ESTRO 38 Abstract book

S814 ESTRO 38

had positive paraaortal LN. All pts were treated with image guided RChT. A dose of 50.4 Gy was prescribed to the elective pelvic nodal volume. Primary tumors smaller than 4 cm in diameter received an additional boost of 5.4 Gy, primary tumors larger than 4 cm in diameter received a boost of 9 Gy. Pts with positive LN detected with 18 FDG- PET/CT received a simultaneous integrated boost to a total dose of 64 Gy. Chemotherapy was administered according to institutional standards. After completion of the external beam RChT all pts were referred to our hospital for image guided HDR Brachytherapy in 4 once weekly fractions of 6-7 Gy. Follow up included clinical investigation at 6 weeks and at 3 months after therapy and a 18 FDG-PET/CT at 6 months. Results Median time to the first 18 FDG-PET/CT after therapy completion was 6 months (1 - 8 months). Pathological findings were found in 21 (40%) pts. 3 pts (6%) showed local tumor persistence and 2 pts (4%) were diagnosed with loco-regional persistence which were later histologically reclassified as benign. In 16 pts (30%) systemic metastasis was diagnosed, of those 12 received palliative systemic treatment and/or palliative radiation, 2 were operated upon and 2 were followed up. In total 19 (36%) pts were diagnosed and confirmed with having malignant disease, to date just 7/19 died as a direct consequence of their disease. Conclusion 18 FDG-PET/CT conducted 6 months after therapy completion is a valuable imaging tool in assessing treatment response of cervical cancer patients treated with definitive RChT. 18 FDG-PET/CT findings lead to therapeutic consequences in the majority of pts. EP-1505 Is locally advanced cervix adenocarcinoma less radiosensitive than squamous cell carcinoma? K. Vandecasteele 1 , E. De Jaeghere 2 , P. Tummers 3 , A. Makar 3 , P. De Visschere 4 , K. Van de Vijver 5 , E. Naert 2 , H. Denys 2 1 UZ Gent, Radiation Oncology, Gent, Belgium ; 2 UZ Gent, Medical Oncology, Gent, Belgium ; 3 UZ Gent, Gynaecology, Gent, Belgium ; 4 UZ Gent, Radiology, Gent, Belgium ; 5 UZ Gent, Pathology, Gent, Belgium Purpose or Objective Previous studies on cervical cancer reported a worse outcome for adenocarcinoma (AC) compared with squamous cell carcinoma (SCC). Nevertheless, standard treatment remains identical. Insight in the impact of histological types on biological behavior and pathological complete response rates might result in a treatment paradigm shift. Material and Methods Since 2006, 114 locally advanced (FIGO IB2-IVA and IVB in case of para-aortic/inguinal lymph nodes metastases only) cervical cancer (LACC) patients were treated consecutively with neo-adjuvant chemoradiation (NA-CRT) and surgery. RT was performed using an Intensity Modulated Arc Technique up to a minimal dose (D98) of 45Gy to the elective lymph nodes and primary target volume and 62/60Gy (SIB) to the tumor/affected lymph nodes. From 1/2/2009 onwards, para-aortic lymph node irradiation was performed in case of positive pelvic lymph nodes. Brachytherapy was applied in case of doubtful or positive margins after surgery or if surgery could not be performed. Chemotherapy was administered concomitantly (cisplatin or 5-FU). Six patients were excluded for analysis due to a synchronous second primary (n=5) or previous liver transplant (n=1). Clinicopathological characteristics, pathological response and survival rates were compared between AC (n=19) and SCC (n=89) LACC patients. Statistics were performed using SPSS vs 25.0. Results Clinicopathological characteristics before treatment are

78 days (49-102 days) for IC-BT-HDR boost pts and 56 days (44-114 days) for EBRT boost pts. The median follow-up time was 67 months (5-129 months) for all pts. Pelvic failure was detected in 20,7% of pts and distant failure in 12%. The 3-year RFS rate was 61% for all pts, 45% for EBRT boost pts and 84% for IC BT-HDR boost pts (Log-rank p<0,001). The 3-year OS rate was 76% for all pts, 66% for EBRT boost pts and 89% for IC BT-HDR pts (Log-rank p=0,005).

In multivariate analysis controlling for maximum tumor dimension, lymph node status and FIGO stage (fig.1), EBRT boost was associated with a statistical significant increase in the risk of recurrence (HR 3,56; CI 95% 1,27-10,02 p=0,016) and a trend towards an increase in the risk of death (HR 3,14; CI 95% 0,97-10-17 p=0,056). Conclusion IC-BT-HDR boost is considered standard of care combined with CCRT in the treatment of cervical cancer not amenable by surgery. In some cases IC BT-HDR boost is not technically feasible and department guidelines recommend an EBRT boost up to 66,6Gy. This retrospective study demonstrates that the EBRT boost is associated with a three fold increase in the risk of recurrence. Better alternatives need to be studied for pts where a BT boost is not possible. EP-1504 Role of PET/CT in assessing treatment response of cervical cancer after definitive RadioChemotherapy A. Tsikkinis 1 , E. Vlaskou Badra 1 , N. Cihoric 1 , D. Aebersold 1 , K. Lössl 1 1 Inselspital- Universität Bern, Radiation-Oncology, Bern, Switzerland Purpose or Objective To evaluate the value of 18 FDG-PET/CT in the follow-up of patients (pts) with cervical cancer after definitive radio/chemotherapy (RChT). Material and Methods From 11/2010 to 08/2016, 53 (100%) patients (pts) with cervical cancer (FIGO stage IB1 to IVA) were treated with definitive radio-chemotherapy (RChT).. The median age at the time of diagnosis was 54 (29 -83) years. All pts were staged with a clinical exam and a pre-treatment 18 FDG- PET/CT. 29 (55%) pts were treated in our hospital and 24 (45%) in other referring institutions (n:7). 13 (25%) pts were lymph node (LN) negative and 40 (75%) LN positive. 12 (23%) pts had 1 positive LN, 9 (17%) two, 7 (13%) pts with 3-5 LN and 9 (17%) with >5 positive LN. 17 (32%) pts