Abstract
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 VMATI 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 (n=4) or five‐field (n=9) 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 (VMATI, 91 control points) and two arcs (VMATII, 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 V9547.5Gy(95%), PTV mean dose, Dmax, PTV dose conformity (Van't Riet conformation number (CN)), mean lung dose, lung V20 and V5, liver V30, and Dmax 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 VMATI with fixed‐field IMRT demonstrated equivalent target coverage; statistically no significant difference were found in PTV D99 (p=0.47), PTV mean (p=0.12), PTV D95 and PTV V9547.5Gy (95%) (p=0.38). However, Dmax in VMATI plans was significantly lower compared to IMRT (p=0.02). The Van't Riet dose conformation number (CN) was also statistically in favor of VMATI plans (p=0.04). VMATI achieved lower lung V20 (p=0.05), whereas lung V5 (p=0.35) and mean lung dose (p=0.62) 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 VMATI plans was reduced by up to 55% (p=5.8E−10) and MUs reduced by up to 16% (p=0.001). Integral dose was not statistically different between the two planning techniques (p=0.99). There were no statistically significant differences found in dose distribution of the two VMAT techniques (VMATI vs. VMATII) Dose statistics for both VMAT techniques were: PTV D99 (p=0.76), PTV D95 (p=0.95), mean PTV dose (p=0.78), conformation number (CN) (p=0.26), and MUs (p=0.1). However, the treatment delivery time for VMATII increased significantly by two‐fold (p=3.0E−11) compared to VMATI. 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 VMATI was the reduction in treatment delivery time and MUs, and improvement in dose conformality. In our study, we found no significant difference in VMATII over single‐arc VMATI for PTV coverage or OARs doses. However, we observed significant increase in delivery time for VMATII compared to VMATI.PACS number: 87.53.Kn, 87.55.‐x
Highlights
Recent technological advances in radiation treatment have progressively changed the practice in esophageal cancer.[1,2] These new technological developments in radiation therapy help to improve target dose coverage while reducing the organs-at-risk doses, and improve the precision in delivering accurate radiation doses to the tumor while minimizing the risk of damaging surrounding healthy tissues. In this retrospective planning and delivery study, we evaluate the feasibility of volumetricmodulated arc therapy (VMAT) as a technique to address some of the limitations of fixed-field intensity-modulated radiation therapy (IMRT) treatments for the large planning target volumes (PTVs) of distal esophageal cancers
There were some differences in dosimetric parameters, it is likely that the IMRT and VMAT treatment plans would be clinically indistinguishable
We examined the differences in integral dose, volume receiving different dose levels (2 Gy or more) between IMRT and VMATI plans, and phantom dosimetry validation for both IMRT and VMATI techniques, which make our study unique among the recently published studies demonstrating the use of VMAT for esophageal cancers
Summary
Recent technological advances in radiation treatment (e.g., intensity-modulated radiotherapy, image-guided radiotherapy) have progressively changed the practice in esophageal cancer.[1,2] These new technological developments in radiation therapy help to improve target dose coverage while reducing the organs-at-risk doses, and improve the precision in delivering accurate radiation doses to the tumor while minimizing the risk of damaging surrounding healthy tissues In this retrospective planning and delivery study, we evaluate the feasibility of volumetricmodulated arc therapy (VMAT) as a technique to address some of the limitations of fixed-field intensity-modulated radiation therapy (IMRT) treatments for the large planning target volumes (PTVs) of distal esophageal cancers. All angles are available to deliver radiation to the target while avoiding critical structures, and the delivery time is used efficiently because the radiation delivery does not stop in between different beam angles.[3,4] Whereas for standard step-and-shoot IMRT, delivery of all static beams would take a longer time to complete the treatment
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