Author: Hao Gao, Qiang Li, Yuting Lin, Wei Wang, Wei Wu, Weijie Zhang 👨🔬
Affiliation: Institute of Modern Physics, Chinese Academy of Sciences, China, Department of Radiation Oncology, University of Kansas Medical Center 🌍
Purpose: Carbon minibeam radiation therapy (cMBRT) offers high peak-to-valley dose ratio (PVDR) and relative biological effectiveness. A key challenge is balancing uniform target coverage with PVDR preservation in organs at risk (OAR). This study presents the scissor-beam (SB) technique to optimize this balance in cMBRT.
Methods: The SB method introduces scissor beam splitting. Each original beam is divided into a primary beam and a complementary beam. The primary beam maintains the same angle as the original beam, while the complementary beam is rotated by a small degree. This rotation angle is determined based on the center-to-center (ctc) distance and the relative positions of the OAR and the target. Monte Carlo simulation using GATE/GEANT4 was performed for dose calculations. The effectiveness of SB was evaluated in comparison to conventional cMBRT method (CONV) and crossfire method (CF) in terms of target dose uniformity, OAR sparing, and PVDR in OAR across three clinical cases: lung, pancreas, and head-and-neck (HN) cancers.
Results: SB showed marked improvement over CONV (dctc = 4 mm) in conformity index (CI) (lung case: 0.83 vs 0.31) while maintaining comparable PVDR values (lung case at 0º, 120º, 240º: 3.97, 2.15, 2.54 vs 4.47, 2.19, 2.61). Compared to CF, SB achieved enhanced OAR sparing (lung case: left lung Dmean 0.08Gy vs 0.12Gy) with similar CI (lung case: 0.8 vs 0.74) and PVDR values (lung case at 0º, 120º, 240º: 3.97, 2.15, 2.54 vs 4.27, 2.14, 2.57).
Conclusion: We have proposed a novel SB method for cMBRT. SB provides a better balance between uniform target dose and PVDR in OAR compared to CONV. Additionally, SB demonstrates superior OAR protection compared to CF. This innovative approach holds significant potential to enhance the therapeutic ratio of cMBRT, offering improved treatment outcomes and reduced risks for patients.