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Description
The dosimetry of beta-emitting sources presents significant challenges at short distances due to steep dose gradients. Phosphorus-32 (³²P) sources have been proposed as promising alternatives in brachytherapy, particularly for the palliative treatment of spinal tumors, since the short range of beta particles enables high dose deposition in the target while sparing the spinal cord. The aim of this study was to perform a dosimetric evaluation of a flexible polymeric ³²P source developed at the IPEN/USP, with dimensions of 5×5×0.04 cm³ and a total activity of 1969 MBq. Monte Carlo simulations were performed using MCNP6.2 code. The F6 tally was applied to calculate percent depth dose (PDD), while *FMESH4 with DE/DF multipliers was used to obtain lateral dose profiles and spatial dose distributions. The emission spectrum was obtained from the IAEA website. Contributions from bremsstrahlung photons were also considered, although electrons dominated energy deposition up to approximately 7.2 mm. Additional simulations were conducted in water, soft tissue, cortical bone, compact bone, and air. The effect of source thickness variation was analyzed to assess geometric sensitivity and its impact on dosimetric parameters. In water, the dose rate at 1 mm depth was 0.365 Gy/min, corresponding to approximately 27 minutes to deliver a prescribed dose of 10 Gy. The lateral dose profile at 1 mm depth showed a 90% field width of 4.62 cm, corresponding to the region where the prescribed dose would adequately cover the tumor volume. An exponential fit applied to the PDD curve showed excellent agreement (R² = 0.9974), consistent with the expected physical behavior of beta particle dose fall-off. Results were compared with published data for ³²P beta sources and are being evaluated against theoretical dose point kernel (DPK) calculations. In conclusion, accurate dosimetric evaluation is essential; simulations indicate optimized dose delivery and reduced tissue exposure, advancing brachytherapy.