The effect of rectal gas on dose distribution during prostate cancer treatment using full arc and partial arc Volumetric Modulated Arc Therapy (VMAT) treatment plans

Motoharu Sasaki; Hitoshi Ikushima; Akira Tsuzuki; Wataru Sugimoto

doi:10.1016/j.rpor.2020.09.013

The effect of rectal gas on dose distribution during prostate cancer treatment using full arc and partial arc Volumetric Modulated Arc Therapy (VMAT) treatment plans

Rep Pract Oncol Radiother. 2020 Nov-Dec;25(6):974-980. doi: 10.1016/j.rpor.2020.09.013. Epub 2020 Oct 11.

Authors

Motoharu Sasaki¹, Hitoshi Ikushima¹, Akira Tsuzuki², Wataru Sugimoto³

Affiliations

¹ Department of Therapeutic Radiology, Institute of Biomedical Sciences, Tokushima University Graduate School, 3-18-15 Kuramoto-cho, Tokushima, Tokushima 770-8503, Japan.
² Department of Radiological Technology, Kochi Medical School Hospital, 185-1 Kohasu, Oko-cho, Nankoku-shi, Kochi 783-8505, Japan.
³ Department of Radiological Technology, Tokushima Prefectural Central Hospital, 1-10-3 Kuramoto-cho, Tokushima, Toksuhima 770-8539, Japan.

Abstract

Background/aim: In this study, we investigated the effect of rectal gas on the dose distribution of prostate cancer using a volumetric modulated arc therapy (VMAT) treatment planning.

Materials and methods: The first is the original structure set, clinical target volume (CTV), the rectum, and the bladder used clinically. The second is a structure set (simulated gas structure set) in which the overlapping part of the rectum and PTV is overwritten with Hounsfield Unit -950 as gas. Full arc and limited gantry rotation angle with VMAT were the two arcs. The VMAT of the full arc was 181°-179° in the clockwise (CW) direction and 179°-181° in the counterclockwise (CCW) direction. Three partial arcs with a limited gantry rotation angle were created: 200°-160 °CW and 160°-200 °CCW; 220°-140 °CW and 140°-220 °CCW; and finally, 240°-120 °CW and 120°-240 °CCW. The evaluation items were dose difference, distance to agreement, and gamma analysis.

Result: In the CTV, the full arc was the treatment planning technique with the least effect of rectal gas. In the rectum, when the gantry rotation angle range was short, the pass rate tended to reduce for all evaluation indices. The bladder showed no characteristic change between the treatment planning techniques in any of the evaluation indices.

Conclusions: The VMAT treatment planning with the least effect on dose distribution caused by rectal gas was shown to be a full arc.

Keywords: Dose distribution; Gas; Prostate cancer; Volumetric modulated arc therapy.