A CT-AIDED PC-BASED PHYSICAL TREATMENT PLANNING OF TBI - A METHOD FORDOSE CALCULATION

Background and purpose: As for conventional radiotherapy, one of the b asic requirements in Total Body Irradiation (TBI) is to know accuratel y the dose delivered to the entire body. Both the dosimetry and the tr eatment planning need to be improved. Physical, technical and dosimetr ical aspects of TBI have been widely discussed in the literature. Howe ver, to our knowledge, no planning systems specifically designed for T BI are commercially available. This article describes a CT-aided PC-ba sed planning system (TBI-Plansys) and its dose calculation algorithm, which applies scatter and inhomogeneity corrections, developed for the TBI technique currently in use at our centre (AP/PA irradiation with patient positioned on his side). Material and method: A description of the material and method followed in the dosimetrical procedure is inc luded as it constitutes the basis of the proposed dose calculation alg orithm (more than 2D). A Windows programming environment has been used to develop the software. Results: TBI-Plansys uses patient CT data an d indicates absolute and relative dose distributions along midline (at reference points), the transversal axis at the specification point an d on transverse sections. The system also calculates the appropriate t hicknesses of bolus and shielding to modify undesired dose distributio ns. TBI-Plansys has been checked against two other well-established sy stems (beam-zone method and our in vivo semiconductor probe-based syst em): The checks showed good accuracy with dose differences less than 1 % and 3% for homogeneous and inhomogeneous tissues, respectively. Conc lusions: CT calculations by TBI-Plansys allow us to detect undesired d istributions which may go unnoticed by calculations at only some speci fic points. The system has shown clear advantages for routine clinical use as it generates more detailed and accurate information than manua l calculations and diminishes the time requirements. (C) 1997, Elsevie r Science Ireland Ltd.