Scanning electron microscopy and transmission electron microscopy of the ciliated cells of the trachea of the rabbit treated with misonidazole alone and in combination with ionizing radiation

Late radiation response of the canine trachea with change in dose per fraction

Seventy-two dogs were given 36 to 74 Gy to the trachea in either 2, 3, or 4 Gy per fraction. Tracheal sections were histologically and morphometrically evaluated 6 months after irradiation to determine the relative percentage of goblet cells, submucosal glands, connective tissue and blood vessels. The percent of each tissue component was plotted against total dose, regression lines calculated and isoeffective doses obtained for construction of isoeffect curves. Probit analysis for probability of surface ulceration also was done. Another group of 32 dogs received either 36, 44, or 52 Gy in 4 Gy fractions and tracheas were similarly analyzed at 1, 3, and 12 months after irradiation. Goblet cells and submucosal glands decreased with increasing total dose in each of the dose per fraction groups while connective tissue increased. Lower doses per fraction had more shallow dose response curves and higher total doses were required to produce an isoeffect. The alpha/beta ratios for tissues at 6 months after irradiation were 3.5 Gy for decrease in goblet cells, 4.7 Gy for probability for surface ulceration, 4.5 Gy for decrease in submucosal glands and 1.8 Gy for increase in connective tissue. Goblet cells and submucosal gland numbers decreased within 1 month and remained significantly decreased at higher doses at 12 months. Although there was no dose response for vasculature volume at 6 months, significant perivascular and intimal fibrosis was observed. This study revealed significant damage to the trachea at high total doses and large doses per fraction. The relatively low alpha/beta ratios obtained indicates that these adverse effects are late effects. Significant sparing of the adverse late effects was present at lower doses per fraction. These results indicate that coarser fractionation schemes that include the trachea in the treatment volume could be potentially dangerous.

Reaction of the vascular system in the trachea of the rabbit exposed to fractionated irradiation with and without the addition of misonidazole

As the radiation field used in the radiation therapy of malignancies in the thoracic cavity often exposes the trachea to ionizing irradiation, it is important to ascertain the effects of radiation on this tissue either as a single therapy or in combination with radiosensitizers. In the study reported here the vascular area in the subepithelial layer of the trachea has been calculated in 160 rabbits treated in four ways: (1) 10 rabbits received no treatment and served as controls; (2) 50 rabbits were given 100 mg misonidazole daily on consecutive days, with the individual total dose ranging from 100 to 1000 mg; (3) 50 rabbits were treated with misonidazole in the same way, but were also exposed to radiation (2 Gy/F) at 15-30 min later; (4) 50 rabbits received only fractionated radiation (2 Gy/F). The total radiation dose in the irradiated animals ranged from 2 to 20 Gy. In the treated groups, an oedema was observed in both the ciliary cell layer and in the subepithelial area. In the group given only irradiation, this oedema was dose-dependent, but no such dose-dependency was observed in the two groups treated with misonidazole. The vascular area in the groups treated with misonidazole was significantly increased as compared with the group given only irradiation and the control group; this was valid both with and without correction for the oedema. There was a significant correlation between the oedema and the vascular area in the groups treated with misonidazole, which was not found in the group irradiated without the drug.