Clinical brachytherapy with neutron emitting 252Cf sources and adherence to AAPM TG-43 dosimetry protocol

Using Monte Carlo methods, neutron dosimetry for 252Cf Applicator Tube (AT) type medical sources available from Oak Ridge National Laboratory (ORNL) has for the first time been determined in terms of TG-43 formalism. This approach, as compared to previous "along-away" formalisms, demonstrates the relative angular independence of dose rate data, when the geometry factor has been removed. As the ORNL-made 252Cf AT type sources are considerably physically larger than most clinical sources used today, the radial dose function increases for radii less than 3.0 mm due to breakdown of the line source model. A comparison of the 252Cf neutron radial dose function with those for other medical sources revealed similarities with that from 137Cs. Differences with respect to previous 252Cf AT source neutron dosimetry data generally increased at increasing distances. This was attributed to differences in the various 252Cf AT source models and phantom compositions. The current status of 252Cf medical source fabrication and calibration procedures at ORNL is presented.