Associating Dose-Volume Characteristics With Theoretical Radiobiological Metrics For Rapid Gamma Knife Stereotactic Radiosurgery Plan Evaluation

Purpose To examine general dose-volume characteristics in Gamma Knife (GK) plans which may be associated with higher tumor control probability (TCP) and equivalent uniform dose (EUD) using characteristic curve sets. Methods Two sets of dose-volume histograms (DVHs) were exported alongside an analytical purpose-generated DVH: (a) single-shot large collimator (8 or 16 mm) emulated with multiple shots of 4 mm collimator. (b) shot-within-shot (SWS) technique with isodose lines (IDLs) of 40-75%. TCP, average dose, EUD in single-fraction (EUDT) and 2 Gy fractionated regimens (EUDR) were examined for trends with cumulative DVH (cDVH) shape as calculated using a linear-quadratic cell survival model (alpha/beta = 10.0 Gy, N-0 = 1 x 10(6)) with both alpha = 0.20 Gy(-1)and alpha = 0.23 Gy(-1). Results Using alpha = 0.20 Gy(-1)(alpha = 0.23 Gy(-1)), plans in the analytical set with higher shoulder regions had TCP, EUDT, EUD(R)increased by 180%, 5.9%, 10.7% (11.2%, 6.3%, 10.0%), respectively. With alpha = 0.20 Gy(-1)(alpha = 0.23 Gy(-1)), plans with higher heels had TCP, EUDT, EUD(R)increased by 4.0%, <1%, <1% (0.6%, <1%, <1%), respectively. In emulating a 16 (8) mm collimator, 64 (12) shots of the small collimators were used. Plans based on small collimators had higher shoulder regions and, with alpha = 0.20 Gy(-1)(alpha = 0.23 Gy(-1)), TCP, EUDT, EUD(R)was increased up to 351.4%, 5.0%, 8.8% (270.4%, 5.0%, 6.8%) compared with the single-shot large collimator. Delivery times ranged from 10.2 to 130.3 min. The SWS technique used 16:8 mm collimator weightings ranging from 1:2 to 9.2:1 for 40-75% IDL. With alpha = 0.20 Gy(-1)(alpha = 0.23 Gy(-1)), the 40% IDL plan had the highest shoulder with increased TCP, EUDT, EUD(R)by 130.7%, 9.6%, 17.1% (12.9%, 9.1%, 16.4%) over the 75% IDL plan. Delivery times ranged 6.9-13.8 min. Conclusions The magnitude of the shoulder region characteristic to GK cDVHs may be used to rapidly identify superior plan among candidates. Practical issues such as delivery time may require further consideration.