ESTRO 36 Abstract Book

S519 ESTRO 36 _______________________________________________________________________________________________

doses were 54 Gy in 9 fractions as monotherapy and 30 Gy in 5 fractions as combination of EBRT. In 10 patients who had irradiation history, lower doses (36 to 48 Gy in 6 to 8 fractions) were selected. We implanted 7–16 (median, 13) applicators under transrectal ultrasonography guidance. We used free-hand implantation with ambulatory technique for later 42 patients. Magnetic resonance imaging (MRI)-assisted image-based treatment planning was also performed. Clinical target volumes (CTV) were the gloss tumor volume with or without 10 mm of vaginal margin for patients with or without non-irradiation The median follow-up time was 41 months (range; 4-115 months). The median D90(CTV)s were 91.3 Gy and 75.6 Gy for patients with or without non-irradiation history. The 4- year local control and overall survival rates were 78% and 67% for all patients. The 4-year local control rates were 83% and 60% for patients with or without non-irradiation history (p=0.02). Tumor diameter, primary site and histology were not significant prognostic factors of local control. The 4-year overall survival rates were 73, 65, 100 and 20% for SCC, AD, MAD and the others (P=0.06). The D90(CTV)s were 93.5±24.3 Gy and 81.4±9.2 Gy for local control and failure patients (p=0.1). Grade ≥3 late complications occurred in 11 patients (23%). Ileus was only observed for patients receiving EBRT. Conclusion Our treatment result of image-guided HDR-ISBT showed good local control result. However, previous irradiation history was a worse prognostic factor of local control. Dose-volume histogram seems to be useful for dose prescription. PO-0938 Should we use point A dose for image-guided adaptive brachytherapy reporting in cervix cancer? R. Mazeron 1 , I. Dumas 2 , A. Escande 1 , W. Bacorro 1 , R. Sun 1 , C. Haie-Meder 1 , C. Chargari 1 1 Institut Gustave Roussy, Radiation Oncology, Villejuif, France 2 Institut Gustave Roussy, Medical Physics, Villejuif, France Purpose or Objective The recent ICRU report 89 recommends continuing the reporting of point A dose in the era of Image-guided adaptive brachytherapy (IGABT). The study aim was to evaluate the interest of such recommendation by testing the value of point A as a surrogate of volumetric dosimetric parameters and as a predicting factor of local control. Material and Methods The dosimetric data from patients treated with a combination of chemoradiation and intracavitory image- guided adaptive brachytherapy were confronted to their outcomes. Prescribing followed the GEC-ESTRO recommendations. Point A was used for reporting, without specific planning aim. All doses were converted in 2-Gy equivalent, summing brachytherapy and EBRT doses. The relationships between the D 90 CTV HR and CTV IR and point A doses were studied. Dose-effect relationships based on the probit model and log-rank tests were assessed using the different dosimetric parameters. Results Two hundred and twelve patients were included with a median follow-up of 53.0 months. MRI guidance was used in 89.6% of the cases. A total of 28 local relapses were reported resulting in a local control rate of 86.6% at 3 years. Mean D 90 CTV HR , D 90 CTV IR and point A doses were respectively: 79.7±10.4 Gy, 67.4±5.8 Gy and 66.4±5.6 Gy. The mean D 90 CTV HR and CTV IR were significantly different from the mean point A dose (p=p<0.0001, and 0.022 respectively). Both D 90 CTV were independent from point A doses, even in bulky (width >5cm) tumors at diagnosis or in large CTV HR lesions (≥ 30cm 3 ) Whereas significant history. Results

relationships between the probability of achieving local control and the D 90 CTV HR and CTV IR (p=0.08 and 0.025 respectively) were observed, no significant relationship between point A dose and local control probability could have been established (Figure). Moreover, a trend towards an inverse relation was observed. After sorting patients according to 3 levels of doses, highest local control rates werereported in patients with D 90 CTV HR ≥85 Gy, whereas the patients with point A doses ≥ 70 Gy had the worst outcomes.

Conclusion In patients treated with IGABT, point A dose is not predictive of local control, and nor correlated to D 90 . It tends to be inversely related to D 90 and therefore to be a surrogate of the irradiated volume. The pertinence of reporting point A dose should be questioned. PO-0939 Comparison of brachytherapy sources of endometrial cancer: Electronic brachytherapy source and 192Ir S. Lozares 1 , J.A. Font Gómez 1 , A. Gandía Martínez 1 , A. Miranda Burgos 2 , A. Méndez Villamón 2 1 Hospital Universitario Miguel Servet, Medical Physics and Radiation Protection Department, Zaragoza, Spain 2 Hospital Universitario Miguel Servet, Oncologic Radiotherapy Department, Zaragoza, Spain Purpose or Objective To compare 29 endometrial cancer patients treated in our center with cylindrical applicators and Axxent (Xoft Inc.) electronic brachytherapy with an equivalent planning 29 patients previously treated with Axxent (50 kV source) have been replanned with Ir-192 source. The calculation for both types of sources were performed on BrachyVision (Varian Inc.) treatment planning system. The prescription was 5 Gy per fraction applied in 3 fractions or 5 fractions depending on previous radiotherapy treatment. The planning parameters of the planning target volume (PTV) countoured from the cylinder surface to 5 mm along the active length were evaluated. V150 and V200 data for PTV and D2cc, V50% and V35% for organs at risk (OAR) were evaluated, the percentage of the volume receiving 35% and 50% of the prescription dose, respectively, and D2cc, highest dose to a 2 cubic centimetre volume of an OAR. Results for bladder, rectum and sigmoid are showed. made for Ir-192 source. Material and Methods