220.6: Effective radiation dose and bone marrow radiation exposure as a result of radiological investigation in a cohort of multivisceral transplant patients

Abstract

Introduction: A patient who experienced a rare form of leukaemia following multivisceral transplantation prompted an investigation of cumulative radiation exposure due to radiological investigations in a cohort of multivisceral transplant patients from our centre. In addition, bone marrow dosimetry was calculated in view of the high incidence of bone marrow suppression in this group of patients. Methods: Dose data for CT examinations was retrospectively collected using PACS. Effective doses for each phase of each scan were estimated using 2016 updated conversion coefficients. The total number of scans and total effective dose were calculated for each patient and the stochastic risks for general cancer risk of 4.1%/Sv and leukaemia risk of 0.63%/Sv stated by the International Commission on Radiological Protection (ICRP) were estimated. Bone marrow dose per Dose-Length-Product (DLP) conversion factors were created for each anatomical region using the ImPACT Calculator, which allowed total bone marrow doses to be estimated for each patient. Bone marrow dose rates were compared against the acute radiation dose rate threshold for reduced haematopoiesis of 0.25–0.5 Gy/year suggested by the ICRP. Results: Radiation doses were calculated for 80 patients undergoing multivisceral transplant procedures (+/- liver) at Addenbrooke’s Hospital, Cambridge UK between 1998 and 2018. The average age was 49 years (range 16 – 61). The majority of the radiation dose was incurred by CT scans – 1700 in total over an average of 4.4 years per patient (SD 2.6yrs). Mean number of scan phases per patient was 33.7 (SD 17.8). Maximum number of scan phases for one patient was 83. Mean effective dose was 291 mSv (SD 224 mSv), Maximum effective dose was 1057 mSv (4.3% general cancer risk, 1.1% Leukaemia risk). 5 patients received cumulative doses in excess of 800mSv and 2 exceeded 1Sv. The highest bone marrow dose was 0.66Gy, 0.4Gy/month. 74 patients exceeded the ICRP recommended limit of 0.02 Gy/month and 11 exceeded 0.25 Gy/year and 11 patients exceeded the monthly threshold for >120 days. Conclusions: Significant radiation exposure is experienced by this cohort of patients and the threshold dose rate for reduced haematopoiesis is often exceeded with significant potential implications for the development of cancer and bone marrow suppression.