Abstract

This study seeks to compare fixed‐field intensity‐modulated radiation therapy (FF IMRT), RapidArc (RA), and helical tomotherapy (HT) to discover the optimal treatment modality to deliver SBRT to the peripheral lung. Eight patients with peripheral primary lung cancer were reviewed. Plans were prescribed a dose of 48 Gy and optimized similarly with heterogeneity corrections. Plan quality was assessed using conformality index (CI100%), homogeneity index (HI), the ratio of the 50% isodose volume to PTV (R50%) to assess intermediate dose spillage, and normal tissue constraints. Delivery efficiency was evaluated using treatment time and MUs. Dosimetric accuracy was assessed using gamma index (3% dose difference, 3 mm DTA, 10% threshold), and measured with a PTW ARRAY seven29 and OCTAVIUS phantom. CI100%,HI, and R50% were lowest for HT compared to seven‐field coplanar IMRT and two‐arc coplanar RA (p<0.05). Normal tissue constraints were met for all modalities, except maximum rib dose due to close proximity to the PTV. RA reduced delivery time by 60% compared to HT, and 40% when compared to FF IMRT. RA also reduced the mean MUs by 77% when compared to HT, and by 22% compared to FF IMRT. All modalities can be delivered accurately, with mean QA pass rates over 97%. For peripheral lung SBRT treatments, HT performed better dosimetrically, reducing maximum rib dose, as well as improving dose conformity and uniformity. RA and FF IMRT plan quality was equivalent to HT for patients with minimal or no overlap of the PTV with the chest wall, but was reduced for patients with a larger overlap. RA and IMRT were equivalent, but the reduced treatment times of RA make it a more efficient modality.PACS numbers: 87.53.Ly87.55.N‐, 87.55.D‐, 87.56.bd

Highlights

  • Lung cancer is the most common noncutaneous malignancy world-wide and accounts for the most cancer deaths in both men and women.[1]

  • Trial investigating Stereotactic body radiation therapy (SBRT) for patients with medically inoperable stage I/II peripheral non-small cell lung cancer (NSCLC). This protocol established a common way for clinics to simulate, plan, and treat lung cancer with SBRT.[4]. Use of heterogeneity corrections (HC) in dose calculation and planning with intensity-modulated radiation therapy (IMRT) were not allowed in Radiation Therapy Oncology Group (RTOG) 0236

  • This inhomogeneity causes a decrease in plan quality which needs to be examined.[5]. In addition, there has been an increase in use of IMRT to treat SBRT of the lung,(3,6-9) yet these different types of IMRT have not been fully evaluated

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Summary

Introduction

Lung cancer is the most common noncutaneous malignancy world-wide and accounts for the most cancer deaths in both men and women.[1]. Trial investigating SBRT for patients with medically inoperable stage I/II peripheral NSCLC This protocol established a common way for clinics to simulate, plan, and treat lung cancer with SBRT.[4] Use of heterogeneity corrections (HC) in dose calculation and planning with intensity-modulated radiation therapy (IMRT) were not allowed in RTOG 0236. HC are important for SBRT of the peripheral lung because there is much tissue inhomogeneity in the thorax, especially at the lung and chest wall interface where these peripheral lung tumors tend to develop This inhomogeneity causes a decrease in plan quality which needs to be examined.[5] In addition, there has been an increase in use of IMRT to treat SBRT of the lung,(3,6-9) yet these different types of IMRT have not been fully evaluated. Varian RapidArc (RA) is one version of VMAT, and was used in this study

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