Dosimetric variation in preoperative partial breast radiosurgery assessed by deformable image registrations.

OBJECTIVE

To assess dosimetric variation caused by breast deformation in breast radiosurgery based on deformable image registration.

METHODS

This study included 30 patients who were treated in the prone position for preoperative partial breast radiosurgery. The biopsy clip in CBCT was aligned to the one from the planning CT. Deformable image registration (DIR) was performed to deform the planning CT into the CBCT, focusing on the breast shape. The treated plan (P) was recalculated based on the deformed CT. Thus, P represented the actual treatment delivered to the patient and was compared to the original plan (P).

RESULTS

The mean differences of target volumes covered by 95% and 100% of the prescribed dose between P and P were less than 0.5%. The mean differences ± standard division for skin maximum dose (D), dose to 1cc (D) and D were 0.3 ± 0.7 Gy, 0.3 ± 0.6 Gy and 0.6 ± 0.6Gy between P and P, respectively.

CONCLUSION

The treated plan was accurately recalculated based on the deformed CT. Despite slight variance in breast deformation, the dosimetric variation was very small, ensuring that adequate target coverage and skin dose were maintained during treatment as planned originally.