Comparison of CT on Rails With Electronic Portal Imaging for Positioning of Prostate Cancer Patients With Implanted Fiducial Markers

Owen, Rebecca; Kron, Tomas; Foroudi, Farshad; Milner, Alvin; Cox, Jennifer; Duchesne, Gillian; Cleeve, Laurence; Zhu, Li; Cramb, Jim; Sparks, Laura; Laferlita, Marcus

doi:10.1016/j.ijrobp.2009.01.054

« Previous Next »International Journal of Radiation Oncology * Biology * Physics
Volume 74, Issue 3 , Pages 906-912, 1 July 2009

Comparison of CT on Rails With Electronic Portal Imaging for Positioning of Prostate Cancer Patients With Implanted Fiducial Markers

Rebecca Owen, B. App. Sc.
- Radiation Therapy Services, Peter MacCallum Cancer Centre, Victoria, Australia
- School of Medical Radiation Sciences, University of Sydney, New South Wales, Australia
- Reprint requests to: Ms Rebecca Owen, Radiation Therapy Services, Peter MacCallum Cancer Centre, Locked Bag 1, A'Beckett Street, Victoria, 8006 Australia. Tel: +61 3 9656 1111; Fax: +61 3 9656 1490
Tomas Kron, Ph.D.
- Department of Physical Sciences, Peter MacCallum Cancer Centre, Victoria, Australia
Farshad Foroudi, M.B.B.S., F.R.A.N.Z.C.R.
- Division of Radiation Oncology, Peter MacCallum Cancer Centre, Victoria, Australia
Alvin Milner, Ph.D.
- Centre for Biostatistics and Clinical Trials, Peter MacCallum Cancer Centre, Victoria, Australia
Jennifer Cox, Ph.D.
- School of Medical Radiation Sciences, University of Sydney, New South Wales, Australia
Gillian Duchesne, M.D., F.R.A.N.Z.C.R.
- Division of Radiation Oncology, Peter MacCallum Cancer Centre, Victoria, Australia
Laurence Cleeve, M.B.B.S., F.R.A.C.S.
- Division of Surgical Oncology, Peter MacCallum Cancer Centre, Victoria, Australia
Li Zhu, Ph.D.
- Department of Physical Sciences, Peter MacCallum Cancer Centre, Victoria, Australia
Jim Cramb, M.Sc.
- Department of Physical Sciences, Peter MacCallum Cancer Centre, Victoria, Australia
Laura Sparks, B. Sc. (Hons).
- Radiation Therapy Services, Peter MacCallum Cancer Centre, Victoria, Australia
Marcus Laferlita, B. App. Sc.
- Radiation Therapy Services, Peter MacCallum Cancer Centre, Victoria, Australia

Received 12 August 2008; received in revised form 23 January 2009; accepted 29 January 2009.

Purpose

The objective of this investigation was to measure the agreement between in-room computed tomography (CT) on rails and electronic portal image (EPI) radiography.

Methods and Materials

Agreement between the location of the center of gravity (COG) of fiducial markers (FMs) on CT and EPI images was determined in phantom studies and a patient cohort. A secondary analysis between the center of volume (COV) of the prostate on CT and the COG of FMs on CT and EPI was performed. Agreement was defined as the 95% probability of a difference of ≤3.0 mm between images. Systematic and random errors from CT and EPI are reported.

Results

From 8 patients, 254 CT and EPI pairs were analyzed. FMs were localized to within 3 mm on CT and EPI images 96.9% of the time in the left-right (LR) plane, 85.8% superior-inferior (SI), and 89% anterior-posterior (AP). The differences between the COV on CT and the COG on EPI were not within 3 mm in any plane: 87.8% (LR), 64.2% (SI), and 70.9% (AP). The systematic error varied from 1.2 to 2.9 mm (SI) and 1.8–2.9 mm (AP) between the COG on EPI and COV on CT.

Conclusions

Considerable differences between in-room CT and EPI exist. The phantom measurements showed slice thickness affected the accuracy of localization in the SI plane, and couch sag that occurs at the CT on rails gantry could not be totally corrected for in the AP plane. Other confounding factors are the action of rotating the couch and associated time lag between image acquisitions (prostate motion), EPI image quality, and outlining uncertainties.

In-room CT, EPI, FM, IGRT