Room: Exhibit Hall | Forum 1
Purpose: Applying radiation treatments to skin cancers of the head and neck region is a difficult process, with many centers using different approaches to treat complex geometries while sparing normal tissues. This study compares the dosimetric benefits of several techniques available at our institution when applied to lesions on the scalp.
Methods: CT planning images were acquired on an anthropomorphic Solid Water head phantom. A PTV was drawn on the superior scalp spanning roughly 10 cm wide by 10 cm long by 1 cm deep. Brain and optic structures were contoured. Treatment plans were generated using en face electron, 3D-CRT, VMAT, and Ir-192 HDR techniques. External beam methods used a 5mm bolus, while HDR used a multichannel Freiburg flap applicator. Plan doses were normalized so 95% of PTV volume received 100% of prescription dose. For comparison, doses are expressed as percent of prescription.
Results: PTV dose gradients for electrons, 3D, VMAT, and HDR techniques were 87-116%, 91-110%, 92-108%, and 80-228% respectively. Optic max doses for external beam techniques were <1%, while for HDR it was 12%. Brain D0.1cc values for electrons, 3D, VMAT and HDR were 100%, 102%, 50%, and 91%, and D10cc values were 82%, 100%, 13%, and 79%.
Conclusion: For the same coverage, the VMAT technique has by far the lowest brain dose. 3D-CRT treats large volumes of normal tissue to the full dose. Electrons have a slightly higher PTV gradient but slightly less brain dose. HDR has less brain volume dose than other non-VMAT techniques, but more optic dose.