Figure 3.

Tumor volumes obtained form serial MR images of four individual rats are displayed versus time after 9L cell implantation. In each case, the individual volume measurements are shown along with the line corresponding to the least-squares fit. (A) A representative plot of an untreated intracerebral 9L tumor that reveals the exponential growth characteristic (Td = 67, r² = 0.997) of this tumor over the life span of the animal. For BCNU-treated animals, the individual volume measurements are shown along with the pretreatment (solid) and posttreatment (dashed) exponential growth fits after treatment with (B) 0.5, (C) 1, and (D) 2 × LD₁₀ BCNU. Pre- and post-BCNU doubling times (Td) were (B) 53 and 70 h, (C) 55 and 86 h, and (D) 46 and 99 h, respectively, revealing a decrease in growth rate during posttreatment exponential tumor regrowth. Calculated log cell kill values were (B) 0.4, (C) 0.9, and (D) 1.6. In D, the arrows denoted by a, b, c, and d correspond with the rat brain MR images shown in Fig. 2 obtained at 330, 593, 763, and 1105 h, respectively.