ESTRO 2024 - Abstract Book

S986

Clinical - Gynaecology

ESTRO 2024

439

Mini-Oral

Bone marrow sparing RT does not prevent bone marrow fat increase and lymphopenia in cervical cancer

Anouk Corbeau 1 , Eleftheria Astreinidou 1 , Piotr A Wielopolski 2 , Sander C Kuipers 3,4 , Jérémy Godart 3,4 , Uulke A van der Heide 1,5 , Carien L Creutzberg 1 , Remi A Nout 3 , Stephanie M de Boer 1 1 Leiden University Medical Center, Department of Radiation Oncology, Leiden, Netherlands. 2 University Medical Center Rotterdam, Department of Radiology and Nuclear Medicine, Rotterdam, Netherlands. 3 Erasmus MC Cancer Institute, University Medical Center Rotterdam, Department of Radiotherapy, Rotterdam, Netherlands. 4 HollandPTC, Department of Medical Physics & Informatics, Delft, Netherlands. 5 The Netherlands Cancer Institute, Department of Radiation Oncology, Amsterdam, Netherlands

Purpose/Objective:

Bone marrow (BM) damage caused by chemoradiotherapy for women with locally advanced cervical cancer (LACC) leads to an increase in BM fat content, which might result in hematologic toxicity (HT), especially lymphopenia. HT may lead to dose reduction or discontinuation of chemotherapy and poorer long-term outcomes. There has been increasing interest in bone marrow sparing (BMS) radiotherapy techniques to reduce HT. Since pelvic bone (PB) dose was found to be associated with HT and the delineation of this organ-at-risk does not require advanced imaging techniques, PB dose reduction is of interest to attain BMS. However, the effect of PB sparing on fat content and HT is unclear. The aim of this study was to evaluate BM fat changes and the incidence of HT in women with LACC treated with PB sparing radiotherapy.

Material/Methods:

Women with LACC who were included in the volumetric modulated arc therapy (VMAT) group of the prospective multicenter PROTECT study (NCT05406856) were evaluated[1]. Treatment consisted of PB sparing external beam radiotherapy (45 Gy in 1.8 Gy fractions) with five cycles of weekly cisplatin (40 mg/m2), followed by MR-guided brachytherapy (three to four fractions of 7 Gy to the high risk clinical target volume for an EQD2 D90 of 90-95 Gy), according to the EMBRACE-II protocol. PB were delineated from the inferior border of the ischial tuberosities up to 24-25 mm superior to the planning target volume and V10Gy<90%, V20Gy<65%, and V40Gy<15-20% were used as dose constraints. Water-fat MR scans of the whole vertebral column and PB were acquired at baseline, during, and at three and twelve months after treatment. For BM fat evaluation, regions of interest (ROIs) were positioned in each vertebra, the femoral heads, and the most active BM of the PB[2]. Vertebras were grouped with respect to the cervical (C3-C7), thoracic (T1-T12), and lumbar region (L1-L5). Lumbar vertebras with a minimum dose >5 Gy were considered as in-field and with a maximum dose <1 Gy as out-field. Additionally, the PB was subdivided into three anatomical regions including the ilium, lower pelvis, and sacrum[3]. The fat fraction [%] across the vertebral and pelvic ROIs was averaged to obtain a mean fat fraction [%] per region. Grading of HT according to CTCAEv5.0 was based on blood samples taken at baseline, during treatment, and at one, two, three, and twelve months after treatment. Since follow-up is still in progress, data for twelve months after treatment is not yet complete and will be updated.

Results: