Dosimetric effects of styrofoam in 6 MV photon beam radiotherapy(PDF)
《中国医学物理学杂志》[ISSN:1005-202X/CN:44-1351/R]
- Issue:
- 2021年第4期
- Page:
- 397-403
- Research Field:
- 医学放射物理
- Publishing date:
Info
- Title:
- Dosimetric effects of styrofoam in 6 MV photon beam radiotherapy
- Author(s):
- LI Shi; LUO Huanli; TAN Xia; MENG Wanli; LI Bo; LI Guang; SHEN Zhengwen; ZHONG Mingsong; WANG Ying; JIN Fu
- Radiation Oncology Center, Chongqing University Cancer Hospital, Chongqing 400030, China
- Keywords:
- Keywords: styrofoam skin dose immobilization device dose attenuation radiotherapy
- PACS:
- R815.6
- DOI:
- DOI:10.3969/j.issn.1005-202X.2021.04.001
- Abstract:
- Abstract: Objective To evaluate the dosimetric effects of styrofoam in 6 MV photon beam radiotherapy. Methods Ten pieces of styrofoam phantoms with 2 cm thick were made, and their CT images were imported into treatment planning system for calculating the average linear attenuation coefficient which was then verified by ionization chamber measurement. The styrofoam phantoms of 2, 4, 6, 8, 10 cm thick which were formed by superimposing one over one another was placed on the surface of a solid equivalent water phantom to estimate the dosimetric effects caused by Styrofoam of different thicknesses. Furthermore, the doses distributions of 9-field intensity-modulated radiotherapy plan for 8 nasopharyngeal cancer patients immobilized with Styrofoam were calculated in the case of body structure contour with styrofoam or not. Results The average linear attenuation coefficient calculated by treatment planning system was (0.16×10-2) cm-1. The gamma passing rate (1% /1 mm) was less than 90% when styrofoam thickness was larger than 4 cm, and the thicker the Styrofoam was, the lower the gamma passing rate was. Furthermore, styrofoam had larger effects on dose built-up area than dose-drop area, and the relative surface dose was increased from 16.22% to 63.73% when only a piece of Styrofoam of 2 cm thick was placed on the surface of a solid equivalent water phantom. Due to styrofoam, the mean doses of PTVnd+nx, PTV1 and PTV2 were reduced from (72.61±0.98) Gy to (72.12±1.00) Gy, (69.11±0.79) Gy to (68.72±0.77) Gy, (62.61±1.04) Gy to (62.22±1.03) Gy, respectively, and the corresponding 100% prescription dose coverage rate was decreased from 0.97%±0.01% to 0.95%±0.03%, 0.98%±0.01% to 0.97±0.01%, 0.94%±0.04% to 0.92%±0.05%, respectively. The gamma passing rate (1%/1 mm) of overall dose was 94.06%±0.86%. Conclusion The dosimetric effects is increasing with the increasing of styrofoam thickness, which led to a significant dose increase in dose built-up area and surface dose. The attenuation effects of styrofoam reduce both mean dose sand 100% prescription dose coverage rates at target areas. It is recommended that the thickness of styrofoam should no exceed 4 cm, and that styrofoam should be included in body structure contour to assess whether the skin dose is safe.
Last Update: 2021-04-29