Volumetric‐modulated arc therapy for the treatment of a large planning target volume in thoracic esophageal cancer

Recently, volumetric‐modulated arc therapy (VMAT) has demonstrated the ability to deliver radiation dose precisely and accurately with a shorter delivery time compared to conventional intensity‐modulated fixed‐field treatment (IMRT). We applied the hypothesis of VMAT technique for the treatment of thoracic esophageal carcinoma to determine superior or equivalent conformal dose coverage for a large thoracic esophageal planning target volume (PTV) with superior or equivalent sparing of organs‐at‐risk (OARs) doses, and reduce delivery time and monitor units (MUs), in comparison with conventional fixed‐field IMRT plans. We also analyzed and compared some other important metrics of treatment planning and treatment delivery for both IMRT and VMAT techniques. These metrics include: 1) the integral dose and the volume receiving intermediate dose levels between IMRT and [Formula: see text] plans; 2) the use of 4D CT to determine the internal motion margin; and 3) evaluating the dosimetry of every plan through patient‐specific QA. These factors may impact the overall treatment plan quality and outcomes from the individual planning technique used. In this study, we also examined the significance of using two arcs vs. a single‐arc VMAT technique for PTV coverage, OARs doses, monitor units and delivery time. Thirteen patients, stage T2‐T3 N0‐N1 (TNM AJCC 7th edn.), PTV volume median 395 cc (range 281–601 cc), median age 69 years (range 53 to 85), were treated from July 2010 to June 2011 with a four‐field [Formula: see text] or five‐field [Formula: see text] step‐and‐shoot IMRT technique using a 6 MV beam to a prescribed dose of 50 Gy in 20 to 25 F. These patients were retrospectively replanned using single arc ([Formula: see text] , 91 control points) and two arcs ([Formula: see text] , 182 control points). All treatment plans of the 13 study cases were evaluated using various dose‐volume metrics. These included PTV D99, PTV D95, PTV [Formula: see text] , PTV mean dose, [Formula: see text] , PTV dose conformity (Van't Riet conformation number (CN)), mean lung dose, lung V20 and V5, liver V30, and [Formula: see text] to the spinal canal prv3mm. Also examined were the total plan monitor units (MUs) and the beam delivery time. Equivalent target coverage was observed with both VMAT single and two‐arc plans. The comparison of [Formula: see text] with fixed‐field IMRT demonstrated equivalent target coverage; statistically no significant difference were found in PTV D99 [Formula: see text] , PTV mean [Formula: see text] , PTV D95 and PTV [Formula: see text]. However, [Formula: see text] in [Formula: see text] plans was significantly lower compared to IMRT [Formula: see text]. The Van't Riet dose conformation number (CN) was also statistically in favor of [Formula: see text] plans [Formula: see text]. [Formula: see text] achieved lower lung [Formula: see text] , whereas lung [Formula: see text] and mean lung dose [Formula: see text] were not significantly different. The other OARs, including spinal canal, liver, heart, and kidneys showed no statistically significant differences between the two techniques. Treatment time delivery for [Formula: see text] plans was reduced by up to 55% [Formula: see text] and MUs reduced by up to 16% [Formula: see text]. Integral dose was not statistically different between the two planning techniques [Formula: see text]. There were no statistically significant differences found in dose distribution of the two VMAT techniques ([Formula: see text] vs. [Formula: see text]) Dose statistics for both VMAT techniques were: PTV [Formula: see text] , PTV [Formula: see text] , mean PTV dose [Formula: see text] , conformation number (CN) [Formula: see text] , and MUs [Formula: see text]. However, the treatment delivery time for [Formula: see text] increased significantly by two‐fold [Formula: see text] compared to [Formula: see text]. VMAT‐based treatment planning is safe and deliverable for patients with thoracic esophageal cancer with similar planning goals, when compared to standard IMRT. The key benefit for [Formula: see text] was the reduction in treatment delivery time and MUs, and improvement in dose conformality. In our study, we found no significant difference in [Formula: see text] over single‐arc [Formula: see text] for PTV coverage or OARs doses. However, we observed significant increase in delivery time for [Formula: see text] compared to [Formula: see text]. PACS number: 87.53.Kn, 87.55.‐x