Abstract
PurposeTo assess the performance of a simple optimisation method for improving target coverage and organ-at-risk (OAR) sparing in intensity-modulated radiotherapy (IMRT) for cervical oesophageal cancer.MethodsFor 20 selected patients, clinically acceptable original IMRT plans (Original plans) were created, and two optimisation methods were adopted to improve the plans: 1) a base dose function (BDF)-based method, in which the treatment plans were re-optimised based on the original plans, and 2) a dose-controlling structure (DCS)-based method, in which the original plans were re-optimised by assigning additional constraints for hot and cold spots. The Original, BDF-based and DCS-based plans were compared with regard to target dose homogeneity, conformity, OAR sparing, planning time and monitor units (MUs). Dosimetric verifications were performed and delivery times were recorded for the BDF-based and DCS-based plans.ResultsThe BDF-based plans provided significantly superior dose homogeneity and conformity compared with both the DCS-based and Original plans. The BDF-based method further reduced the doses delivered to the OARs by approximately 1–3%. The re-optimisation time was reduced by approximately 28%, but the MUs and delivery time were slightly increased. All verification tests were passed and no significant differences were found.ConclusionThe BDF-based method for the optimisation of IMRT for cervical oesophageal cancer can achieve significantly better dose distributions with better planning efficiency at the expense of slightly more MUs.
Highlights
Oesophageal cancer is a frequently diagnosed cancer worldwide [1]
It is challenging to achieve optimal Intensity-modulated radiotherapy (IMRT) plans for cervical oesophageal cancer. Common reasons for this difficulty include the rapidly changing neck-to-shoulder anatomy and the presence of dose-limiting OARs; another important reason is the dose discrepancy between optimiser plans and calculated plans. This discrepancy is caused by an optimisation-convergence error (OCE) that originates from the following major sources, as described by Dogan et al.: tissue heterogeneity, the buildup effect, multi-leaf collimator (MLC) modulation and the optimisation algorithm [13,14]
The most obvious advantage of the BDF-based method is that it substantially improves dose homogeneity. Such improvement may be clinically beneficial for patients with cervical oesophageal cancer because the planning target volume (PTV) for the treatment of this type of cancer commonly include such tissues as submucosal tissue, mucosa, and bone, which may suffer complications after receiving significantly heterogeneous high doses [21]
Summary
For 20 selected patients, clinically acceptable original IMRT plans (Original plans) were created, and two optimisation methods were adopted to improve the plans: 1) a base dose function (BDF)-based method, in which the treatment plans were re-optimised based on the original plans, and 2) a dose-controlling structure (DCS)-based method, in which the original plans were re-optimised by assigning additional constraints for hot and cold spots. The Original, BDF-based and DCS-based plans were compared with regard to target dose homogeneity, conformity, OAR sparing, planning time and monitor units (MUs). Dosimetric verifications were performed and delivery times were recorded for the BDF-based and DCS-based plans. No additional external funding was received for this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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