Associating dose-volume characteristics with theoretical radiobiological metrics for rapid Gamma Knife stereotactic...

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.

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 (EUD_T ) and 2 Gy fractionated regimens (EUD_R ) were examined for trends with cumulative DVH (cDVH) shape as calculated using a linear-quadratic cell survival model (α/β = 10.0 Gy, N₀  = 1 × 10⁶ ) with both α = 0.20 Gy^-1 and α = 0.23 Gy^-1 .

Using α = 0.20 Gy^-1 (α = 0.23 Gy^-1 ), plans in the analytical set with higher shoulder regions had TCP, EUD_T , EUD_R increased by 180%, 5.9%, 10.7% (11.2%, 6.3%, 10.0%), respectively. With α = 0.20 Gy^-1 (α = 0.23 Gy^-1 ), plans with higher heels had TCP, EUD_T , 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 α = 0.20 Gy^-1 (α = 0.23 Gy^-1 ), TCP, EUD_T , 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 α = 0.20 Gy^-1 (α = 0.23 Gy^-1 ), the 40% IDL plan had the highest shoulder with increased TCP, EUD_T , 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.

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.