Inter- and intrafractional 4D dose accumulation for evaluating ANTCP robustness in lung cancer

Background and purpose: Model-based selection of proton therapy patients relies on a predefined reduc-tion in normal tissue complication probability (NTCP) with respect to photon therapy. The decision is necessarily made based on the treatment plan, but NTCP can be affected when the delivered treatment deviates from the plan due to delivery inaccuracies. Especially for proton therapy of lung cancer, this can be important because of tissue density changes and, with pencil beam scanning, the interplay effect between the proton beam and breathing motion.Materials and methods: In this work, we verified whether the expected benefit of proton therapy is retained despite delivery inaccuracies by reconstructing the delivered treatment using log-file based dose reconstruction and inter-and intrafractional accumulation. Additionally, the importance of two uncertain parameters for treatment reconstruction, namely deformable image registration (DIR) algorithm and a/b ratio, was assessed.Results: The expected benefit or proton therapy was confirmed in 97% of all studied cases, despite regular differences up to 2 percent point (p.p.) NTCP between the delivered and planned treatments. The choice of DIR algorithm affected NTCP up to 1.6 p.p., an order of magnitude higher than the effect of a/b ratio.Conclusion: For the patient population and treatment technique employed, the predicted clinical benefit for patients selected for proton therapy was confirmed for 97.0% percent of all cases, although the NTCP based proton selection was subject to 2 p.p. variations due to delivery inaccuracies.(c) 2023 The Author(s). Published by Elsevier B.V. Radiotherapy and Oncology 182 (2023) 1-6 This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

By reconstructing the delivered treatment, it was found that despite delivery inaccuracies, there is still an expected benefit for proton therapy in lung cancer patients. The choice of deformable image registration algorithm and a/b ratio were assessed for their importance.