Harmonization of dose prescription for lung stereotactic radiotherapy

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).

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 $$ 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.

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.

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).