Stepping Towards Conformal Flash Delivery: A Uhdr Multiple-Beam Study.
Abstract
Purpose
The goal of this project was to investigate whether the FLASH effect can be preserved when an ultra-high-dose-rate (UHDR) delivery is split into multiple beams (2, 4 or 6), all delivered within a time window (5 sec) that was previously shown to preserve the sparing effect.
Methods
Mice were irradiated at two dose levels (24 Gy and 26 Gy) divided into five radiation groups: single-beam UHDR , two-beam UHDR, four-beam UHDR, six-beam UHDR, and conventional dose rate (CDR). In order to measure tissue oxygen at the time of treatment, all mice were prior injected with a molecular oxygen probe, Oxyphor PdG4, and monitored by a fiber probe. To follow damage response, all mice were photographed for thirty days post-irradiation, and skin damage scores were evaluated by a trained observer. After thirty days, all animals were sacrificed, and skin samples were collected for histological analysis.
Results
The FLASH skin-sparing effect was preserved for all UHDR deliveries at the 24 Gy dose level. An ANOVA contrast test showed a statistically significant difference between the skin scores of the CDR group and those of the four UHDR groups. The 26 Gy dose level showed no statistical difference between any of the radiation groups, attributed to the damage level saturating the skin score assay.
Conclusion
This study represents a promising step toward multiple-beam delivery with UHDRs, which is required for eventual conformal techniques. Multiple UHDR beams delivered within five seconds provide the same degree of skin sparing as a single UHDR beam. Future work will continue forming the foundation for conformal UHDR delivery and analyze the effects of dose versus oxygen in damage response.