Dosimetric effects of rounding subfield monitor units up for step-and-shoot IMRT plan of nasopharyngeal carcinoma(PDF)
《中国医学物理学杂志》[ISSN:1005-202X/CN:44-1351/R]
- Issue:
- 2018年第10期
- Page:
- 1128-1133
- Research Field:
- 医学放射物理
- Publishing date:
Info
- Title:
- Dosimetric effects of rounding subfield monitor units up for step-and-shoot IMRT plan of nasopharyngeal carcinoma
- Author(s):
- TIAN Wei; DAI Jianrong
- National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100021, China
- Keywords:
- ; Keywords: nasopharyngeal carcinoma; treatment planning system; intensity-modulated radiotherapy; decimal monitor unit; dosimetry
- PACS:
- R815
- DOI:
- DOI:10.3969/j.issn.1005-202X.2018.10.003
- Abstract:
- Abstract: Objective To investigate the dosimetric effects of rounding subfield monitor units (MU) up to their nearest integers in step-and-shoot intensity-modulated radiotherapy (IMRT) plans for nasopharyngeal carcinoma (NPC) which was designed by Prowess5.1 planning system. Methods The IMRT plans for 33 NPC patients with definite pathological diagnosis were enrolled into this study. These IMRT plans were divided into two groups, namely Porig and Pnew. Porig was composed of all the original plans which had been optimized completely by the treatment planning system itself. Pnew was a new group of which all the subfield monitor unit were rounded up to their nearest integers based on Porig, and the shapes of segments in Pnew were all the same as those in Porig. The dosimetric characteristics and MU differences were recorded and compared between Porig and Pnew. Results The conformity index and homogeneity index of target areas in two groups were similar, without statistical significance. The target coverage, the D98, D95, D2, Dmean of PGTVnd, and the D98, D95 of PTV2 in Pnew were lower than those in Porig (P<0.05). The V100% of PGTVnd, PTVnx and PTV1 were decreased by 1.807%, 0.655% and 1.258%, respectively. For organs-at-risk, only the Dmean of left temporal lobe showed statistical differences between two groups (P<0.05). For P1 plans, the MU per fraction in Pnew was increased by 1.600 MU as compared with Porig (519.758±46.410 vs 518.158±46.693, P<0.05). Conclusion When Prowess5.1 planning system is used to design step-and-shoot IMRT plan for NPC, the tiny changes of subfield monitor units will cause dosimetric differences. Hence the calculation of monitor units should be paid attention to in clinical practice.
Last Update: 2018-10-22