Distribution of gamma pass rates for ultra-long target volumes of cervical cancer based on two measurement methods
10.3760/cma.j.cn112271-20240928-00387
- VernacularTitle:两种测量方式下宫颈癌超长靶区γ通过率的分布情况
- Author:
Junjie LEI
1
;
Jiren LIU
;
Xiaopeng PAN
;
Xu HOU
;
Xiaoli JIN
Author Information
1. 山西省汾阳医院放疗科，汾阳 032200
- Publication Type:Journal Article
- Keywords:
Cervical cancer;
Ultra-long target volume;
Dose verification;
γ-pass rate
- From:
Chinese Journal of Radiological Medicine and Protection
2025;45(9):870-875
- CountryChina
- Language:Chinese
-
Abstract:
Objective:To compare gamma pass rates for ultra-long target volumes of cervical cancer between individual measurements by moving the phantom isocenter and segmented measurements combined with merging and to assess the influence of scattering blocks on verification result during segmented measurements.Methods:A retrospective study was conducted on 24 cervical cancer patients with ultra-long target volumes (lengths: 23.5–36.0 cm) treated using helical tomotherapy. Two measurement methods were used to verify the gamma pass rates: individual measurements by moving the phantom isocenter and segmented measurements combined with merging. For the first measurement method, the patients′ treatment plans were transferred to the ArcCheck phantom. After the dose distribution was calculated and exported, the gamma pass rates measured and calculated were compared. For the segmented measurements, a 50-cm-long virtual phantom was imported, and the treatment plans of patients were then transferred to the virtual phantom. Afterward, the dose distribution of the virtual phantom was calculated and exported. Then, two dose measurements were conducted under upward and downward setup of the ArcCheck phantom. Two dose measurement files were obtained and then fused to produce a merged file. Then, the γ pass rates were calculated. Repeated measurements were conducted after scattering blocks were installed. The γ-pass rates were assessed using varying dose criteria.Results:Under various evaluation criteria, no statistically significant differences in γ pass rates were observed between the individual measurements by moving the phantom isocenter and the segmented measurement in the presence of scattering blocks ( P > 0.05). In contrast, there existed statistically significant differences in γ pass rates between the individual measurements by moving the phantom isocenter and the segmented measurement in the absence of scattering blocks according to the (global) criterion of 3%/2 mm absolute dose ( Z = -2.31, P = 0.02). Additionally, the segmented measurement in the presence of scattering blocks enhanced pass rates, with statistical significant difference under the criterion of 3%/2 mm relative dose ( Z = -2.11, P = 0.04). Conclusions:In the case where ArcCheck is used to measure the dose distribution of ultra-long target volumes in cervical cancer, it is advisable to preferentially use individual measurements by moving the phantom isocenter. When segmented measurements combined with merging are required, it is necessary to install scattering blocks during measurements. This will improve γ-pass rates during verification and ensure the accuracy of dose verification.
