Effects of collimator angles on planning and dose verification of volumetric modulated arc therapy for nasopharyngeal carcinoma(PDF)
《中国医学物理学杂志》[ISSN:1005-202X/CN:44-1351/R]
- Issue:
- 2019年第11期
- Page:
- 1249-1254
- Research Field:
- 医学放射物理
- Publishing date:
Info
- Title:
- Effects of collimator angles on planning and dose verification of volumetric modulated arc therapy for nasopharyngeal carcinoma
- Author(s):
- WU Xinglei; WU Aidong; WU Ailin
- West Branch of the First Affiliated Hospital of University of Science and Technology of China, Hefei 230031, China
- Keywords:
- nasopharyngeal carcinoma; volumetric modulated arc therapy; collimator rotation; dose verification
- PACS:
- R815.6
- DOI:
- DOI:10.3969/j.issn.1005-202X.2019.11.002
- Abstract:
- Objective To study the effects of collimator rotation on the planning and dosimetric verification of volumetric modulated arc therapy (VMAT) for nasopharyngeal carcinoma. Methods Ten patients with stage T3 nasopharyngeal carcinoma were selected and 10 VMAT plans with collimator angles of 0°, 5°, 10°, 15°, 20°, 25°, 30°, 35°, 40°and 45° were designed for each patient. Dosimetric parameters, such as target coverage, the dose to organs-at-risk and normal tissues as well as monitor units, were compared among different plans, and dose verification was performed on each plan. Results The PGTVnx, PTV1, and PTV2 in VMAT plan with a collimator angle of 10° had the lowest average homogeneity index and the largest average conformity index (P<0.05). The differences in average homogeneity index of PGTVnd among all plans was trivial (P>0.05), and the maximum average conformity index occurred at 5°-30° (P<0.05). The maximum doses to brain stem, spinal cord and eyeball were relatively lower at 5°-20° (P<0.05); the maximum doses to optic chiasm and mandible were relatively smaller at 15°-25°; and the smallest parotid gland V30 was at 35°. For the normal tissue outside the target areas (B-P), the minimum radiation volume in low-dose region (V5, V10, V15 and V20) was at 0°and 5°, while that in high dose region (from V25 to V50) was at 10°. Among all plans, the average monitor unit is minimum for the plan with collimator angles of 0° and was maximum for the plan with collimator angles of 30° (P<0.05). The average gamma passing rates for all plans were above 98%, and the plan with collimator angles of 20° had the highest gamma passing rate. Conclusion In VMAT planning for nasopharyngeal carcinoma, collimator angle can be set at 10°-20° to obtain better target dose distribution, reduce the doses to organs-at-risk and normal tissues while maintaining the passing rate of dose verification.
Last Update: 2019-11-28