ESTRO 2020 Abstract book

S810 ESTRO 2020

examination might not be preferment due to staff concern about foetus radiosensitivity and legal aspect of the examination. Material and Methods The F18-FDG PET procedure on Philips Gemini TF scanner has been under evaluation, all relevant parameters from our procedure and our practice have been taken into account. The CODE (Conceptus Dose Estimation Tool) has been used to determine the CT dose. The materials from EFOMP workshop (Vienna ECR 2016) ‘radiation protection of pregnant and lactating patients in nuclear medicine’ has been used to estimate foetal whole body dose form F18- FDG. The International Basic safety standards and recommendation as well as local regulations have been checked in order to find weather PET/CT examination of pregnant patient might be justified. Results Due to available TOF (time-of-flight) option on PET/CT scanner 3.7 MBq /kg optimized dose is used. Total foetal whole body dose associated with F18-FDG PET/CT examination has been estimated as 2.5 cGy which is 25% of the safe limit introduced by ICRP (10cGy), this dose include 0.6 cGy coming from optimized 18-FDG PET, and around 1.7 cGy coming from the whole body CT. Theoretical additional risk of childhood cancer associated with this examination, using LNT approach, is 0.15% (0.3% background), resulting in total 0.45% risk (ICRP pub84). Conclusion F18-FDG PET/CT is a ‘must have’ procedure during Hodgkin lymphoma treatment. Benefits for mother coming from proper diagnosis and therefore further minimizing irradiated volume to CTV delineated based on PET/CT significantly overcomes potential risk for foetus associated with PET/CT examination. This means that F18-FDG PET/CT for pregnant patient with Hodgkin Lymphoma is justified and should be performed. Each department should optimize PET/CT procedure and assess relevant doses on their equipment to use more accurate dose data to make final clinical decision. Basic Safety Standard and local law requirement do not forbid PET/CT examination as long as it is clinically justified, optimized and communicated to pregnant patient prior treatment. PO-1433 Out-of-Field doses in radiotherapy for prostate cancer with CyberKnife – phantom measurement M. Kruszyna 1 , A. Skrobala 2 , P. Romanski 1 , N. Matuszak 2 , W. Suchorska 2 , K. Kulcenty 3 , I. Piotrowski 3 , J. Malicki 2 1 Greater Poland Cancer Centre, Medical Physics Department, Poznan, Poland ; 2 University of Medical Sciences, Electroradiology Department, Poznan, Poland ; 3 Greater Poland Cancer Centre, Radiobiology Laboratories- Medical Physics Department, Poznan, Poland Purpose or Objective Dose minimization outside the irradiated volume is one of the goals in radiation protection of patient during RT. Various advanced radiotherapy techniques for prostate cancer patients are currently available. It is important to estimate the dose distribution also for healthy tissues located at large distance from the irradiated volume. The aim of the study was to assess the dose distribution outside the irradiated volume of prostate using CyberKnife (CK, Accuray) and to find correlations in selected radiation beam parameters to reduce out-of-field doses. Material and Methods A quasi-anthropomorphic phantom (built-in elements simulating lung and chosen bone tissue) dedicated for measurement of out-of-field doses were specially designed and built. All the measurements were made with an ionization chamber (0.125cc) in 5 points, named and localized as follows: the prostate (target), intestine (+15 cm), right lung (+34 cm), thyroid (+52 cm), and head (+78 cm), using CK (6FFF MV). In the first part of the research

of the patients as rendered by the planning CT datasets together with the isocenter details in each plan. Results The CBCT model was successfully implemented in the TOPAS Monte Carlo code. Both the depth-dose curves and the lateral profiles were within 4% of the measured data for all three protocols considered. Patient data exported from the TPS was also successfully imported in TOPAS (as demonstrated in Figure 1 for an anthropomorphic phantom). Correct positioning of the DICOM volume was achieved based on TPS data and the RT structure sets were properly implemented, allowing for dose calculations in each individual organ that has been delineated thanks to TOPAS embedded volume-based dose filters. The model will be used for patient-specific dose calculations which will be evaluated from the point of view of diagnosis and age groups.

Figure 1. Single angle CBCT irradiation on DICOM CT Data. The imported RT structures are shown in red (liver) and yellow (spleen), while in green are the photon tracks. Conclusion A workflow to allow for patient-specific calculations of proton CBCT doses has been developed based on TOPAS. It allows for an easy and individual determination of doses from such system to specific organs, which could show to be significant in some cases. PO-1432 Hodgkin Lymphoma in Pregnancy - Justification of whole body F18-FDG PET/CT before treatment. A. Kuchcinska 1 , E. Lampka 2 , W. Bulski 3 , B. Mirocha 4 , M. Rubach 5 , D. Kiprian 6 1 Maria Skłodowska-Curie Institute-Oncology Centre, Radiotherapy Department, Warsaw, Poland ; 2 Maria Skłodowska-Curie Institute-Oncology Centre, Lymphoid Malignancies Department, Warsaw, Poland ; 3 Maria Skłodowska-Curie Institute-Oncology Centre, Medical Physics Department, Warsaw, Poland ; 4 Maria Skłodowska-Curie Institute-Oncology Centre, Endocrine Oncology and Nuclear Medicine Department, Warsaw, Poland ; 5 Maria Skłodowska-Curie Institute-Oncology Centre, Chemotherapy Day Ward, Warsaw, Poland ; 6 Maria Skłodowska-Curie Institute-Oncology Centre, Head and Neck Cancer Department, Warsaw, Poland Purpose or Objective In pregnancy, Hodgkin Lymphoma is one next most common type of tumour after breast cancer. Our institute has more than 30 years of experience with successful treatment of pregnant patients including 147 with Hodgkin Lymphoma. Over time treatment approach has developed due to technological and clinical changes. Now a days the ISRT (Involved site radiation therapy) has replaced MANTEL fields approach. The ISRT requires a PET/CT examination before treatment to accurate delineate CTV after chemotherapy and monitor clinical response for chemotherapy during treatment. The F18- FDG PET-CT procedure is commonly used for the patients, but for a pregnant patient the justification of the procedure is still a very sensitive topic, and this relevant