Critical Structure Sparing in Stereotactic Ablative Radiotherapy for Central Lung Lesions: Helical Tomotherapy vs. Volumetric Modulated Arc Therapy

Alexander Chi,Jing Jin,Ritsuko Komaki,Guishan Fu,Pan Ma,Nam P Nguyen,Jinrong Dai,James S Welsh,Si Young Jang,Gerry Hobbs

doi:10.1371/journal.pone.0059729

Abstract

BackgroundHelical tomotherapy (HT) and volumetric modulated arc therapy (VMAT) are both advanced techniques of delivering intensity-modulated radiotherapy (IMRT). Here, we conduct a study to compare HT and partial-arc VMAT in their ability to spare organs at risk (OARs) when stereotactic ablative radiotherapy (SABR) is delivered to treat centrally located early stage non-small-cell lung cancer or lung metastases.Methods12 patients with centrally located lung lesions were randomly chosen. HT, 2 & 8 arc (Smart Arc, Pinnacle v9.0) plans were generated to deliver 70 Gy in 10 fractions to the planning target volume (PTV). Target and OAR dose parameters were compared. Each technique’s ability to meet dose constraints was further investigated.ResultsHT and VMAT plans generated essentially equivalent PTV coverage and dose conformality indices, while a trend for improved dose homogeneity by increasing from 2 to 8 arcs was observed with VMAT. Increasing the number of arcs with VMAT also led to some improvement in OAR sparing. After normalizing to OAR dose constraints, HT was found to be superior to 2 or 8-arc VMAT for optimal OAR sparing (meeting all the dose constraints) (p = 0.0004). All dose constraints were met in HT plans. Increasing from 2 to 8 arcs could not help achieve optimal OAR sparing for 4 patients. 2/4 of them had 3 immediately adjacent structures.ConclusionHT appears to be superior to VMAT in OAR sparing mainly in cases which require conformal dose avoidance of multiple immediately adjacent OARs. For such cases, increasing the number of arcs in VMAT cannot significantly improve OAR sparing.

Highlights

Stereotactic ablative radiotherapy (SABR), or stereotactic body radiotherapy (SBRT), has been shown to be an excellent treatment option for early-stage non-small cell lung cancer (NSCLC) and lung metastases when a biologically effective dose (BED) of $100 Gy10 is delivered [1,2,3,4]
We have demonstrated the feasibility of Helical tomotherapy (HT)-based stereotactic ablative radiotherapy (SABR) for centrally located lung lesions which are very close to critical organs at risk (OARs) in the thorax; while volumetric modulated arc therapy (VMAT) has been shown to be superior to intensity-modulated radiotherapy (IMRT) or 3D-CRT for lung SABR in OAR sparing [22,23,24,25]
HT and VMAT SABR plans were generated for all 12 patients to meet the planning target volume (PTV) dose coverage criteria

Summary

Introduction

Stereotactic ablative radiotherapy (SABR), or stereotactic body radiotherapy (SBRT), has been shown to be an excellent treatment option for early-stage non-small cell lung cancer (NSCLC) and lung metastases when a biologically effective dose (BED) of $100 Gy10 is delivered [1,2,3,4]. Treatment related death from severe pulmonary toxicities, hemoptysis, or esophagitis, has been reported when various dose fractionation schedules were delivered to treat centrally located lesions [5,6,7,8,9]. This happened mainly when a large fractional dose has been delivered, leading to the overdosing of the organs at risk (OARs) adjacent to the tumor target. We conduct a study to compare HT and partial-arc VMAT in their ability to spare organs at risk (OARs) when stereotactic ablative radiotherapy (SABR) is delivered to treat centrally located early stage non-small-cell lung cancer or lung metastases

Methods

Results

Discussion

Conclusion