ESTRO 2020 Abstract Book

S603 ESTRO 2020

(1%) and in 4 patients late complications Grade 3. Statistically significant association was found only with the rectal toxicity observed at the external beam radiotherapy treatment (p = 0.008). 13.5% of the patients (n=20) had locoregional recurrence and 20 patients distant recurrence. The median follow-up was 19 months and in that time, 15 patients died (8%). The results show an increase in acute grade 1 vaginal mucosal toxicity in our study respect HDR Ir-192 brachytherapy (32% vs 15.8%), but with a decrease in acute grade 2 toxicity (1% EBT, 4.8% Ir-192) and almost absolute reduction of late vaginal mucosal toxicities (1% EBT, 23% Ir-192). The figures of vaginal vault recurrence and the death rate were concordant with the literature. Conclusion Electronic brachytherapy at endometrial cancer is a feasible alternative to HDR brachytherapy with Iridium 192 in effectiveness with an acceptable grade 1 acute toxicity. It has given long-term benefits for patients, providing the same dosimetric coverage in the area of treatment as HDR brachytherapy with Iridium 192 with a marked reduction in the dose of organs at risk. PO-1145 Radiotherapy-induced changes in lymphocytes count important for immunotherapy of uterine cancers K. Holub 1,2 , G. Louvel 2 1 Universitat de Barcelona- Hospital Clínic, Radiation Oncology, Barcelona, Spain ; 2 Gustave Roussy, Radiation Oncology, Villejuif- Paris, France Purpose or Objective Although the chemotherapy-induced depletion of circulating white blood cells (WBC) is well recognised, the impact of exclusive radiotherapy (RT) on different subpopulations of WBC remains unexplored. However, this may be of interest for an implementation of immunotherapy based on the immune checkpoint inhibitors in combination with RT in many cancer settings, but especially in endometrial (EC) and cervical cancer (CC), both characterized by a high mutational burden and usually treated with RT or CRT. Material and Methods We compared the differences between pre- and post- treatment WBC mean values in two retrospective cohorts of EC and CC patients (p) treated with cisplatin-based chemoradiation (CRT) or exclusive RT (mean dose external RT 46Gy+/-brachytherapy 10Gy) in a large European centre from 2009 to 2016. A total of 202 consecutive patients with uterine cancers staged FIGO I-IV at diagnosis and with available basal and post-treatment blood tests were evaluated. Patients who presented basal cytopenia or received treatment for cytopenia were excluded. EC and CC patients were analysed separately and as an entire cohort of EC or CC. The analysis was performed using two- sided T-test for paired samples, X2 Pearson test, p-value <0.05 was considered as statistically significant (SPSS v.23). Results In the cohort of 63p with EC, 29p were treated with CRT and 34p underwent exclusive RT. In the cohort of 139p with CC, 105p received CRT and 34p exclusive RT. There were no significant differences between RT and CRT cohort concerning basal WBC levels, as well as mean and median values of WBC in both cancer settings. Both in CC and EC patients, CRT affected significantly all WBC subtypes. The only subtype of WBC depleted after exclusive RT were lymphocytes (p=0.000). Conclusion The selective depletion of lymphocytes after RT is important for immunotherapy with checkpoint inhibitors administrated after RT and CRT. These findings.may suggest that RT promotes recruitment of T cells within the tumour microenvironment producing their depletion in peripheral blood. Our results are of interest for the further

research and should be applied in the design of clinical trials with immunotherapy for uterine cancers. PO-1146 Evaluation of Dose to pelvic lymphnodes in CT- based High DoseRate Brachytherapy in Carcinoma Cervix S. Mitra 1 , A. Dewan 2 , S. Aggarwal 3 , I. Singh Wahi 3 , S. Barik 4 , K. Dobriyal 5 , J. Mukhee 5 , H. Khurana 6 1 Rajiv Gandhi Cancer Institute & Research Centre, Senior Consultant Radiation Oncologist, Rohini- Delhi, India ; 2 Rajiv Gandhi Cancer Institute & Research Centre, Consultant Radiation Oncologist, Rohini- Delhi, India ; 3 Rajiv Gandhi Cancer Institute & Research Centre, Attending Consultant Radiation Oncologist, Rohini- Delhi, India ; 4 Rajiv Gandhi Cancer Institute & Research Centre, Senior Resident Radiation Oncologist, Rohini- Delhi, India ; 5 Rajiv Gandhi Cancer Institute & Research Centre, Resident Radiation Oncologist, Rohini- Delhi, India ; 6 Rajiv Gandhi Cancer Institute & Research Centre, Research asisstant, Rohini- Delhi, India Purpose or Objective Treatment of locally advanced cervical cancer includes use of external beam radiotherapy (45-50Gy/25-28#) along with concurrent chemotherapy followed by high-dose-rate (HDR) brachytherapy. Treatment goal is to deliver an EQD2 radiotherapy dose of 85-90Gy. At present, grossly enlarged nodes tend to receive a sequential or simultaneous integrated tumoricidal boost dose of 55-60Gy. Dosimetric contribution to pelvic nodes is less certain with brachytherapy. Aim of the present study was to assess the dosimetric contribution of image-based HDR intracavitary brachytherapy (ICRT) to pelvic lymphnodes and to estimate its co-relation to Point-B dose. Material and Methods Between January’2018 - December’2018, fifty patients with locally advanced cervical cancer were enrolled in prospective observational study conducted at Rajiv Gandhi Cancer Institute and Research Centre, India. All patients had previously received intensity modulated radiotherapy (IMRT) to a dose of 45Gy/25# and was planned for three fractions of 3D-based high dose rate (HDR) brachytherapy. Three fractions of HDR brachytherapy to a dose of 7.5Gy/# to 90% high risk CTV (HR-CTV) were planned. CT scan with 3mm slice thickness for brachytherapy planning with IV contrast was taken. Pelvic nodal regions including external iliac (EIL), internal iliac (IIL), obturator and pre-sacral lymphnodes were delineated on the brachytherapy planning CT scan as per standard contouring guidelines. HR-CTV and intermediate risk CTV (IR-CTV) were additionally contoured. Brachytherapy planning was done and dosimetric assessment using dose volume histogram (DVH) was done. Mean dose to point B was recorded and correlated with pelvic nodal dose. Results High risk CTV volume received a mean dose of 7.52+0.56Gy per fraction to 90% volume. Maximal dose was received by bilateral obturator lymphnodal regions. Mean dose to EIL (Right 0.72+0.37, Left, 0.88+0.23), IIL (Right 1.37+0.55, Left, 1.32+0.46), obturator (Right 1.73+0.42, Left, 1.74+0.62) and presacral nodes (1.12+0.70) per fraction was noted. Mean dose to point B significantly differed from dose to pelvic nodes and showed a low degree of correlation. Also, approximately 35% of points B’s were located outside the pelvic lymphnodal regions. Conclusion Pelvic nodes tend to receive a significant dosimetric contribution from HDR image based brachytherapy. In order to decrease pelvic toxicity, this fact must be taken into account while planning intensity modulated radiotherapy boost to gross nodal disease. Also, Point B is a poor indicator of the dose delivered to the pelvic lymph nodes.