Proton Stereotactic Centralized Ablative Radiation Therapy for treating Bulky Tumor: A treatment plan study

Tengxiang LI ^1,2 Xinsen Yao ³ Jinhu Chen ² Ruimin He ¹ Shuai Wang ^4,5 Qingtao Qiu ^2* Quan Tang ^1* Yong Yin ^1,5*

• ¹ School of Nuclear Science and Technology, University of South China, Hengyang, China
• ² Department of Radiation Physics, Department of Medical Oncology, Shandong Cancer Hospital, Shandong University, Jinan, Shandong Province, China
• ³ Department of Radiotherapy Center, The First People's Hospital of Chenzhou, Chenzhou, Hunan Province, China
• ⁴ School of Nuclear Science and Technology, University of Science and Technology of China, Hefei, Anhui Province, China
• ⁵ Department of Radiation Oncology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui Province, China

Objective: Stereotactic Centralized/Core Ablative Radiation Therapy (SCART) is a novel radiotherapy approach. This study investigates the potential benefits of Proton based SCART (pSCART) by leveraging the dosimetric advantages of protons and integrating them with the SCART technique.Methods: Five clinical cases previously treated with conventional proton therapy were selected for this study. pSCART plans utilizes a relative biological effectiveness (RBE) prescription dose of 24 Gy (RBE) × 3 fractions, with each plan consisting of three to five fields. The prescribed dose for CyberKnife SCART were the highest value meeting the OARs dose limits and the tumor edge dose limits. The dose distributions of CyberKnife-based SCART and pSCART plans were compared using five criteria: (ⅰ) prescription dose, (ⅱ) 80% prescription dose volume, targets coverage at 80% and 20% dose levels, and the 80%/20% ratio, (ⅲ) volume receiving > 5 Gy outside the tumor edge, (ⅳ) dose tolerance limits to organs-at-risk (OARs), (ⅴ) mean dose to OARs.Results: pSCART can deliver a higher prescription dose of 24 Gy × 3 fractions versus SCART's 15 Gy × 2-3 fractions or 18 Gy × 2 fractions. Specifically, pSCART outperforms SCART in terms of the 80% prescription dose volume, and 80% dose level coverage of Stereotactic Centralized/Core Target Volumes (SCTV) achieving 69.77%-100.00% versus SCART's 43.6%-99.5%. The 20% dose level coverage for Gross Target Volumes (GTV) is slightly lower for pSCART, achieving 88.96%-98.64% versus SCART's 90.1%-99.9%. The maximum point dose outside the target volume is lower for pSCART, at 4.58 Gy-6.19 Gy versus SCART's 4.78 Gy-6.67 Gy, additionally, the V5Gy at tumor edge is significantly smaller for pSCART, at 5.93 cm 3 -23.72 cm 3 versus SCART's 6.85 cm 3 -151.66 cm 3 . The average dose to most OARs in the pSCART plan is lower than in the SCART plan.This work provides initial insights into evaluating treatment plans for bulky tumors using pSCART. Compared to CyberKnife SCART, pSCART generates significantly higher prescription dose and larger high-dose region within the GTV, while delivers lower doses at the tumor edge, enhancing normal tissue sparing.