title: Effects of ROI Placement on PET-Based Assessment of Tumor Response to Therapy.
abstract: Purpose. Quantitative PET response assessment during therapy requires regions of interest (ROI). Commonly, a fixed-size ROI is placed at the maximum uptake point in the pretreatment study. For intratreatment, the ROI is placed either at the maximum uptake point (ROIpeak) or at the same location as the pretreatment ROI (ROIsame). We have evaluated the effects of the ROI placement on response assessment. Methods. PET scans of 15 head and neck cancer patients were used to evaluate the effects of the two ROI methods on response assessment. Results. The average intratreatment ROIpeak uptake was 13.4% higher than the ROIsame uptake (range -14% to 38%). The average relative change in ROIpeak uptake was 7.9% lower than ROIsame uptake (range -5% to 36%), resulting in ambiguous tumour classification in 19% of the tumours. Conclusion. Quantitative PET response assessment using a fixed-size ROI is sensitive the ROI placement. The difference between ROIpeak and ROIsame could be substantial resulting in ambiguous response assessment. Although the fixed-size ROI is simple to implement, it is also prone to the limitations and should be used with caution. Clinical trial data are necessary to establish reliable thresholds for fixed-size ROI techniques and to evaluate their efficacy for response assessment.
authors.affiliation: Department of Medical Biophysics, University of Toronto, Ontario Cancer Institute, Princess Margaret Hospital, 610 University Avenue, Room 7-411, Toronto, ON, Canada M5G 2M9 ; Department of Medical Physics, Odette Cancer Centre, Sunnybrook Health Sciences Center, 2075 Bayview Avenue, Room TG-217, Toronto, ON, Canada M4N 3M5.
authors.forename: Mike
authors.initials: M
authors.lastname: Sattarivand
authors.forename: Curtis
authors.initials: C
authors.lastname: Caldwell
authors.forename: Ian
authors.initials: I
authors.lastname: Poon
authors.forename: Hany
authors.initials: H
authors.lastname: Soliman
authors.forename: Katherine
authors.initials: K
authors.lastname: Mah