Search

Purpose Our group previously introduced an in vivo proton range verification methodology in which a silicon diode array system is used to correlate the dose rate profile per range modulation wheel cycle of the detector signal to the water-equivalent path length (WEPL) for passively scattered proton beam delivery. The implementation of this system requires a set of calibration data to establish a beam-specific response to WEPL fit for the selected ‘scout’ beam (a 1 cm overshoot of the predicted detector depth with a dose of 4 cGy) in water-equivalent plastic. This necessitates a separate set of measurements for every ‘scout’ beam that may be appropriate to the clinical case. The current study demonstrates the use of Monte Carlo simulations for calibration of the time-resolved diode dosimetry technique. Methods Measurements for three ‘scout’ beams were compared against simulated detector response with Monte Carlo methods using the Tool for Particle Simulation (TOPAS). The ‘scout’ beams were then applied in the simulation environment to simulated water-equivalent plastic, a CT of water-equivalent plastic, and a patient CT data set to assess uncertainty. Results Simulated detector response in water-equivalent plastic was validated against measurements for ‘scout’ spread out Bragg peaks of range 10 cm, 15 cm, and 21 cm (168 MeV, 177 MeV, and 210 MeV) to within 3.4 mm for all beams, and to within 1 mm in the region where the detector is expected to lie. Conclusion Feasibility has been shown for performing the calibration of the detector response for three ‘scout’ beams through simulation for the time-resolved diode dosimetry technique in passive scattered proton delivery.

In 2010, all young patients treated for intrathoracic Hodgkin lymphoma (HL) at one of 10 radiotherapy centers in the province of Quebec received 3D conformal photon therapy. These patients may now be at risk for late effects of their treatment, notably secondary malignancies and cardiac toxicity. We hypothesized that more complex radiotherapy, including intensity‐modulated proton therapy (IMPT) and possibly IMRT (in the form of helical tomotherapy (HT)), could benefit these patients. With institutional review board approval at 10 institutions, all treatment plans for patients under the age of 30 treated for HL during a six‐month consecutive period of 2010 were retrieved. Twenty‐six patients were identified, and after excluding patients with extrathoracic radiation or treatment of recurrence, 20 patients were replanned for HT and IMPT. Neutron dose for IMPT plans was estimated from published measurements. The relative seriality model was used to predict excess risk of cardiac mortality. A modified linear quadratic model was used to predict the excess absolute risk for induction of lung cancer and, in female patients, breast cancer. Model parameters were derived from published data. Predicted risk for cardiac mortality was similar among the three treatment techniques (absolute excess risk of cardiac mortality was not reduced for HT or IMPT (p>0.05,p>0.05) as compared to 3D CRT). Predicted risks were increased for HT and reduced for IMPT for secondary lung cancer (p

Purpose: With the aim of reducing acute esophageal radiation toxicity in pediatric patients receiving craniospinal irradiation (CSI), we investigated the implementation of an in-vivo, adaptive proton therapy range verification methodology. Simulation experiments and in-phantom measurements were conducted to validate the range verification technique for this clinical application. Methods: A silicon diode array system has been developed and experimentally tested in phantom for passively scattered proton beam range verification for a prostate treatment case by correlating properties of the detector signal to the water equivalent path length (WEPL). We propose to extend the methodology to verify range distal to the vertebral body for pediatric CSI cases by placing this small volume dosimeter in the esophagus of the anesthetized patient immediately prior to treatment. A set of calibration measurements was performed to establish a time signal to WEPL fit for a “scout” beam in a solid water phantom. Measurements are compared against Monte Carlo simulation in GEANT4 using the Tool for Particle Simulation (TOPAS). Results: Measurements with the diode array in a spread out Bragg peak of 14 cm modulation width and 15 cm range (177 MeV passively scattered beam) in solid water were successfully validated against proton fluence rate simulations in TOPAS. The resulting calibration curve allows for a sensitivity analysis of detector system response with dose rate in simulation and with individual diode position through simulation on patient CT data. Conclusion: Feasibility has been shown for the application of this range verification methodology to pediatric CSI. An in-vivo measurement to determine the WEPL to the inner surface of the esophagus will allow for personalized adjustment of the treatment plan to ensure sparing of the esophagus while confirming target coverage. A Toltz acknowledges partial support by the CREATE Medical Physics Research Training Network grant of the Natural Sciences and Engineering Research Council (Grant number: 432290).

Purpose: A method to refine the implementation of an in vivo, adaptive proton therapy range verification methodology was investigated. Simulation experiments and in-phantom measurements were compared to validate the calibration procedure of a time-resolved diode dosimetry technique. Methods: A silicon diode array system has been developed and experimentally tested in phantom for passively scattered proton beam range verification by correlating properties of the detector signal to the water equivalent path length (WEPL). The implementation of this system requires a set of calibration measurements to establish a beam-specific diode response to WEPL fit for the selected ‘scout’ beam in a solid water phantom. This process is both tedious, as it necessitates a separate set of measurements for every ‘scout’ beam that may be appropriate to the clinical case, as well as inconvenient due to limited access to the clinical beamline. The diode response to WEPL relationship for a given ‘scout’ beam may be determined within a simulation environment, facilitating the applicability of this dosimetry technique. Measurements for three ‘scout’ beams were compared against simulated detector response with Monte Carlo methods using the Tool for Particle Simulation (TOPAS). Results: Detector response in water equivalent plastic was successfully validated against simulation for spread out Bragg peaks of range 10 cm, 15 cm, and 21 cm (168 MeV, 177 MeV, and 210 MeV) with adjusted R2 of 0.998. Conclusion: Feasibility has been shown for performing calibration of detector response for a given ‘scout’ beam through simulation for the time resolved diode dosimetry technique.

