Minimum dose rate estimation for pulsed FLASH radiotherapy: A dimensional analysis
- 12 April 2020
- journal article
- research article
- Published by Wiley in Medical Physics
- Vol. 47 (7), 3243-3249
- https://doi.org/10.1002/mp.14181
Abstract
Purpose/Objectives To provide an order of magnitude estimate of the minimum dose rate (Rmin) required by pulsed ultra‐high dose rate radiotherapy (FLASH RT) using dimensional analysis. Materials/Methods In this study, we postulate that radiation‐induced transient hypoxia inside normal tissue cells during FLASH RT results in better normal tissue sparing over conventional dose rate radiotherapy. We divide the process of cell irradiation by an ultra‐short radiation pulse into three sequential phases: I) The radiation pulse interacts with the normal tissue cells and produces radiation‐induced species. II) The radiation‐induced species react with oxygen molecules and reduce the cell environmental oxygen concentration ([O2]) . III) Oxygen molecules, from nearest capillaries, diffuse slowly back into the resulted low [O2] regions. By balancing the radiation‐induced oxygen depletion in phase II and diffusion‐resulted [O2] replenishment in phase III, we can estimate the maximum allowed pulse repetition interval to produce a pulse‐to‐pulse superimposed [O2] reduction against the baseline [O2]. If we impose a threshold in radiosensitivity reduction to achieve clinically observable radiotherapy oxygen effect and combine the processes mentioned above, we could estimate the Rmin required for pulsed FLASH RT through dimensional analysis. Results The estimated Rmin inside the cell, and inversely proportional to the product of the square of the oxygen diffusion distance and the drop of intracellular [O2] per unit radiation dose. Under typical conditions, our estimation matches the order of magnitude with the dose rates observed in the recent FLASH RT experiments. Conclusions The Rmin introduced in this paper can be useful when designing a FLASH RT system. Additionally, our analysis of the chemical and physical processes may provide some insights into the FLASH RT mechanism.Keywords
This publication has 48 references indexed in Scilit:
- Targeting hypoxia in cancer therapyNature Reviews Cancer, 2011
- Labile iron pool and ferritin content in developing rat brain γ-irradiated in uteroNeuroToxicology, 2009
- Cycling hypoxia and free radicals regulate angiogenesis and radiotherapy responseNature Reviews Cancer, 2008
- The rate of cellular hydrogen peroxide removal shows dependency on GSH: Mathematical insight intoin vivoH2O2and GPx concentrationsFree Radical Research, 2007
- Hypoxia — a key regulatory factor in tumour growthNature Reviews Cancer, 2002
- Oxygen Depletion in Cells Irradiated at Ultra-high Dose-rates and at Conventional Dose-ratesInternational Journal of Radiation Biology and Related Studies in Physics, Chemistry and Medicine, 1974
- Radiation Dose-Rate: A Factor of Importance in Radiobiology and RadiotherapyThe British Journal of Radiology, 1972
- Modification of the Oxygen Effect when Bacteria are given Large Pulses of RadiationNature, 1959
- Role of Oxygen in Modifying the Radiosensitivity of E. Coli B.Nature, 1956
- The Concentration of Oxygen Dissolved in Tissues at the Time of Irradiation as a Factor in RadiotherapyThe British Journal of Radiology, 1953