FLASH radiotherapy (FLASH-RT) is a treatment modality that delivers ultra-high dose rate and ultra-fast radiation for cancer treatment. Compared to conventional dose rate radiotherapy, FLASH-RT can yield similar efficacy for tumors and achieve normal tissue protection, translating to an increased therapeutic window. Due to this unique feature, FLASH-RT is attracting increasing attention from the radiotherapy community, both academia and industry. Due to its unique Bragg peak as well as intrinsic high dose rate, application of FLASH has more value and profound significance in proton therapy while achieving highly conformal dose deposition simultaneously. This article reviews research progress on FLASH-RT, relevant cell and animal studies, experimental conditions and results. Moreover, this article also investigates the potential biological mechanisms, technical challenges for implementation and potential clinical applications of FLASH-RT.

ObjectiveTo understand the human immunodeficiency virus（HIV） infection status and related factors by using the HIV/AIDS sentinel surveillance data of men who have sex with men（MSM） in Jinhua City， Zhejiang Province. MethodsSnowball sampling method was used to recruit MSM receiving HIV sentinel surveillance from 2016 to 2021.The inclusion criteria were aged 18 years old and above， reported having anal sex with man in recent 6 months. Questionnaire-based interviews were conducted on a one-on-one basis. Data including the characteristics of demography and ethology were collected. Five milliliter of blood samples were taken after the questionnaire. HIV and syphilis was screened. The time trend was analyzed with χ² test. Multivariate logistic regression model was used to analyze the factors associated with HIV infection status among MSM. ResultsThe positive rate of HIV was 8.0% （127/1 597）， with an increasing trend （P=0.002）， but the linear correlation was weak（r=0.075）. The positive rate of syphilis was 5.2% （83/1 597）， with no significant difference （P=0.661）.The constituent ratios showed an increasing trend （P<0.05） in using condoms consistently， finding male sexual partners through Internet or dating software， having anal sex in the past week， using condoms every time during anal sex in the past 6 months， accepting prevention services of AIDS in the last year， and the overall awareness of AIDS related knowledge. Multivariate logistic regression analysis showed that who was from national minority （OR=2.27， 95%CI： 1.08‒4.73） and from other provinces （OR=1.68， 95%CI： 1.08‒2.62）， who failed to consistently use condoms every time during anal sex in the past six months （OR=3.03， 95%CI： 2.02‒4.54）， who never accepted prevention services of AIDS in the last year （OR=2.17，95%CI：1.44‒3.27）， who don’t know the knowledge of AIDS （OR=1.86， 95%CI： 1.12‒3.07）， and who was infected with syphilis （OR=2.35， 95%CI： 1.20‒4.61） were at higher risk for HIV infection among MSM. ConclusionThe positive rate of HIV remains at a certain level among MSM in Jinhua. High-risk groups such as the patients with syphilis infections and floating population from other provinces need to be paid close attention. It is suggested to further strengthen the promotion of the use of condoms， awareness of AIDS and syphilis， warning education and comprehensive intervention services.