Room: AAPM ePoster Library
Purpose: perform a dosimetric analysis of radioactive bone cements loaded either by brachytherapy seeds or by a uniformly distributed radioisotope for the treatment of spinal metastases.
Methods: CT scan images were imported in Geant4 toolkit and two tumor locations were defined separately. An ellipsoid shape overlapped with nearly 75% of the tumor was defined as the bone cement. In the case of seed-loaded bone cements, I-125, Pd-103 and Cs-131 seeds were implanted in the cement, while for the other case, beta emitter radioisotopes, i.e. P-32, Y-90, or Ho-166, were uniformly distributed in the cement. The minimum dose covered 95% of the tumor was considered as the reference dose. The dose volume histograms were obtained after tumor and the spinal cord segmentation.
Results: bone cements present a better tissue sparing, due to their high gradient dose. Cs-131 and Y-90 show better tumor coverage for seed-loaded and beta-emitting bone cements, respectively. The minimum mean dose covered 100% of the tumor volume was 77.4%, 69.2%, 79.2%, 35%, 43.4% and 50.6% for I-125, Pd-103, Cs-131, P-32, Ho-166 and Y-90, respectively. The presence of cold spots in dose distributions obtained with bone cements loaded by P-32 is more likely. The maximum volume of the spinal cord that receives 10% of the reference dose reaches up to 49% for Cs-131 seeds, when the tumor is in contact with the spinal canal.
Conclusion: results indicate that brachytherapy seeds are useful for large tumors with more than 10 mm in depth. If the tumor is located near the spinal cord, beta emitting bone cements is recommended to be employed, otherwise Pd-103 seeds with more than 5 mm distance from the spinal cord may be useful. The dose distributions obtained from different radioactive bone cements can be utilized in the brachytherapy treatment planning systems.