Correction to Kasibhatla et al. How much radiation is the chemotherapy worth in advanced head and neck cancer? (Int j radiat oncol biol phys 2007;68:1491-1495).
OBJECTIVE
To correct several elementary radiobiologic errors in the otherwise admirable article by Kasibhatla, Kirkpatrick, and Brizel (2007) on estimating the equivalent radiation effect of the concomitant chemotherapy in head-and-neck chemoradiotherapy.


METHODS
(1) Their equation was wrong because it omitted the lag or onset time of repopulation in tumors, Tk. Instead of zero days this should be 18-35 days. (2) Instead of a doubling time of 5 days, at most 3 days should be used for head-and-neck tumors. (3) Their slope "S" (the gamma-50 slope) for head-and-neck tumors should be 1.7, not 1.1. The same percentages of increased locoregional control as quoted by Kasibhatla et al. are used.


RESULTS
The average time-corrected biologically effective dose for the 16 schedules listed should be 72.4 instead of 63.1 Gy(10). The average gains in locoregional tumor control are the equivalent of 8.8 Gy(10), not 10.6 Gy(10) (p = 0.05).


CONCLUSIONS
The equivalent number of 2-Gy fractions of concomitant chemotherapy as used in the 16 listed schedules is 3.6 (95% confidence interval, 2.7-4.1), not 5 as claimed by Kasibhatla et al. The difference is statistically significant (p < 0.001).
Fowler
Jack F
JF
Department of Human Oncology and Medical Physics, University of Wisconsin, Madison, WI, USA. jackfowler@btinternet.con
D000465:Algorithms; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D049109:Cell Proliferation; D002470:Cell Survival; D003131:Combined Modality Therapy; D004307:Dose-Response Relationship, Radiation; D006258:Head and Neck Neoplasms / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy; D006801:Humans; D012062:Relative Biological Effectiveness; D012107:Research Design; D013997:Time Factors
D000970:Antineoplastic Agents