Breast Treatments Using Pencil Beam Scanning Pseudo Arcs In Prone Position
Abstract
Purpose
Prone breast treatment is a known approach in radiation therapy. In addition to the benefits in lowering the OAR dose, an MRI imaging to guide preoperative radiation can be used. A fixed beam Proton PBS using a flat table top with prone couch beam therapy for breast treatments holds major advantages. Proton PBS allows conformal tumor coverage while using pseudo arcs. In addition, one can use low energy Proton beams produce by the synchrotron to reduce skin sparing when needed.
Methods
We sought to pilot prone breast treatments with the P-Cure (Shilat, ISRAEL) system and compare to photon prone treatments, showing this approach feasibility. We chose five patient cases that were treated in prone position in our clinic using the Orfit Industries NV (Wijnegem, Belgium) prone couch overlay. We have re-planned them on the P-Cure system with table top using RaySearch inc. (Stockholm, SW). A 26 Gy to the breast and 30 Gy SIB to the tumor bed in 5 fractions was conducted. We used pseudo 90 degrees arc in 9 fields plans. starting with a superior- inferior beam and concluding with a lateral beam. The Proton plans were compared to prone plans that were recalculated on the True Beam (Varian inc. Palo Alto USA).
Results
All Proton plans showed about 0.1 Gy mean Lungs dose and 0.02 Gy mean heart dose. A conformal tumor bed coverage with small additional dose to the non-boost-PTV. The volume of the PTV receiving about 103% that varied between 12% to 22% for the C-Arm Linac, while the Prone PBS it was found between 3.5% to 4.0%.
Conclusion
The Prone PBS delivery allows treating the breast itself without the risk of overshooting to the lungs at the distal edge. We showed conformal SIB with minimum hot spot to the PTV.