ESTRO 2023 - Abstract Book

S652

Monday 15 May 2023

ESTRO 2023

J. Grefve 1 , K. Sandgren 1 , J. Jonsson 1 , A. Keeratijarut Lindberg 1 , E. Nilsson 1 , S. Strandberg 2 , A. Bergh 3 , K. Söderkvist 4 , B. Zackrisson 4 , A. Gunnlaugsson 5 , M. Moreau 6 , C. Thellenberg Karlsson 4 , L. E. Olsson 7 , B. Friedrich 8 , A. Widmark 4 , L. Blomqvist 9 , V. Berg Loegager 10 , J. Axelsson 1 , M. Ögren 2,2 , K. Riklund 11 , T. Nyholm 1 1 Umea University, Department of Radiation Sciences, Radiation Physics, Umea, Sweden; 2 Umea University, Department of Radiation Sciences, Diagnostic Radiology, Umea, Sweden; 3 Umea University, Department of Medical Biosciences, Pathology, Umea, Sweden; 4 Umea University, Department of Radiation Sciences, Oncology, Umea, Sweden; 5 Skane University Hospital, Department of Hematology, Oncology and Radiation Physics, Lund, Sweden; 6 Skane University Hospital, Department of Hematology, Oncology and Radiation Physics, Lund , Sweden; 7 Lund University, Department of Translational Medicine, Medical Radiation Physics, Malmo, Sweden; 8 Umea University, Department of Surgical and Perioperative Sciences, Urology and Andrology, Umea, Sweden; 9 Karolinska Institute, Department of Molecular Medicine and Surgery, Solna, Sweden; 10 Copenhagen University Hospital in Herlev, Department of Radiology, Herlev, Denmark; 11 Umea University, Department of Radiation Sciences, Diagnostic Radiology, Umea , Sweden Purpose or Objective There is growing evidence that focal boost to intra-prostatic lesions is beneficial for patients with high-risk prostate cancer. Delineation of boost regions can be done using MRI with T2w imaging, diffusion-weighted imaging (DWI) or perfusion (dynamic contrast-enhanced, DCE) imaging, or with PET, where PSMA currently is one of the dominant radiotracers for prostate cancer. The delineation guided by the different modalities will result in a variation in gross tumor volumes (GTV), which may impact the effectiveness of the treatment. In the present study we investigate the characteristics of manual intra-prostatic GTV delineations based on different MR sequences and PSMA-PET using whole-mount histopathology as gold standard. Materials and Methods 15 prostate cancer patients with high risk profile (Gleason >=8) were imaged with PSMA-PET/MR prior to surgery. The prostate specimens were placed in individualized prostate molds with slits (5 mm separation) corresponding to the imaging planes for the histopathology slicing. Gleason grade regions 3, 4 and 5 were delineated in each slice and through a careful registration procedure transferred to the coordinate system of the PET/MR examination. Four radiation oncologists individually delineated GTVs, based on T2w-MRI, diffusion-MRI (DW-MRI), DCE-MRI, and PSMA-PET, respectively. The Staple algorithm was used to combine the delineations for each modality. Results All results are presented for the combined (Staple algorithm) GTV delineation for each imaging modality. In regions with Gleason grade 4 (15 patients) the mean volumetric overlap with standard deviation was 38% ± 23% (T2w-MRI), 37% ± 22% (DW-MRI), 34% ± 20% (DCE-MRI) and 51% ± 27% (PSMA-PET). For regions with Gleason grade 5 (3 patients) the overlap was 36% ± 36% (T2w-MRI), 69% ± 29% (DW-MRI), 37% ± 52% (DCE-MRI) and 71% ± 17% (PSMA-PET). For regions with Gleason grade 3 (14 patients) the overlap was 25% ± 24% (T2w-MRI), 26% ± 24% (DW-MRI), 18% ± 21% (DCE-MRI) and 25% ± 31% (PSMA-PET). Including regions with all Gleason grades the overlap was 35% ± 24% (T2w-MRI), 37% ± 24% (DW-MRI), 31% ± 18% (DCE-MRI) and 42% ± 27% (PSMA-PET). A combination of the different modalities yielded a mean volumetric overlap (all Gleason grades) of 51% ± 25% for the combination of T2w-MRI + DW-MRI; by also including DCE-MRI it became 55% ± 24% and by combining all four modalities the overlap was 60% ± 25%. The mean Dice score (all Gleason grades) with standard deviation was 38% ± 23% (T2w-MRI), 39% ± 22% (DW-MRI), 36% ± 19% (DCE-MRI) and 38% ± 20% (PSMA-PET).

Figure 1 a) Histopathology slice with delineated Gleason grade regions, b) PSMA-PET uptake, c) GTV delineations from the four different observers and d) the combined GTV from the Staple algorithm. Conclusion The largest overlap between ground truth and the delineated lesions was found for higher Gleason grades (>=4) using PSMA- PET or combinations of modalities. The variation in overlap between patients was significant and warrants further analysis.

Proffered Papers: Impact on daily treatment planning