ESTRO 2022 - Abstract Book

S245

Abstract book

ESTRO 2022

Proffered Papers: Applications of photon treatment planning

OC-0285 Personalized trade-off: elective nodal coverage vs. NTCP in head-and-neck cancer using automated MCO

L.P. Kaplan 1,2,3,4 , L. Rossi 4 , B.J.M. Heijmen 4 , A.I.S. Holm 1 , J.G. Eriksen 5 , S.S. Korreman 6,3,1

1 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 2 Aarhus University, Departmenet of Clinical Medicine, Aarhus, Denmark; 3 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus, Denmark; 4 Erasmus Medical Center, Department of Radiation Oncology, Rotterdam, The Netherlands; 5 Aarhus University Hospital, Department of Experimental Clinical Oncology, Aarhus, Denmark; 6 Aarhus University, Department of Clinical Medicine, Aarhus, Denmark Purpose or Objective The current standard in curative radiotherapy (RT) for head-and-neck squamous cell carcinoma (HNSCC) is to prioritize dose coverage highly for all patients, even for the elective nodal CTV (CTV E ). The risk of microscopic spread is not uniform throughout CTV E , however. Some patients might benefit from trading a slightly reduced dose in sub-volumes of CTV E where risk of microscopic spread is lowest for lower organ-at-risk (OAR) doses. Our aim was to develop an automated multi-criteria optimization (MCO) planning workflow to systematically explore such patient-specific trade-offs between low-risk CTV E coverage and normal tissue complication probability (NTCP). Materials and Methods For 40 HNSCC patients, baseline VMAT plans (68/60/50 Gy SIB, PTV margin 5mm) were retrospectively created following our clinical treatment protocol using an in-house automated MCO software. Sub-volumes of CTV E /PTV E with lower risk of microscopic spread were defined individually for each patient (termed trade- off CTV E /PTV E ). Trade-off CTV E was defined as the total CTV E minus lymph levels containing a nodal metastasis (GTV + 1cm isotropic extension, see Fig.1). The goal for total PTV E near-minimum dose (D 99% ) was reduced from ≥ 47.5Gy to 45Gy and 42.5Gy in two trade-off plans (TP 45/42.5 ). Minimum dose to trade-off CTV E was constrained to 45Gy in both TPs (47.5Gy in baseline plans). All other planning objectives and constraints (OARs and remaining targets) were the same in all plans. Target dose reduction relative to baseline plans was allowed only in trade-off CTV E /PTV E . OAR doses, total PTV E V 47.5Gy , and NTCP for xerostomia and dysphagia (models used in the DAHANCA35 study, based on doses to salivary glands or oral cavity and swallowing muscles, respectively) were compared between baseline plans and TPs. The location of voxels (interpolated to size 0.25x0.25x0.25 mm 3 ) with doses below 47.5 and 45Gy in trade-off PTV E was quantified by distance to the volume’s outer contour.