance level. In addition, 21 datasets from nine institutions were obtained for array evaluation. Five institutions used ArcCHECK, while the others used Delta4. Global gamma analysis was performed with 3%/2 mm criteria (the dose denominator was the maximum calculated dose), 10% threshold dose, and 95% tolerance level. The film calibration and gamma analysis were conducted with in‐house software developed using Python (version 3.9.2). Results: The means ± standard deviations of the gamma passing rates were 99.4 ± 1.5% (range, 92.8%–100%) and 99.2 ± 1.0% (range, 97.0%–100%) in the film and array evaluations, respectively. Conclusion: This pilot study demonstrated the feasibility of virtual audits. The proposed virtual audit system will contribute to more efficient, cheaper, and more rapid trial credentialing than on‐site and postal audits; however, the limitations should be considered when operating our virtual audit system. [ABSTRACT FROM AUTHOR]

The purpose of this work is to show the usefulness of a prediction method of tumor location based on partial least squares regression (PLSR) using multiple fiducial markers. The trajectory data of respiratory motion of four internal fiducial markers inserted in lungs were used for the analysis. The position of one of the four markers was assumed to be the tumor position and was predicted by other three fiducial markers. Regression coefficients for prediction of the position of the tumor-assumed marker from the fiducial markers' positions is derived by PLSR. The tracking error and the gating error were evaluated assuming two possible variations. First, the variation of the position definition of the tumor and the markers on treatment planning computed tomograhy (CT) images. Second, the intra-fractional anatomical variation which leads the distance change between the tumor and markers during the course of treatment. For comparison, rigid predictions and ordinally multiple linear regression (MLR) predictions were also evaluated. The tracking and gating errors of PLSR prediction were smaller than those of other prediction methods. Ninety-fifth percentile of tracking/gating error in all trials were 3.7/4.1 mm, respectively in PLSR prediction for superior–inferior direction. The results suggested that PLSR prediction was robust to variations, and clinically applicable accuracy could be achievable for targeting tumors. [ABSTRACT FROM AUTHOR]

Background: Real-time measurement of thermal neutrons in the tumor region is essential for proper evaluation of the absorbed dose in boron neutron capture therapy (BNCT) treatment. The gold wire activation method has been routinely used to measure the neutron flux distribution in BNCT irradiation, but a real-time measurement using gold wire is not possible. To overcome this issue, the scintillator with optical fiber (SOF) detector has been developed. The purpose of this study is to demonstrate the feasibility of the SOF detector as a real-time thermal neutron monitor in clinical BNCT treatment and also to report issues in the use of SOF detectors in clinical practice and their solutions.Material and Methods: Clinical measurements using the SOF detector were carried out in 16 BNCT clinical trial patients from December 2002 until end of 2006 at the Japanese Atomic Energy Agency (JAEA) and Kyoto University Research Reactor Institute (KURRI).Results: The SOF detector worked effectively as a real-time thermal neutron monitor. The neutron fluence obtained by the gold wire activation method was found to differ from that obtained by the SOF detector. The neutron fluence obtained by the SOF detector was in better agreement with the expected fluence than with gold wire activation. The estimation error for the SOF detector was small in comparison to the gold wire measurement. In addition, real-time monitoring suggested that the neutron flux distribution and intensity at the region of interest (ROI) may vary due to the reactor condition, patient motion and dislocation of the SOF detector.Conclusion: Clinical measurements using the SOF detector to measure thermal neutron flux during BNCT confirmed that SOF detectors are effective as a real-time thermal neutron monitor. To minimize the estimation error due to the displacement of the SOF probe during treatment, a loop-type SOF probe was developed. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the effectiveness of the stereotactic body frame (SBF), with or without a diaphragm press or a breathing cycle monitoring device (Abches), in controlling the range of lung tumor motion, by tracking the real-time position of fiducial markers. Methods and Materials: The trajectories of gold markers in the lung were tracked with the real-time tumor-tracking radiotherapy system. The SBF was used for patient immobilization and the diaphragm press and Abches were used to actively control breathing and for self-controlled respiration, respectively. Tracking was performed in five setups, with and without immobilization and respiration control. The results were evaluated using the effective range, which was defined as the range that includes 95% of all the recorded marker positions in each setup. Results: The SBF, with or without a diaphragm press or Abches, did not yield effective ranges of marker motion which were significantly different from setups that did not use these materials. The differences in the effective marker ranges in the upper lobes for all the patient setups were less than 1mm. Larger effective ranges were obtained for the markers in the middle or lower lobes. Conclusion: The effectiveness of controlling respiratory-induced organ motion by using the SBF+diaphragm press or SBF + Abches patient setups were highly dependent on the individual patient reaction to the use of these materials and the location of the markers. They may be considered for lung tumors in the lower lobes, but are not necessary for tumors in the upper lobes. [Copyright &y& Elsevier]

