ESTRO 2022 - Abstract Book

S1200

Abstract book

ESTRO 2022

Results Results: We examined a total of 443 CBCTs. Table 1 reported results of median shifts and rectum and bladder filling variations calculated for the first 4 CBCTs, for the following weekly CBCTs and for the total of CBCTs. For all CBCTs median prostate displacements along the three axes (x, y and z) averaged over all patients were: 0.03 (IQR: -0.16 to 0.22) cm in x, -0.10 (IQR: -0.24 to 0.23) cm in y and -0.10 (IQR: -0.39 to 0.19) cm in z, and median rectum and bladder filling variation were -0.0 cc (-10.3, 8.7) and -27.3 cc (-109.5, 44.7), respectively. Performing the analyses of all CBCTs for relationship between prostate shift along all three axes and rectum and bladder filling variations, a statistically significant correlation was demonstrated only for rectum only in x and z axes (p=0.036 and p=0.039, respectively). Moreover, correlations analyses in CBCTs obtained after systematic set up correction found a statistically significant in y and z axes (p=0.013 and p=0.045, respectively) for bladder and in x (p=0.035) for rectum filling variations.

Conclusion Conclusion: Daily treatment uncertainties related to setup and organ motion seems to be well controlled with the use of Image Guided Radiotherapy (IGRT). Our results seem to validate our setup protocol for rectum and bladder preparations demonstrated by small prostate shifts.

PO-1416 DUAL ENERGY COMPUTED TOMOGRAPHY APPLICATIONS FOR PROSTATE RADIOTHERAPY: ADVANTAGES IN TARGET AND OAR CONTOURING

S. Cozzi 1 , A. Botti 2 , G. Blandino 1 , L. Bardoscia 3 , G. Timon 1 , M.P. Ruggieri 1 , M. Manicone 1 , G. Sceni 4 , P. Ciammella 1 , C. Iotti 1

1 Azienda USL-IRCCS di Reggio Emilia, Radiation Oncology Unit, Reggio Emilia, Italy; 2 Azienda USL-IRCCS di Reggio Emilia, Medical Physics , Reggio Emilia, Italy; 3 S. Luca Hospital, Healthcare Company Tuscany Nord Ovest, Radiation Oncology Unit, Lucca, Italy; 4 AUSL-IRCCS, Reggio Emilia, Medical Physics Unit, Reggio Emilia, Italy Purpose or Objective Dual Energy Computed Tomography (DECT) captures images in different voltages, potentially allowing a better definition of organs due to different tissues densities (. The aim of this work is to evaluate the impact of DECT simulation in inter- observer variability (IOV) for prostate gland (PG) and organs at-risk (OARs) contouring. Materials and Methods Five radiation oncologists, with different expertise in prostate cancer (PC) treatment, performed the contouring of PG and OARs of 10 patients who underwent DECT simulation. The contouring was carried out on basal CT scan and also on 80 kV, 140 kV, mixed and 55 KeV mono-energetic reconstructions. Consistency in target volume delineation was expressed by the IOV. Dice Similarity Index (DSI), center of mass distance (dCOM) and volumes were then calculated. Median values and accompanying ranges were used to describe the data, since not all variables were normally distributed. A Wilcoxon signed- rank test was performed to compare paired variables using R Core Team (2021). Results A total of 750 structures were collected: 250 clinical target volumes (CTV), 250 rectum and bladder volumes were included in the study. The analysis did not reach statistically significant differences in the variability between the different CT reconstructions. For CTVs the median DSI values were 0.17, 0.58, 0.99, 0.93, 0.47 for basal CT, 55 kV, 80 kV, 140 KeV and mixed reconstruction, respectively. For rectum and bladder the same values were 0.33, 0.43, 0.63, 0.39, 0.53. and 0.17, 0.58, 0.99, 0.93, .047 respectivly. The median percentage differences of the CTV volumes were 7.5%, 6.2%, 5.5%, 5.3%, 5.7% for basal CT, 80 kV, 140 kV, 55 KeV and mixed, respectively. Rectum differences accounted to 6.4%, 6.8%, 7.4%, 5.6%, 7.4%, whereas bladder variability were 1.6%, 1.3%, 2.1%, 1.7% and 1.6%. surprisingly, the data show how basal CT, used daily for the definition of targets, is associated with a greater IOV