PV QA 4 - Poster Viewing Q&A 4
TU_2_3336 - Breast Board Comined with a Thermoplastic Head Mask Immobilization Can Improve the Reproducibility of the Treatment Setup for Breast Cancer Patients Who Received Both Whole Breast and Supraclavicular Nodal Region Irradiation
Tuesday, October 23
2:45 PM - 4:15 PM
Location: Innovation Hub, Exhibit Hall 3
Breast Board Comined with a Thermoplastic Head Mask Immobilization Can Improve the Reproducibility of the Treatment Setup for Breast Cancer Patients Who Received Both Whole Breast and Supraclavicular Nodal Region Irradiation
M. Ma1,2, S. Wang1, S. Qin1, J. Zhang1, Y. Tang1, S. Qi3, S. Chen1, Y. Ma1, X. Liu1, and Y. Li1; 1National Cancer Canter/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China, 2Department of Radiation Oncology, Peking University First Hospital, Beijing, China, 3State Key Laboratory of Molecular Oncology and Department of Radiation Oncology, National Cancer Center/Cancer Hospital, Chinese Academy of Medical Sciences (CAMS) and Peking Union Medical College (PUMC), Beijing, China
Purpose/Objective(s): To quantify the setup errors measured with CBCT using breast board with or without a thermoplastic head mask in breast cancer patients who received whole breast and supraclavicular nodal region irradiation. CTV to PTV in 3 directions were also calculated.
Materials/Methods: 30 patient received whole breast and supraclavicular nodal region irradiation and were treated on linear accelerators between June 2016 and January 2018. The setup error data were retrospectively analyzed. All the patients were immobilized in the supine position on a breast board system with both arms raised and supported at the upper arms and wrists. 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. Registration with the planning CT was performed using automatic bone algorithm and adjusted to match the target volume of the supraclavicular nodal region and the cervical vertebra by experienced medical staff, the position of the arms and the breast were also considered. For all patients the couch shifts in left-right (X), superior-inferior (Y), anterior-posterior (Z) were recorded. Statistical analysis included two-tails significance tests (t-Student and Manne-Whitney test for means, Fisher and X2 test for variances). Tests with p-values >0.05 were scored as not significant. Population of the two groups was compared in terms of distribution of the mean shift (systematic error) and their SDs (random error) in terms of setup margin defined as MPTV＝2.5Σ＋0.7δ.
Results: 56 images and 109 images were acquired in breast board only group and head mask group, respectively. Shifts of the breast board only group and the head mask group in X,Y, Z were 0.212±0.174 cm vs. 0.272±0.242 cm, p=0.07; 0.364±0.246 cm vs. 0.242±0.171 cm，p=0.001;0.423±0.302 cm vs. 0.364±0.269 cm, p=0.204. 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. Table 1 shows the quantified Systematic and random setup errors. The CTV to PTV margin in X,Y, Z were 0.595cm,0.865 cm,1.139cm in breast board only group and 0.699 cm, 0.647 cm,0.990 cm in head mask group, respectively. Table 1 Systematic and random setup errors
| || left-right (X) || || superior-inferior (Y) || || anterior-posterior (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 |
Conclusion: for the alignment and immobilization of patients who received whole breast and supraclavicular nodal region irradiation, using a breast board in combination of 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 device or patient alignment methods are needed to be further explored.to improve the accuracy.
Author Disclosure: M. Ma: None. S. Wang: None. S. Qin: None. J. Zhang: None.