Comparison of radiography- and computed tomography-based treatment planning in cervix cancer in brachytherapy with specific attention to some qualityassurance aspects

Introduction: A modern approach in treatment planning for cervix carcinoma is based on a series of computed tomography (CT) sections and 3D dose compu tation. When these techniques were not yet available, dose evaluation was b ased on orthogonal radiographs. The CT based planning provides information on target and organ volumes and dose-volume histograms. The radiography bas ed planning provides only dimensions and doses at selected points. The aim of the presented study is to correlate the information obtained with the tw o approaches for high dose-rate (HDR) brachytherapy of cervix carcinoma. Methods: For the study 28 patients with 35 applications receiving HDR treat ment with Ir-192 were investigated The planning system PLATO (Nucletron) wa s used. The different aspects of available data, results and inaccuracies r egarding quality assurance were looked at. Results: From the CT based planning, the volume, location and dose-volume h istograms were calculated for the CTV, rectum and bladder. From the radiogr aphy-based planning, the dose to point A (prescription), point B, rectum an d bladder ICRU reference points [14], points related to the bony structures could be evaluated as well as volumes receiving different dose levels. The se two sets of information were compared and following mean Values derived. For a dose prescription of 7 Gy at point A, as an average, 83% (44 cm(3)) of the clinical target volume (CTV) receives at least 7 Gy. The mean dose a t the rectum ICRU reference point is 4.3 Gy, and 12% (9 cm(3)) of the rectu m is encompassed by the 4.3 Gy isodose. The mean dose at the bladder ICRU r eference point is 5.8 Gy, and 8% (16 cm(3)) of the bladder is encompassed b y the 5.8 Gy isodose. The maximum dose to the rectum is 1.5 times higher th an the dose at the ICRU reference point, and for the bladder 1.4 times high er. Uncertainties caused by the reconstruction of the applicator and mergin g of isodoses could be evaluated. Discussion: The subdivision of different approaches and the transfer from p oint doses to Volumes in treatment planning is possible and practical for t he treatment of cervix carcinoma in brachytherapy. (C) 2001 Elsevier Scienc e Ireland Ltd. All rights reserved.