ESTRO 2022 - Abstract Book

S106

Abstract book

ESTRO 2022

In a two-centre randomized phase-II trial, Adaptive Dose-Painting-By-Numbers (A-DPBN) compared favourably to non- adaptive standard IMRT (S-IMRT) in head and neck cancer (HNC) in terms of short-term outcomes. This study presents the dosimetric evaluation. Materials and Methods 95 HNC were randomized. In A-DPBN, the treatment was given in 3-phases (Figure 1), the first two treatment plans (fractions 1-10 and 11-20) being created with a dose-painting (DP) technique based on the 18 F-FDG-PET-CTs acquired prior to the treatment and after the 8 th fraction. A CT acquired after the 18 th fraction was used to make the plan for fractions 21-30. The protocol dose prescription is given in Figure 1. Because of unexpected late grade 3-4 mucosal ulcers, the dose- escalation was reduced twice during the trial. Two DP planning methods were applied in the two centres: voxel-intensity-based optimisation versus a technique using segmentation of the GTV in 3-4 regions of the uptake value. Dose reporting was performed on the pretreatment CT, deformable image-registration being used to accumulate the adapted plan doses (RayStation, v6.1.1). Mann-Whitney U tests were calculated using SPSS (v27.0.1), p-values<0.05 were considered significant.

Results No volume differences were observed between A-DPBN and S-IMRT in the primary GTV target (GTV-T) and the lymph node GTV (GTV-N) (p=0.386) on the pretreatment CT. The mean D 2 , D 50 were higher (p < 0.001) for GTV-T in A-DPBN (79.5±3.8, 72.5 ± 3.2 Gy) compared to the S-IMRT (70.9 ± 0.8, 69.4 ± 0.5 Gy). Conversely, mean D 98 was lower (66.9±2.6 and 68.0±0.9, respectively, p<0.001). For GTV-N, D 2 and D 98 differed (p<0.001) in A-DPBN (75.5±5.5 and 64.0±3.2 Gy), compared to S-IMRT (71.0±0.9 and 66.6±2.7 Gy). No difference (p=0.112) was found for the D 50 (69.8±3.6 and 69.4±0.6 Gy, respectively). The D 2 and D 50 of the ipsilateral parotid in A-DPBN (56.5±9.3 and 25.6±11.3 Gy) were lower (p<0.001 and 0.002) compared to S-IMRT (63.1±6.8 and 35.1±16.3 Gy). In the contralateral parotid, the D 2 and D 50 in A-DPBN (50.9±8.0 and 19.0±5.4 Gy) were lower (p<0.001 and 0.004) compared to S-IMRT (57.4±4.9 and 22.6±6.1 Gy) The D 50 and D 98 in the union of the swallowing structures (47.3±10.2 and 27.8±12.3 Gy) were lower in A-DPBN compared with S-IMRT (59.4±10.4 and 41.1±14.0 Gy, p<0.001). No statistical difference (p=0.052) was observed between A-DPBN and S-IMRT for the D 2 (respectively 69.3±5.4 and 70.1). Conclusion The use of the A-DPBN technique enabled higher doses to the GTV. A combination of A-DPBN and a reduced dose prescription to the elective neck resulted in lower doses on the swallowing structures and parotids. Lower D 98 doses reported on the pretreatment GTV volumes by the anti-chronological dose accumulation was an effect of the treatment adaptation. A follow-up study of the disease control will provide more information regarding the long-term efficiency of the method.

OC-0130 Pareto front analysis for implementing bone marrow sparing VMAT strategy for cervical cancer

S. Kuipers 1,2 , J. Godart 2,1 , A. Corbeau 3 , A. Sharfo 1 , S. Breedveld 1 , J. Mens 1 , R. Nout 1 , M. Hoogeman 1,2

1 Erasmus MC Cancer Institute, Department of Radiotherapy, Rotterdam, The Netherlands; 2 HollandPTC, Department of Medical Physics and Informatics, Delft, The Netherlands; 3 Leiden University Medical Center, Department of Radiation Oncology, Leiden, The Netherlands