Improving breast cancer radiotherapy through the use of an optical surface scanner and intensity modulated delivery techniques

Abstract

Purpose: Many advancements in breast cancer radiotherapy aim at a highly accurate dose delivery to the tumor. The purpose of this Master's Thesis was to contribute to the improvement of breast cancer therapy by fulfilling two tasks. Firstly, a new margin concept was derived, based on the data generated by the optical surface scanner Catalyst HD (C-RAD, Sweden). Secondly, retrospective treatment planning was performed and it was tested whether there is a treatment technique which is superior compared to routinely used techniques in breast cancer radiotherapy.Materials and Methods: The optical surface scanner Catalyst HD (C-RAD, Sweden) is used for patient positioning and patient monitoring during dose delivery at the Department of Radiation Oncology at AKH Wien and Medical University of Vienna (MUW). The main tasks of this thesis were:• Catalyst HD data of 22 patients during 322 fractions was evaluated in terms of inter- and intrafraction motion. 11 of the patients were left-sided breast cancer patients being treated in DIBH (deep inspiration breath hold) and the other 11 patients had right-sided BC and were treated in FB (free breathing) mode. The results were used to derive a new margin concept for breast cancer therapy and the resulting margins were compared to the currently used margin at the Department of Radiation Oncology at AKH/MUW.• The Pearson correlation coefficient was employed to specify the correlation between Catalyst HD and the current standard position verification systems (portal imaging and cone-beam computed tomography (CBCT)).• Treatment plans were retrospectively developed for 10 randomly selected patients in the treatment planning system (TPS) RayStation 7. Statistical analysis including equivalence testing was performed for the treatment plans on basis of the achieved clinical goals by also taking the original treatment plans from a different TPS into account.Results: Margin calculation entirely based on Catalyst HD data yielded mCAT,lat=4.4mm, mCAT,long=4.7mm and mCAT,vert=4.7mm for lateral, longitudinal and vertical direction, respectively. No correlation between Catalyst HD and the standard position verification methods (portal imaging and CBCT) was found. The evaluation of the treatment plans created in RayStation 7 showed that DMLC (dynamic multi leaf collimator) and VMAT (volumetric modulated arc therapy) techniques yielded the best results in terms of target coverage and effective sparing of organs at risk for lymph node-negative breast cancer patients. Only VMAT technique could achieve clinically acceptable coverage of a target volume with simultaneous lymph node irradiation. A significant higher low dose exposure of the contralateral lung was observed for VMAT treatment plans.Conclusion: The Catalyst HD system is a valuable addition to the current positioning protocols at the Department of Radiation Oncology at AKH/MUW, but it should be used in combination with X-ray based imaging methods to ensure correct dose delivery. Any future changes to the current margin concept should be performed with care as Catalyst HD shows no significant correlation with the standard imaging methods and the derived margins provide only a lower limit for the safety margin. It was found that DMLC and VMAT techniques yielded the best results in lymph node-negative breast cancer radiotherapy. VMAT is superior for dose delivery to a target volume with simultaneous lymph node irradiation.