Effect of radiation fraction size on local control rates for early glottic carcinoma. A model analysis for in vivo tumor growth and radio-response parameters.
BACKGROUND
Two recent studies have suggested that the probability of local control for early glottic carcinoma (stages T1 and T2) following radiation therapy is lower when daily fractions of 1.8 Gy are given instead of 2.0 Gy when the total dose is kept constant at approximately 66 Gy.


METHODS
We reviewed our experience with a total of 42 patients with T1, N0, M0 squamous cell carcinoma of the glottic larynx who were treated with radiation alone during the period 1979 to 1989. All patients received conventional fractionation radiation therapy (one treatment per day, 5 days per week). Eight patients received 2.0 Gy per fraction for an average total dose of 64.8 Gy, and 34 patients received 1.8 Gy per fraction for an average total dose of 66.7 Gy. We also calculated overall survival statistics. Combining the clinical data from our series and those of patients from other series (171 total patients), we analyzed the tumor response curve and doubling time for early glottic carcinoma by using a time-dependent, linear quadratic equation model. The analysis is valid for the typical range of radioresponsiveness for most tumors in healthy tissue.


RESULTS
Using statistical z analysis, we noted a significant difference in the local control rates at 5 years, with better local control in the group that received 2.0 Gy per fraction (100% vs 70%). Our results for the calculated doubling time and tumor response curves correspond with experimental values for in vitro squamous cell carcinoma systems.


CONCLUSIONS
It appears from the literature and from our data that the control rates for T1, N0, M0 glottic carcinoma may be significantly improved by using 2.0 Gy per fraction dose vs 1.8 Gy per fraction dose. Our analysis has provided a model of in vivo tumor response of early glottic carcinomas based on reported local control rates using these two different treatment regimens.
Department of Otolaryngology-Head and Neck Surgery, University of Washington Medical Center, Seattle.
E J
EJ
Ricciardelli
E A
EA
Weymuller
W J
WJ
Koh
M
M
Austin-Seymour
M G
MG
DeSautel
G E
GE
Laramore
D002294:Carcinoma, Squamous Cell / Q000401:mortality / Q000473:pathology* / Q000532:radiotherapy*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005500:Follow-Up Studies; D005931:Glottis; D006801:Humans; D007822:Laryngeal Neoplasms / Q000401:mortality / Q000473:pathology* / Q000532:radiotherapy*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D011836:Radiation Tolerance; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D015996:Survival Rate; D013997:Time Factors