ESTRO 37 Abstract book

S829

ESTRO 37

Results The data showed a significantly correlation between WBC and the maximum dose of the right and left FH (p=0.005 and p=0.008, respectively) as well as the relative mean volume receiving 5 Gy (V5%) and 40 Gy (V40%) of the PB (p=0.006 and p=0.04). The hemoglobin levels correlated significantly with the mean and maximum doses of both FH. No correlation with PB dose-volumes were observed. The platelets correlated significantly with the absolute volume receiving 5 Gy (V5, p=0.001) and 10 Gy (V10, p=0.006) as well as with V10% of the PB. A significant correlation between hemoglobin levels and OS as well as progression free survival (PFS) could not be found. Under RT the mean GTV dropped 49.1% (25.4 cm³; n=22). Comparing deltaGTV with OS and PFS no significant correlation was observed. Conclusion The results show that blood levels correlate with distinct dosimetric subvolumes in the femoral heads and the pelvis. It was described earlier that low hemoglobin levels correlate with a poorer outcome in cervical cancer patients. These results could not be reproduced in this study, maybe due to a limited follow-up and a small patient group. Prospective studies with higher case numbers are additionally necessary. However, sparing PB and FH with Intensity Modulated Radiation Therapy (IMRT) techniques could probably lead to better OS in the future. EP-1530 Dosimetric comparison of MR, MR & Interstitial needles & CT guided brachytherapy in cervical cancer A. Sarwar 1 , N. Lalli 1 , G. Eminowicz 1 1 University College Hospital, Radiotherapy Department, London, United Kingdom Purpose or Objective MR guided brachytherapy (BT) ensures accurate target volume delineation and is essential for accurate cervical BT delivery. Its importance has been identified and forms part of the GEC ESTRO recommendations. Interstitial BT can achieve better target volume coverage where standard applicators fail, particularly in cases with extensive parametrial invasion. Optimal imaging with MR and the use of interstitial needles, we hypothesise, will improve dose distribution to the target volume and avoid OARs. We therefore compared the dosimetric variation achieved with CT guided HDR BT versus MR guided HDR BT with and without interstitial needles. Material and Methods A retrospective dosimetric analysis of 30 cervical cancer patients treated with HDR BT between 2016-2017 was undertaken; 10 CT planned, 10 MR and 10 MR with interstitial needles. All patients were treated with EBRT (50.4 Gy in 28 fractions) followed by BT (21 Gy in 3 fractions). Data was collated from the Oncentra planning Of the 10 patients treated with CT guided BT, 7 had stage 1 or 2 and 3 had stage 3 or 4 disease. For the MR guided cohort, 5 were stage 1 or 2 and 5 were stage 3 or 4 and MR with needles were 1 stage 1 or 2 and 9 stage 3 or 4. The average HRCTV volume was 42.1cc, 35.7cc and 51.6cc for CT, MR and MR with needles. All doses are quoted as EQD2 dose delivered over 3 fractions for CT planned, MR planned and MR with needles respectively. Average HRCTV D90 was 19.9Gy, 35Gy and 30.5Gy. Average rectal D2cc was 20.0Gy, 21.4Gy and 25.7Gy. system. Results

Average bladder D2cc was 41.7Gy, 34.0Gy, and 34.7Gy (table 1).

Analysis was also performed for patients with stage 1/2 and with stage 3/4. Average HRCTV volume was 36.1cc, 22.9cc and 28.3cc for stage 1/2 compared to 56.1cc, 44.3cc and 54.2cc for stage 3/4. Average HRCTV D90 was 20.4Gy, 43.4Gy and 39Gy for stage 1/2 and 18.8Gy, 29.3Gy and 29.6Gy in stage 3/4. Average rectum D2cc was 19.2Gy, 16.5Gy and 19.9Gy in stage 1/2 and 21.8Gy, 24.6Gy and 26.3Gy for stage 3/4. Average bladder D2cc was 46.2Gy, 27.9Gy, and 24.4Gy for stage 1/2, and 31.2Gy, 38.1Gy and 35.8Gy for stage 3/4 (table 2).

Conclusion MR guided BT improves HRCTV dose coverage dramatically. In our cohort average HRCTV D90 increased by more than 20Gy for stage 1/2 and more than 10GY for stage 3/4 disease. Improvements were also seen in the OARs; bladder D2cc more than rectal D2cc. The reduction in bladder dose was largest for stage 1/2 disease. The use of needles allowed similar dose coverage despite a large difference in the HRCTV volume. The benefits of image guided BT with interstitial needles is therefore seen in HRCTV coverage as well as OAR dose. To achieve the EMBRACE2 tolerances, further reductions in OAR doses, especially rectum, are necessary to facilitate an increase in the BT dose fractionation to 28Gy in 4 fractions with EBRT dose at 45Gy in 25 fractions. This will improve with experience or perhaps the use of oblique needles to treat side wall disease more effectively. EP-1531 Hyperthermia (mEHT) as a radiosensitser in HIV positive cervical cancer patients: effects/toxicities C. Minnaar 1 , A. Baeyens 2 , J. Kotzen 3 1 University of the Witwatersrand, Radiobiology, Johannesburg, South Africa 2 Ghent University, Basic Medical Sciences, Ghent, Belgium 3 University of the Witwatersrand, Radiation Oncology, Johannesburg, South Africa Purpose or Objective To report on the effects of modulated electro- hyperthermia (mEHT) as a radiosensitiser on toxicity and local disease control in HIV positive cervical cancer patients. Material and Methods 136 participants were prescribed 50Gy external beam radiation, 3 doses of 8Gy high dose rate brachytherapy and cisplatin as a radiosensitiser. Participants were randomised, based on HIV status, FIGO stage of disease, and age, into a control group or study group. The study group received 10 mEHT treatments plus the prescribed chemoradiotherapy regime. Each mEHT treatment was 55 minutes at a target power of 130W. HIV positive