ESTRO 36 Abstract Book

S978 ESTRO 36 _______________________________________________________________________________________________

Spain 6 Hospital Clínic Universitari, Radiation Oncology Dpt, Barcelona, Spain 7 Hospital General de Alicante, Radaition Oncology Dpt, Barcelona, Spain 8 Hospital Clínic Universitari, Radiation Oncology, Barcelona, Spain 9 Hospital Rebagliati, Radiation Oncology Dpt., Lima, Peru 10 Hospital Clínic Universitari, Radiation Oncolgy, Barcelona, Spain 11 Hospital Clínic Universitari, Radiation Oncology Dpt, Barclona, Spain 12 Hospital Sant Joan de Reus, Radiation Oncology Dpt, Reus, Spain at 0.1cc, 1cc and 2cc of vagina in cylinder vaginal-cuff brachytherapy (VBT) ±external beam irradiation (EBI) is associated with G2 toxicity in postoperative endometrial carcinoma (P-EC). Material and Methods From June 2014-November 2015, 67 consecutive P-EC patients received VBT±EBI: 54 EBI (median 45Gy, range 44- 50.4)) +VBT (7Gy) and 13 exclusive BT (6Gy x 3 fractions). 2.5cm of vagina was delineated after CT for 3D treatment planning. The active source length was 2.5cm. The BT dose was prescribed at 5mm from the applicator surface. Patients were treated with HDR 192 Ir source using a MicroHDR source projector (Nucletron®). D90, V100 and EQD2 (α/β=3) at 0.1cc, 1cc and 2cc were calculated. The mean follow-up was: 23.2 months (range 7.6-46.8). D90 (cc): median 7.8 (range 4.6-8.9); V100 (Gy): median 7.9 ( range 4.4-10.8). Vaginal toxicity was prospectively assessed using objective LENT-SOMA scores. Late vaginal toxicity: 17/67 (25%) 8 with G1 and 9 G2. For this analysis G0 and G1 patients were considered as no late toxicity (58/67, Group-1) and 9 patients with G2 (9/67,Group-2) were considered as having late toxicity. Statistics: t-Student test and Chi squared, alpha=5%. Results The median EQD2 (α/β=3) doses were 88.6Gy (62.8-177.6) for 0.1cc, 72.4Gy (57.1-130.4) for 1cc and 69Gy (53-113.4) for 2cc. There were no differences in toxicity and EQD2 (α/β=3) between exclusive VBT vs. EBI+VBT. EQD2 (α/β=3) : The mean EQD2 (α/β=3) : at 0.1cc was 92.9Gy (SD 17.7) for Group-1 and 96.3Gy (SD 31.6) for Group-2 (p=0.62); being 72.3Gy (SD 6) at 1cc for Group-1 and 73.5Gy (SD 5.3) for Group-2 (p= 0.58); and 67.6Gy (SD 6.2) at 2cc for Group-1 and 73.1Gy (SD 10.8) for Group-2 (p=0.03). 20.5% of patients receiving doses ≥68Gy EQD2 (α/β=3) at 2cc of vagina developed G2 toxicity. All patients with G2 toxicity had received doses ≥68Gy EQD2 (α/β=3) at 2cc (p=0.04). Conclusion 68Gy EQD2 (α/β=3) doses at 2cc were related to G2 toxicity in P-EC VBT. In view of these results patients receiving these doses should be informed of their risk and individual characteristics should be considered in treatment planning and follow-up to reduce G2 toxicity. Grant: Spanish Association Against Cancer (AECC) Foundation . EP-1781 statistical and dosimetric analysis of air gaps in vaginal cuff brachytherapy S. Abdollahi 1 , L. Rafat-Motavalli 2 , H. Miri-Hakimabad 2 , M. Mohammadi 1 , E. Hoseinian-Azghadi 2 , N. Mohammadi 2 , N. Rafat-Motavalli 2 , L. Sobhkhiz-Sabet 1 1 Reza Radiation Oncology Center RROC, medical physics, Mashad, Iran Islamic Republic of 2 Ferdowsi University of Mashhad, Physics, Mashhad, Iran Islamic Republic of Purpose or Objective To evaluate if EQD2 (α/β=3)

for low risk histology (i.e. G1-2 endometrial adenocarcinoma) was 100% at 1 and 6 years (p=0.05). Acute toxicity was registered in 2 (12%) patients: G2 nausea and G2 proctitis in 1 patient (6%), G2 diarrhea, G2 anemia and G2 proctitis in 1(6%) patient. Two patients (12%) had G1 late rectal bleeding. Conclusion Conclusion: Our data show a good LC particularly in patients with stage I low risk histology endometrial cancer. Though number of patients is limited, definitive HDR-BRT could be an alternative treatment option for inoperable elderly patients with good compliance and limited toxicity. Histology is a prognostic factor for LC.

Table 1. Dose schedules

HDR-BRT = high-dose rate brachytherapy EQD2: Equivalent dose of 2 Gy per fraction calculated using the equation EQD2 = ([d+ α/β]/[2Gy+α/β]) derived from linear quadratic model. Legend: * patients submitted to external beam radiotherapy and brachytherapy EP-1780 Postoperative endometrium: 68Gy EQD2(α/β=3) at 2cc of vagina is related to G2 late toxicity. A. Rovirosa 1 , M. Aguilera 2 , C. Ascaso 3 , A. Herreros 4 , J. Sánchez 5 , J. Garcia-Miguel 6 , S. Sabater 7 , G. Oses 8 , P. Makiya 9 , S. Cortes 10 , J. Solà 6 , E. Agusti 11 , A. Huguet 6 , A. Garrido 6 , A. Lloret 6 , C. Baltrons 6 , M. Arenas 12 1 Hospital Clinic Universitari, Radiation Oncology Dpt., Barcelona, Spain 2 Hospital Universitario de Caracas, Radiation Oncology Dpt, Caracas, Venezuela 3 Faculty of Medicine- Universitat de Barcelona, Clinical Basics Dpt, Barcelona, Spain 4 Hospital Clínic, Radiation Oncology Dpt., Barcelona, Spain 5 Hospital Clinic Universitari, Finance Dpt, Barcelona,