Monte Carlo calculations and experimental measurements of dosimetry parameters of a new 103Pd source

Permanent prostate implantation using I-125 (iodine) or Pd-103 (palladium) sources is a popular treatment option in the management of early prostate cancer. As sources of new designs are developed and marketed for application in permanent prostate implantations, their dosimetric characteristics must be carefully determined in order to maintain the accuracy of patient treatment. This report presents the results of experimental measurements and Monte Carlo calculations of the dosimetric parameters performed for a newly available Pd-103 Seed source. The measurements were performed in a large scanning water phantom using a diode detector. The positioning of the source and detector was achieved by a computer-controlled positioning mechanism in the scanning water phantom. The dose rate constant in water for the new Pd-103 source was determined from measurements with the diode detector calibrated with I-125 sources of known air-kerma strength. The radial dose function values for the source were measured using the diode detector. Monte Carlo photon transport calculations were then used to calculate the dosimetric parameters of dose rate constant, radial dose function, and anisotropy function using an accurate geometric model of the source. The measured dose rate constant of 0.693 cGy/U-hr compares well with the Monte Carlo calculated value of 0.677 cCy/U-hr. These results are further compared with data on existing Pd-103 sources. (C) 2000 American Association of Physicists in Medicine. [S0094-2405(00)03605-1].