Author: Richard Bakst, Arpit M. Chhabra, J Isabelle Choi, Chanda Guha, Minglei Kang, Nancy Y Lee, Haibo Lin, Hang Qi, Charles B. Simone, Pingfang Tsai, Milo Vermeulen, Shouyi Wei, Xiaodong Wu, Lee Xu, Irini Yacoub, Xingyi Zhao, Ajay Zheng 👨🔬
Affiliation: University of Miami, Peking University, New York Proton Center, Montefiore Medical Center and Albert Einstein College of Medicine, icahn school of medicine at mount sinai, Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, Department of Human Oncology, University of Wisconsin-Madison 🌍
Purpose:
Three-dimensional lattice radiation therapy (3D-LRT) effectively achieves local tumor control with limited morbidity. Pencil beam scanning (PBS) proton therapy provides precise dose conformity and reduced exit doses, making it suitable for 3D-LRT. However, high entrance doses to normal tissues remain a challenge. Ultra-high dose rate (UHDR) beams may mitigate this through the FLASH effect, which protects normal tissues. This study evaluates the feasibility of PBS UHDR beams for 3D-LRT.
Methods:
Two PBS UHDR techniques, two-field and single-field, were developed for 3D-LRT in conjunction with intensity-modulated proton therapy (IMPT) for gross tumor volume (GTV) coverage. The two-field approach used range compensators and apertures to sharpen the lateral penumbra, thus enhancing the peak-to-valley dose ratio (PVDR). The single-field technique employed a ridge filter to ensure uniform vertex coverage. Treatment plans were created for head and neck, liver, and lung cases, prescribing 18 GyRBE to vertices and 3 GyRBE to GTV. Plans were evaluated for dose conformity, UHDR coverage, and robustness.
Results:
The two-field technique achieved an average PVDR of 4.0±0.2, compared to 4.8±0.7 with the single-field technique. Vertex D90% was higher for two-field plans (19.2±0.04 GyRBE) than single-field plans (18.7±0.5 GyRBE). The two-field technique reduced skin doses significantly (D1cc: 10.8±0.3 GyRBE vs. 15.0±0.4 GyRBE). Both techniques provided high UHDR coverage, favoring FLASH protection, with an average V40GyRBE/s to the skin of 80% for two-field plans and 100% for single-field plans. Plan robustness was comparable across techniques in terms of PVDR, D90%, and skin D1cc.
Conclusion:
Proton PBS UHDR 3D-LRT is a viable, innovative approach. The proposed techniques achieve high PVDR, robust dose delivery, and UHDR coverage to normal tissues, enhancing the potential for FLASH-mediated protection. These findings establish a strong foundation for clinical implementation to improve therapeutic outcomes.