ESTRO 36 Abstract Book

S707 ESTRO 36 2017 _______________________________________________________________________________________________

A. Otero-Romero 1 , A. Pérez-Rozos 1 , R. Correa-Generoso 1 , I. Jerez-Sainz 1 , M.J. García-Anaya 1 , I. Zapata-Martínez 1 , A. Román-Jobacho 1 , M.D. Toledo-Serrano 1 , R. Ordoñez- Marmolejo 1 , I. García-Ríos 1 , J. Goméz-Millan 1 , J.A. Villalobos-Martín 2 , T. Díaz-Antonio 2 , J.A. Medina- Carmona 1 1 Hospital Virgen de la Victoria, Radiation Oncology, Málaga, Spain 2 Hospital Virgen de la Victoria, Radiology, Málaga, Spain Purpose or Objective CT (Computer Tomography) is the standard for conformal radiotherapy treatment planning of prostate cancer, however T2-weighed MRI (Magnetic Resonance) allows better definition of apex of prostate, seminal vesicles and the rectum-prostate interface. Analyse intra and inter-observer variability and whether implementing systematic image fusion with CT and MRI could improve prostate contouring accuracy. Material and Methods MR was requested to complete tumour staging and performed in a different centre due to the unavailability of MRI scan in our hospital. Planning CT was carried out in our department, slices of 3 mm, with empty bladder and rectum, in supine position using knee and feet immobilization devices. Image fusion was performed with T2-weighed MRI and CT scans matching on bony structures of the pelvis. We conducted the study in two parts. First part of the study consisted in contouring the prostate and seminal vesicles of a single patient on CT images and then on MRI fusion images by 9 Radiation Oncologists (including training doctors) In the second part of the study two Radiation Oncologists, specialized in prostate cancer, and a Radiologist trained in MRI contoured the prostate of 5 patients on CT images and then on MRI fusion images. The contour of the Radiologist was considered the gold standard. Comparison of volumes measured on CT and MRI using Pinnacle planning system was made. Intraobserver and interobserver variability was assessed taking into account the percentage of coincident volume with the gold standard, analysing the distance of the direction with more differences, and calculating sensitivity (S) and Paccard indexes (I paccard ;P=delineated prostate; C=gold standard). Results Accurate CT-MRI image fusion was not always achieved with bony matching due to the different pelvis position and needed soft tissue correction. Volumes of the first part of the study range was 29.1-52.4 cc for prostate and 10.8-16.7 cc for seminal vesicles on CT, and 29.5-57.2 cc for prostate and 11.6-16.1 cc for seminal vesicles on MRI. Comparing CT and MRI volumes the intraobserver ratio was 1.13 (1.02-1.26) for prostate and 1.12 (1.01-1.21) for seminal vesicles. In the second part of the study mean volumes range on CT scan was 13-21 cm3 while on MRI was 18-26 cm3. Mean volume% comparing to the gold standard volume range was 62%-67% on CT and 81%-86% on MR. Variability in distance in the different directions were 3-9 mm in the longitudinal axis, 3-4 mm in the lateral axis and 2-3 mm in the anterior- posterior axis. Mean sensitivity index was 0.58 on CT and 0.80 on MRI, and mean Paccard index was 0.48 and 0.76 on CT and MRI respectivel

y. Conclusion

Prostate MRI enables more accurate planning contouring than CT. In our study CT volumes tend to be smaller than on MRI. The longitudinal axis is the direction where more contouring differences have been found. MRI and CT could be made in the same pelvis position to achieve reduced uncertainty image registration. EP-1333 Impact of 18F-Choline PET scan acquisition time on delineation of GTV in Prostate cancer C. Parkinson 1 , J. Chan 2 , I. Syndikus 2 , C. Marshall 3 , J. Staffurth 4 , E. Spezi 1 1 Cardiff University, School of Engineering, Cardiff, United Kingdom 2 Clatterbridge Cancer Centre, Clinical Oncology, Liverpool, United Kingdom 3 Cardiff and Vale University Health Trust, Wales Research & Diagnostic PET Imaging Centre, Cardiff, United Kingdom 4 Velindre Cancer Centre, Clinical Radiotherapy Trials, Cardiff, United Kingdom Purpose or Objective Dose painting radiotherapy requires accurate outlining of primary tumour volumes in the prostate. T2-Weighted (T2W) Magnetic Resonance Imaging (MRI) is the best imaging method for defining the gross tumour volume (GTV). Choline positron emission tomography (PET) is currently a controversial tracer. The image acquisition differs significantly in published studies. Many used early static imaging. One study found that 18F-choline PET/CT with late image acquisition has superior accuracy to T2W MR and functional MR alone. We investigate whether increasing 18F-Choline PET scan acquisition time from 60 (PET-60) to 90 (PET-90) minutes improves GTV TVD. Material and Methods Analysis was performed on 9 18F-Choline PET scans. Patients were injected with 370MBq of activity. Three clinicians (C1, C2 and C3) independently and without reference to each other contoured GTVs on each of the T2W-MRI, PET-60 and PET-90 scans at differing times. Scans were registered by a clinician using rigid co- registration. The treating clinicians MRI contour was used as a reference contour. The resulting PET and MRI GTVs were transferred to the PET-60 and PET-90 scans after image registration. The Dice Similarity Coefficient (DSC), Specificity (Sp) and Sensitivity (S) were calculated from contour mask voxel analysis. Results Table 1 shows the mean and range DSC, S and Sp scores on MRI, PET-60 and PET-90 for C1, C2 and C3 in comparison to the treating clinicians contour on MRI (C1). A 2 sampled T-test (P < 0.01) showed, no significant difference in the Sp, S and DSC between GTVs on PET-60 and PET-90 scans. Further to this, as shown in Figure 1, variability in GTV delineation is significant between observers in a singular case as well as across imaging modalities.