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Is long planar imaging time necessary for targeted radiotherapy treatment planning?

¹ Radiology, Johns Hopkins Medical Institutions, Baltimore, Maryland

1203

Objectives: Quantitatively estimating organ uptake and bio-kinetics is an essential part of targeted radionuclide therapy. This usually involves the use of whole body scans acquired at multiple time points using acquisition time chosen based more on image quality considerations rather than the minimum needed for precise quantitation. In previous studies at clinical count levels, we observed significantly larger effects from variations in anatomy and uptake than from statistical variations. This suggests that acquisition time could be reduced without increasing the variation of accuracy. To test this, we compared the accuracy and variation in accuracy of organ activity estimates obtained from planar scans at various count levels.

Methods: A simulated phantom population with clinically realistic variations in anatomy and biodistribution was used to model variability in a patient population. Planar projections were simulated using previously validated Monte Carlo simulation tools. We simulated noise corresponding to 1.5-30 minute whole body scans. The projections were processed using a previously-described quantitative planar (QPlanar) processing method based on the ML-EM algorithm which uses model-based compensation for image degrading effects. The acquisition times were compared in terms of mean and standard deviation over the population of errors in the organ activity estimates.

Results: There were no significant differences in mean or standard deviation of error over the ranges of scan times studied.

Conclusions: Reducing acquisition time by a factor of 20 may be acceptable for estimating whole organ dose in targeted radiation therapy treatment planning. This reduction is feasible because variations in accuracy from patient variability are larger than those from statistical noise.

This Article Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Google Scholar Articles by He, B. Articles by Frey, E. PubMed Articles by He, B. Articles by Frey, E.