FLASH Stereotactic Body Radiation Therapy for Spine Tumors Using a Single-Energy Proton Pristine Bragg Peak Delivery Technique

Balaji Selvaraj; Xingyi Zhao; Haibo Lin; Jiajian Shen; Chingyun Cheng; Alex Bookbinder; Hui Wu; Huifang Zhai; J Isabelle Choi; Arpit M Chhabra; Shaakir Hasan; Charles B Simone 2nd; Yoshiya Yamada; Minglei Kang

doi:10.1016/j.adro.2025.101776

FLASH Stereotactic Body Radiation Therapy for Spine Tumors Using a Single-Energy Proton Pristine Bragg Peak Delivery Technique

Adv Radiat Oncol. 2025 Apr 3;10(6):101776. doi: 10.1016/j.adro.2025.101776. eCollection 2025 Jun.

Authors

Balaji Selvaraj¹, Xingyi Zhao¹, Haibo Lin^{1

2}, Jiajian Shen³, Chingyun Cheng⁴, Alex Bookbinder¹, Hui Wu⁵, Huifang Zhai¹, J Isabelle Choi^{1

2}, Arpit M Chhabra¹, Shaakir Hasan¹, Charles B Simone 2nd^{1

2}, Yoshiya Yamada², Minglei Kang^{1

4}

Affiliations

¹ New York Proton Center, New York, New York.
² Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, New York.
³ Department of Radiation Oncology, Mayo Clinic, Phoenix, Arizona.
⁴ Department of Human Oncology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin.
⁵ Department of Radiation Oncology, the Affiliated Cancer Hospital of Zhengzhou University & Henan Cancer Hospital, Zhengzhou, China.

Abstract

Purpose: To investigate the dosimetric performance and dose rate of Bragg peak FLASH (BP-FLASH) for spinal cord stereotactic body radiation therapy (SBRT).

Methods and materials: Ten consecutive patients with spinal tumors treated with conventional intensity modulated proton therapy (CONV-IMPT) SBRT (40 Gy in 5 fractions) were selected for this study. These patients were reoptimized using an in-house FLASH algorithm and a single-energy Bragg peak approach. The dose distributions and dose metrics for target coverage and critical organs-at-risk (OARs) were compared. BP-FLASH plans dose rates were calculated using an average-dose-rate. The FLASH ratios (V_40Gy/s) were assessed with dose thresholds at 0.2, 2, and 5 Gy. The doses and dose rates for the 10 patients were averaged, and a t test was performed comparing CONV-IMPT and BP-FLASH.

Results: Dosimetric analysis revealed that the BP-FLASH plans deliver a similar dose as CONV-IMPT plans to critical OARs. However, in BP-FLASH, the clinical target volume received a higher maximum dose than CONV-IMPT (115.1% versus 108.9%, P = .001). No notable differences were observed in the maximum doses to the spinal cord (P = .122) or esophagus (P = .327). FLASH dose rates for all the OARs exceeded 80% with 2 Gy dose threshold. When increased to 5 Gy, V_40Gy/s increased to >95% for composite plan doses.

Conclusions: BP-FLASH SBRT is a promising treatment for challenging spinal cord cancers, which achieved ultra-high-dose rates for FLASH effect and maintained the same dosimetry quality as the CONV-IMPT plans.