Scripted spot removal in PBS proton therapy planning

Abstract

Background It is well known in proton therapy that the relative biological effectiveness (RBE) is not constant across the entire Bragg peak, with higher RBE at the distal end of the Bragg peak due to higher linear energy transfer (LET). Treatment planning systems are moving toward LET optimization to mitigate this potentially higher biological impact at a track end. However, using a simple script, proton users can begin to simulate this process by deleting spots from critical structures during optimization. In most cases, nominal target coverage and plan robustness remain satisfactory. Methods In our clinic, we developed a script that allows the user to delete spots in all organs at risk (OARs) of interest for one or more treatment beams. The purpose of this script is to potentially reduce side effects by eliminating Bragg peaks within OARs. The script was first used for prostate patients where spots in the rectum and sigmoid, outside of the overlap with the target, were deleted. We then began to use the script for head and neck (H&N) and breast/chestwall patients to reduce acute side effects of the skin by removing spots in a 0.5‐cm skin rind. Conclusions By utilizing a simple script for deleting spots in critical structures, we have seen excellent clinical results thus far. We have noted reduced skin reactions for nearly all H&N and breast patients.

Proton PBS Planning Techniques, Robustness Evaluation, and OAR Sparing for the Whole-Brain Part of Craniospinal Axis Irradiation

“…In addition, the optimization robustness settings are also taken into account by the algorithm, which results in also placing the spots inside of the avoidance ROIs. To circumvent these issues, an algorithm was created by Hedrick et al [ 25 ] that allows for spot editing after the initial spot placement is conducted by RayStation. In this work, the algorithm was used to remove spots placed less deep than 5 mm from the skin surface (see Figure 3 ), which follows the clinical practice at the Provision clinic (S. Hedrick, Provision CARES Proton Therapy Center, Knoxville, TN, USA, personal communication).…”