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Partial and Full Arc Volumetric Modulated Arc Therapy in Lung Cancer Stereotactic Body Radiotherapy with Different Definitions of Internal Target Volume Based On 4D CT

X Jin

X Jin*, J Yi , C Xie , the 1st Affiliated Hospital of Wenzhou Medical University, Wenzhou, Zhejiang


SU-I-GPD-T-516 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Respiratory induced tumor motion is a crucial consideration in determination an internal margin around gross tumor volume (GTV) to form an internal target volume (ITV) in lung cancer stereotactic body radiotherapy (SBRT), which can avoid both inadequate tumor coverage and unnecessary surrounding normal tissue irradiation for individual patient. The purpose of this study is to investigate volumetric and dosimetric effects of different ITV definitions, as well as the feasibility of partial arc volumetric modulated arc therapy (VMAT) in lung cancer SBRT.

Methods: Fourteen patients with primary and metastatic lung disease underwent SBRT were enrolled in this study. Full and partial VMAT plans were generated with four different ITVs: ITVall, ITVMIP, ITVAIP and ITV2phases, representing ITVs generated from all 10 respiratory phases, maximum intensity projection (MIP), average intensity projection (AIP). Volumetric and dosimetric differences, as well as MU and delivery time were investigated.

Results: The average percent volume differences of ITVMIP, ITVAIP and ITV2phases to ITVall were 8.6%, 13.4%, and 25.2%, respectively. There were no significant differences on target coverage and organ at risks (OARs) sparing among four ITVs. Partial arc VMAT irradiated more dose at 2 cm away from planning target volume (PTV) (P=0.002), however, it achieved better protection on mean lung dose , lung V5, spinal cord, heart and esophagus compared with full arc VMAT. The average MU and delivery time of partial arc VMAT were 240 and 1.6 min less than those of full arc VMAT.

Conclusion: although ITVMIP, ITVAIP and ITV2phases were smaller than ITVall, no significant dosimetric differences resulted due to a relative small target volume of lung SBRT. Partial arc VMAT was feasible and more efficient for lung SBRT.

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