Chest wall dose reduction using non-coplanar volumetric modulated arc radiotherapy for lung stereotactic ablative radiotherapy

Publication date: Available online 19 December 2017
Source:Practical Radiation Oncology
Author(s): Amy S. Yu, Peter G Maxim, Billy W Loo, Michael F Gensheimer
PurposeStereotactic ablative radiotherapy (SABR) to lung tumors close to the chest wall can cause rib fractures or chest wall pain. We evaluated and propose a clinically practical solution of using non-coplanar volumetric modulated arc radiotherapy (VMAT) to reduce chest wall dose from lung SABR.Methods and materialsTwenty lung SABR VMAT plans in which the chest wall volume receiving 30Gy or higher (V30) exceeded 30cc were re-planned by non-coplanar VMAT with opposite 15-degree couch kicks. Dosimetric parameters including chest wall V30 and V40, lung V5, V10, V20, and mean dose, Paddick high-dose conformity index, intermediate-dose conformity index, and monitor units (MU) for each plan were used to evaluate the plan quality. The treatment time was also estimated by delivering the entire treatment. Two-sided paired t-test was used to evaluate the difference of the dosimetric parameters between coplanar one arc (cVMAT1), coplanar two arcs (cVMAT2), and non-coplanar two arcs (nVMAT2) plans, and differences with p < 0.05 were considered statistically significant.ResultsV30 and V40 for chest wall were reduced on average by 20%±9% and 15%±11% (mean±SD) from cVMAT2 plans to nVMAT2 plans (p < 0.01 for both comparisons), and 8%±7% and 16%±13% from cVMAT1 plans to cVMAT2 plans (p < 0.003 for both comparisons). The differences in lung mean dose were less than 0.2Gy among cVMAT1, cVMAT2 and nVMAT2. There were no significant differences in lung V5, V10, and V20. On average, the number of MU increased 14% for nVMAT2 compared to cVMAT2. The Paddick high-dose conformity indexes were 0.88±0.03, 0.89±0.04 and 0.91±0.03, and intermediate-dose conformity indexes were 3.88±0.49, 3.80±0.44 and 3.51±0.38 for cVMAT1, cVMAT2 and nVMAT2, respectively.ConclusionsWe found that non-coplanar VMAT plans are feasible, clinically practical to deliver, and significantly reduce V30 and V40 of chest wall without increasing lung dose.



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