Compared with conventional high energy X-ray radiotherapy, proton/carbon ion has obvious advantages because of its Bragg peak dose distribution. However, proton heavy ion facility has complex structure, high energy and various radiation types due to various nuclear reaction processes, the radiation protection safety brought by the operation of facilities has gradually attracted attention. Taking the proton/carbon ion radiotherapy facility of Shanghai Proton and Heavy Ion Center as an example, the author mainly analyzed the operation principle of proton/carbon ion treatment facility, the basis of radiation protection, analysis of key radiation source points, etc., so as to provide theoretical support and experience for radiation protection.
China ; Heavy Ion Radiotherapy ; Heavy Ions ; Occupational Exposure/prevention & control* ; Protons ; Radiation Protection ; Radiotherapy

Objective To assess the occupational exposure doses received by the physicians in clinical practice at Shanghai Proton and Heavy Ion Center ( SPHIC ) . Methods A total of 40 patients treated from September to November in 2016, including 20 proton cases and 20 carbon cases at SPHIC, were selected using simple random sampling method. Particle type, total particle number and prescribed doses were recorded for all the cases. The dose rates in the control room were measured by using a photon and neutron personal radiation detector during patient treatment. The dose rates around the surface of the patient's tumor 1 min after completion of beam delivery and the dose rates about 30 cm to the tumor surface (where a physician stands) were also measured during unfixing and assisting the patients. Finally, the dose rates surrounding the fixtures, couch, robotic arm and window of BAMS were measured. The factors affecting the occupational exposure of physician were analyzed and the annual dose equivalent was assessed for physicians in SPHIC. Results Proton and heavy ion released nearly all energy in the tumor for Bragg peak advantage, so there was no induced radioactivity in the treatment room. However, the tumor became the main induced radioactivity source to the occupational exposure dose to physicians in clinical practices. The dose rate around the surface of the patient's tumor 1 min after completion of beam delivery was (20. 68 ± 21. 91) μSv/h, which was the highest in the working places of physicians, thus regarded as the main source. A significant positive correlation (r=0. 828, P<0. 05) was shown between dose rates and total number of particles delivered for the treatment. The dose rate measured in the control room was (0. 08 ± 0. 01 )μSv/h, and the dose rate measured surrounding the fixtures, couch, robotic arm and BAMS window was ( 0. 09 ± 0. 01 )μSv/h. No neutron was detected. The dose rate about 30 cm to the tumor surface ( where physicians stand) was ( 2. 03 ± 2. 84 ) μSv/h during unfixing and assisting the patients. The average annual dose to physicians was about 0. 508 mSv. Conclusions The average annual dose to physicians was at a low level in SPHIC

In order to improve the biological effect of proton therapy,the authors first propose a new method of boron-based proton-enhanced radiotherapy in a"ternary"radiotherapy mode,based on the existing sensitizing effect of proton radiotherapy:i.e,Boron-based mediators(11B and 10B)induce the proton-hydrogen-boron fusion reaction of the low-energy protons arriving at the Bragg peak region of the tumor target area(p+11B→3α)and thermal neutron capture(10B+n→7Li3+(0.84 MeV)+4He2+(1.47 MeV)+γ(0.477 MeV)),which release low-energy α-particles with high LETs to enhance the biological effect of proton dose in the target area,thus improve the clinical effect of proton therapy.Then,the advantages and disadvantages of the"ternary"model were analyzed from the theoretical basis and current research status,and finally,the"ternary"model is summarized and prospected.

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