TABLE 4

Segmentation of Activity Maps Improves Computational Efficiency

Tallies	No. of histories^*	CPU time^† (h)	Tumor mean dose^‡ (Gy)
50,000	4,000,000	4,642.3	63.7
20	200,000	16.8	60.6
10	30,000	4.0	60.4
5	4,000	0.5	53.5

↵* Photon transport for activity and density maps from SPECT/CT scan at 27 h.
↵† CPU time is sum of all CPU time spent on each node of Beowulf cluster.
↵‡ Absorbed doses to tumors are calculated using MTD of 27.25 Gy to normal lungs.