Dose and Fractionation:
When comparing multiple regimens in the literature for relapse incidence, transplant- related mortality, DFS and OS “more biologic effective dose (BED) is better”= high dose TBI preferable and taking into account lung and kidney toxicity in particular ( Kal et al Radioth Oncol 73 ( suppl 1 ): S206, 2004
Increasing the number of fractions allows one to increase total dose for same biological effect.
Greater dose rate effect in lung than in leukemic cells but insignificant with highly fractionated schemes (Vitale et al, Bone Marrow Transplant 4 (Suppl 1 ): 233, 1989.)
At any dose rate, the antileukemic effect, relative to lung toxicity effect, is favoured with highly fractionated regimen. This also allows for the greatest total dose to be delivered.
O’ Donoghue and collegues (61) comparing schedules using mathematical model for leukemic cell kill, “accelerated hyperfractionation” schedules optiomal, with a minimum of 6 hours between fractions for maximal repair, two fractions per day practical ( O’ Donogue et al, Br J Radiol 60: 279, 1987)
A reasonable regime 1.3- 1.5Gy per fraction for 10 fractions over 5 days