ABSTRACT
Objective:To assess the shielding requirements of low energy X-ray intraoperative radiotherapy room under the domestic and foreign standards and guidelines, to measure the sured transmission factors for a range of shielding materials, the ambient dose equivalent rate around concerned positions and the shielding effect of protective devices, so as to provide references for shielding design of such radiotherapy units and applications of radiological protection devices.Methods:The required shielding thicknesses for a treatment room with INTRABEAM intraoperative radiotherapy system were calculated under the Chinese national standard GBZ 121, IPEM report No. 75 and NCRP report No. 151, respectively. The transmission factors for a range of shielding materials including solid water slab, shielding sheet and shielding apron were measured. Moreover, the ambient dose equivalent rates were measured under the simulated working conditions and the shielding effectiveness of a lead screen was evaluated.Results:The required lead thicknesses calculated under different standards and guidelines were less than 0.6 mm for all the concerned points, with the differences at sub-millimeter level. The low energy X-rays generated by this equipment attenuated rapidly in the shielding materials. The measured transmission factors of 0.05 mm lead equivalent shielding sheet and 0.25 mm lead equivalent shielding apron were 0.068 and 0.003 8, respectively. When the radiation was delivered using spherical applicator without any attenuation, the ambient dose equivalent rates at 1 m and 2 m from the X-ray source were 10.7 and 2.6 mSv/h, respectively. The corresponding measurement values decreased to 3.8 and 0.9 μSv/h, respectively, when the spherical applicator was inserted into a small water tank. Meanwhile, the ambient dose equivalent rate at 2 m was reduced to the background level when using protective screen.Conclusions:The shielding requirements for a low energy X-ray intraoperative radiotherapy facility are minimal, with low effective energy of X-rays generated by this equipment, but the dose rate close to the unshielded radiation source is high. The shielding scheme of treatment room should be optimized in design and the protective device should be used in a reasonable way.
ABSTRACT
Objective To implement the finite discontinuity?volumetric modulated arc therapy ( FD?VMAT) in the Pinnacle planning system, and to investigate its clinical significance. Methods Eight patients with thoracic esophageal cancer in our hospital were enrolled as subjects. FD?VMAT was fulfilled in the Pinnacle planning system using a developed program. FD?VMAT, VMAT, and fixed?field intensity?modulated radiotherapy ( IMRT ) plans were designed for each patient. The conformity index ( CI ) and homogeneity index ( HI) of the planning target volume ( PTV) ,doses to organs at risk,passing rate for plan verification,number of monitor units,and treatment time were used to evaluate the plans. Comparison between different plans was made by paired t test. Results For the PTV,there was no significant difference in CI between FD?VMAT and VAMT ( P=0?186 );FD?VMAT had a significantly worse HI than VMAT ( P=0?001);however,both the CI and HI were significantly improved in FD?VMAT than in IMRT ( P=0?006, 0?002) . Compared with IMRT, FD?VMAT, retaining the advantage of VMAT, had pulmonary V20 and V30 significantly reduced by 19?79% and 20?32%,respectively (P=0?000,0?000).For the pulmonary low?dose regions (≤V5 ) ,FD?VMAT retained the advantage of IMRT and had lower doses than VMAT. Particularly, pulmonary V2 was significantly reduced by 16?79%(P=0?000).The mean lung dose was significantly lower in FD?VMAT than in VMAT or IMRT (P=0?001,0?000).There were no significant differences in D1cc to spinal cord PRV,heart V30,or passing rate for plan verification between the three therapies. The heart V40 and mean heart dose in FD?VMAT were similar to those in VMAT (P=0?175,0?468),but significantly lower than those in IMRT ( P=0?021,0?002) . FD?VMAT had a larger number of monitor units and longer treatment time than VMAT. Compared with IMRT, the number of monitor units and treatment time were reduced by 13?6% and 49?6% in FD?VMAT,respectively. Conclusions Compared with VMAT and IMRT, the application of the developed FD?VMAT in the treatment of thoracic esophageal cancer can further reduce the lung dose while keeping the PTV coverage,protection of the heart and spinal cord,and high efficacy. FD?VMAT is a new therapy available for thoracic esophageal cancer.