ESTRO 2022 - Abstract Book

S1365

Abstract book

ESTRO 2022

Purpose or Objective To evaluate pelvic bone marrow (PBM) dose and correlation with grade 2 or higher hematological toxicity (HT) in patients with cervical cancer treated by three- dimensional conformal pelvic radiotherapy (3D-CRT) . Materials and Methods Retrospective study including 20 patients with local advanced cervical cancer treated at Radiation Oncology Departement of Farhat Hached hospital in Tunisia between 2018 and 2020 . Medical records and data on patient and tumour characteristics, Common Toxicity Criteria (CTC) scores, laboratory tests, and treatment data were retrieved and analyzed. The clinical target volume consisted of the pelvic and presacral lymph nodes , uterus and cervix, upper vagina, and parametrial tissue.The external contour of the (PBM), which comprised the lumbosacral spine and ilium and the ischium, pubis, and proximal femur was delineated on the planning CT scan .We reported volume and DVH parameters (V10, V20, V40 and Dmax) of PBM and of ilium separetelly. The hematological parameters during RT were analyzed for higher than grade 2 HT (Radiation Therapy Oncology Group) and correlated with DVH parameters using log regression analysis ( P < 0.05 significant). Results The median age of patients was 52 years old(28-70).Clinical symptomatology was dominated by metrorrhagia in 100% of cases. 80% of patients had stage IIB disease, one patient had stage IIIC1 with enlarge nodes on MRI ( ≥ 10 mm) (FIGO 2018). All patients underwent 3D-CRT, using four-field box technique consisted of anterior, posterior, right, and left lateral beam directions. Concurrent weekly cisplatin was administered in 90% cases for a median of 4 courses(1-5) .The median treatment time was 41days (30-51) . Low dose Brachytherapy (LDR) using 192Iridium implant was delivred to 75% cases . Only 3 patients underwent hysterectomy after overall treatment. In our experience, acute Grade 3 or greater HT was 35%, although Grade 2 or greater HT has approached 60%. The leukopenia, neutropenia, anemia, and thrombocytopenia higher than grade 2 was noted in 20%, 10%, 55%, and20 %, respectively .The mean DVH parameters V10, V20, and V40 for PBM were 92 %, 86% and 42 %; the mean Dmax was 49,84 Gy( 64-69). Whole pelvis V40 was ≥ 37% in 17 cases. The mean DVH parameters V10, V20, and V40 for ilium were 96%, 88%,and 45% .On univariate analyses, whole pelvis V40 ≥ 40% correlated with HT grade 2 or higher was no significant (p =0.06) .The median follow up was 7months (3-35).No late hematotoxicities was revealed . Conclusion Our dosimetric analysis suggests that, in patients undergoing 3D-CRT concurrent chemotherapy for local advanced cervical cancer, bone marrow and cortical bone sructure are all often neglected as organs at risk and receives significantly high doses . Further prospective studies validating significance of high-dose effects and identifying correlation of bioimaging with CT contouring are warranted. 1 National Physical Laboratory, Medical Radiation Physics, Teddington, United Kingdom; 2 University College London (UCL), Medical Physics and Biomedical Engineering, London, United Kingdom; 3 University College London (UCL), Cancer Institute, London, United Kingdom Purpose or Objective Total Body Irradiation (TBI) of mice is used to generate models of diseases such as leukaemia, by suppressing the haematopoietic system prior to systemic tumour cell engraftment. Such models can be used to evaluate the outcomes of different therapeutic methods. Dosimetry of TBI in image guided preclinical irradiators is challenging. The main problem arises from the variety of pre- clinical irradiation conditions and the difficulties in relating those to the recommendations from well-established clinical dosimetry protocols in the range of medium energy x-rays. In this study, a methodology for accurate and standardized deliveries of dose to mice during TBI was experimentally determined. Dose across different regions of the mouse and the effect of the mouse positioning system were assessed. As a consequence, a reproducible irradiation protocol, for the use of the Small Animal Radiation Research Platform (SARRP), was established. Materials and Methods The SARRP’s reference dosimetry was performed with the local secondary standard system with a calibration traceable to the National Physical Laboratory’s Air Kerma primary standard. Measurements were performed in a solid water slab phantom following manufacturer’s recommendations. Alanine verification of the output was determined, in the same conditions of irradiation of the ionization chamber measurements. [1]. EBT3 Gafchromic film and alanine pellets were subsequently used to measure dose delivered to three mice phantoms, mimicking positioning of real mice during TBI irradiations. The mice phantoms were different in their material composition [2] and the type of detectors that they were able to hold: film, alanine or both (Figure 1). Irradiation times to film and alanine were different, considering that alanine uncertainties are lower for dose over 10 Gy. PO-1584 Dosimetry standardization of Total Body Irradiation of mice in a SARRP irradiator I. Silvestre Patallo 1,2 , F. Shi 2 , R. Carter 3 , A. Nisbet 2