A technique for cranial-spinal irradiation

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Abstract
While carefully applied alternative methods yield adequate results, this technique has 2 advantages over others currently in widespread use. Methods which involve shifting the level of abutting ports over the cervical spine introduce a volume of high dose inhomogeneity due to beam divergence. This is practically eliminated by the use of spoilers with overlapping fields. Techniques involving gap calculations require a gap calculations require a high degree of reproducible precision with each daily setup, and an error of several millimeters on the skin can produce marked variations in the depth dose. A 4 mm error in the gap on the skin can produce, depending on beam energy and collimation, up to a 100% variation in dose at depth. Owing to the gradual attentuation induced by the spoilers, this same error in set-up results in a 10% dose variation at depth with this method. These advantages make this technique an attractive alternative to other popular solutions to this junctional problem, and are worth the initial extra effort required in the construction of the spoilers in treating human medulloblastomas.

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