Standard effective doses for proliferative tumours.
This study was undertaken to investigate the treatment schedules used clinically for highly proliferative tumours, particularly with reference to the effects of fraction size, fraction number and treatment duration. The linear quadratic model (with time component) is used here to compare non-standard treatment regimens (e.g. accelerated and hyperfractionated schedules), currently the focus of randomized trials, with each other and some common 'standard regimens'. To ensure easy interpretation of results, two parameters known as proliferative standard effective dose one (PSED1) and proliferative standard effective dose two (PSED2) have been calculated for each regimen. Graphs of PSED1 and PSED2 versus potential doubling time (Tp) have been generated for a range of fractionation regimens which are currently under trial in various randomized studies. From these graphs it can be seen that the highly accelerated schedules (such as CHART) only show advantages for tumours 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 agree 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 greater the tumour control, which can be expected. However, as has been seen with clinical trials, this higher cell kill also results in higher acute effects which have proved too great for some accelerated schedules to continue.
Jones
L C
LC
Department of Medical Physics, Prince of Wales Hospital, Randwick, NSW, Australia. lois.jones@swsahs.nsw.gov.au
Metcalfe
P
P
Hoban
P
P
Fox
C
C
D002455:Cell Division / Q000528:radiation effects; D019583:Dose Fractionation, Radiation; D006801:Humans; D016014:Linear Models; D008954:Models, Biological; D009361:Neoplasm Invasiveness; D009369:Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D011874:Radiometry / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted