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Clinical application of in vivo treatment delivery verification based on PET/CT imaging of positron activity induced at high energy photon therapy
Stockholm University, Faculty of Science, Department of Physics. Karolinska Institutet, Sweden.
Stockholm University, Faculty of Science, Department of Physics. Karolinska Institutet, Sweden.
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2013 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 58, no 16, 5541-5553 p.Article in journal (Refereed) Published
Abstract [en]

The purpose of this study was to investigate in vivo verification of radiation treatment with high energy photon beams using PET/CT to image the induced positron activity. The measurements of the positron activation induced in a preoperative rectal cancer patient and a prostate cancer patient following 50 MV photon treatments are presented. A total dose of 5 and 8 Gy, respectively, were delivered to the tumors. Imaging was performed with a 64-slice PET/CT scanner for 30 min, starting 7 min after the end of the treatment. The CT volume from the PET/CT and the treatment planning CT were coregistered by matching anatomical reference points in the patient. The treatment delivery was imaged in vivo based on the distribution of the induced positron emitters produced by photonuclear reactions in tissue mapped on to the associated dose distribution of the treatment plan. The results showed that spatial distribution of induced activity in both patients agreed well with the delivered beam portals of the treatment plans in the entrance subcutaneous fat regions but less so in blood and oxygen rich soft tissues. For the preoperative rectal cancer patient however, a 2 +/- (0.5) cm misalignment was observed in the cranial-caudal direction of the patient between the induced activity distribution and treatment plan, indicating a beam patient setup error. No misalignment of this kind was seen in the prostate cancer patient. However, due to a fast patient setup error in the PET/CT scanner a slight mis-position of the patient in the PET/CT was observed in all three planes, resulting in a deformed activity distribution compared to the treatment plan. The present study indicates that the induced positron emitters by high energy photon beams can be measured quite accurately using PET imaging of subcutaneous fat to allow portal verification of the delivered treatment beams. Measurement of the induced activity in the patient 7 min after receiving 5 Gy involved count rates which were about 20 times lower than that of a patient undergoing standard F-18-FDG treatment. When using a combination of short lived nuclides such as O-15 (half-life: 2 min) and C-11 (half-life: 20 min) with low activity it is not optimal to use clinical reconstruction protocols. Thus, it might be desirable to further optimize reconstruction parameters as well as to address hardware improvements in realizing in vivo treatment verification with PET/CT in the future. A significant improvement with regard to O-15 imaging could also be expected by having the PET/CT unit located close to the radiation treatment room.

Place, publisher, year, edition, pages
2013. Vol. 58, no 16, 5541-5553 p.
National Category
Radiology, Nuclear Medicine and Medical Imaging Biomedical Laboratory Science/Technology
Identifiers
URN: urn:nbn:se:su:diva-93559DOI: 10.1088/0031-9155/58/16/5541ISI: 000322775300015OAI: oai:DiVA.org:su-93559DiVA: diva2:647571
Note

AuthorCount:9;

Available from: 2013-09-11 Created: 2013-09-10 Last updated: 2017-10-11Bibliographically approved
In thesis
1. Verification of high energy photon therapy based on PET/CT imaging of photonuclear reactions
Open this publication in new window or tab >>Verification of high energy photon therapy based on PET/CT imaging of photonuclear reactions
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

For classical and intensity modulated radiation therapy of deep-seated tumors, high-energy photons are the optimal radiation modality from an integral dose point of view. By using narrow scanned beams the treatment outcome can be improved substantially by delivering biologically optimized intensity modulated distributions often with sharp dose gradients. This requires using photons with energies well above 15 MV enabling verification of the treatment delivery in vivo by PET/CT imaging in a manner not previously possible. This new technique is based on the production of positron emitting radionuclides when the incoming high-energy photons interact through photonuclear reactions with the body tissues. The produced radionuclides, commonly 11C, 15O and 13N can then be monitored by PET and the distribution of activated nuclei show exactly where the radiation has penetrated the patient. In the subcutaneous fat, present in all humans, a high induced activity produces a perfect visualization of the location and even the intensity modulation of the incident beams. The reason for this is the high carbon content in combination with a low biological perfusion in fat tissues. Errors in the patient positioning such as setup errors or misplacement of the beams will thus show up in the PET images as a deviation from the actual radiation treatment plan. Interestingly, the imaged activity distribution from the subcutaneous fat also visualizes how the dose delivery can be deformed when the patient is erroneously positioned on the treatment couch as seen on the cover figure. Furthermore, the different half-lives of the produced radionuclides (20 min, 2 min, and 10 min, for 11C, 15O and 13N, respectively) allows for analysis of the dynamic behavior of tissue activity with the possibility of retrieving information such as tissue composition, biological and physical half-lives. The present thesis shows that considerable clinical information regarding the treatment delivery with high-energy photon beams can be obtained using PET/CT imaging. Although the study is based on the use of 50 MV photons the method may apply for beams with energies > 20 MV at higher doses.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2012. 49 p.
Keyword
Photonuclear reactions, PET/CT treatment verification, High-energy photon therapy
National Category
Natural Sciences
Research subject
Medical Radiation Physics
Identifiers
urn:nbn:se:su:diva-72385 (URN)978-91-7447-461-9 (ISBN)
Public defence
2012-03-09, föreläsningssalen, Radiumhemmet, Karolinska universitetssjukhuset, Solna, 10:00 (English)
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Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Submitted. Paper: Manuscript.

Available from: 2012-02-16 Created: 2012-02-09 Last updated: 2017-10-11Bibliographically approved

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