Abstract
BackgroundTo evaluate spot-scanning proton arc therapy (SPArc) and multi-field robust optimized intensity modulated proton therapy (RO-IMPT) in treating stage III non-small-cell lung cancer (NSCLC) patients.MethodsTwo groups of stage IIIA or IIIB NSCLC patients (group 1: eight patients with tumor motion less than 5 mm; group 2: six patients with tumor motion equal to or more than 5 mm) were re-planned with SPArc and RO-IMPT. Both plans were generated using robust optimization to achieve an optimal coverage with 99% of internal target volume (ITV) receiving 66 Gy (RBE) in 33 fractions. The dosimetric results and plan robustness were compared for both groups. The interplay effect was evaluated based on the ITV coverage by single-fraction 4D dynamic dose. Total delivery time was simulated based on a full gantry rotation with energy-layer-switching-time (ELST) from 0.2 to 4 s. Statistical analysis was also evaluated via Wilcoxon signed rank test.ResultsBoth SPArc and RO-IMPT plans achieved similar robust target volume coverage for all patients, while SPArc significantly reduced the doses to critical structures as well as the interplay effect. Specifically, compared to RO-IMPT, SPArc reduced the average integral dose by 7.4% (p = 0.001), V20, and mean lung dose by an average of 3.2% (p = 0.001) and 1.6 Gy (RBE) (p = 0.001), the max dose to cord by 4.6 Gy (RBE) (p = 0.04), and the mean dose to heart and esophagus by 0.7 Gy (RBE) (p = 0.01) and 1.7 Gy (RBE) (p = 0.003) respectively. The average total estimated delivery time was 160.1 s, 213.8 s, 303.4 s, 840.8 s based on ELST of 0.2 s, 0.5 s, 1 s, and 4 s for SPArc plans, compared with the respective values of 182.0 s (p = 0.001), 207.9 s (p = 0.22), 250.9 s (p = 0.001), 509.4 s (p = 0.001) for RO-IMPT plans. Hence, SPArc plans could be clinically feasible when using a shorter ELST.ConclusionsThis study has indicated that SPArc could further improve the dosimetric results in patients with locally advanced stage NSCLC and potentially be implemented into routine clinical practice.
Highlights
To evaluate spot-scanning proton arc therapy (SPArc) and multi-field robust optimized intensity modulated proton therapy (RO-IMPT) in treating stage III non-small-cell lung cancer (NSCLC) patients
In terms of D99%, D1% dose to the target volume and conformality index, SPArc was able to significantly reduce the dose to all the critical structures evaluated
SPArc plans decreased the average integral dose from 77.3 J to 72.0 J, by 7.4% (p = 0.001) compared to RO-IMPT plans
Summary
To evaluate spot-scanning proton arc therapy (SPArc) and multi-field robust optimized intensity modulated proton therapy (RO-IMPT) in treating stage III non-small-cell lung cancer (NSCLC) patients. For patients with locally advanced lung cancer, radiotherapy alone or concurrent chemoradiotherapy has been widely used. Unlike photon radiotherapy, has inherent physical characteristics which are advantageous to treat disease sites such as locally advanced lung cancer, due to its sharp distal dose fall-off. Compared to passive scatter proton therapy (PSPT) [13], intensity modulated proton therapy (IMPT) has shown potentials to further reduce the dose to the adjacent normal tissues while maintaining similar or superior target coverage [14,15,16,17] in a more efficient way without having the need to use beam
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