Near real-time automated dose restoration in IMPT to compensate for daily tissue density variations in prostate cancer

Abstract

Proton therapy is very sensitive to daily density changes along the pencil beam paths. The purpose of this study is to develop and evaluate an automated method for adaptation of IMPT plans to compensate for these daily tissue density variations. A two-step restoration method for 'densities-of-the-day' was created: (1) restoration of spot positions (Bragg peaks) by adapting the energy of each pencil beam to the new water equivalent path length; and (2) re-optimization of pencil beam weights by minimizing the dosimetric difference with the planned dose distribution, using a fast and exact quadratic solver. The method was developed and evaluated using 8-10 repeat CT scans of 10 prostate cancer patients. Experiments demonstrated that giving a high weight to the PTV in the re-optimization resulted in clinically acceptable restorations. For all scans we obtained V ⩾ 98% and V ⩽ 2%. For the bladder, the differences between the restored and the intended treatment plan were below +2 Gy and +2%-point. The rectum differences were below +2 Gy and +2%-point for 90% of the scans. In the remaining scans the rectum was filled with air, which partly overlapped with the PTV. The air cavity distorted the Bragg peak resulting in less favorable rectum doses.

Evaluation of an Open Source Registration Package for Automatic Contour Propagation in Online Adaptive Intensity-Modulated Proton Therapy of Prostate Cancer

“…To avoid overdose the optimization ensures that less than 2% of the target volumes receive more than 107% of the highest prescribed dose ( V 107% ≤ 2%). Target dose conformity and low dose to the OARs was achieved by including artificial rings around the target and including OARs in the wishlist (51). For the recontouring to be clinically acceptable the automatically generated treatment plans should still fulfill these criteria.…”

Correlations between the shifts in prompt gamma emission profiles and the changes in daily target coverage during simulated pencil beam scanning proton therapy

“…We generated the high-dose planning target volume (PTV high ; prostate + 4 mm) and the low-dose PTV (PTV low ; seminal vesicles + lymph nodes + 7 mm). In addition, there was the intermediate-dose PTV (PTV inter ), which consisted of part of the PTV low that was situated in the 15 mm ring surrounding the PTV high that was used to regulate the dose gradient around the PTV high during plan optimization (Jagt et al 2017). The PTV inter was excluded from the PTV low , thus these two volumes did not overlap.…”

Model based patient pre-selection for intensity-modulated proton therapy (IMPT) using automated treatment planning and machine learning

“…Although implemented in a commercial treatment planning system (TPS), to our knowledge this has not been clinically implemented as of yet. Apart from automated IMRT and VMAT plan generation, the Erasmus-iCycle optimizer also has an option for fully-automated IMPT planning [17][18][19][20][21][22][23]. This feature is not in clinical use, and can therefore not replace the manual IMPT planning with the clinical TPS for selection of our patients for IMPT at the Holland Particle Therapy Center (HollandPTC).…”