Table of Contents
International Journal of Molecular Imaging
Volume 2013, Article ID 132804, 9 pages
Research Article

Effects of ROI Placement on PET-Based Assessment of Tumor Response to Therapy

1Department of Medical Biophysics, University of Toronto, Ontario Cancer Institute, Princess Margaret Hospital, 610 University Avenue, Room 7-411, Toronto, ON, Canada M5G 2M9
2Department of Medical Physics, Odette Cancer Centre, Sunnybrook Health Sciences Center, 2075 Bayview Avenue, Room TG-217, Toronto, ON, Canada M4N 3M5
3Department of Medical Imaging, Faculty of Medicine, University of Toronto, 263 McCaul Street, 4th Floor, Toronto, ON, Canada M5T 1W7
4Department of Radiation Oncology, University of Toronto, FitzGerald Building, 150 College Street, Room 106, Toronto, ON, Canada M5S 3S2
5Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Center, Toronto, ON, Canada M4N 3M5

Received 4 September 2012; Revised 15 January 2013; Accepted 7 February 2013

Academic Editor: Adriaan A. Lammertsma

Copyright © 2013 Mike Sattarivand et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


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.