Why Psasgr is more useful than PSADT

As noted in Figure 10, when SGR is fast and increases 1% from 4 to 5%/day, the doubling time changes 1.3-fold from 4 to 3 days (a slight change). However, when the SGR is slower and increases 1% from 1 " 2%/d, doubling time changes four-fold from 69 to 17 days (a large change). A DT of 1-day does not represent the same growth rate when the tumor is slowing as when the tumor is rapidly growing. As the absolute value of SGR approaches zero, DT approaches infinity and is of no practical use other than to say the tumor or marker is stable. Because of the DT-SGR relationship at the extremes of tumor or marker growth, therapy-induced changes in doubling times at the extremes of SGR do not accurately represent the magnitude of the impact of therapy.

Tumor marker doubling times for tumors are not symmetrically distributed as are Specific Growth Rate constants.

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Doubling time (DT) changes relative to changes in tumor specific growth rate (SGR). Slow growing tumors are associated with large changes of DT while DT's of rapidly growing tumors (high SGR's) are small and do not accurately reflect the rate of tumor growth.

Doubling time (DT) changes relative to changes in tumor specific growth rate (SGR). Slow growing tumors are associated with large changes of DT while DT's of rapidly growing tumors (high SGR's) are small and do not accurately reflect the rate of tumor growth.

Figure 10. This figure, modified from Mehrara [70], displays the variation of tumor volume doubling time or tumor marker doubling time (DT) per unit change of tumor specific growth rate (SGR) based on:.

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