Definition of dose rate for FLASH pencil‐beam scanning proton therapy: A comparative study
(2023) Medical Physics — Vol. 50, n° 9, p. 5784-5792 (2023)
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- Background:FLASH proton therapy has the potential to reduce side effectsof conventional proton therapy by delivering a high dose of radiation in a veryshort period of time. However, significant progress is needed in the develop-ment of FLASH proton therapy.Increasing the dose rate while maintaining doseconformality may involve the use of advanced beam-shaping technologies andspecialized equipment such as 3D patient-specific range modulators, to takeadvantage of the higher transmission efficiency at the highest energy avail-able. The dose rate is an important factor in FLASH proton therapy, but itsdefinition can vary because of the uneven distribution of the dose over timein pencil-beam scanning (PBS).Purpose:Highlight the distinctions,both in terms of concept and numerical val-ues, of the various definitions that can be established for the dose rate in PBSproton therapy.Methods:In anin silicostudy, five definitions of the dose rate, namely the PBSdose rate,the percentile dose rate,the maximum percentile dose rate,the aver-age dose rate, and the dose averaged dose rate (DADR) were analyzed firstthrough theoretical comparison, and then applied to a head and neck case. Tocarry out this study,a treatment plan utilizing a single energy level and requiringthe use of a patient-specific range modulator was employed.The dose rate val-ues were compared both locally and by means of dose rate volume histograms(DRVHs).Results:The PBS dose rate, the percentile dose rate, and the maximum per-centile dose are definitions that are specifically designed to take into accountthe time structure of the delivery of a PBS treatment plan. Although they mayappear similar, our study shows that they can vary locally by up to 10%. Onthe other hand,the DADR values were approximately twice as high as those ofthe PBS,percentile,and maximum percentile dose rates,since the DADR disre-gards the periods when a voxel does not receive any dose. Finally, the averagedose rate can be defined in various ways, as discussed in this paper. The aver-age dose rate is found to be lower by a factor of approximately 1/2 than thePBS, percentile, and maximum percentile dose rates.Conclusions:We have shown that using different definitions for the dose ratein FLASH proton therapy can lead to variations in calculated values rangingfrom a few percent to a factor of two.Since the dose rate is a critical parameterin FLASH radiation therapy, it is essential to carefully consider the choice ofdefinition.However,to make an informed decision,additional biological data andmodels are needed.
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Deffet, S., Hamaide, V., & Sterpin, E. (2023). Definition of dose rate for FLASH pencil‐beam scanning proton therapy: A comparative study. Medical Physics, 50(9), 5784-5792. https://doi.org/10.1002/mp.16607 (Original work published 2023)