Assessment of dose variation for accelerated partial breast irradiation using rigid and deformable image registrations

Publication date: Available online 23 June 2016
Source:Practical Radiation Oncology
Author(s): Vikneswary Batumalai, Lois Holloway, Amy Walker, Michael Jameson, Geoff P. Delaney
PurposeThe aim of this study was to estimate the delivered dose to the target and organs at risk (OAR) for external beam accelerated partial breast irradiation (APBI) accounting for day-to-day setup uncertainties, using rigid and deformable image registration.Methods and MaterialsOne planning computed tomography (CT) scan and five cone-beam CT (CBCT) scans for each of 25 patients previously treated with tangential breast radiotherapy were used. All CBCT scans were registered to the planning-CT scan using three techniques; i) rigid registration based on bony-anatomy only, ii) rigid registration based on soft-tissue only, and iii) deformable image registration. For each patient, four dose distributions were calculated for APBI. The first dose distribution was the original plan. The other three were "dose-of-the-day" for each of the registration approaches. The effects of image registrations on estimating delivered dose to targets and organs at risk (OAR) were determined.ResultsThe average reductions in V95 (percentage of the PTV that received 95% of the prescribed dose) were 6%, 7%, and 5% for bone, soft-tissue and deformable registrations, respectively. The average increase in mean dose to the heart were 9%, 9% and 18% for bone, soft-tissue and deformable registrations, respectively, while the average increase in maximum dose to the contralateral breast were 19%, 20%, and 28%, respectively.ConclusionsThe results of this study have shown that there are differences between the planned and estimated delivered dose for APBI due to day-to-day setup uncertainties which may need to be accounted for. Estimated dosimetric impact of setup variation and breast deformation assessed using deformable registration was greater for OARs and smaller for target volumes compared to rigid registration.



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