Purpose: The purpose of this study is to evaluate the clinical results of treatment with a high dose of 3-dimensional conformal boost (3DCB) using a real-time tracking radiation therapy (RTRT) system in cervical cancer patients. Materials and Methods: Between January 2001 and December 2004, 10 patients with cervical cancer were treated with a high dose 3DCB using RTRT system. Nine patients received whole pelvis radiation therapy (RT) with a median dose of 50 Gy (range, 40-50 Gy) before the 3DCB. The median dose of the 3DCB was 30 Gy (range, 25-30 Gy). Eight patients received the 3DCB twice a week with a daily fraction of 5 Gy. The determined endpoints were tumor response, overall survival, local failure free survival, and distant metastasis free survival. The duration of survival was calculated from the time of the start of radiotherapy. Results: All patients were alive at the time of analysis and the median follow-up was 17.6 months (range, 4.9-27.3 months). Complete response was achieved in nine patients and one patient had a partial response. The 1- and 2-year local failure free survival was 78.8% and 54%, respectively. The 1- and 2-year distant metastasis free survival was 90% and 72%, respectively. Late toxicity of a grade 2 rectal hemorrhage was seen in one patient. A subcutaneous abscess was encountered in one patient. Conclusion: The use of the high dose 3DCB in the treatment of cervical cancer is safe and feasible where intracavitary brachytherapy (ICBT) is unable to be performed. The escalation of the 3DCB dose is currently under evaluation. [ABSTRACT FROM AUTHOR]

An MLC control algorithm for delivering intensity modulated radiation therapy (IMRT) to targets that are undergoing two-dimensional (2D) rigid motion in the beam’s eye view (BEV) is presented. The goal of this method is to deliver 3D-derived fluence maps over a moving patient anatomy. Target motion measured prior to delivery is first used to design a set of planned dynamic-MLC (DMLC) sliding-window leaf trajectories. During actual delivery, the algorithm relies on real-time feedback to compensate for target motion that does not agree with the motion measured during planning. The methodology is based on an existing one-dimensional (1D) algorithm that uses on-the-fly intensity calculations to appropriately adjust the DMLC leaf trajectories in real-time during exposure delivery [McMahon et al., Med. Phys. 34, 3211–3223 (2007)]. To extend the 1D algorithm’s application to 2D target motion, a real-time leaf-pair shifting mechanism has been developed. Target motion that is orthogonal to leaf travel is tracked by appropriately shifting the positions of all MLC leaves. The performance of the tracking algorithm was tested for a single beam of a fractionated IMRT treatment, using a clinically derived intensity profile and a 2D target trajectory based on measured patient data. Comparisons were made between 2D tracking, 1D tracking, and no tracking. The impact of the tracking lag time and the frequency of real-time imaging were investigated. A study of the dependence of the algorithm’s performance on the level of agreement between the motion measured during planning and delivery was also included. Results demonstrated that tracking both components of the 2D motion (i.e., parallel and orthogonal to leaf travel) results in delivered fluence profiles that are superior to those that track the component of motion that is parallel to leaf travel alone. Tracking lag time effects may lead to relatively large intensity delivery errors compared to the other sources of error investigated. However, the algorithm presented is robust in the sense that it does not rely on a high level of agreement between the target motion measured during treatment planning and delivery. [ABSTRACT FROM AUTHOR]

