sIMRT in daily routine - cfTBI.*

Abstract

In 1983 our department started to perform total body irradiation (TBI) in a special Imanner. To realize a homogeneous dose distribution within the entire body we used individual hemibody compensators to deliver 12 Gy within 6 fractions, excluding parts of the lungs, which received 11 Gy accomplished by an integrated lung block. Taking into consi-deration the geometrical settings and possibilities, radiobiological sights and the comfort of the patient we decided for a bilateral-opposing field technique. For application of 12 Gy and 11 Gy for the lung respectively, it takes an overall treatment time of about 25 min per fraction (beam-on time; positioning of patient and compensator; verification). The mean actual dose rate (= 12 cGy/min) is mainly set by the primary dose rate of the treatment unit, the focal-spot-midplane-distance and the lateral diameter of the patient. This early technique was called compensated fractionated total body irradiation (crTBI) or nowadays, in a more fashionable term, sIMRT (static intensity modulated radiotherapy). The fluence matrix is calculated on the basis of a series of CT-scans, geometrical and beam data, and subsequently transferred to an automatically working SD-cutting and milling machine. For compensating of missing tissue and density imhomogeneities an appropriate material is used. Several QA-tests are done before treating the patient. By changing the compensating material this sIMRT-system is also applicable to standard IMRT, based on inverse planning, but with increased spatial and dosimetrical resolution because of non-MLC technique.