An indexed rotational immobilization system was developed for supine total body irradiation (TBI). Treatment plans had multi-isocentric volumetric modulated arc therapy (VMAT) beams to the upper body and parallelopposed fields to the lower body, with a 12 Gy prescription dose to > 90% of the body and mean lung dose ∼8 Gy. In the end-to-end test, point dose measurements had < 10% error. Compared to conventional TBI, the VMAT-based TBI technique increased the mean dose to the body by ∼1.0-1.5 Gy and decreased the mean dose to the lung by ∼1.0-1.5 Gy. Overall treatment time was ∼1.5 h, similar to conventional TBI. 2.2. IRIS-VMAT-TBI treatment workflow During simulation, the IRIS was aligned and anchored to the CT couch. The patient was immobilized in a supine position in a Vac-Lok

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Compared with adults, the number of children requiring radiotherapy each year is very small (of 3000 new patients treated annually at the Bristol Radiotherapy and Oncology Centre, 50 are children) but the treatment of a child may make greater demands on time and resources than an adult. There are important differences between adults and children that must be considered by the radiotherapist. The greatest of these lies in the child's potential for growth, development, reproduction, and longevity. Radiation induced tumours rarely occur earlier than 10 years from treatment: therefore children cured of cancer have ahead of them many years of life, carrying a steadily increasing risk of a second tumour as age advances. The late effects of radiotherapy in children have been well described by Shalet and others. ' Although nearly all childhood cancers are radiosensitive, radiotherapy is used sparingly in children because of these late effects. The dose required for cure is similar to that needed in adult tumours but it is frequently given in smaller fractions over a longer period in the hope of reducing late damage. Other differences relate to the child's size at the time of treatment as this can lead to practical problems of geometrical accuracy due to small field size.