Maximar-100

The Maximar-100 is a radiation therapy device that was made by General Electric to deliver superficial x-rays.

Maximar 100 X-Ray Unit Superficial Therapy

The Maximar-100's x-ray source is the GE SRT-1,^[1] an x-ray tube specifically designed for use in the Maximar-100. This is a fixed-anode, reflection-type x-ray tube, whose name is composed of three parts: "SR" meaning self-rectified, "T" meaning therapeutic, and "1" indicating a 1-mm diameter nominal focal spot size. Its beryllium window produces a beam with very low inherent filtration but it is subject to beam non-uniformity due to heel effect.

The generator produces a voltage that is continuously adjustable between 30 and 100 kVp and a continuously adjustable current between 0 and 5 mA.^[2] An analog indicator and rheostat is provided allowing for feedback, so adjustments can be made to compensate for drift during treatment.

Maximar 100 X-Ray Unit Superficial Therapy - Cones

The unit uses a set of interchangeable aluminum filters of 0.25, 0.5, 1, 2, and 3 mm thickness which filter the beam's spectrum, but also substantially effects its intensity.^[3] Collimation is achieved using two sets of open ended circular applicators. The first are cylindrical and provide fields of 1, 1.5, 2, 3, 4, and 5 cm diameter at a 15 cm source-to-skin distance. The second are conical and provide fields of 5, 10, 15, and 20 cm diameter at a 30 cm source-to-skin distance.

The unit was first manufactured in 1953 and proved durable. It was rated for a 50% duty cycle,^[4] i.e. 4 hours of operation at full power, 100 kVp and 5 mA, in any 8 hour period. As of 2022, at least one unit had been in clinical service continually since 1953.^[5] Where this unit has been replaced by newer technology, it remains a clinical touchstone and basis for comparison.^[6]