The most common radiation quality used for grenz rays is 10 kV; in the United States some dermatologists prefer 15 to 25 kV grenz rays.
The interval be tween treatments recommended by different authors varies from 1 to 3 weeks.
In our opinion, an interval of 1 week.is suitable, and four to six treatments are usually necessary. The areas of skin vary in their radiosensitivity, which must be taken into account. Palms, soles, and scalp are the least sensitive and 400 cGy for each treatment can be administered safely. The anogenital area is the most sensitive and thus the dose must be reduced to 50 to 200 cGy for each treatment.
Light-skinned and/or light-sensitive patients tolerate radiation less well and the dose must be reduced. Scales and hair absorb an important quantity of the dose (34) and in the case of thick hair, the dose must be doubled when treating the scalp. Scales must be removed before treatment by using a salicylic-acid ointment. The maximum cumulative dose for a certain area of skin should not exceed an arbitrary limit of 10,000cGy.
In situations where it seems advisable to go beyond this limit, the patient should be monitored closely and the treated area should be examined for malignant transformations every 10,000cGy. The only large-scale study of the carcinogenic effect of grenz-ray therapy (11) did not reveal any increased risk of cancer development in 481 patients who had received at least 10,000 cGy on the same body area.
In my opinion, palms, soles, and scalp tolerate grenz-ray therapy very well, and can be safely exposed to much more than 10,000 cGy of grenz rays in a lifetime.