BERYLLIUM tube x-ray units capable of delivering very soft irradiation have come into wide clinical use during recent years. Although a considerable number of reports on the effects of very soft x-rays on various diseases affecting the skin are available, interpretation of papers published prior to 1945-1950 is difficult. Older so-called grenz-ray units were relatively crude pieces of apparatus, with tubes of uneven wall thickness and inadequate means of controlling voltage and amperage precisely. Moreover, the calibrations of output from these units were made by methods which, on the basis of more recent physical studies, may be regarded as highly inaccurate.
Great emphasis has been placed upon the relative safety of very soft irradiation. This emphasis is probably well justified in the case of x-rays generated at 6 or 8 kv.; in fact, if such rays are used in the treatment of skin having a thick layer of stratum
PILLSBURY DM, BLANK H, MADDEN DJ. LOW-VOLTAGE X-RAY THERAPY IN DISEASES OF THE SKIN. AMA Arch Derm Syphilol. 1954;70(1):16–48. doi:10.1001/archderm.1954.01540190018002