Dose painting with Gamma Knife: Two techniques for delivering different doses to areas of recurrent or residual tumor after resection of brain metastases

Purpose: We investigated the feasibility of using Gamma Knife (GK) radiosurgery for "dose painting" to deliver higher doses to residual or recurrent nodules and surgical cavity after resection of brain metastases. Methods and materials: Two integrated boost techniques were developed with GK. The single-target technique delineated both the surgical cavity (cavity) and gross disease (nodule) as a single target. Dose was prescribed to the target with the goal of covering the nodule with a higher dose. The 2-target technique delineated the cavity and nodule as separate target volumes, each prescribed to its own dose and planned separately. Two cases were used to illustrate each technique. The single-target technique was used to deliver 16 Gy to a smaller cavity (7 cm³) and a 20-Gy integrated boost to 2 nodules (case 1). The 2-target technique was used to deliver 12 Gy to a larger cavity (21.5 cm³) and 20 Gy to a single nodule (case 2). Results: For both cases, the cavity coverage with the prescribed dose was 100% with the standard plan and integrated boost techniques. For case 1, compared with a standard plan, the single-target technique improved the 20-Gy nodule coverage from 89.7% (nodule 1) and 97.9% (nodule 2) to 100% (both) and increased the minimum dose from 16.6 Gy to 20.8 Gy (nodule 1) and from 19.4 Gy to 20.8 Gy (nodule 2). For case 2, compared with a standard plan, the 2-target technique improved the 20-Gy nodule coverage from 4% to 100% and the minimum dose from 13.8 Gy to 21 Gy. Conclusions: Both GK integrated boost approaches allowed for effective delivery of higher doses to residual or recurrent nodules in a surgical cavity. In our experience, the single-target technique works well for small cavities, whereas the 2-target technique is well suited for larger cavities.