Purpose To report a method for explicitly designing a planning target volume (PTV) for treatment planning and evaluation in heterogeneous media for passively scattered proton therapy and scanning beam proton therapy using single-field optimization (SFO). Methods and Materials A beam-specific PTV (bsPTV) for proton beams was derived by ray-tracing and shifting ray lines to account for tissue misalignment in the presence of setup error or organ motion. Range uncertainties due to inaccuracies in CT-based range estimation were calculated for proximal and distal surfaces of the target in the beam direction. The bsPTV was then constructed based on local heterogeneity. The bsPTV thus can be used directly as a planning target as if it were in photon therapy. To test the robustness of the bsPTV, we generated a single-field proton plan in a virtual phantom. Intentional setup and range errors were introduced. Dose coverage to the clinical target volume (CTV) under various simulation conditions was compared between plans designed based on the bsPTV and a conventional PTV. Results The simulated treatment using the bsPTV design performed significantly better than the plan using the conventional PTV in maintaining dose coverage to the CTV. With conventional PTV plans, the minimum coverage to the CTV dropped from 99% to 67% in the presence of setup error, internal motion and range uncertainty. However, plans using the bsPTV showed minimal drop of target coverage from 99% to 94%. Conclusions The conventional geometry-based PTV concept used in photon therapy does not work well for proton therapy. We investigated and validated a beam-specific PTV method for designing and evaluating proton plans.

Purpose The anthropomorphic phantom program at the Houston branch of the Imaging and Radiation Oncology Core (IROC-Houston) is an end-to-end test that can be used to determine whether an institution can accurately model, calculate, and deliver an intensity-modulated radiation therapy (IMRT) dose distribution. Currently, institutions that do not meet IROC-Houston’s criteria have no specific information with which to identify and correct problems. In this work an independent recalculation system is developed that can identify treatment planning system (TPS) calculation errors. Methods A recalculation system was commissioned and customized using IROC-Houston measurement reference dosimetry data for common linear accelerator classes. Using this system, 259 head and neck phantom irradiations were recalculated. Both the recalculation and the institution’s TPS calculation were compared with the delivered dose that was measured. In cases where the recalculation was statistically more accurate by 2% on average or 3% at a single measurement location than was the institution’s TPS, the irradiation was flagged as having a “considerable” institutional calculation error. Error rates were also examined according to the linac vendor and delivery technique. Results Surprisingly, on average, the reference recalculation system had better accuracy than the institution’s TPS. Considerable TPS errors were found in 17% (45) of head and neck irradiations. 68% (13) of irradiations that failed to meet IROC-Houston criteria were found to have calculation errors. Conclusion Nearly 1 in 5 institutions were found to have TPS errors in their IMRT calculations, highlighting the need for careful beam modeling and calculation in the TPS. An independent recalculation system can help identify the presence of TPS errors and pass on knowledge to the institution.

No abstract

No abstract

Purpose-To determine whether a 3-mm isotropic target margin adequately covers the prostate and seminal vesicles (SVs) during administration of an intensity-modulated radiation therapy (IMRT) treatment fraction, assuming that daily image-guided setup is performed just before each fraction.Methods and Materials-In-room computed tomographic (CT) scans were acquired immediately before and after a daily treatment fraction in 46 patients with prostate cancer. An eight-field IMRT plan was designed using the pre-fraction CT with a 3-mm margin and subsequently recalculated on the post-fraction CT. For convenience of comparison, dose plans were scaled to full course of treatment (75.6 Gy). Dose coverage was assessed on the post-treatment CT image set.Results-During one treatment fraction (21.4 ± 5.5 minutes), there were reductions in the volumes of the prostate and SVs receiving the prescribed dose (median reduction 0.1% and 1.0% respectively, p <0.001) and in the minimum dose to 0.1 cm 3 of their volumes (median reduction 0.5 Gy and 1.5 Gy, p <0.001). Of the 46 patients, three patients' prostates and eight patients' SVs did not maintain dose coverage above 70 Gy. Rectal filling correlated with decreased percentage-volume of SV receiving 75.6, 70, and 60 Gy (p <0.02). CONFLICTS OF INTEREST NOTIFICATIONNone of the authors have any actual or potential conflicts of interest.Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access