We describe a novel code system, TRiP, dedicated to the planning of radiotherapy with energetic ions, in particular 12C. The software is designed to cooperate with three-dimensional active dose shaping devices like the GSI raster scan system. This unique beam delivery system allows us to select any combination from a list of 253 individual beam energies, 7 different beam spot sizes and 15 intensity levels. The software includes a beam model adapted to and verified for carbon ions. Inverse planning techniques are implemented in order to obtain a uniform target dose distribution from clinical input data, i.e. CT images and patient contours. This implies the automatic generation of intensity modulated fields of heavy ions with as many as 40000 raster points, where each point corresponds to a specific beam position, energy and particle fluence. This set of data is directly passed to the beam delivery and control system. The treatment planning code has been in clinical use since the start of the GSI pilot project in December 1997. Forty-eight patients have been successfully planned and treated.

Reliable treatment planning of highly conformal scanned ion beam therapy demands accurate tools for the determination and characterization of the individual pencil-like beams building up the integral dose delivery and related mixed radiation field. At present, clinically practicable inverse treatment planning systems (TPSs) can only rely on fast-performing analytical algorithms. However, the rapidly emerging though more computationally intensive Monte Carlo (MC) methods can be employed to complement analytical TPS, e.g., via accurate calculations of the input beam-model data, together with a considerable reduction of the measuring time. Here we present the work done for the application of the FLUKA MC code to support several aspects of scanned ion beam delivery and treatment planning at the Heidelberg Ion Beam Therapy Center (HIT). Emphasis is given to the generation of the accelerator library and of experimentally validated TPS input basic data which are now in clinical use for proton and carbon ion therapy. Additionally, MC dose calculations of planned treatments in water are shown to represent a valuable tool for supporting treatment plan verification in comparison to dosimetric measurements. This paper can thus provide useful information and guidelines for the start-up and clinical operation of forthcoming ion beam therapy facilities similar to HIT.

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