DOSE3D: EGS4 Monte Carlo code-based software for internal radionuclide dosimetry

MIRDOSE3 software is currently the main tool available in clinical practice to evaluate absorbed dose in nuclear medicine. Because MIRDOSE3 provides d osimetric parameters for specific anatomic models that cannot be modified b y the user, it cannot be used to obtain information concerning metastases o r to consider patients whose anatomy differs significantly from that of the standard models. Methods: To address some of these inconveniences, we deve loped an original program based on the EGS4 Monte Carlo code, DOSE3D, which calculates dosimetric parameters for anthropomorphic phantoms defined with combinatorial geometry. DOSE3D allows the user to add spheres within the p hantom for simulating tumors, to change the shape of one or more organs and , for organs defined by pair, to calculate individual dosimetric parameters for each organ. The program was validated for I-131 and Tc-99m by calculat ing S values for the Medical Internal Radiation Dose (MIRD) adult male phan tom and comparing these results with data provided by MIRDOSE3. Moreover, t wo studies were performed to illustrate DOSE3D features. The first one conc erned the evaluation of the individual influence of two bone metastases (lo cated in the pelvis and in the lower spine and containing I-131) On testes in terms of S Values compared with the influence on testes of other source Organs (kidneys, liver, lungs, spleen, thyroid gland and urinary bladder co ntents). The second study determined the differences of S values between ri ght and left lungs and right and left kidneys when I-131 is contained in th e liver. Results: The DOSE3D S values were on average within 20% of the MIR DOSE3 results for both radionuclides. Regarding the bone metastases study, S(testes<--metastases) and S(testes<--any source organs) were of the same o rder of magnitude. In the second study, the S values ratio between right an d left organs was 7.7 for the lungs and 5.2 for the kidneys. Conclusion: Th e agreement between DOSE3D and MIRDOSE3 results for most organs shows the v alidity of DOSE3D. The presented examples of calculation show that DOSE3D c ould provide additional data to dosimetric parameters given by MIRDOSE3 for a more patient-specific. dosimetric approach.