New dosimetry for childhood skin hemangioma treatments with 226Ra needles or tubes

Marie Lundell, Mattias Karlsson, Åsa Carlsson Tedgren

The Stockholm Hemangioma Cohort is important for evaluation of late effects after exposure to ionizing radiation during childhood. Dose estimates in this cohort were based on both measurements and calculations using an old treatment planning system. We compare previously published and calculated dose estimates with new ones, obtained by Monte Carlo simulations, which mimic the hemangioma treatments with (226)Ra needles and tubes. The distances between the (226)Ra sources and the thyroid and breasts, respectively, were reassessed. The Monte Carlo calculations showed significantly lower dose values than those obtained earlier. The differences depended both on the modeling of the sources and on further individualized distances from the sources. The mean value of the new calculated doses was 25% of the old breast doses and 46% of the old thyroid doses. New dosimetry for hemangioma treatments gives significantly lower organ doses for the few cases receiving the highest absorbed dose values. This implies that radiation risk estimates will increase and have to be recalculated. For retrospective studies it is now possible to calculate organ doses from radium treatments using modern treatment planning systems by modeling the source geometry carefully and apply the TG-43 formalism. It is important to be aware of the large uncertainties in calculated absorbed dose values.