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TDF Plan: Comparing Regimens

One way to compare regimens is to directly manipulate the parameters in the IMR calculator. You can work with any two of the three inter-related parameters: total dose, # fractions, and Rx dose/fraction by locking the parameter you wish to hold constant. Unlocked parameters have enabled editable text fields and "up/down" arrow bumpers. You can modify the parameters in predefined increments using the arrow bumpers, or enter exact values from the keyboard. The BED (E/α) is automatically updated when any of the parameters is changed.

For example, lets begin with a course of 30 fractions of 200 cGy. The total dose is 6000 cGy and the biologically effective dose is 72.00 Gy(10.0).

Figure 1

Now, lock the total dose field and change the new number of fractions to 25. The dose/fraction will change to 240 in order to maintain the locked total dose of 6000 cGy and the biologically effective dose readout will calculate 74.4 Gy(10.0).

Figure 2

Now, lock the number of fractions at 25 and reduce the dose/fraction field (to about 234 cGy) until the biologically effective dose returns to approximately 72 Gy(10.0). If the assumption of an α/β ratio ≈ 10.0 is valid, the regimens 60 Gy delivered in 30 fractions and 58.5 Gy delivered in 25 fractions should result in equivalent acute biological effects.

Figure 3

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