Author: Shifeng Chen, Mariana Guerrero, Michael J. MacFarlane, Huijun Xu, Baoshe Zhang, Jinghao Zhou 👨🔬
Affiliation: University of Maryland School of Medicine, Department of Radiation Oncology, University of Maryland School of Medicine, Capital Region Medical Center, University of Maryland Shore Regional Cancer Center 🌍
Purpose: The clinical value of surface-guided radiotherapy (SGRT) in prone breast cancer setups is much less established than in supine setups. This study explores SGRT's potential for prone breast patient setup.
Methods:
A retrospective analysis was performed on eight breast cancer patients treated in the prone position using tangential fields. On the first fraction, patient setup involved free-breathing SGRT (using VisionRT), orthogonal kV and tangential MV imaging, skin flash adjustment, and the creation of a diamond-shaped light field (DSLF). The subsequent treatment fractions, which employed MV imaging and consistency checks for DSLF and skin flash, were divided into two groups: (1) VisionRT was used for initial alignment before any other setup methods, and (2) VisionRT was not used for setup. All positional corrections utilized a 6-DOF couch. Daily setup time and couch correction magnitudes were compared between the two groups. To simulate the dosimetric impact of VisionRT-only alignment, doses to PTV and OARs (heart, lung, and chest wall) were recomputed by reverse-shifting couch positions from the CT plan, which is assumed equivalent to the delivered doses.
Results:
For Group 1 (53 fractions), the total couch correction magnitude was 0.82±0.49 cm, with the VsionRT-based and MV-based setup times being 2.6±2 minutes and 3.4±2.5 minutes, respectively. For Group 2 (89 fractions), the total couch correction magnitude was 0.85±0.38 cm, while the MV-based setup time was 4±3.64 minutes. Patients using VisionRT for initial setup experienced less PTV D95 dose degradation (5.4%(Group-1) vs. 9%(Group-2)). Notably, one patient with Group-1 fractions only demonstrated the best dosimetric distribution to targets and OARs, suggesting that MV imaging may be unnecessary for certain cases using VisionRT.
Conclusion:
While SGRT does not significantly improve setup efficiency for the general prone breast patients, it may provide patient-specific benefits. Further studies are warranted to justify its role for individualized setups.