Abstract 187
Background
To quantify the setup errors measured with kV CBCT using breast board with or without a thermoplastic head mask in breast cancer patients who received whole breast and supraclavicular nodal region irradiation.
Methods
30 patients received both whole breast and supraclavicular nodal region irradiation and were treated on Elekta Versa HD linear accelerators (Elekta Oncology Systems, Crawley, UK) between June 2016 and January 2018. The setup error data were retrospectively analyzed. Patients were immobilized in the supine position on a breast board system with both arms raised. In 20 of the patients a thermoplastic head mask was added in order to avoid the neck rotation and the uncertainty of the relative position between neck and the board. The shifts in left-right(X), superior-inferior(Y), anterior-posterior(Z) were recorded by CBCT. Population of the two groups was compared in terms of distribution of the mean shift (systematic error) and their standard deviations (random error) and in terms of Van Herk's setup margin defined as MPTV (2.5Σ) 0.7δ.
Results
Shifts of the breast board only and head mask group in X, Y, Z were 0.212±0.174 vs. 0.272±0.242cm, p = 0.07;0.364±0.246 vs. 0.242±0.171cm, p = 0.001; 0.423±0.302 vs. 0.364±0.269 cm, p = 0.204, respectively. Proportion of the shift less than 5mm in the breast board only group and the head mask group were 91.07% vs. 85.32%, p = 0.294 (67.86% vs. 89.91%, p = 0.001; 67.86% vs. 74.31%, p = 0.381, respectively. The CTV to PTV margin were 0.595, 0.865, 1.139cm in breast board only group and 0.699, 0.647, 0.990 cm in the head mask group.Table: 28P
| X | Y | Z | ||||||
|---|---|---|---|---|---|---|---|---|
| Σ | δ | Σ | δ | Σ | δ | |||
| Breast board only group | 0.222 | 0.057 | 0.318 | 0.102 | 0.427 | 0.102 | ||
| Head mask group | 0.266 | 0.050 | 0.239 | 0.071 | 0.368 | 0.101 | ||
| P | 0.503 | 0.596 | 0.156 | 0.802 | 0.442 | 0.212 |
Conclusions
for the alignment and immobilization of patients who received whole breast and supraclavicular nodal region irradiation, using a breast board in combination with a thermoplastic head mask may significantly help to reduce the shift variance in superior-inferior direction compared to using breast board only. The anterior-posterior error is relatively large, other immobilization devices or patient alignment methods are needed to be further explored to improve accuracy.
Editorial acknowledgement
Clinical trial identification
Legal entity responsible for the study
Prof. Shulian Wang.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.