Dose rate and dose robustness for proton transmission FLASH-RT treatment in lung cancer

Abstract

PurposesTo evaluate the plan quality and robustness of both dose and dose rate of proton pencil beam scanning (PBS) transmission FLASH delivery in lung cancer treatment.Methods and materialsAn in-house FLASH planning platform was used to optimize 10 lung cancer patients previously consecutively treated with proton stereotactic body radiation therapy (SBRT) to receive 3 and 5 transmission beams (Trx-3fds and Trx-5fds, respectively) to 34 Gy in a single fraction. Perturbation scenarios (n=12) for setup and range uncertainties (5 mm and 3.5%) were introduced, and dose-volume histogram and dose-rate-volume histogram bands were generated. Conventional proton SBRT clinical plans were used as a reference. RTOG 0915 dose metrics and 40 Gy/s dose rate coverage (V40Gy/s) were used to assess the dose and dose rate robustness.ResultsTrx-5fds yields a comparable iCTV D2% of 105.3%, whereas Trx-3fds resulted in inferior D2% of 111.9% to the clinical SBRT plans with D2% of 105.6% (p<0.05). Both Trx-5fds and Trx-3fds plans had slightly worse dose metrics to organs at risk than SBRT plans. Trx-5fds achieved superior dosimetry robustness for iCTV, esophagus, and spinal cord doses than both Trx-3fds and conventional SBRT plans. There was no significant difference in dose rate robustness for V40Gy/s coverage between Trx-3fds and Trx-5fds. Dose rate distribution has similar distributions to the dose when perturbation exists.ConclusionTransmission plans yield overall modestly inferior plan quality compared to the conventional proton SBRT plans but provide improved robustness and the potential for a toxicity-sparing FLASH effect. By using more beams (5- versus 3-field), both dose and dose rate robustness for transmission plans can be achieved.

Implementation of novel measurement‐based patient‐specific QA for pencil beam scanning proton FLASH radiotherapy

“…Besides the mean ADR metric, the V40Gy/s was used to quantify the dose rate performance for FLASH plans, which is defined as the voxels ratio that received doses with a dose rate >40 Gy/s in OARs and target structures. A DRVH was also used to evaluate the dose rate distribution versus volume for a region of interest 28 …”

“…A DRVH was also used to evaluate the dose rate distribution versus volume for a region of interest. 28…”

“…Ridge‐filter‐based SOBP 26 and compensator‐based single‐energy Bragg peak 15 delivery techniques were proposed to improve the dose rate by eliminating the necessity of energy switching while maintaining dose conformity compared to transmission delivery. However, high‐energy transmission delivery, which is characteristic of high current and less sensitivity to range uncertainties, is more practical to accommodate FLASH dose rates to be used for preclinical studies on animals 14,27,28 . The first clinical trial enrolling up to 10 patients with bone metastases treated with uniform transmission proton fields has demonstrated the safety and feasibility of PBS FLASH irradiation 29 .…”

“…However, high-energy transmission delivery, which is characteristic of high current and less sensitivity to range uncertainties, is more practical to accommodate FLASH dose rates to be used for preclinical studies on animals. 14,27,28 The first clinical trial enrolling up to 10 patients with bone metastases treated with uniform transmission proton fields has demonstrated the safety and feasibility of PBS FLASH irradiation. 29 Several treatment planning studies have investigated the FLASH feasibility of applying transmission proton PBS beams to more comprehensive and realistic clinical scenarios, including the head and neck (H&N), [30][31][32] lung, 33,34 and liver cancers.…”

FLASH instead of proton arc therapy is a more promising advancement for the next generation proton radiotherapy

“…18,19,83 With substantial resources and time devoted to refining the FLASH irradiation system, quality assurance devices, and radiation biology models, the path toward clinical implementation is being actively pursued. [87][88][89][90] Proton FLASH therapy may gain momentum as more clinical evidence and biological data are accumulated. These two developments are not mutually exclusive, and their coexistence can bring a new era of fast, efficient, precise, and effective personalized therapy.…”