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Session: Therapy General ePoster Viewing [Return to Session]

Treatment Planning to Suppress Sublethal-Damage Repair by Modulating Spatio-Temporal Patterns of Spot-Scanning Proton Dose Delivery: An Initial Study

H Hosoi1*, K Kasamatsu2, K Miyazaki3, S Takao3, S Tanaka4, Y Chen3, N Miyamoto3, K Nishioka5, T Hashimoto5, H Aoyama5, T Matsuura3, (1) Graduate School of Engineering, Hokkaido University, Sapporo, Japan, (2) Graduate School of Biomedical Science and Engineering, Hokkaido University, Sapporo, Japan, (3) Faculty of engineering, Hokkaido University, Sapporo, Japan, (4) Quantum Life and Medical Science Directorate, National Institutes for Quantum Science and Technology, Chiba, Japan, (5) Department of Radiation Oncology, Faculty and Graduate School of Medicine, Hokkaido University, Sapporo, Japan


PO-GePV-T-124 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: To identify treatment plans to suppress sublethal-damage repair (SLDR) following the delivery of protons to tumors during a single treatment session by modulating the spatio-temporal pattern of dose delivery.

Methods: Parallel-opposed field plans were created in prostate phantom with a prescribed dose of 60 Gy (RBE = 1.1) in 20 fractions using VQA treatment planning system (Hitachi Ltd., Japan). Three different plans were investigated: (1) single-field uniform dose (SFUD) plan, (2) downslope-dose plan (each field provides a dose covering the whole target with downslope-dose distribution), and (3) split-target plan (each field provides a dose to the left or right hemisphere of target only). The total beam delivery time was between 0 (acute radiation) and 30 min. An extended linear-quadratic model, which includes the effects of both linear energy transfer and spatio-temporal pattern of dose delivery, was used to evaluate the relative decrease of biological dose (RDD) and tumor control probability (TCP). Cell-specific parameters of α/β = 3.1 Gy, repair half-time = 16 min, and number of clonogens = 3.0 × 10⁶ were used to analyze SLDR.

Results: The split-target plan resulted in a highest biological dose in acute radiation with lowest RDD across the target while the SFUD plan resulted in lowest biological dose with highest RDD. The TCP decreased by 3.9%, 1.2%, and 0.1% for the SFUD, downslope-dose, and split-target plans, respectively, when the beam was delivered in 10 min and 21.8%, 6.5%, and 0.6%, respectively, when the beam was delivered in 30 min. Higher sensitivity to the range error was observed with the downslope-dose and split-target plans compared with the SFUD plan.

Conclusion: Utilizing the spatio-temporal flexibility of scanning beam delivery appears to enable suppression of SLDR during prolonged single treatment sessions. However, the increased sensitivity to the range errors needs to be resolved before clinical implementation.

Funding Support, Disclosures, and Conflict of Interest: Koichi Miyazaki is paid by Hitachi, Ltd .


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