Radiation exposure during liver surgery after treatment with 90Y microspheres, evaluated with computer simulations and dosimeter measurements

Purpose. Two patients with liver tumours were planned for a combined treatment, including surgery with preceding injections of β− radiation emitting 90Y microspheres (SIRTEX®). The aim of this paper is to present a method of pre-surgical computer simulations of the absorbed dose rate on the surface of tumour tissue, combined with measurements of the actual absorbed dose rate on resected tissue, in order to estimate the absorbed dose to a surgeon's fingers during such surgery procedures. Methods and Materials. The dose rates from β− radiation on the surface of tumour tissue were simulated with the software VARSKIN® Mod 2. The activity concentrations in tumours were estimated, based on SPECT/CT distribution studies of 99mTc-MAA and confirmed by SPECT/CT bremsstrahlung studies of 90Y microspheres. The activity distributions were considered as homogeneous within the tumour regions. The absorbed dose rates at different tumour tissue spots were calculated based on measurements with thermo-luminescent dosimeters (TLD) fastened on resected tissue. Results. The simulations showed a good agreement with the averaged absorbed dose rates based on TLD measurements performed on resected tissue, differing by 13% and 4% respectively. The absorbed dose rates at the measured maximum hotspots were twice as high as the average dose rates for both patients. Conclusion. The data is not sufficient in order to draw any general conclusions about dose rates on tumour tissue during similar surgeries, neither about the influence of dose rate heterogeneities nor about average dose rates. However, the agreement between simulations and measurements on these limited data indicate that this approach is a promising method for estimations of the radiation exposure to the surgeons' fingers during this kind of surgery procedure. More data from similar surgeries are necessary in order to validate the method. (paper)