Metastasis dosimetric evaluation applied to systemic radiotherapy

In the cancer pathology the metastases are the major reason for death. The systemic radiotherapy proposes the prescription of systemic radiopharmaceuticals that, through their many ways of affinity with the cancerous cells, will concentrate radioisotopes on the tumor and in its metastasis, generating a possible control dose for the colony propagation. Herein, a Monte Carlo based computational model is proposed to evaluate the physical dose in an arbitrary cancerous colony of ∼104 small lung cancer cells, considering all possible nuclear, biological, and morphological parameters, as well as the specific compartment cellular uptakes. As result, physical absorbed dose in MeV/g was obtained in the cell's nucleus, in the cytoplasm and in the interstice, provided by x-rays, gamma rays, Auger electrons and Beta particles emitted from the following radioisotope decays: Es-89, Y-90, In-111, Sm-153, Dy-165, Ho-166, Er-169 e Re-188. It can be verified, from the reduced colony model, that the Auger electrons are responsible for a large part of the total absorbed dose, despite of the Beta energy emitted. Issuing the Auger electrons emitted by radioisotopes, as In-111 and Sm-153, reached the largest doses in the nucleus of the colony's model. The present data, conjugated with a simple biokinetics model, histological data, and medical cintilographic images allow an improvement in the evaluation of the radiopharmaceutical concentration to be prescribed for the patient. (author)