Objective: Praseodymium-142 [T 1/2 = 19.12 h, [Formula: see text] = 2.162 MeV (96.3%), Eγ = 1575 keV (3.7%)] is one of the (141)Pr radioisotopes. Many studies have been attempted to assess the significance of usage (142)Pr in radionuclide therapy. In many studies, the dosimetric parameters of (142)Pr sources were calculated by modeling (142)Pr sources in the water phantom and scoring the energy deposited around it. However, the medical dosimetry calculations in water phantom consider Bremsstrahlung production, raising the question: "How important is to simulate human tissues instead of using water phantom?" This study answers these questions by estimation of (142)Pr Bremsstrahlung parameters.
Methods: The Bremsstrahlung parameters of (142)Pr as therapeutic beta nuclides in different human tissues (adipose, blood, brain, breast, cell nucleus, eye lens, gastrointestinal tract, heart, kidney, liver, lung deflated, lymph, muscle, ovary, pancreas, cartilage, red marrow, spongiosa, yellow marrow, skin, spleen, testis, thyroid and different skeleton bones) were calculated by extending the national council for radiation protection model. The specific Bremsstrahlung constant (Γ Br), probability of energy loss by beta during Bremsstrahlung emission (P Br) and Bremsstrahlung activity (A release)Br were estimated. It should be mentioned that Monte Carlo simulation was used for estimation of (142)Pr Bremsstrahlung activity based on the element compositions of different human tissues and the calculated exposures from the anthropomorphic phantoms.
Results: Γ Br for yellow marrow was smallest amount (1.1962 × 10(-3) C/kg-cm(2)/MBq-h) compared to the other tissues and highest for cortical bone (2.4764 × 10(-3) C/kg-cm(2)/MBq-h), and, overall, Γ Br for skeletal tissues were greater than other tissues. In addition, Γ Br breast was 1.8261 × 10(-3) C/kg-cm(2)/MBq-h which was greater than sacrum and spongiosa bones. Moreover, according to (A release)Br of (142)Pr, the patients receiving (142)Pr do not have to be hospitalized for radiation precautions and the Bremsstrahlung production does not prevent the therapy for outpatients.
Conclusion: However, modeling (142)Pr source in water phantom for simulation of (142)Pr source in soft tissues could be acceptable due to similarity of Γ Br in water and soft tissues; this approximation is a gross computation in the mediums encompassing high atomic numbers. These data may be practical in the investigation of Bremsstrahlung absorbed dose where (142)Pr is involved in radionuclide therapy.