Automated Planning to Improve Linac-Based Stereotactic Radiosurgery Plan Quality in Patients with 4 up to 10 Brain Metastases

Abstract

Stereotactic radiosurgery (SRS) is a promising treatment option for patients with multiple brain metastases (BM). We studied whether automated planning can improve LINAC-based SRS plan quality for multiple BM. Additionally, the use of one isocenter instead of separate isocentres for each metastasis was studied. For 12 patients with 4 up to 10 brain metastases, five non-coplanar LINAC-based SRS plans were created for 6MV photons: a manually planed dynamic conformal arc (DCA) plan with a separate isocenter for each metastasis, a dynamic IMRT plan with one isocenter, a VMAT plan with one isocenter, two DCA plans with one isocenter for 3 and 5 couch rotations. The last three plans were automatically generated. The maximum allowed gross tumor volume to planning target volume (PTV) margin was 1 mm. The prescription dose was 21 Gy or 18 Gy in a single fraction or 8.5 Gy in 3 fractions depending on the PTV volume. All plans were calculated with Monte Carlo, except the VMAT which was calculated with Collapsed Cone algorithm. The PTV coverage should be at least 98%. To assess SRS plan quality, the Paddick conformity index (CI), the Paddick gradient index (GI), the total V12Gy and V5Gy were studied and reported as MEAN±1SD. The number of monitor units (MU) and irradiation time were also compared. The mean total CI was the highest for dynamic IMRT (see table). The lowest GI was for DCA plans with the separate-isocenter approach (3.7±0.6) and automatically generated DCA plans with one isocenter, whereas the highest GI was for VMAT plans (7.0±3.0). Moreover, the GI was 4.4±0.6 and 4.2±0.6 for automatically generated DCA plans with 3 couch and 5 couch rotations, respectively. The total V12Gy of automatically generated DCA plans with one isocenter (4.7±5.6% and 4.1±4.3% for 3 and 5 couch rotations, respectively) and dynamic IMRT plans (4.4±4.5%) were comparable with the manual DCA plans (3.6±3.7%). For the total V5Gy, quite the same behaviour as for the GI was found. The number of MU was the smallest for VMAT plans, followed by automatically generated DCA and IMRT plans and much lower than the manual DCA plans. The irradiation time was the smallest for automatically planned DCA plans followed by VMAT and IMRT plans. Automatically generated LINAC-based SRS plans for multiple BM in one isocenter can make the number of MU and irradiation time smaller with a comparable plan quality to manual DCA plans with the separate-isocenter approach. Based on all compared parameters, dynamic IMRT and DCA plans with one isocenter were the best and comparable with manual DCA plans with separate isocentres for each metastasis. Moreover, we can conclude that automated DCA plans with 5 couch and 3 couch rotations were comparable.Abstract 3798; Table 1Conf IGIV12Gy [%]V5Gy [%]MUIrradiation time [s]Separate-isocenter DCA0.713.73.619146641832IMRT 1 isoc0.724.84.42675171235VMAT 1 isoc0.707.05.7374123976Multimets DCA 1 isoc 3 table rotations0.694.44.7206130820Multimets DCA 1 isoc 5 table rotations0.714.24.1185403724 Open table in a new tab