ABSTRACT
In recent years, ultra-high dose rate (FLASH) radiotherapy has become one of the most advanced research topics in the field of radiotherapy. Experimental data indicate that FLASH radiotherapy can significantly reduce the irradiation damage in normal tissues while being as effective as clinical conventional dose rate radiotherapy in tumor control. The oxygen depletion hypothesis is considered as one of the key mechanisms underlying the FLASH effect. In this article, research progress on the discovery, experimental evidence and reaction principle of oxygen depletion was reviewed, the measurement methods and biological effect modeling methods of the oxygen depletion hypothesis were summarized, and the oxygen depletion difference between normal tissue and tumor was also discussed.
ABSTRACT
Background and purpose:As a new and important radiotherapy technique,intensity-modulated radiation therapy(IMRT) has been widely used in the clinic,but it requires longer time to deliver for one treatment session.The purpose of this study was to investigate the radiobiological effects of CNE and A549 cell lines irradiated by IMRT model.Methods:Part Ⅰ:The radiobiological characteristics of CNE and A549 cell lines were studied with standard clonogenic assays,using standard liner-quadratic model and incomplete repair model to fit the dose-survival curves.Part Ⅱ:a total dose of 8 Gy was given in two fractions with different interfraction intervals to compare the differences of cell surviving fractions(SF).Part Ⅲ:fractionated irradiation of 2 Gy,2 Gy?2,2 Gy?3,2 Gy?4 were given with one fraction per day simulating clinical dose-time-fractionation pattern in 2,20 and 40 min per fraction,respectively.Results:The ?/? of CNE and A549 was 1.76 and 12.41 Gy,respectively;the cell surviving fractions increased when the interfraction interval was longer,The values of SF2 were 0.0237 and 0.0243 in 2 min irradiation group,0.0304 and 0.0296 in 20 min irradiation group,and increased to 0.0378 and 0.0359 in 40 min irradiation group,respectively.Conclusion:The prolonged fraction delivery time would significantly decrease theradiobiological effects,it is strongly recommended that the delivery time be kept as short as possible,or do appropriate dose compensation.