SU‐GG‐T‐325: Improved Organ Sparing by Electronic Brachytherapy: A Monte Carlo Study

Purpose: To compare the absorbed dose delivered per photon to the lungs, heart wall, and breast by irradiation of a breast tumor via a novel electronic x‐ray brachytherapy source to that delivered by a standard192 Ir seed. Method and Materials: X‐ray spectra for 20–50 keV monoenergetic electrons, in 5 keV increments, were generated using the GEANT4 Monte Carlo code and realistic apparatus geometry. These spectra were then used as simulated point sources located 2 cm beneath the surface of a breast of a female voxelized phantom, generating 10 8 photons. The emission spectra of192 Ir was used to simulate a point source in the same location for comparison. Results: An average decrease by a factor of 1.75 in dose to breast was revealed for when compared to192 Ir . Dose to the lungs showed a decrease by factors of 2 × 10 3 and 11 at 20 and 50 keV electron energy, respectively, while the heart wall exhibited a decrease varying by factors of 1.5 × 10 4 to 17.6 for the same energies. Conclusion: The lower dose (factor of 1.75 on average)delivered to localized tissue by a x‐ray brachytherapy source is more than compensated by a substantial decrease of dose (up to a factor of 1.5 × 10 4 ) delivered to vital organs adjacent to the treatment area. Due to the softer specta a novel electronic x‐ray brachytherapy source spares better the healthy tissues.