Dosimetric impact of computed tomography calibration on a commercial treatment planning system for external radiation therapy

The Hounsfield units into density conversion for a commercial treatment pla nning system (TPS) is discussed. The impact of an average calibration table provided by the manufacturer on computed doses was investigated when a cus tomer calibration could not be included in the TPS. The maximum error deter mined on the computed monitor units per Gy was found to be about 2%, being below 1% on average. The relative importance of the parameters used for CT image acquisition is also discussed. The applied voltage was the most relev ant parameter leading to errors in the reconstructed Hounsfield numbers of about 300 units for high densities. (C) 1998 Elsevier Science ireland Ltd. All rights reserved.