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I wish to describe an extremely simple method for accurately spacing and centering the tube head of the Profexray skin therapy machine. Although the apparatus which I have devised is not available commercially, it is easily constructed at a cost of less than $1. The device is used with the detachable narrow treatment cone of 15 cm. focus-skin distance, supplied with the machine, and enables one to treat an open field at any chosen longer distance. For illustration, I shall choose a focus-skin distance of 20 cm.
The device consists of a cylindrical block of wood measuring 5 cm. longer than the cone and of such diameter that it just fits inside the cone. A circular piece of tin is nailed to its upper end, serving as a flange to prevent the cylinder from dropping through the cone (Figure 1).
1, cylindrical block of wood with circular piece of tin
SNYDER W. SIMPLE DISTANCE-MEASURING AND CENTERING DEVICE FOR X-RAY THERAPY MACHINE. AMA Arch Derm Syphilol. 1954;69(3):374. doi:10.1001/archderm.1954.01540150120016
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