Iodine-131 S-values of post-thyroidectomy adult Filipino mesh-type computational phantoms.

PURPOSE: Adult Filipinos are highly susceptible to differentiated thyroid carcinoma (DTC), which is managed with thyroidectomy followed by radioactive iodine (RAI) therapy. Currently, there is a lack of iodine-131 S-values for adult Filipinos undergoing RAI therapy post-thyroidectomy, posing internal dose assessment challenges. This study established iodine-131 S-values of post-thyroidectomy adult Filipino mesh-type computational phantoms, enabling organ-level internal dose assessment.

METHODS

The phantoms were developed by scaling the adult mesh-type reference computational phantoms (MRCPs) based on anthropometric data acquired from the University of the Philippines‒Philippine General Hospital. The thyroid of the scaled phantoms were modified to simulate the effect of thyroidectomy. The S-values of 37 target organs using nine source structures were determined using Particle and Heavy Ion Transport code System. Lastly, the S-values were compared with those of the MRCPs and the Mesh-type Reference Korean Phantoms (MRKPs). Nine phantoms were developed for each sex, representing different sizes of adult Filipinos.

RESULTS

Deviations were observed between their S-values and those of the adult MRCPs due to phantom scaling and thyroid size reduction. Deviations were also observed upon comparison with the S-values of the MRKPs due to organ-level anatomical differences, which persisted even when compared with adult Filipino phantoms with the closest anatomical measurements to the MRKPs. Additionally, the thyroid-thyroid S-values of the developed phantoms were independent of phantom size, highlighting the effect of thyroidectomy.

CONCLUSION

The collated S-values are essential in organ-level internal dose assessment, a crucial procedure for Filipinos given their high susceptibility to DTC.