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Open Access Highly Accessed Original research

Dynamic PET/CT measurements of induced positron activity in a prostate cancer patient after 50-MV photon radiation therapy

Sara Janek Strååt1*, Hans Jacobsson2, Marilyn E Noz3, Björn Andreassen1, Ingemar Näslund4 and Cathrine Jonsson5

Author Affiliations

1 Department of Medical Radiation Physics, Karolinska Institutet and Stockholm University, Stockholm, PO Box 260, SE-171 76, Sweden

2 Department of Molecular Medicine and Surgery, Karolinska Institutet, Stockholm, SE-171 76, Sweden

3 Department of Radiology, School of Medicine, New York University, New York, NY, 10016, USA

4 Department of Oncology and Pathology, Karolinska Institutet, Stockholm, SE-171 76, Sweden

5 Department of Medical Physics, Section of Imaging Physics, Karolinska University Hospital, Stockholm, SE-171 76, Sweden

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EJNMMI Research 2013, 3:6  doi:10.1186/2191-219X-3-6

Published: 23 January 2013

Abstract

Background

The purpose of this work was to reveal the research interest value of positron emission tomography (PET) imaging in visualizing the induced tissue activity post high-energy photon radiation treatment. More specifically, the focus was on the possibility of retrieving data such as tissue composition and physical half-lives from dynamic PET acquisitions, as positron-emitting radionuclides such as 15O, 11C, and 13N are produced in vivo during radiation treatment with high-energy photons (>15 MeV). The type, amount, and distribution of induced positron-emitting radionuclides depend on the irradiated tissue cross section, the photon spectrum, and the possible perfusion-driven washout.

Methods

A 62-year-old man diagnosed with prostate cancer was referred for palliative radiation treatment of the pelvis minor. A total dose of 8 Gy was given using high-energy photon beams (50 MV) with a racetrack microtron, and 7 min after the end of irradiation, the patient was positioned in a PET/computed tomography (CT) camera, and a list-mode acquisition was performed for 30 min. Two volumes of interests (VOIs) were positioned on the dynamic PET/CT images, one in the urinary bladder and the other in the subcutaneous fat. Analysis of the measured relative count rate was performed in order to compute the tissue compositions and physical half-lives in the two regions.

Results

Dynamic analysis from the two VOIs showed that the decay constants of activated oxygen and carbon could be deduced. Calculation of tissue composition from analyzing the VOI containing subcutaneous fat only moderately agreed with that of the tabulated International Commission on Radiation Units & Measurements (ICRU) data of the adipose tissue. However, the same analysis for the bladder showed a good agreement with that of the tabulated ICRU data.

Conclusions

PET can be used in visualizing the induced activity post high-energy photon radiation treatment. Despite the very low count rate in this specific application, wherein 7 min after treatment was about 5% of that of a standard 18F-FDG PET scan, the distribution of activated tissue elements (15O and 11C) could be calculated from the dynamic PET data. One possible future application of this method could possibly be to measure and determine the tumor tissue composition in order to identify any hypoxic or necrotic region, which is information that can be used in the ongoing therapy planning process.

Trial registration

The official name of the trial committee of this study is ‘Regionala etikprövningsnämnden i Stockholm’ (FE 289, Stockholm, SE-17177, Sweden). The unique identifying number is 2011/1789-31/2.

Keywords:
High-energy photons; PET; Induced tissue activity; Photonuclear reactions; Radiation therapy; Treatment beam verification.