Original Research
AB003. Optimizing postoperative proton radiotherapy in thymic epithelial tumors: added value of breath hold?
Esther Kneepkens1, Marije Velders1, Judith van der Stoep1, Maud Cobben1, Maud van den Bosch1, Nicole Hendrix1, laria Rinaldi1, Dirk De Ruysscher1, Dianne Hartgerink1, Judith Van Loon1, Florit Marcuse2, Stephanie T. H. Peeters1
1Department of Radiation Oncology (Maastro), GROW School for Oncology and Reproduction, Maastricht University Medical Centre+, Maastricht, the Netherlands;
2Department of Pulmonology, Maastricht University Medical Comprehensive Cancer Center, GROW School for Oncology and Reproduction, Maastricht University Medical Centre+, Maastricht, the Netherlands
Correspondence to: Stephanie T. H. Peeters, MD, PhD. Department of Radiation Oncology (Maastro), GROW School for Oncology and Reproduction, Maastricht University Medical Centre+, Maastro, Dr. Tanslaan 12, Maastricht, Maastricht, 6229ET, the Netherlands. Email: stephanie.peeters@maastro.nl.
Background: Postoperative radiotherapy for thymic epithelial tumors (TETs) is indicated for more advanced/aggressive disease or incomplete resection. At Maastro, postoperative proton therapy is guided by the Dutch model-based approach to minimize the estimated risk of heart toxicity, pneumonitis, and dysphagia. Inspiratory breath hold (BH) may increase lung volume and alter heart positioning, potentially improving dose distributions. This study aimed to evaluate whether BH could enhance proton therapy planning for TET patients.
Methods: Since BH computed tomography (CT) scans were unavailable for TET patients, we used data from 10 lymphoma patients. The free breathing (FB) clinical target volumes (CTVs) were derived from matched TET patients using deformable image registration. To generate a BH CTV, the 50% exhalation phase and the BH CT were deformably registered. The FB CTV was copied to the BH CT, adapted to anatomy and checked for consistency and comparable volume. For each patient two intensity-modulated proton therapy plans were made: one based on an average FB 4D-CT and another on the BH CT, using the same beam setup. Both were optimized to deliver 45 GyRBE over 25 fractions, with robust optimization considering 5 mm setup and 3% range uncertainties. Plans were compared by analyzing mean doses to the heart (MHD), lungs (MLD), and esophagus (MED).
Results: The impact of BH on normal tissues varied among patients (Figure 1): 1/10 patients showed a MHD reduction >1 GyRBE, and 1/10 had a MED reduction >1 GyRBE. However, in three patients, normal tissue doses increased by >0.5 GyRBE with BH. While individual reductions up to −0.8 GyRBE (MLD), −1.3 GyRBE (MHD), and −2.0 GyRBE (MED) were observed with BH, overall differences from FB plans were not statistically significant: −0.1±0.5 GyRBE (MLD), −0.1±0.7 GyRBE (MHD), and −0.3±0.7 GyRBE (MED).
Conclusions: The benefits of intensity-modulated proton therapy with BH for TET patients are anatomy-dependent. Although most patients showed minimal change, about 10% experienced notable dose reductions, which may be clinically meaningful for long-term survivors.
Keywords: Postoperative radiotherapy; thymic epithelial tumor (TET); proton radiotherapy; breath hold
Acknowledgments
None.
Funding: None.
Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://med.amegroups.com/article/view/10.21037/med-25-ab003/coif). D.D.R. received grants from AstraZeneca, BMS, Beigene, Philips, Olink and Eli-Lilly. J.V.L. received payment or honoraria from Dutch and Belgian society for lung cancer and serve as the unpaid Board of Dutch Platform for proton therapy. S.T.H.P. received grants from Hanarth grant. The other authors have no conflicts of interest to declare.
Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the institutional review board of Maastro (No. W 22 12 00046) and individual consent for this retrospective analysis was waived.
Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.
doi: 10.21037/med-25-ab003
Cite this abstract as: Kneepkens E, Velders M, van der Stoep J, Cobben M, van den Bosch M, Hendrix N, Rinaldi l, De Ruysscher D, Hartgerink D, Van Loon J, Marcuse F, Peeters STH. AB003. Optimizing postoperative proton radiotherapy in thymic epithelial tumors: added value of breath hold? Mediastinum 2025;9:AB003.
