Dose reconstruction with Compton camera during proton therapy via subset-driven origin ensemble and double evolutionary algorithm

Compton camera-based prompt gamma(PG) imaging has been proposed for range verification during proton therapy. However, a deviation between the PG and dose distributions, as well as the difference between the reconstructed PG and exact values, limit the effectiveness of the approach in accurate range monitoring during clinical applications. The aim of the study was to realize a PG-based dose reconstruction with a Compton camera, thereby further improving the prediction accuracy of in vivo range verification and providing a novel method for beam monitoring during proton therapy. In this paper, we present an approach based on a subset-driven origin ensemble with resolution recovery and a double evolutionary algorithm to reconstruct the dose depth profile(DDP) from the gamma events obtained by a cadmium-zinc-telluride Compton camera with limited position and energy resolution. Simulations of proton pencil beams with clinical particle rate irradiating phantoms made of different materials and the CT-based thoracic phantom were used to evaluate the feasibility of the proposed method. The results show that for the monoenergetic proton pencil beam irradiating homogeneous-material box phantom,the accuracy of the reconstructed DDP was within 0.3 mm for range prediction and within 5.2% for dose prediction. In particular, for 1.6-Gy irradiation in the therapy simulation of thoracic tumors, the range deviation of the reconstructed spreadout Bragg peak was within 0.8 mm, and the relative dose deviation in the peak area was less than 7% compared to the exact values. The results demonstrate the potential and feasibility of the proposed method in future Compton-based accurate dose reconstruction and range verification during proton therapy.

Low-dose ionizing radiation exposure and risk of leukemia: results from 1950-1995 Chinese medical X-ray workers’ cohort study and meta-analysis

Background:It has been well-established that acute radiation exposures increase the risk of leukemia.However,it is still unknown whether these leukemia risk estimates could be extrapolated to occupational populations who receive repeated low-dose radiation exposure.The purpose of this study was to estimate quantified associations between low-dose radiation exposures and leukemia.Methods:The Chinese medical X-ray worker study(CMXW)included 27,011 medical X-ray workers employed at major hospitals in 24 provinces in China from 1950 to 1980,and a control population of 25,782 physicians matched by hospital,who were unexposed to X-ray equipment.Poisson regression models were used to esti-mate the excess relative risk(ERR)and excess absolute risk(EAR)for the incidence of leukemia associated with cumulative doses.A meta-analysis of the published literature on low-dose occupational radiation exposure and leukemia risk was also conducted.Results:The incidence rates of leukemia in X-ray workers and the control group were 6.70 and 3.39 per 100,000 person-years,respectively.Among X-ray workers,the average cumulative red bone marrow dose was 0.046 Gy.We found a positive relationship between 2-year lagged cumulative red bone marrow dose and risk of leukemia excluding chronic lymphocytic leukemia(CLL)(ERR=0.66 per 100 mGy,90%CI:0.09,1.53;EAR=0.29 per 104 PY-100 mGy,90%CI:0.07,0.56).The excess risk was largely driven by myeloid leukemia(ERR=1.06 per 100 mGy,90%CI:0.22,2.51).Based on the meta-analysis,the pooled ERR at 100 mGy was 0.19(95%CI:0.08,0.31).Conclusion:This study provides strong evidence of a positive and linear doseresponse relationship between cu-mulative red bone marrow dose and the incidence of non-CLL leukemia.

Physical dosimetric reconstruction of a case of large area back skin injury due to overexposure in an interventional procedure

To estimate the physical dose of skin and key organs in a case of overexposure during a cardiac interventional procedure.Methods The female patient aged 50 suffered from owerexposure during ardiac interventional therapy in a hospital,Xinxiang city,Henan province,China in January 2020.The mesh-type phantom for the patient was constructed based on the adult mesh-type reference computational phantoms(MRCPs)released by the International Comission on Radiological Protection Publication 145 (ICRP145)and phantom deformation technology.Models of exposure scenario were constructed and simulated with particle and heavy ion transport code system(PHTTS)according to exposure conditions.Resuts:The maximum absorbed dose of key organs/tissues under iradiation in posteroanterior(PA)and 30°left anterior oblique directions(LOA)was 632.4 and 305.6 mGy,respectively.The let lung,heart,and left mammary gland received a larger dose under both iradiation conditions.The ratio of the absorbed dose with and without shielding was a lculated,and the relative difference in most organs was<1%between two directions.The iso-dose curve of the back skin revealed the ditribution of the absorbed dose(0.1-5.2 Gy).The dose estimate of key tssues/organs was higher than the conventional level,especially the local skin,up to 5.2 Gy.Concusions The interventional procedure in this ase resulted in a higher dose.Monte Carlo codes combined with the MRCPs can be employed to estimate physical dose to individuals in concrete irradia tion scenarios.