Underprediction of human skin erythema at low doses per fraction by the linear quadratic model.
OBJECTIVE
The erythematous response of human skin to radiotherapy has proven useful for testing the predictions of the linear quadratic (LQ) model in terms of fractionation sensitivity and repair half time. No formal investigation of the response of human skin to doses less than 2 Gy per fraction has occurred. This study aims to test the validity of the LQ model for human skin at doses ranging from 0.4 to 5.2 Gy per fraction.


METHODS
Complete erythema reaction profiles were obtained using reflectance spectrophotometry in two patient populations: 65 patients treated palliatively with 5, 10, 12 and 20 daily treatment fractions (varying thicknesses of bolus, various body sites) and 52 patients undergoing prostatic irradiation for localised carcinoma of the prostate (no bolus, 30-32 fractions).


CONCLUSIONS
Gender, age, site and prior sun exposure influence pre- and post-treatment erythema values independently of dose administered. Out-of-field effects were also noted. The linear quadratic model significantly underpredicted peak erythema values at doses less than 1.5 Gy per fraction. This suggests that either the conventional linear quadratic model does not apply for low doses per fraction in human skin or that erythema is not exclusively initiated by radiation damage to the basal layer. The data are potentially explained by an induced repair model.
Hamilton
C S
CS
Radiation Oncology Department, Newcastle Mater Misericordiae Hospital, NSW, Australia.
Denham
J W
JW
O'Brien
M
M
Ostwald
P
P
Kron
T
T
Wright
S
S
Drr
W
W
D000368:Aged; D004307:Dose-Response Relationship, Radiation; D004890:Erythema / Q000209:etiology*; D005260:Female; D018859:Hair Follicle / Q000528:radiation effects; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D010166:Palliative Care; D011471:Prostatic Neoplasms / Q000188:drug therapy; D011836:Radiation Tolerance; D011855:Radiodermatitis / Q000175:diagnosis / Q000453:epidemiology* / Q000209:etiology; D011879:Radiotherapy Dosage; D011882:Radiotherapy, High-Energy / Q000009:adverse effects*; D012307:Risk Factors; D012867:Skin / Q000528:radiation effects*; D013053:Spectrophotometry / Q000379:methods