Fractionation and late rectal toxicity.

E ate rectal bleeding is well established as a key doseimiting end point in prostate radiotherapy (1–6) and is an mportant consideration in cervical cancer radiotherapy (7– ). Consequently, much effort has been devoted to estabishing dose–response relations for rectal bleeding (1–8). linically, however, little has been directly established bout the response of this end point to changes in fractiontion (as quantified, for example, by the / ratio [8]), hough there have been increasing suggestions in the literture that at least part of the late rectal response is a consequential” late effect, directly correlated with early ectal damage (10–12). If this is the case, one might expect hat the response of this end point to changes in fractiontion might be intermediate between a classic late effect typical / value: 1 to 3 Gy) and a classic early response typical / value: 8 to 10 Gy); indeed, the / ratios stimated for late rectal damage in rodents do seem to be in his intermediate range (13–19). So new clinical data on the response of late rectal damage o changes in fractionation are of interest, both from a echanistic standpoint and also because there has been uch recent interest in hypofractionated prostate radiotherpy (20, 21). Akimoto et al. (22) report in this issue on late ectal bleeding after hypofractionated radiotherapy of the rostate, in which they delivered 69 Gy in 3 Gy fractions, sing three-dimensional conformal radiotherapy (3D-CRT) ithout rectal blocking or explicit dose–volume histogram DVH) based criteria. Akimoto et al. (22) report a late adiation Therapy Oncology Group (RTOG) Grade 2 comlication rate of 25% (mean follow-up, 31 months), virtully identical to that reported by the M.D. Anderson Cancer enter (5) using a 3D-CRT dose of 78 Gy delivered in onventional 2 Gy fractions. Akimoto et al. (22) report also, s have others (2, 23, 24), that diabetes is a highly signifiant predictor of late rectal sequelae. As well as being of interest in their own right, these new ypofractionation data allow, for the first time, a quantitaive estimate of the / ratio for late rectal bleeding, quanifying how rectal bleeding risks would be expected to hange with changes in fractionation. This is possible be-