Accuracy assessment of inter-fraction dose accumulation using non-rigid deformation models: study in cubic silicon phantoms.

Fekkes, Stein;van Elmpt, Wouter;Orban de Xivry, Jonathan;Janssens, Guillaume;Lambin, Philippe;et.al.
(2008) ESTRO27 meeting, European Society for therapeutic radiology and oncology — Location: Göteborg, Sweden (14.September.2008)

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  • Fekkes, SteinMaastricht University Medical Center (MUMC), Netherlands
    Author
  • van Elmpt, WouterMaastricht University Medical Center (MUMC), Netherlands
    Author
  • Orban de Xivry, JonathanUCLouvain
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  • Janssens, GuillaumeUCLouvain
    Author
  • Lambin, PhilippeMaastricht University Medical Center (MUMC), Netherlands
    Author
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Abstract
Purpose: In radiotherapy, inter-fraction dose accumulation is necessary to evaluate the dose distribution of an entire course of treatment by adding up the multiple dose distributions of the different fractions. This summation of dose distributions is difficult due to changes in tumour volume and possible changes in the patient anatomy during treatment. For this purpose, we have investigated the accuracy of a non-rigid deformation method in terms of dose accumulation. Materials: CT images were acquired using our Siemens Oncor MV cone beam CT imager and dose calculations were performed on these CT scans using CMS XiO treatment planning system . In total , 5 arbitrary deformations with maximum displacements up to 3 em were applied to a cubic silicon phantom with 27 implanted markers . Before registering the silicon was masked in order to erase the markers and force homogeneous density, the CT scans were registered to the CT scan at the phantom in non-deformed condition using 'morphons', a non-rigid deformation method. The calculated deformation field was applied to the dose distributions of the 5 CT scans, and the accumulated dose per voxel was calculated. Three different dose distributions were investigated; a simple 2 beam plan , a standard 3 beam conformal plans with wedges and a highly conformal 8 beam plan . To asses the accuracy of the non-riqid registration, the dose values at the 27 marker positions in the original CT images were taken as the reference dose values and compared to the dose values found with and without non-rigid deformation applied. Results: The maximum shift in marker position was 28 mm Which lead to a maximum dose difference of 38%. The absolute dose difference due to deformation over all markers and CT scans for the 3 plans was 7.4±7.5%, 8.1± 6.6% and 6.3±9.4%, respectively. Using non-deformable registration a decrease of the absolute dose difference to 4.2±3.9%, 2.4±2.4%, and 1.7±2.8% was achieved. Overall a significant (p<O.Ol) decrease in both the mean absolute dose difference and variance was demonstrated using nonrigid registration. Conclusions: Dose deformation using the non-rigid registration method is possible using on-line CT imaging . This opens possibilities for inter-fraction dose accumulation and adaptation of treatment to incorporate possible differences in planned and delivered dose to the target volume and organs at risk due to anatomical deformations. Applying the deformation models to patient data and verification using MOSFET detectors is currently under investigation. Acknowledgment: We thank the Medical Informatics laboratory of Linköping University for sharing their implementation of the Morphons method.
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Fekkes, S., van Elmpt, W., Orban de Xivry, J., Janssens, G., Dekker, A., & Lambin, P. (2008). Accuracy assessment of inter-fraction dose accumulation using non-rigid deformation models: study in cubic silicon phantoms. Radiotherapy & Oncology, 88(Supplement 2), S363. https://hdl.handle.net/2078.5/41364 (Original work published 2008)