Table 4 Summary of imaging modalities for target volumes delineation and dose/fractionations for postoperative resection cavity of brain metastases

Imaging for target delineation

Isotropic post-contrast-enhanced 3D T1-weighted MRI sequences with 1 mm thick slices and T2-weighted images. Additional images include preoperative contrast-enhanced T1-weighted MRI sequences to identify the preoperative tumor extent and dural involvement

Gross Tumor Volume (GTV)

Surgical cavity on postoperative contrast-enhanced T1-weighted MR images (typically represented by the rim of enhancement at the edge of the resection cavity) with inclusion of any residual nodular enhancement

Clinical Tumor Volume (CTV)

The CTV is defined as the GTV plus 0–1 mm margins constrained at anatomical barriers such as the skull. GTV-to-CTV margins up to 5–10 mm are applied along the bone flap/meningeal margin, with larger margins used for tumors in contact with the dura preoperatively. Vasogenic edema and surgical corridor (for deep lesions) are not usually included

Planning Target Volume (PTV)

A margin of up to 3 mm is usually added to the CTV to generate the PTV, depending on the radiation technique. For frame-based SRS, no additional safety margin is necessary; with frameless SRS and SRT, a GTV-to-PTV safety margin of 1–3 mm is usually applied according to Institutional practice

Timing of treatment

There is a general consensus to perform postoperative SRS/HSRT to the resection cavity within 4 weeks after surgery with planning MRI acquired < 7 days before treatment to limit negative impact of cavity changes on clinical outcomes

Dose and fractionation

12–18 Gy using single-fraction SRS; 24–27 Gy in 3 fractions and 30–35 Gy in 5 fractions using HSRT, typically for larger resection cavity; less commonly 30–40 Gy in 10 fractions