Improving DIBH-PBS treatment for NSCLC: reducing delivery time with advanced spot reduction techniques

Objective.Breath-hold (BH) is a promising approach for proton therapy of moving targets, but multiple BHs per field are needed to compensate for long irradiation time. In pencil beam scanning therapy, two factors define the treatment delivery time: the beam-on time and the dead time, which is the time required for energy-layer and spot-position adjustments. This study examines the interplay of various spot-reduction techniques to decrease delivery time without sacrificing robustness or plan quality.Approach.We created treatment plans for a cohort of 12 non-small cell lung cancer patients, combining a range modulator (RM) that broadens the Bragg peak into a Gaussian shape with three different spot placement algorithms (SPA):a fixed grid-based spot placement technique, an energy-dependent grid-based on the beam's size in air and water, and two types of optimization: a conventional and a spot suppression (SS.) optimization. These configurations were compared in terms of plan quality and clinical acceptability.Main results.RM combined with a fixed grid, leads to the best performance regarding plan quality and robustness. All SPAs reduce treatment time similarly. The SS. optimization reduces the number of spots but does not impact the treatment time. Given the time efficiency of the non-SS. algorithm, the reference optimization algorithms seem to be a better choice.Significance.By combining RM with a spot placement algorithm based on a fixed grid, we can obtain treatment plans with good clinical quality and low irradiation time, thus potentially improving BH treatment efficiency.