Purpose: Evaluate the risk of induction of secondary lung cancer and any solid cancer for patients receiving external beam radiotherapy in the abdomen using intensity modulated photon therapy (IMRT) or 3D conformal radiotherapy (3D'CRT) as compared to intensity modulated proton therapy (IMPT). Methods: Six patients (5 male, 1 female; ages 3–24; previously treated with IMRT or 3D‐CRT in the abdomen) were re‐planned for IMPT using commercially available treatment planning software. Plan dose volume histograms were used to assess the risk of induction of secondary cancer, specifically lung cancer and any solid tumor in the body. Excess Absolute Risk for lung cancer was predicted using the Schneider modified linear quadratic model. Risk for secondary solid cancer in the body was predicted using two Methods: Excess Relative Risk (ERR) based on a linear relationship between risk and integral dose, and Excess Absolute Risk (EAR) and lifetime cumulative risk implementing the Schneider Organ Equivalent Dose using linear, linear‐exponential, and plateau models. An estimate of risk due to neutron dose was calculated for each patient and included in IMPT risk calculations. Results: EAR for lung cancer was on average reduced for IMPT by 49% and 48% as compared to 3D‐CRT and IMRT respectively. ERR for secondary solid cancer was on average reduced for IMPT by 28% and 24% as compared to 3D‐CRT and IMRT respectively. EAR for secondary solid cancer was on average reduced for IMPT by 32% and 36% as compared to 3D‐CRT and IMRT respectively. Lifetime cumulative risk for secondary cancer induction was on average reduced for IMPT by 31% and 35% as compared to 3D‐CRT and IMRT respectively. Conclusions: Models predict the risk for induction of secondary lung cancer and any solid cancer is reduced for IMPT as compared to 3D‐CRT and IMRT for all patients in this study. This work is supported by a grant from the Fonds de recherche sante Quebec.

Purpose: To predict the risks of late, radiation‐induced effects for young patients with Hodgkin's lymphoma (HL), non‐Hodgkin's lymphoma (NHL), or breast cancer (BC) if treated with intensity modulated proton therapy (IMPT) compared to 3D conformal photonradiotherapy (3D‐CRT). Late effects considered were cardiac mortality and secondary cancer in the lungs and breasts (for female patients). Methods: Patient data were acquired for twenty‐six patients (ages 12–29) who were treated with 3D‐CRT for HL, NHL, or BC in 2010. Original CT simulation images were used to re‐plan the patients with IMPT using commercially‐available treatment planning software. The contours of the organs at risk were reviewed by a single physician and modified for consistency. The dose‐volume data of the 3D‐CRT plans and the new IMPT plans were analyzed to model the risks of late effects. The relative seriality model was used to predict excess risk of cardiac mortality at fifteen years post‐irradiation. A modified linear quadratic model was used to predict the Excess Absolute Risk (EAR) for induction of lungcancer and breast cancer at thirty years post‐irradiation. Results: For 3D‐CRT and IMPT respectively, the mean excess risks of cardiac mortality were 0.9% and 0.5%. Mean EARs for lungcancer were 17.5 cases per 10,000 persons per year (PY) and 10.1 PY. Mean EARs for breast cancer were 8.2 PY and 2.8 PY. Conclusions: IMPT may significantly reduce the risks of radiation‐induced cardiac mortality and secondary cancer in the lungs and breasts of young patients receiving radiotherapy for HL, NHL, or breast cancer.

Purpose: To evaluate the potential reduction of risk of late radiation‐ induced effects for young patients with Hodgkin's lymphoma treated with intensity modulated proton therapy (IMPT) as compared to 3D conformal involved‐field photonradiotherapy. The late effects considered were cardiac mortality and secondary cancer in the lungs and breasts (for female patients). Methods: Patient data was acquired for eleven patients who were under thirty years of age and were treated with radiotherapy for Hodgkin's lymphoma in Quebec in 2010. The original CT simulation images were used to re‐plan the patients with IMPT using commercially‐available treatment planning software. The contours of the critical organs of interest were reviewed for each patient by a physician and modified when necessary for consistency. The dose‐volume matrices of the original photon plans and the new proton plans were analyzed using radiobiological models to assess the risk of late effects. The relative seriality model was utilized to predict excess risk of fatal cardiotoxicity. The organ equivalent dose concept was utilized in conjunction with a modified linear quadratic model to predict the excess absolute risk for induction of lungcancer and breast cancer. Parameters for each model were derived from retrospective studies in the literature. Results: Mean excess risk of fatal cardiotoxicity was 0.9% for photon plans and 0.6% for proton plans. Mean excess absolute risk of developing lungcancer thirty years post‐treatment was 11.9/10,000 patients per year (PY) for photons and 6.9/10,000 PY for protons. Mean excess absolute risk of developing breast cancer thirty years post‐treatment was 6.0/10,000 PY for photons and 2.1/10,000 PY for protons.Conclusions: IMPT has the potential to reduce the risk of fatal, radiation‐induced late cardiotoxicity as well as the risk of radiation‐induced secondary cancers in the lungs and breasts of young patients receiving radiotherapy for Hodgkin's lymphoma. This work has been funded in part by a grant from the Fonds de recherche SantA© Quebec (FRSQ).