Verification and assessment of the PTV margin in the treatment of brain metastases with mono-fractionated radiosurgery

This study evaluated the margins between gross target volume (GTV) and planned target volume (PTV) for brain metastases treated using the stereotactic radiosurgery (SRS) technique.Methods and Materials: 10 patients who received SRS treatment for brain metastases provided the setup data. To evaluate systematic and random errors, 30 cone beam computed tomography (CBCT) was evaluated. Following that, we used the Van Herk formula to calculate and evaluate our optimal PTV to obtain a result comparable to other studies without exceeding tolerable values. Results: We found that the proper margin for single-fraction SRS cases in 10 brain metastases was about 2 mm for our department in this study. Setup margins obtained were X1.23, Y 0.93, and Z 1.04 mm translation, and 1.56, 1.36, 1.47 in Pitch, Roll, and Yaw in rotation.Conclusion: Treatment of brain metastases with SRS requires an optimal PTV to ensure better coverage and normal brain sparing. A PTV margin of 2 mm is an optimal margin in our department.