Standard effective doses for proliferative tumours

This study was undertaken to investigate the treatment schedules used clini cally for highly proliferative tumours, particularly with reference to the effects of fraction size, fraction number and treatment duration. The linea r quadratic model (with time component) is used here to compare non-standar d treatment regimens (e.g. accelerated and hyperfractionated schedules), cu rrently the focus of randomized trials, with each other and some common 'st andard regimens'. To ensure easy interpretation of results, two parameters known as proliferative standard effective dose one (PSED1) and proliferativ e standard effective dose two (PSED2) have been calculated for each regimen . Graphs of PSED1 and PSED2 versus potential doubling time (T-p) have been ge nerated for a range of fractionation regimens which are currently under tri al in various randomized studies. From these graphs it can be seen that the highly accelerated schedules (such as CHART) only show advantages for tumo urs with very short potential doubling times. Calculations for most of the schedules considered showed at least equivalent tumour control expected for the trial schedule compared with the control arm used and these values agr ee quite well with clinical results. These calculations are in good agreement with clinical results available at present. The greater the PSED1 or PSED2 for the schedule considered the gr eater the tumour control, which can be expected. However, as has been seen with clinical trials, this higher cell kill also results in higher acute ef fects which have proved too great for some accelerated schedules to continu e.