Dosimetric effects of immobilization device on intensity-modulated radiotherapy for nasopharyngeal carcinoma(PDF)
《中国医学物理学杂志》[ISSN:1005-202X/CN:44-1351/R]
- Issue:
- 2019年第3期
- Page:
- 271-276
- Research Field:
- 医学放射物理
- Publishing date:
Info
- Title:
- Dosimetric effects of immobilization device on intensity-modulated radiotherapy for nasopharyngeal carcinoma
- Author(s):
- GU Shiyong1; CHEN Li2; MA Yan1; YU Yizhen1
- 1. Department of Radiation Oncology, the Sixth Affiliated Hospital of Sun Yat-sen University, Guangzhou 510655, China; 2. Department of Radiation Oncology, Sun Yat-sen University Cancer Center/State Key Laboratory of Oncology in South China/Collaborative Innovation Center for Cancer Medicine, Guangzhou 510060, China
- Keywords:
- Keywords: nasopharyngeal carcinoma; head and neck immobilization device; intensity-modulated radiotherapy; dosimetric effect
- PACS:
- R815.6
- DOI:
- DOI:10.3969/j.issn.1005-202X.2019.03.005
- Abstract:
- Abstract: Objective To investigate the dosimetric effects of head and neck immobilization device on the dose distribution of intensity-modulated radiotherapy for nasopharyngeal carcinoma (NPC). Methods Nine patients with NPC were randomly selected. Two sets of body contours were established for each patient. One of the body contours did not contain the immobilization device, and the other contained the immobilization device. For the two sets of contours of each patient, 9-field IMRT plan and VMAT plan were designed, and the plans for different sets of contours were recorded as Planwithout and Planwith. The dose differences caused by the head and neck immobilization devices were assessed by the comparative analysis on dose-volume histogram (DVH) parameters and differences in the results of different plans. Results For 9-field IMRT plans, Planwith had lower PTV dose coverage and average dose than Planwithout. Compared with those in Planwithout, the dose coverage of PTVnx, PTVnd, PTV1 and PTV2 in Planwith were decreased by 2.14%, 10.34%, 0.88%, 2.86% (P<0.01, P<0.01, P=0.15, P<0.01), respectively, and their average doses were decreased by 0.96%, 1.94%, 1.07%, 1.26% (all P<0.01). In addition, the mean dose of organs-at-risk except for brainstem was reduced in Planwith (with a maximum deviation of 1.69%, P<0.01) and the back neck skin dose was increased by 10-15 Gy in Planwith. For VMAT plans, the PTV dose coverage and mean dose of Planwith were lower than those of Planwithout. The PTVnx, PTVnd, PTV1 and PTV2 dose coverage in Planwith were decreased by 2.56%, 22.42%, 0.66%, 1.30% (P<0.01, P=0.57, P<0.01, P=0.02), respectively, and their average doses were decreased by 0.86%, 2.45%, 0.93%, 1.59% (P=0.01, P<0.01, P<0.01, P<0.01). The mean doses of organs-at-risk were decreased by 0.52%-1.60% (P<0.01). Meanwhile, back neck skin dose was increased by approximately 6-14 Gy for the immobilization device had changed the scattering of X-ray and surface build-up effects. Conclusion The head and neck immobilization device can cause the attenuation of X-ray and changes in build-up effects, which reduces the dose coverage rate and average dose of the planning target volumes in radiotherapy for nasopharyngeal carcinoma. During treatment planning and dose calculation, the immobilization device should be included within body contour to ensure the accuracy of dose calculation.
Last Update: 2019-03-25