ESTRO 36 Abstract Book

S714 ESTRO 36 _______________________________________________________________________________________________

prostatic bed (n=5, 29.4%) or prostate and local recurrence (n=2 seminal vesicle, ischium 11.8%). Previous treatment consisted on a median total dose of 74 Gy on prostate or prostatic bed (range 66-76). Ten patients had also received radiotherapy on seminal vesicles, four patients on pelvic lymph-nodes. Median time from previous radiotherapy was 80 months (range 26-116). Median PSA at the moment of recurrence was 3.1 ng/ml (average 4, range 1.2-13.5). As a re-irradiation, a median total dose of 25 Gy (range 25-30) was delivered in a median number of 5 fractions (range 5-6). An immediate biochemical response was observed in all cases. Median PSA nadir after treatment was 0.77ng/ml (average 1.33, range 0.19-6.0, p=0.0004)) The sole acute toxicity reported was genito-urinary, mainly represented by pollakiuria and dysuria grad e 1 (n=9, 52.9%) or grade 2 (n=2, 11.8%). One patient (5.9%) had a grade 3 hematuria, was hospitalized and submitted to continuous bladder irrigation. A late grade 1 GU toxicity was observed in 3 patients (17.7%). No other toxicities were observed. At a median follow-up of 16 months (range 6-36, calculated from the time of recurrence diagnosis) 8 patients (47.1%), experienced a biochemical recurrence, confirmed by a positive PET-choline in 5 cases (29.4%). Median BFS was 19 months, 1- and 2-year BFS was 84.6% and 32.2%, respectively. Median LC was 24 months, 1- and 2-year LC was 90.9% and 40.4%, respectively. All patients are still alive, 5 of them with measurable disease. Median OS was 96 months from the initial diagnosis (range 59-151). Conclusion With the technological novelties offered by modern radiotherapy, re-irradiation of patients affected by prostate cancer, and previously treated with radiation therapy, confirms its safety and efficacy. Therefore, it can be considered a valuable option for local recurrence of this disease. EP-1332 Contouring variability with CT and MRI of prostate cancer for radiation planning 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