Dosimetry of Bone-Seeking Radiopharmaceuticals for Palliative Therapy of Bone Metastases: A Simulation Study Using GATE Monte Carlo Code

Abstract

Purpose: Radiopharmaceutical Therapy (RPT) is one of the effective methods for pain palliation of bone metastases. Bone marrow is a critical organ in bone structure whose absorbed dose should be kept below a certain threshold. The purpose of this study was to calculate and compare absorbed doses of bone-seeking radiopharmaceuticals used in the palliative treatment of bone metastases.

Materials and Methods: In this study, the GATE Monte Carlo code was used to simulate a femur bone, which consists of bone marrow, endosteal layer, bone, and soft tissue phantom model. Absorbed doses of the ¹⁵³Sm-EDTMP, ⁸⁹SrCl₂, ¹⁷⁷Lu-EDTMP, ¹⁸⁸Re-HEDP, and ²²³RaCl₂ radiopharmaceuticals were calculated in the femur phantom compartments.

Results: bone absorbed doses per disintegration from alpha particles of ²²³RaCl₂ is approximately 24 times higher than absorbed doses from beta particles of ⁸⁹SrCl₂. Also, absorbed dose per disintegration from beta particles of ⁸⁹SrCl₂ in the bone is approximately 12, 6 and 1.5 times higher than ¹⁷⁷Lu-EDTMP, ¹⁵³Sm-EDTMP, and ¹⁸⁸Re-HEDP, respectively. Moreover, the bone and bone marrow absorbed dose from beta particles of ¹⁵³Sm-EDTMP is 1.9 times higher than ¹⁷⁷Lu-EDTMP. Besides, absorbed dose per disintegration from beta particles of ¹⁸⁸Re-HEDP in the bone marrow is approximately 40, 30, 7, and 4 times higher than ²²³RaCl₂, ⁸⁹SrCl₂, ¹⁷⁷Lu-EDTMP and ¹⁵³Sm-EDTMP, respectively.

Conclusion: Our results show that ²²³RaCl₂ could be a more efficient radiopharmaceutical for radionuclide therapy of bone metastases. Also, ¹⁷⁷Lu-EDTMP, due to low marrow toxicity and comparable bone absorbed dose with ¹⁵³Sm-EDTMP, can be used for achieving bone pain palliation. Moreover, significantly high bone marrow absorbed dose of ¹⁸⁸Re-HEDP should be considered for palliative therapy of metastatic bone patients.