Dosimetric verification of helical tomotherapy for total scalp irradiation

Total scalp irradiation is a treatment technique used for a variety of supercial malignancies.Helical tomotherapy is an effective technique used for total scalp irradiation. Recent publishedwork has shown the TomoTherapy planning system to overestimate the supercial dose. In thisstudy, the supercial doses for a helical tomotherapy total scalp irradiation have been measured onan anthropomorphic phantom using radiochromic and radiographic lm as well as a new skindosimeter, the MOSkin. The supercial dose was found to be accurately calculated by the Tomo-Therapy planning system. This is in contrast to recent reports, probably due to a combination of thesmaller dose grid resolution used in planning and this particular treatment primarily consisting ofbeamlets tangential to the scalp. The supercial dose was found to increase from 33.6 to 41.2 Gyand 36.0 to 42.0 Gy over the rst 2 mm depth in the phantom in selected regions of the PTV,measured with radiochromic lm. The prescription dose was 40 Gy. The supercial dose was at theprescription dose or higher in some regions due to the bolus effect of the thermoplastic head maskand the head rest used to aid treatment setup. It is suggested that to achieve the prescription dose atthe surface 2 mm depth bolus or a custom thermoplastic helmet is use