Abstract：Objective To investigate the effect of cavity thickness,area and distance under the bolus upon the dose in the superficial tissues. Methods An accelerator model was constructed based on Geant4.The model accuracy was validated by the comparison of the calculated data with the measured data. A 30×30×30 cm3 water phantom with the upper surface located at the isocenter level and a 30×30×1 cm3 water film were constructed. Different models with the water film close to or different cavities with the water phantom were established. Under the 10×10 cm2 field with 6 MV X-ray beam,the central axis depth dose distribution and the lateral dose profiles at a depth of 0.1 cm (profile1) of the models with different cavities were calculated. The calculated data of different model with the water film close to or different cavities with the water phantom were statistically compared. Results When the cavity thickness was ≤ 0.5 cm, the cavity exerted slight effect upon the depth of maximum dose (Dmax) and superficial dose. As the cavity thickness was increased,the Dmax was also increased,the PDD at 0.1 cm (PDD1) was decreased rapidly and the profile1 was increased from the cavity center to the edge. Along with the increase of cavity area,the Dmax was initially increased and then decreased,whereas the PDD1 was first decreased followed by an increase. When the cavity area was small,the profile1 was gradually increased from the cavity center to the edge. When the cavity area was large,the profile1 was initially decreased and subsequently increased. When the distance was ≥ 0.2 cm,it was qualified for the clinical requirement and it exerted no effect when the distance was ≥ 1.0 cm. The profile1 distant from the cavity was not affected. Conclusion The cavity under the bolus should be minimized to reduce the cavity thickness,area and distance as possible.
Kong Dong,Hui Lin,Wei Xianding et al. Effect of cavity under bolus on the dose of superficial tissue[J]. Chinese Journal of Radiation Oncology, 2018, 27(11): 1009-1012.
[1] 李士骏.电离辐射剂量学基础[M].苏州:苏州大学出版社. Li Shi-jun. Fundamentals of Ionizing Radiation Dosimetry[M]. Suzhou:Suzhou University Press. [2] 周瑛瑛,邱小平,狄晓云,等."Pretend" Bolus在乳腺癌根治术后调强放疗应用中的剂量学研究[J].中国医学物理学杂志,2013,30(1):3848-3850.DOI:10.3969/j.issn.1005-202X.2013.01.003. Zhou Ying-ying, Qiu Xiao-ping, Di Xiao-yun, et al. The Study of Dose in Intensity Modulated Radiotherapy of Post—operative Patienta with Breast Cancer by “prentend” bolus[J].Chinese Journal of Medical Physics, 2013, 30(1):3848-3850.DOI:10.3969/j.issn.1005-202X.2013.01.003. [3] 陈华,徐义果,庄志邈,等.放疗计划系统中空腔边缘剂量计算准确性研究[J].中华放射肿瘤学杂志,2017,26(1):69-73.DOI:10.3760/cma.j.issn.1004-4221.2017.01.016. Chen Hua, Xu Yiguo, Zhuang Zhimiao, et al. Dose accuracy research on air cavity interface in treatment planning system[J].Chin J Radiat Oncol, 2017, 26(1):69-73.DOI:10.3760/cma.j.issn.1004-4221.2017.01.016. [4] 赵艳群,黎杰,吴丽萍,等.热塑膜对X射线治疗剂量影响的研究[J].中华放射肿瘤学杂志,2010,19(4):336-339.DOI:10.3760/cma.j.issn.1004-4221.2010.04.018. Zhao Yan-qun, Li Jie, Wu Li-ping, et al. Impact of thermoplastic mask on X-ray surface dose calculated with Monte Carlo code[J].Chin J Radiat Oncol, 2010, 19(4):336-339.DOI:10.3760/cma.j.issn.1004-4221.2010.04.018. [5] Geant4 Collaboration. Introduction to Geant4[EB/OL].http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/IntroductionToGeant4/html/index.html,2016-12-9. [6] 孔栋,苗利,赵飞,等.西门子加速器射束特点的Geant4模拟研究[J].辐射研究与研究工艺学报,2013,31(5):58-64. DOI:10.11889/j.1000-3436.2014.rrj.31.050801. Kong Dong, Miao Li, Zhao F, et al. Simulation study on Siemens accelerator beam characteristics with Geant4 code[J]. J. Radiat. Res. Radiat. Process, 2013, 31(5):58-64. DOI:10.11889/j.1000-3436.2014.rrj.31.050801. [7] Sharma S C,John M W.Surface dose perturbation due to air gap between patient and bolus for electron beams[J].Med Phys,1993,20(2):377-378.https://doi.org/10.1118/1.597079. [8] Kong M,Holloway L.An investigation of central axis depth dose distribution perturbation due to an air gap between patient and bolus for electron beams[J].Aust Phys Eng Sci Med,2007,30(2):111-119.DOI:10.1039/b816106b. [9] 李承军,胡健,张爱华,等.6 MV X线时组织等效补偿膜与人体空气间隙对表面剂量的影响[J].医疗卫生装备,2011,32(3):83-84. DOI:10.3969/j.issn.1003-8868.2011.03.033. Li CJ, Hu J, Zhang AH, et al. Serface Dose Perturbation Due to Air Gap Between Patient and Bolus for 6 MV X-ray[J].Chinese Medical Equipment Journal, 2011,32(3):83-84.DOI:10.3969/j.issn.1003-8868.2011.03.033. [10] 王兴安,谭丽娜,孙晓欢,等.Bolus与皮肤间隙大小对皮肤表面剂量影响的研究[J].中华放射肿瘤学杂志,2015,24(3):299-300. DOI:10.3760/cma.j.issn.1004-4221.2015.03.017. Wang XA, Tan LN, Sun XH, et al. Research of Serface Dose Perturbation Due to Gap Between Patient and Bolus[J]. Chin J Radiat Oncol, 2015,24(3):299-300. DOI:10.3760/cma.j.issn.1004-4221.2015.03.017. [11] 王峻峰,李定宇,黄章玲,等.Merkel细胞癌电子线放疗中3D打印补偿物的模拟应用[J].中华放射肿瘤学杂志,2016,25(9):999-1002.DOI:10.3760/cma.j.issn.1004-4221.2016.09.022. Wang JF, Li DY, Huang ZL, et al. Simulation and application of 3D printed compensator in electron radiation therapy for Merkel cell carcinoma[J].Chin J Radiat Oncol, 2016, 25(9):999-1002. DOI:10.3760/cma.j.issn.1004-4221.2016.09.022. [12] 张敏,赵波,尹金鹏,等.新型3D打印组织补偿物的放疗应用研究[J].中华放射肿瘤学杂志,2017,26(2):210-214. DOI:10.3760/cma.j.issn.1004-4221.2017.02.018. Zhang M, Zhao B, Yin JP, et al. Application of new three-dimensional printed tissue compensators in radiotherapy[J]. Chin J Radiat Oncol, 2017,26(2):210-214. DOI:10.3760/cma.j.issn.1004-4221.2017.02.018.
2018, Vol. 27 
