Abstract Book

S815

ESTRO 37

positive at local (2/7: partial response, Stage I = 1, Stage III = 1, both with negative biopsies) or nodal/metastatic level (5/7: Stage I, n = 1; Stage II, n = 3; Stage IIIb, n = 1). Twenty-three patients presented no signs of local or distant relapse. Nevertheless, a MRI was prescribed: in 20/23 (87%) MRI was negative In 3/20 MRI was positive, with positive biopsy (Stade I, n =1; Stade IIIB, n = 2). One patient with a negative digital rectal examination (DRE) and a negative PET/CT presented positive MRI. One patient with a negative DRE presented positive pelvic nodes and a vulvar metastasis at MRI, In both patients, a confirmatory biopsy was positive. Patients with a suspicious clinical examination received PET/CT (n = 11) and/or MRI (n = 12). PET/CT and MRI were useful, respectively, in 5/11 pts (Stade I, n = 2; Stade IIIB, n = 3, confirmed with following biopsy) and in 3/12 pts (Stade I, n = 1; Stade IIIB, n = 2), as they showed a local relapse (2/3 and 3/3 patients for PET/CT and MRI, respectively) or a nodal or a metastatic disease (1/3 patients for PET/CT). Ten and 12 pts presented different findings between DRE and PET/CT and/or MRI, respectively. 5/10 presented negative imaging despite positive clinical findings. Of them, 10 patients underwent a biopsy, 2 in the PET/CT population and 8 in the MRI one: all biopsies were negative. Globally, PET/CT and/or MRI added further important information usually in Stage II-III pts. Conclusion In our experience, PET/CT and MRI should not be always prescribed in the follow-up of anal cancer patients, and should be reserved only to patients with more initial advanced T and/or N disease or with suspicious clinical findings. EP-1503 Rectal motion in patients receiving neoadjuvant radiotherapy for rectal cancer in supine position K. Nugent 1 , B. O'Neill 1 , J. Lynch 1 , M. Higgins 1 , V. Brennan 1 , M. Dunne 1 , C. Skourou 1 1 St Lukes Radiation Network, Radiation Oncology, Dublin, Ireland Purpose or Objective With the move towards more conformal radiotherapy for patients with rectal cancer, comes a requirement for a reduction in systematic and random uncertainty in target localisation. The rectum is an organ susceptible to internal motion. Typically, large isotropic margins are placed around the target to ensure full coverage of the tumour. This comes at a cost to the healthy surrounding tissue and therefore any potential reduction is beneficial to the patient. Previous studies have reported margins to account for the internal rectal motion of patients treated in the prone position. With the introduction of intensity modulated techniques, more patients are now treated in the supine position. Data informing specific margins for this treatment position is sparse. Our study investigates the pattern of internal rectal motion in patients treated with radiotherapy in the supine position to propose the minimum adequate margin for such patients. Material and Methods Twenty (20) male patients treated in the supine position were evaluated in this retrospective study. The site of disease varied along the rectum. All patients were treated with a comfortably full bladder. The rectum, bladder and femoral heads were delineated on the planning CT (PCT) and six cone beam CTs (CBCT). Image

registration was used to map each CBCT onto the PCT to quantify the rectal motion throughout the patients’ treatment. The rectum was divided into three 5cm segments (inf, med, and sup) and the volume of each segment and average diameter were acquired. The motion of the rectum was quantified on a slice to slice comparison (15cm) between PCT and CBCT using fixed anatomical landmarks as references ( namely the x axis being through the mid left femoral head, y axis through the mid sacral vertebrae with superior-inferior motion measured using L5/S1 as a reference point). Each slice was described by an anterior, a posterior, and 2 lateral motions. Results On the comparison between the 3 rectal segments, the mean motion of each segment was less than 2.5mm in any direction with standard deviations representing random positions up to 15mm. A notable difference was found in the mean motion with the largest variability present in the upper rectum anterior motion (µ=0.5mm, σ=15.1mm), followed by mid rectum anterior motion (µ=0.8mm, σ=9.6mm) and the inferior rectum anterior motion (µ=0.4mm, σ=5.4mm). Lateral motion was more pronounced in the superior rectum, with =2.4mm, σ=8.4mm). Average diameter of the rectum also varied, with the largest mean diameter seen mid-rectum (µ=36mm, σ=0.93mm) while the greatest variability was seen in the upper rectum (σ= 1.36mm). Rectal volume varied the most in mid rectum (σ= 14.21cc). Conclusion Variability in the position of the rectum was observed along the length of the rectum, with a more pronounced anterior motion in the upper rectum. The data has not shown any link of rectal motion to rectal volume or diameter. Possible link to bladder volume is currently being examined. EP-1504 Postoperative radiotherapy for endometrial carcinoma in elderly patients. A. Rovirosa 1 , C. Ascaso 2 , S. Cortes 3 , A. Glickman 4 , S. Valdes 4 , A. Herreros 3 , C. Camacho 3 , J. Sánchez 5 , S. Sabater 6 , O. Cordova 7 , J. Sola 3 , S. Garrrido 3 , A. Huguet 3 , A. Torne 4 , M. Arenas 3 1 Hospital Clínic Universitari- Faculty of Medicine- University of Barcelona, Radiation Oncology Dpt. Gynecological Cancer Unit, Barcelona, Spain 2 Faculty of Medicine- University of Barcelona, Health Dpt, Barcelona, Spain 3 Hospital Clínic Uiversitari, Radiation Oncology Dpt, Barcelona, Spain 4 Hospital Clínic Uiversitari, Gynecological Cancer Unit, Barcelona, Spain 5 Hospital Clínic Uiversitari, Economics Dpt, Barcelona, Spain 6 Hospital General de Albacete, Radiation Oncology Dpt, Albacete, Spain 7 Hospital Rebagliati, Radiation Oncology Dpt, Lima, Peru Purpose or Objective To analyze the impact of age on radiotherapy results based on cancer-specific survival [CSS] and complications analysis in 438 patients [pt ] with endometrial carcinoma [EC] receiving postoperative radiotherapy [PRT]. Electronic Poster: Clinical track: Gynaecological (endometrium, cervix, vagina, vulva)