METHODS FOR TRANSFERRING PATIENT AND PLAN DATA BETWEEN RADIOTHERAPY TREATMENT PLANNING SYSTEMS

The effectiveness of conformal radiotherapy can ultimately only be ass essed by the use of clinical trials. As large multicentre clinical tri als become more widespread, methods of transferring patient and plan d ata between radiotherapy treatment planning systems become increasingl y important. In this paper, the general strategy for the transfer of d ata is discussed, and also illustrated with reference to two specific systems: TARGET 2 (GE Medical Systems) and VOXELPLAN (DKFZ-Heidelberg) . The transfer method involves using a computer program to translate t he data formats used by each of the two systems for CT scans, patient outlines, plan information and block descriptions. This paper does not address the question of transferring beam data between systems: beam data must first be entered separately into both machines. The physical concepts encountered when transferring plans are described, with spec ific reference to the two planning systems used. Differences in the st rategies used by the two planning systems for definition of irregular field shapes are compared. The dose calculations used by the two syste ms are also briefly evaluated. Isodoses produced by VOXELPLAN around a circular target volume are found to be up to 3 mm different in locati on to those produced by TARGET 2, owing to the use of a smooth field s hape contour as opposed to a stepped field shape which closely models the leaves of a multileaf collimator. In general, dose distributions g enerated by both systems are comparable, but some differences are foun d in the presence of large tissue inhomogeneities. It is concluded tha t the transfer of patient and plan data between two different treatmen t planning systems is feasible, provided that any differences in field shape definition methods or dose calculation methods between the two systems are understood.