ESTRO 2024 - Abstract Book

S4718

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTR0 2024

While MRI-derived sCT is feasible for MRI-only workflow in photon therapy of HNC, these preliminary results show that sCT may not be feasible for proton therapy. However, whether the large difference between the proton dose based on pCT and sCT was due to the sCT or the methodology of this study is not clear yet. The effect of inaccurate patient positioning and image registration of sCT and pCT will be investigated further.

Keywords: Synthetic CT, Proton therapy, Head and neck cancer

References:

[1] Palmér E, Karlsson A, Nordström F, Petruson K, Siversson C, Ljungberg M, et al. Synthetic computed tomography data allows for accurate absorbed dose calculations in a magnetic resonance imaging only workflow for head and neck radiotherapy. Phys Imaging Radiat Oncol 2021;17:36–42. https://doi.org/10.1016/j.phro.2020.12.007.

2852

Mini-Oral

Balancing plan robustness and adaptation rate for proton therapy of lung cancer patients

Vlad M. Badiu 1,2 , Vicki T. Taasti 3 , Gilles Defraene 1 , Wouter van Elmpt 3 , Edmond Sterpin 1,4

1 KU Leuven, Department of Oncology, Laboratory of Experimental Radiotherapy, Leuven, Belgium. 2 Particle Therapy Interuniversity Center Leuven, PARTICLE, Leuven, Belgium. 3 Department of Radiation Oncology (Maastro), GROW School for Oncology and Reproduction, Maastricht University Medical Centre+,, Maastricht, Netherlands. 4 Université catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Center of Molecular Imaging, Radiotherapy and Oncology (MIRO), Brussels, Belgium

Purpose/Objective:

Robust planning is essential in proton therapy for ensuring accurate delivery of prescription doses in the presence of uncertainties [1-3]. An increase in plan robustness leads to larger irradiated volumes and consequently a higher dose to adjacent organs-at-risk (OARs), and thereby an increased chance of post-treatment toxicities [4]. The opposite occurs with plans with a higher dose conformity to the target and subsequently sparing of healthy surrounding tissue at the expense of a higher sensitivity to anatomical changes, resulting in work and cost demanding adaptations [5]. In this study, we will assess the impact of treatment plan robustness on the adaptation rate and how this relates to patient outcomes post-treatment in terms of normal tissue complication probability (NTCP).

Material/Methods:

Treatment planning was performed on a patient database consisting of 40 lung cancer patients, each including a planning 4DCT and up to eight weekly repeated 4DCTs (reCTs). For each patient, plans were made with three different levels of robustness based on setup uncertainty of 3, 6 and 9 mm, all with a range uncertainty of 2.6%. All plans had