Cellular dosimetry of 111In using Monte Carlo N-particle (MCNP) computer code: Comparison with reported analytical methods and predictive value

Objectives Our goal was to compare MCNP self- and cross-doses to the nucleus of breast cancer (BC) cells from the Auger electron-emitter ¹¹¹In to those calculated by reported analytical methods (Goddu et al. and Farragi et al.). We also incorporated different cell geometries and experimental conditions and determined if MCNP could predict clonogenic survival of BC cells exposed in vitro to ¹¹¹In-DTPA-hEGF.

Methods MCNP was used to simulate the transport of all electrons emitted by ¹¹¹In from locations at cell surface (CS), cytoplasm (CY) or nucleus (N). The doses to N per decay (S values) were calculated for single, closely packed monolayer cells or clusters of cells with various cell and nuclear dimensions.

Results For self-doses, MCNP S_N→N-values agreed well with those of Goddu et al. [relative difference (RD) of 0.5– 4.0%] and Faraggi et al. (RD -1.1– -2.4%). MCNP S-values of CY and CS to N compared fairly well with the reported values for cells with radii >7 um (RD -7.9 –13.5% for Goddu et al.; -4.9–5.8% for Faraggi et al.). S-values of monolayer cells were significantly different than those of single cell and cell clusters. The predicted cell survival based on calculated S values for monolayer MDA-MB-468, MDA-MB-231 and MCF-7 cells, and cell fractionation data and gamma-ray survival correlated well with experimental data (RD 3.1, -1.0 and 1.7%).

Conclusions MCNP is feasible and can reliably assess cellular dosimetry of Auger electron-emitters. S values for monolayer cells predicted the cell survival of BC cells after exposure to ¹¹¹In-DTPA-hEGF better than S values of Goddu et al. and Faraggi et al.

Research Support Canadian Breast Cancer Research Alliance (Grant No. 19374).