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3D Dosimetry of a Simulated Prostate Treatment in the Presence Metallic Femoral Prostheses

O Baffa

D Cuevas Rojas , J Pavoni , O Baffa*, Universidade de Sao Paulo, Ribeirao Preto, SP


SU-I-GPD-T-374 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Tridimensional dosimetry in the prostate region as well as measurements at specific points far from the planed target volume (PTV) were performed in a phantom to verify the accuracy of the treatment planning and possible regions and/or organs at risk.

Methods: The polymeric gel Magic-f associated with magnetic resonance imaging was used to measure the tridimensional dose in the volume around the phantom’s prostate region. The dose at several points at the bone metal interface and sacrum region and other points were measured using thermoluminescence and alanine dosimetry. The phantom consisted of cylinders of acrylic and real bones with prostheses in place. Soft tissue was simulated by water.

Results: The comparison of dose distributions calculated by TPS and measured in the gel was made using by gamma analysis (3% / 3mm), in this case, the distribution of dose measurement agrees with the distributions expected by TPS. The absorbed dose values at the bone-metal interface are determined by the TL dosimeters, presented a dose increase of 89.5% and 84% in the region of the sacral bone, and another increase between 16% and 28% were found in the regions as the head of the femur and the hip. Similarly, for alanine dosimeters were found increases in the dose of 40% and 80.6% in the region of sacral bone. All these increases are caused due to the effective atomic number of the hip prostheses, which combined with radiation energy, field size and thickness cause a dispersion in the radiation and as results risk organs such as bladder and rectum are affected.

Conclusion: The combination of 3D dosimetry and measurements at specific points in the phantom allowed a comprehensive view of the dose distribution showing that care must also be paid to regions outside the PTV.

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