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Objectives: This study compares tumour response assessment by automated CT volumetry and standard manual measurements regarding the impact on treatment decisions and patient outcome. Methods: 58 consecutive patients with 203 pulmonary metastases undergoing baseline and follow-up multirow detector CT (MDCT) under chemotherapy were assessed for response to chemotherapy. Tumour burden of pulmonary target lesions was quantified in three ways: (1) following response evaluation criteria in solid tumours (RECIST); (2) following the volume equivalents of RECIST (i.e. with a threshold of -65/ +73%); and (3) using calculated limits for stable disease (SD). For volumetry, calculated limits had been set at ±38% prior to the study by repeated quantification of nodules scanned twice. Results were compared using non-weighted k-values and were evaluated for their impact on treatment decisions and patient outcome. Results: In 15 (17%) of the 58 patients, the results of response assessment were inconsistent with 1 of the 3 methods, which would have had an impact on treatment decisions in 8 (13%). Patient outcome regarding therapy response could be verified in 5 (33%) of the 15 patients with inconsistent measurement results and was consistent with both RECIST and volumetry in 1, with calculated limits in 3 and with none in 1. Diagnosis as to the overall response was consistent with RECIST in six patients, with volumetry in six and with calculated limits in eight cases. There is an impact of different methods for therapy response assessment on treatment decisions. Conclusion: A reduction of threshold for SD to ±30-40% of volume change seems reasonable when using volumetry. [ABSTRACT FROM AUTHOR]