Dosimetry for 252Cf neutron emitting brachytherapy sources: protocol, measurements, and calculations

The mixed-field dosimetry for 252Cf Applicator Tube (AT) type medical sources available from Oak Ridge National Laboratory (ORNL) has been characterized using ionization chambers, a GM counter, and Monte Carlo methods. Unlike the AAPM Task Group No. 43 (TG-43), specification of dose to muscle instead of water is recommended for clinical dosimetry of 252Cf medical sources. A dosimetry protocol similar to ICRU 45 was formulated with parameters determined specifically for 252Cf brachytherapy. Comparisons of experimental and calculative dosimetry results with Colvett et al. [Phys. Med. Biol. 17, 356-364 (1972)] and Krishnaswamy [Phys. Med. Biol. 17, 56-63 (1972)] were performed, and correction factors were determined to compare the different dosimetry formalisms. Using a Maxwellian model for the 252Cf neutron energy spectrum, kerma relative to muscle was determined for a variety of materials, and compared with relative kermas for external neutron beams of three different energies. Neutron isodose distributions and data necessary for clinical implementation of 252Cf AT sources are also presented.