Impact of actual gantry angle on accuracy of intensity-modulated radiotherapy for nasopharyngeal carcinoma
10.3760/cma.j.issn.1004-4221.2017.10.016
- VernacularTitle:鼻咽癌IMRT中实际机架角度对计划执行准确度影响
- Author:
Yanze SUN
1
;
Gang ZHOU
;
Liesong CHEN
;
Jianjun QIAN
;
Yaqun ZHU
;
Ye TIAN
Author Information
1. 215004 苏州,大学附属第二医院放疗科 苏州,大学肿瘤放射治疗学研究所
- Keywords:
Gantry angle;
Plan optimization;
Dose accuracy;
Nasopharyngeal neoplasms/intensity modulated radiotherapy
- From:
Chinese Journal of Radiation Oncology
2017;26(10):1182-1186
- CountryChina
- Language:Chinese
-
Abstract:
Objective To investigate the impact of actual gantry angle on the accuracy of intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC). Methods A total of 27 patients with NPC were enrolled in this study. IMRT plans were designed with Pinnacle treatment planning system (TPS),and 8 beams with an interval of 30°(within 0°-360°) were selected for each plan. These plans were divided into plan A and plan B according to the beam parameters. In plan A,the minimum sub-field area was 5 cm2 ,the minimum number of sub-field monitor unit ( MU) was 5,and the maximum sub-field number was 80;in plan B,the minimum sub-field area was 8 cm2 ,the minimum number of sub-field MUs was 8,and the maximum sub-field number was 60.The gamma passing rate using the criteria of 3%/3 mm and 2%/2 mm at actual and zero degree gantry angles were calculated using Mapcheck 2 device for dose verification,and were compared with the paired t-test. The relationship between the above differences (Δ value) and the beam angle or the beam parameters was also analyzed. Results In plan A with the criteria of 3%/3 mm, the beams were significantly different (P=0000-0007) except for at angles of 270°,300°,and 300°,and the mean Δ value was 090%;under the criteria of 2%/2 mm,all beams were significantly different ( P=0000-0019) except for at an angle of 300°,and the meanΔvalue was 272%.In plan B with the criteria of 3%/3 mm,the beams showed no significant difference ( P=0052-0639) except for at an angle of 300 ° ,and the mean Δ value was 040%;under the criteria of 2%/2 mm,all beams showed no significant difference ( P>005) except for at angles of 210°,240°,270°,and 300°,and the meanΔvalue was 152%.When the plan B parameters were used, the Δ value was reduced;the results of two verification methods were more consistent,so the accuracy was also improved. Conclusions Compared with the validation method at zero degree gantry angle,the validation method at an actual gantry angle is associated with reduced gamma passing rate because of some factors such as gravity,which is not significantly related to the beam angle,but the beam parameters. In the design of IMRT plans for NPC,the total number of sub-fields should be decreased as far as possible,and the minimum sub-field area and the minimum number of MU should be increased, so as to improve the accuracy of treatment plans.
