Updating the Planar Patterson- Parker Table for Ir-192 and Cs-137 Brachytherapy Sources Using the Most Recent TG-43U1 Recommended Dosimetric Parameters

Background: the patterson-parker table was created in 1934 to determine mg-hrrequired to deliver the prescribed dose to the treatment area. these tables were createdusing the dosimetric data for 226ra that was determined in air and were utilizedfor dose calculations around implants with ra-equivalent radionuclides such as 137csand 192ir. therefore, the differences of the tissue attenuation and anisotropy of theseradionuclides and their impact on dose uniformity of the implants were ignored.objective: in this study, the patterson-parker table has been updated for 137csand 192ir sources using their recent dosimetric data. furthermore, the dose uniformityfor different loading schemes, as a function of the implant area, was tested.methods: the updated paterson-parker tables were generated for 137cs and 192irsources using their published dosimetric parameters that have been determined followingthe american association of physicists in medicine (aapm) task group 43(tg-43u1) recommendations. the accuracies of the updated tables were examinedby two independent methods, monte carlo simulation technique and a commerciallyavailable treatment planning system. in addition to the dose values along the centralaxis of the implant, dose profiles along two orthogonal directions were evaluated forthe selection of the optimal radioactivity distribution in an implant.results: we found that the original paterson-parker loading scheme of the radioactivityas a function of the implant size has to be adjusted to achieve the optimaldose distribution (1000 cgy ±10%) in an implant. in addition, it was shown that thesame implant size for the mg-hr required for 137cs was not identical to that of 192ir.similarly, there were some differences between the updated table and the publishedpaterson-parkers tables. independent monte carlo simulations and treatment planningdata had excellent agreement with the updated data.conclusion: the conventional version of paterson-parker tables are not usefulfor the two commonly used brachytherapy sources. the updated version of the tablesshould be used instead.