Monte Carlo simulations and radiation dosimetry measurements of 142Pr capillary tube-based radioactive implant (CTRI): a new structure for brachytherapy sources.

OBJECTIVE: Previously, a promising ß(-)-emitting praseodymium-142 glass seed was proposed for brachytherapy of prostate cancer. In accordance with the previous study, a (142)Pr capillary tube-based radioactive implant (CTRI) was suggested as a source with a new structure to enhance application of ß(-)-emitting radioisotopes such as (142)Pr in brachytherapy. METHODS: Praseodymium oxide powder was encapsulated in a glass capillary tube. Then, a thin and flexible fluorinated ethylene propylene Teflon(®) layer sealed the capillary tube. The source was activated in the Tehran Research Reactor by the (141)Pr(n,γ) (142)Pr reaction. Measurements of the dosimetric parameters were performed using GafChromic(®) radiochromic film. In addition, the dose rate distribution of (142)Pr CTRI was calculated by modeling (142)Pr source in a water phantom using Monte Carlo N-Particle Transport (MCNP5) Code. RESULTS: The active source was unreactive and did not leak in water. In comparison with the earlier proposed (142)Pr seed, the suggested source showed similar desirable dosimetric characteristics. Moreover, the (142)Pr CTRI production procedure may be technically and economically more feasible. The mass of praseodymium in CTRI structure could be greater than that of the (142)Pr glass seed; therefore, the required irradiation time and the neutron flux could be reduced. CONCLUSION: A (142)Pr CTRI was proposed for brachytherapy of prostate cancer. The dosimetric calculations by the experimental measurements and Monte Carlo simulation were performed to fulfill the requirements according to the American Association of Physicists in Medicine recommendations before the clinical use of new brachytherapy sources. The characteristics of the suggested source were compared with those of the previously proposed (142)Pr glass seed.

Preparation of radioactive praseodymium oxide as a multifunctional agent in nuclear medicine: expanding the horizons of cancer therapy using nanosized neodymium oxide.

OBJECTIVE: Many studies have attempted to assess the significance of the use of the ß(-)particle emitter praseodymium-142 ((142)Pr) in cancer treatment. As praseodymium oxide (Pr(2)O(3)) powder is not water soluble, it was dissolved in HCl solution and the resultant solution had to be pH adjusted to be in an injectable radiopharmaceutical form. Moreover, it was shown that the nanosized neodymium oxide (Nd(2)O(3)) induced massive vacuolization and cell death in non-small-cell lung cancer. In this work, the production of (142)Pr was studied and water-dispersible nanosized Pr(2)O(3) was proposed to improve the application of (142)Pr in nuclear medicine. MATERIALS AND METHODS: Data from different databases pertaining to the production of (142)Pr were compared to evaluate the accuracy of the theoretical calculations. Water-dispersible nanosized Pr(2)O(3) was prepared using a poly(ethylene glycol) (PEG) coating or PEGylation method as a successful mode of drug delivery. Radioactive (142)Pr(2)O(3) was produced via a (142)Pr(n,γ)(142)Pr reaction by thermal neutron bombardment of the prepared sample. RESULTS: There was good agreement between the reported experimental data and the data based on nuclear model calculations. In addition, a small part of nano-Pr(2)O(3) particles remained in suspension and most of them settled out of the water. Interestingly, the PEGylated Pr(2)O(3) nanoparticles were water dispersible. After neutron bombardment of the sample, a stable colloidal (142)Pr(2)O(3) was formed. CONCLUSION: The radioactive (142)Pr(2)O(3) decays to the stable (142)Nd(2)O(3). The suggested colloidal (142)Pr(2)O(3) as a multifunctional therapeutic agent could have dual roles in cancer treatment as a radiotherapeutic agent using nanosized (142)Pr(2)O(3) and as an autophagy-inducing agent using nanosized (142)Nd(2)O(3).

Bremsstrahlung parameters of praseodymium-142 in different human tissues: a dosimetric perspective for (142)Pr radionuclide therapy.

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.