ESTRO 2022 - Abstract Book

S412

Abstract book

ESTRO 2022

The majority of RTTs’ contours are within the range of doctors’ inter-observer variability. The dosimetric and clinical significance of those outside the range will be determined prior to RTTs replacing doctors in the online adaptive workflow. Further investigations of RTT-led online contouring on the MRL are ongoing.

OC-0466 Clinical value of dual energy CT based delineation in the treatment planning for prostate patients

H.K. Mortensen 1 , M.P.R. Mathisen 2 , J. Mortensen 2 , H. Lindberg 3 , L.S. Mouritsen 4 , L.H. Dohn 3 , J.M. Edmund 5

1 Herlev and Gentofte Hospital, University of Copenhagen, Department of Oncology, Radiotherapy Unit, 2730 Herlev, Denmark; 2 Gentofte and Herlev Hospital, University of Copenhagen, Department of Oncology, Radiotherapy Unit, 2730 Herlev, Denmark; 3 Gentofte and Herlev Hospital, University of Copenhagen, Department of Oncology, 2730 Herlev, Denmark; 4 Herlev and Gentofte Hospital, University of Copenhagen, Department of Oncology, 2730 Herlev, Denmark; 5 Gentofte and Herlev Hospital, University of Copenhagen, Radiotherapy Research Unit, Department of Oncology, 2730 Herlev, Denmark Purpose or Objective To explore whether selected dual energy CT (DECT) reconstructions (rec) in addition to standard CT imaging, would add meaningful support to the delineation process in the radiotherapy (RT) planning of prostate cancer patients, specifically to benefit those with contraindication to MR Materials and Methods We performed a standard T2-weighted MR imaging on 10 RT patients with prostate cancer. DECT images were acquired using a dedicated contrast enhanced protocol with a fast 80/140kV switching DECT technique (GE Revolution CT), with a standard 120kVp-like rec (74keV) with CT numbers corresponding to 120kV. 2 additional DECT rec were further investigated: A 40 keV monochromatic rec (40keV) and an iodine material density with water suppression rec (MDIod). All the patients were subject to a combined standard clinical 74keV/MR delineation process performed by varying oncologists on clinical duty. 4 structures; prostate, seminal vesicle (vesicle), rectum and penile bulb delineated as standard combined 74keV/MR imaging, were chosen. These structures were blinded. Three oncologists repeated the delineation of the structures using only the MDIod, 40keV and 74keV images. We compared the structure volumes (vol) as measured in Eclipse (Varian Medical Systems) for prostate and vesicle obtained from 74keV/MR images and the selected DECT rec. After the delineation, each oncologist evaluated the clinical usefulness of the 40keV and MDIod rec in an evaluation scheme graded from 0-3 with 0=unusable, 1=slightly usable, 2=usable and 3= very useful. Student-t tests were carried out to identify significant differences. Results Figures 1 and 2 show boxplots of the 74keV/MR and DECT based structure vol from respectively all patients and oncologists, of the prostate and vesicles. The mean and standard deviation (std) of DECT and 74keV/MR based prostate vol were respectively 39,9 +/- 17.7 and 37,6 +/- 15.1 cm3 and non-significantly different (p=0.55). The outliers in figure 1 were ascribed to one single patient which otherwise indicate a DECT vol with a smaller interquartile range (IQR) of 16.5 vs. 19.0 for the 74keV/MR vol. In figure 2, mean and std of the vesicles were respectively 9,4 +/- 3,9 and 10,8 +/- 3.2 cm3 for the DECT and 74keV/MR and non-significantly different (p=0.60). DECT vol were consistently smaller but with a larger IQR of 5.4 vs. 3.2 for the 74keV/MR.