Total body irradiation-an attachment free sweeping beam technique

Abstract

Introduction: A sweeping beam technique for total body irradiation in standard treatment rooms and for standard linear accelerators (linacs) is introduced, which does not require any accessory attached to the linac. Lung shielding is facilitated to reduce the risk of pulmonary toxicity. Additionally, the applicability of a commercial radiotherapy planning system (RTPS) is examined. Material and Methods: The patient is positioned on a low couch on the floor, the longitudinal axis of the body in the rotational plane of the linac. Eight arc fields and five additional fixed beams are applied to the patient in supine and prone position respectively. The dose distributions were measured in a solid water phantom and in an Alderson phantom. Diode detectors were calibrated for in-vivo dosimetry. The RTPS Oncentra was employed for calculations of the dose distribution. Results: For the cranial 120 cm the longitudinal dose profile in a slab phantom measured with ionization chamber varies between 94 and 107 % of the prescription dose. These values were confirmed by film measurements and RTPS calculations. The transmittance of the lung shields has been determined as a function of the thickness of the absorber material. Measurements in an Alderson phantom and in-vivo dosimetry of the first patients match the calculated dose. Discussion and conclusion: A treatment technique with clinically good dose distributions has been introduced, which can be applied with each standard linac and in standard treatment rooms. Dose calculations were performed with a commercial RTPS and should enable individual dose optimization.