Abstract
Purpose: Intensity modulated radiotherapy (IMRT) for cervical esophageal cancer is challenging. Although IMRT techniques using inverse planning algorithms are facilitating the treatment planning process, the irradiation dose to the normal tissues can be a critical issue. This study was performed to investigate the effect of beam numbers and their directions and local optimization on: (1) dose conformity and homogeneity to the planning target volume (PTV) and (2) dose to the organ at risks (OARs). Methods: Four upper esophageal cancer cases were randomly selected for this treatment planning study. Eight IMRT plans were generated for each case with the same dose-volume constraints but with different beam numbers and arrangements. Local optimization using regular structures drawn automatically around the PTV with margins from 0.5-1.5 cm was performed. IMRT plans were evaluated with respect to isodose distributions, dose-volume histograms (DVHs) parameters, homogeneity index (HI), and conformity index (CI). The statistical comparison between the types of plans was done using the One Way ANOVA test. Results: The results showed that IMRT using three or five beams was not sufficient to obtain good dose optimization. The seven field plans showed the best coverage for the PTV with tolerable doses for the OARs, and the beam orientation was very critical. Increasing beams (Bs) number from 7 to 13 did not show significant differences in the PTV coverage, while the mean lung dose was increased. The PTV coverage were 95.1, 95.1, 98.1, 97.3, 97.3, 97.3, 97.0, and 97.0% for 3Bs, 5Bs, 7Bs, 9Bs, 13Bs, 7Bs(30), 7Bs(60) (beam angles were changed from 0 o to 30 o and 60 o ), and 7Bs(R) (seven IMRT plans with ring), respectively. The mean heart dose did not exceed 0.36 Gy with p 0.05), yet conformity was better with 9Bs and 7Bs(R) IMRT plans with p < 0.05. Conclusion: Seven equispaced coplanar intensity-modulated beams with an addition of a ring structure can produce desirable dose distributions to the PTV. Moreover, dose-volume of exposed normal lung can be reduced with 9Bs and 7Bs(R) IMRT plans.
Highlights
Organ preservation is a common treatment goal for carcinoma of the cervical esophagus.[1, 2, 3] Technical challenges including rapid change in patient contour and dose-limiting adjacent critical structures present difficulty in achieving uniform target coverage.[4, 5] Despite these challenges, radiotherapy is the primary treatment modality for carcinoma of the cervical esophagus
The present study addressed whether different intensity-modulated radiotherapy (IMRT) techniques for esophageal cancer can be used to achieve higher
This goal was achieved with all types of IMRT plans reducing V30 Gy(%) and mean lung dose (MLD)
Summary
Organ preservation is a common treatment goal for carcinoma of the cervical esophagus.[1, 2, 3] Technical challenges including rapid change in patient contour and dose-limiting adjacent critical structures present difficulty in achieving uniform target (tumor) coverage.[4, 5] Despite these challenges, radiotherapy is the primary treatment modality for carcinoma of the cervical esophagus. Innovative technologies in radiation delivery such as intensity-modulated radiotherapy (IMRT) offer the potential for improved tumor coverage, while reducing the dose delivered to the surrounding normal tissues.[6] IMRT has shown to be superior to 3-dimensional conformal radiation therapy (3DCRT) with respect to dose conformity in multiple sites including, but not limited to the larynx, nasopharynx, lung, and prostate.[7] Multiple planning studies have shown IMRT superiority in the treatment of various head and neck sites as well as lower esophageal tumors.[8, 9] These planning studies have used to develop techniques that will produce the best dosimetric results when applied to a group of patients with a specific tumor location.[10] IMRT has become the standard of care for various cancers of the head and neck.[11] No consensus has been reached as to the optimal radiation technique and target volume delineation for treating cervical esophageal cancer. A number of additional limitations and potential concerns regarding IMRT are relevant to cervical esophageal cancer
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