Harmonization of dose prescription for lung stereotactic radiotherapy

BACKGROUND AND PURPOSE: Pulmonary stereotactic treatments can be performed using dedicated linear accelerators as well as robotic-assisted units, and different strategies can be used for dose prescription. This study aimed to compare the doses received by the tumor with a gross tumor volume (GTV)-based prescription on D(98%GTV) using a robotic-assisted unit (method A) and planning target volume (PTV)-based prescription on D(95%PTV) using a dedicated linac (method B). MATERIAL & METHODS: Plans of 32 patients were collected for method A, and a dose of 3 × 18 Gy was prescribed using type A algorithm and recalculated using a Monte-Carlo (MC) algorithm. The plans were normalized to match D(98%GTV) with the mean [Formula: see text] of the cohort. The plans of 23 patients were collected for method B, and a dose of 3 × 18 Gy was prescribed to D(95%PTV) using a MC algorithm. A 4D-sum method was developed to estimate doses for PTV and GTV. For validation, all plans were recalculated using an independent MC double-check software. A dose harmonization on D(98% GTV) was determined for both methods. RESULTS: For method A, mean doses were D(2%GTV) = 59.9 ± 2.1 Gy, D(50%GTV) = 55.6 ± 1.2 Gy, D(98%GTV) = 49.5 ± 0.0 Gy. For method B, the reported doses were D(2%GTV) = 64.6 ± 2.1 Gy, D(50%GTV) = 62.8 ± 1.7 Gy, and D(98%GTV) = 60.0 ± 1.7 Gy. The dose trade-off of D(98%GTV) = 55 Gy was obtained for both methods. For method A, it corresponded to a dose prescription of 3 × 20 Gy using type A algorithm, followed by rescaling to obtain D(98%GTV) = 55 Gy. For method B, it corresponded to a dose prescription of D(95%PTV) = 3 × 16.5 Gy using the MC algorithm. CONCLUSIONS: This study determined similar near-minimum doses D(98% GTV) of approximately 3 × 18.3 Gy (55 Gy) using a GTV-based prescription on a robotic-assisted unit (method A) and a PTV-based prescription on a dedicated linac (method B).