Evaluation of volumetric modulated arc therapy for postmastectomy treatment

Geoffrey P Nichols,Mary Ella Sanders,Jonas D Fontenot,John P Gibbons

doi:10.1186/1748-717x-9-66

Abstract

PurposeTo examine the feasibility of volumetric modulated arc therapy (VMAT) for post mastectomy radiotherapy (PMRT).Methods and materialsFifteen PMRT patients previously treated at our clinic with helical tomotherapy (HT) were identified for the study. Planning target volumes (PTV) included the chest wall and regional lymph nodes. A systematic approach to constructing VMAT that met the clinical goals was devised. VMAT plans were then constructed for each patient and compared with HT plans with which they had been treated. The resulting plans were compared on the basis of PTV coverage; dose homogeneity index (DHI) and conformity index (CI); dose to organs at risk (OAR); tumor control probability (TCP), normal tissue complication probability (NTCP) and secondary cancer complication probability (SCCP); and treatment delivery time. Differences were tested for significance using the paired Student’s t-test.ResultsBoth modalities produced clinically acceptable PMRT plans. VMAT plans showed better CI (p < 0.01) and better OAR sparing at low doses than HT plans, particularly at doses less than 5 Gy. On the other hand, HT plans showed better DHI (p < 0.01) and showed better OAR sparing at higher doses. Both modalities achieved nearly 100% tumor control probability and approximately 1% NTCP in the lungs and heart. VMAT showed lower SCCP than HT (p < 0.01), though both plans showed higher SCCP values than conventional mixed beam (electron-photon) plans reported by our group previously. VMAT plans required 66.2% less time to deliver than HT.ConclusionsBoth VMAT and HT provide acceptable treatment plans for PMRT. Both techniques are currently utilized at our institution.

Highlights

Post-mastectomy radiotherapy (PMRT) presents a challenging treatment geometry
volumetric modulated arc therapy (VMAT) plans showed better conformity index (CI) (p < 0.01) and better organs at risk (OAR) sparing at low doses than helical tomotherapy (HT) plans, at doses less than 5 Gy
HT plans showed better dose homogeneity index (DHI) (p < 0.01) and showed better OAR sparing at higher doses

Summary

Introduction

Post-mastectomy radiotherapy (PMRT) presents a challenging treatment geometry. The target volume - typically consisting of the chest wall (CW) and regional lymph nodes - covers a large, superficial area that is thin and convex in shape, and is immediately adjacent to the lung, heart, and contralateral breast. PMRT was historically treated with a mixed-beam technique consisting of anterior electrons to treat the medial CW and internal mammary nodes (IMN), oblique electrons to treat the lateral CW, and parallel-opposed x-ray to treat the supraclavicular (SC) and axillary (AX) nodes. Because of the need to junction fields, edge feathering was typically utilized to reduce heterogeneities to acceptable levels; residual heterogeneities were inevitable and treatment setup times were lengthy and laborious. Our group previously reported on the use of helical tomotherapy (HT) for PMRT [1] to improve ease of setup and dose conformity and homogeneity of PMRT treatments, albeit at the cost of larger volumes of normal tissue receiving doses less than 25 Gy. our previous findings resulted in HT often being the treatment of choice for PMRT in our clinic. The use of HT has limitations, including limited availability of and access to the technology in addition to the larger low dose volumes noted above

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