Purpose: Dosimetry in brachytherapy is of paramount importance to ensure equality between the prescribed and delivered dose to the patient. Due to the high dose gradient in regions close to the source, experimental dosimetry is highly complex. Therefore, the American Association of Physicists in Medicine (AAPM) recommends using Monte Carlo simulation as an alternative. In this work, the relative depth dose, the radial dose function and the anisotropy function (at the reference distance for dosimetry in brachytherapy, 1 cm) were analyzed, for two sources commonly used in ophthalmic brachytherapy, using Monte Carlo simulation with PENELOPE code.
Methods: The models used were IR06-103Pd and OncoSeed 6711 for ¹⁰³Pd and ¹²⁵I, respectively. Both were modeled and positioned in the center of a 30 cm cubic phantom, filled with water and divided into 101 pixels in the three directions of the Cartesian axis. The 8 and 5 main emission lines were inserted for the ¹⁰³Pd and ¹²⁵I sources, respectively.
Results: Comparing the relative depth dose from the two sources, the source of ¹²⁵I has 5.4 p.p less than ¹⁰³Pd source, due to the distribution of the radioactive material being different in both sources. Analyzing the radial dose function, the major difference was 0.03 at 1.2 cm, being greater for ¹²⁵I. In the anisotropy function, both showed the same behavior, but with higher values for the ¹⁰³Pd source, with the major difference 0.13 at 135°.
Conclusion: For the dosimetric parameters analyzed, the sources of low dose rate showed similar behavior in dosimetric parameters and difference in relative depth dose, due to the distribution of radioactive material by the source geometry. Thus, the PENELOPE package presents as a promising tool for dosimetric calculations for brachytherapy sources.
Funding Support, Disclosures, and Conflict of Interest: Thanks to FAPERGS for the financial support for this research.