• D m,m , D w,w , and D w,m are all used in clinical practice. • To maximize clinical trial impact and interpretability, a single consistent framework is preferred. • The GHG recommends using D m,m when available. To promote consistency in clinical trials by recommending a uniform framework as it relates to radiation transport and dose calculation in water versus in medium. The Global Quality Assurance of Radiation Therapy Clinical Trials Harmonisation Group (GHG; www.rtqaharmonization.org) compared the differences between dose to water in water (D w,w), dose to water in medium (D w,m), and dose to medium in medium (D m,m). This was done based on a review of historical frameworks, existing literature and standards, clinical issues in the context of clinical trials, and the trajectory of radiation dose calculations. Based on these factors, recommendations were developed. No framework was found to be ideal or perfect given the history, complexity, and current status of radiation therapy. Nevertheless, based on the evidence available, the GHG established a recommendation preferring dose to medium in medium (D m,m). Dose to medium in medium (D m,m) is the preferred dose calculation and reporting framework. If an institution's planning system can only calculate dose to water in water (D w,w), this is acceptable. [ABSTRACT FROM AUTHOR]

Purpose: Although the effectiveness of stereotactic radiosurgery for nonacoustic schwannomas is currently being assessed, there have been few studies on the efficacy of stereotactic radiotherapy (SRT) for these tumors. We investigated the long-term outcome of SRT for nonacoustic intracranial nerve schwannomas. Methods and Materials: Seventeen patients were treated between July 1994 and December 2006. Of these patients, 7 had schwannomas located in the jugular foramen, 5 in the trigeminal nerve, 4 in the facial nerve, and 1 in the oculomotor nerve. Radiotherapy was used as an initial treatment without surgery in 10 patients (59%) and after initial subtotal resection in the remaining patients. The tumor volume ranged from 0.3 to 31.3 mL (mean, 8.2 mL). The treatment dose was 40 to 54 Gy in 20 to 26 fractions. The median follow-up period was 59.5 months (range, 7.4–122.6 months). Local control was defined as stable or decreased tumor size on follow-up magnetic resonance imaging. Results: Tumor size was decreased in 3 patients, stable in 13, and increased in 1 after SRT. Regarding neurologic symptoms, 8 patients (47%) had improvement and 9 patients were unchanged. One patient had an increase in tumor size and received microsurgical resection at 32 months after irradiation. No patient had worsening of pre-existing neurologic symptoms or development of new cranial nerve deficits at the last follow-up. Conclusions: SRT is an effective alternative to surgical resection for patients with nonacoustic intracranial nerve schwannomas with respect to not only long-term local tumor control but also neuro-functional preservation. [Copyright &y& Elsevier]

Abstract: Purpose: To investigate the three-dimensional movement of internal fiducial markers near the adrenal tumors using a real-time tumor-tracking radiotherapy (RTRT) system and to examine the feasibility of high-dose hypofractionated radiotherapy for the adrenal tumors. Materials and methods: The subjects considered in this study were 10 markers of the 9 patients treated with RTRT. A total of 72days in the prone position and 61 treatment days in the supine position for nine of the 10 markers were analyzed. All but one patient were prescribed 48Gy in eight fractions at the isocenter. Results: The average absolute amplitude of the marker movement in the prone position was 6.1±4.4mm (range 2.3–14.4), 11.1±7.1mm (3.5–25.2), and 7.0±3.5mm (3.9–12.5) in the left–right (LR), craniocaudal (CC), and anterior–posterior (AP) directions, respectively. The average absolute amplitude in the supine position was 3.4±2.9mm (0.6–9.1), 9.9±9.8mm (1.1–27.1), and 5.4±5.2mm (1.7–26.6) in the LR, CC, and AP directions, respectively. Of the eight markers, which were examined in both the prone and supine positions, there was no significant difference in the average absolute amplitude between the two positions. No symptomatic adverse effects were observed within the median follow-up period of 16months (range 5–21months). The actuarial freedom-from-local-progression rate was 100% at 12months. Conclusions: Three-dimensional motion of a fiducial marker near the adrenal tumors was detected. Hypofractionated RTRT for adrenal tumors was feasible for patients with metastatic tumors. [Copyright &y& Elsevier]