Analysis of late effects data using dose-response models: application to human skin telangiectasia data

Postoperative brachytherapy and electron beam irradiation for keloids: A single institution retrospective analysis

The aim of the present study was to perform a retrospective analysis of the control rate and toxicity of postoperative brachytherapy and electron beam irradiation for keloids. A retrospective review was performed of 116 keloid patients who underwent postoperative brachytherapy and electron beam irradiation between January 1, 2002 and June 30, 2012. Several different radiotherapy techniques and fractionation schedules were performed in the analysis, including high-dose rate (HDR) irradiation with 192Ir at 8 Gy/1 fraction (F)+9 Gy/3F or 20 Gy/4F; HDR brachytherapy with 60Co at 20 Gy/4F or 18 Gy/6F; or external beam electron therapy at 26 Gy/13F or 30 Gy/15F. The endpoints of the study were analysis of the control rate and toxicity. The median observation period was 46.5 months (range, 10.0-120.0 months) for all patients. In total, 18 of the 116 patients relapsed, and 16.7 months (range, 10.0-30.0 months) was the median time to recurrence for these patients. The control rates for the patients who received hypofractionation (>2 Gy per fraction) and conventional fraction (2 Gy per fraction) were 88.5 and 76.3%, respectively (P=0.043). The control rates for the patients whose calculated biological effective doses (BED) were >30 Gy and <30 Gy were 89.7 and 79.3%, respectively (P=0.104). There were no grade 2 or higher adverse effects based on the Common Terminology Criteria for Adverse Events v3.0 in the late phase. No evidence was identified for a link between radiotherapy and the subsequent occurrence of cancer. The results of the present study indicate that hypofractionated radiotherapy played an important role as an adjuvant therapy following surgical excision of keloids. A BED of >30 Gy appears to be sufficient. No definitive evidence was found for an association between radiotherapy and the occurrence of cancer during the follow-up, however, more cases and longer follow-up periods are required.

A radiobiological analysis of multicenter data for postoperative keloid radiotherapy

PURPOSE

To identify factors significantly affecting recurrence rates after postoperative external beam radiotherapy (XRT) of keloids, and to delineate any radiation dose response and effects of radiation dose per fraction.

METHODS AND MATERIALS

A comprehensive literature review was performed to compile a database of 2,515 resected keloids (36.9% earlobe). Postoperative XRT was 45- to 100-kV X-rays in 27.0% or 120- to 250-kV X-rays in 11.1%, Co-60 in 1.9%, Sr-90 in 4.7%, 1.5- to 9-MeV electrons in 26.5%, and no XRT in 28.8%. In the 1,791 irradiated patients, the median radiation parameters were as follows: total dose, 15 Gy (range, 6-30 Gy); dose per fraction, 5.0 Gy (range, 2-15 Gy); fractions, 3 (range, 1-10); and time, 7 days (range, 0-33 days).

RESULTS

Multivariate stepwise logistic regression correlated decreased keloid recurrence with earlobe location (p = 1.98E-10; odds ratio, 0.34), biologically effective dose (p = 1.01E-27), and treatment with electron beam or Co-60 vs. other techniques (p = 0.0014; odds ratio, 0.72). Different radiobiological models calculated values of α/β = 1.12 to 2.86 (mean, 2.08) and time (repopulation) correction factors for biologically effective dose from 0.98 to 2.13 Gy per day (mean, 1.34) starting 10 days after surgery. Different models (with α/β = 2.08) predicted that doses needed for 90% and 95% control with 3 fractions of postoperative electron beam were 16.0 to 16.2 Gy and 18.3 to 19.2 Gy, respectively, in less than 10 days for earlobe keloids and 21.5 to 22.2 Gy and 23.4 to 24.8 Gy, respectively, in less than 10 days for other sites.

CONCLUSIONS

Postoperative keloid radiotherapy requires moderately high doses and optimal technique to be effective. The relatively low α/β ratio indicates that radiotherapy with a limited number of fractions and high doses per fraction is the best strategy.

Fractionated irradiation and late changes in rat parotid gland: effects on the number of acinar cells, potassium efflux, and amylase secretion

Irradiation of head- and neck cancer commonly results in oral dryness and discomfort for the patients due to salivary gland damage. The exact mechanisms behind the inherent radiosensitivity of salivary glands remain to be elucidated. In the present study, we used different in vitro secretory models and quantitative morphological characterization of rat parotid gland following fractionated unilateral irradiation to one gland on a 5-day fraction schedule (Monday-Friday) with 6 MV photons (total dose 30, 35, 40 and 45 Gy) or a two-fractions regimens in 5 days (Monday and Friday) with total dose of 24 and 32 Gy. The contralateral shielded gland served as control, and parallel analyses of irradiated and control glands were performed 180 days following the last irradiation treatment. The relative noradrenaline stimulated electrolyte secretion (86rubidium tracer for potassium) was decreased in the irradiated compared with control glands. The noradrenaline-stimulated exocytotic amylase release was not significantly affected by irradiation, but the gland content of amylase was decreased dose-dependently. The quantitative morphological analysis revealed a dose-dependent decline in the number of acinar cells, whereas the other parenchymal cells (intercalated, striated- and excretory duct cells) were unaffected by the irradiation compared with control glands.