Abstract
Purpose: To investigate the feasibility of partial arc volumetric modulated arc therapy (VMAT) in lung cancer stereotactic body radiotherapy (SBRT), as well the volumetric and dosimetric effects of different internal target volume (ITV) definitions with 4D CT. Methods: Fourteen patients with primary and metastatic lung cancer underwent SBRT were enrolled. Full and partial arc 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), and 2 extreme respiratory phases. Volumetric and dosimetric differences, as well as MU and delivery time were investigated. Results: 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. There were no significant differences on target coverage and organ at risks (OARs) sparing among four ITVs. The average percent volume differences of ITVMIP, ITVAIP and ITV2phases to ITVall were 8.6%, 13.4%, and 25.2%, respectively. Conclusions: Although partial arc VMAT delivered more dose 2 cm out of PTV, it decreases the dose to lung, spinal cord, and esophagus, as well decreased the total MU and delivery time compared with full arc VMAT without sacrificing target coverage. Partial arc VMAT was feasible and more efficient for lung SBRT.
Highlights
Lung cancer remains the leading cause of cancer death in both men and women in the United States [1], Asian countries [2], and the world [3]
Full and partial arc volumetric modulated arc therapy (VMAT) plans were generated with four different internal target volume (ITV): ITVall, ITVMIP, ITVAIP and ITV2phases, representing ITVs generated from all 10 respiratory phases, maximum intensity projection (MIP), average intensity projection (AIP), and 2 extreme respiratory phases
Conclusions: partial arc VMAT delivered more dose 2 cm out of planning target volume (PTV), it decreases the dose to lung, spinal cord, and esophagus, as well decreased the total MU and delivery time compared with full arc VMAT without sacrificing target coverage
Summary
Lung cancer remains the leading cause of cancer death in both men and women in the United States [1], Asian countries [2], and the world [3]. Three dimensional conformal radiation therapy (3DCRT) with 10 - 15 static fields is the most common technique used to create the desired conformal dose distribution for SBRT. The main drawback of 3DCRT planning is the lengthy treatment time relating to patient setup and radiation delivery resulted from many fields needed to create an acceptable treatment plan [7]. Depending on equipment and dose rate utilised, patient setup time can take up to 22 min and 100 min for treatment delivery [8] [9]. Longer treatment time significantly increases the chances of intrafraction motion and error [10]. Many conformal SBRT studies have reported frequently occurring and clinically significant treatment related toxicity complications [11]
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