Biological equivalent dose assessment of the consequences of hypofractionated radiotherapy.
OBJECTIVE
To investigate the changes in biological effective dose (BED) that occur in high-dose regions within a target volume when radiotherapy is hypofractionated.


METHODS
By comparing a standard prescription of 2 Gy per fraction that is matched to give the same BED as a hypofractionated schedule at a standard intersectional prescription point, the BED increments for late-tissue effects at a higher dose region within the planning target volume (PTV) are compared. The alternative approach of BED matching between a conventional and hypofractionated schedule at the high-dose region is also considered. The results are presented as a sequence of calculations that can be understood by practicing radiation oncologists and in graphical form.


RESULTS
The BED increment at the high-dose region is marginally increased by hypofractionation, although the latter effect is relatively small: up to 5% additional BED due to hypofractionation for a 20% increase in physical dose when the prescribed fraction size is 6-7 Gy. BED matching for late effects between a conventional and hypofractionated schedule at the high-dose region produces lower BED values throughout the remaining PTV, but at the expense of a reduced tumor control BED.


CONCLUSIONS
Clinical trials that use BED isoeffect matching for late reacting tissue effects to design a hypofractioned test schedule should include comprehensive calculations of the likely BED in high-dose regions.
Jones
B
B
Cancer Therapeutics Section, Imperial College School of Medicine, Department of Clinical Oncology, Hammersmith Hospital, London, United Kingdom. bleddyn.jones@ic.ac.uk
Dale
R G
RG
Finst
P
P
Khaksar
S J
SJ
D000465:Algorithms; D019583:Dose Fractionation, Radiation; D016014:Linear Models; D008954:Models, Biological; D011853:Radiobiology; D012062:Relative Biological Effectiveness