90Y, 177Lu and 131I therapy optimisation: Monte Carlo calculation of dose distribution and radiobiological eval- uations

F. BOTTA; M. VALENTE; ET AL.

JOURNAL OF NUCLEAR MEDICINE

Societuy of Nuclear Medicine

Año: 2009 vol. 50 p. 1859 - 1860

0161-5505

Objectives: To evaluate dose(D) distribution inside and outside lesions and in infiltrated disease or radiosensitive bordering tissues.To assess tumor control probability (TCP) and the biological effect of the lower contributions of dose profile. Methods: 5 tissue spheres (radii(R) 6,8,15,21,36 mm) uniformly filled with 90Y,177Lu,131I were simulated with PENELOPE code. Dose distribution was tallied in 1 mm3 voxels inside spheres and up to 20mm outside. TCP was evaluated for a 30% washout as derived from clinical experience. Its dependence on lesion dimension, radioisotope, and activity was investigated for typical radiobiological parameters. Results: D% profiles of 131I and 177Lu show uniform irradiation inside and a rapid fall with 20% of Dmax at 0.3-0.5mm from the edge. 90Y offers less homogeneity in the sphere, especially for smaller radii, and a longer tail (20% of Dmax at 0.8-1.2mm outside). As regards TCP, assuming D=100Gy to be therapeutic, 177Lu can cope with control within the sphere completely sparing tissue 0.5mm beyond R. 131I and 90Y show equal TCP profiles if D is prescribed at 1.3, 0.9, 0.7mm from the sphere edge (R=6,15,36 mm). For prescription at farther distances, 131I gives wider local control ( contribution) than 90Y at the expense of higher activities, so a tailored balance between TCP and activity should be done. Conclusions: Treatments should be optimized by tailoring radionuclide and activity choice. The dose distribution and TCP profiles of this work are a quantitative support for single case analysis.