A Pelvic Phantom for Modeling Internal Organ Motions

Kovács, Péter; Sebestyén, Zsolt; Farkas, Róbert; Bellyei, Szabolcs; Szigeti, András; Liposits, Gábor; Hideghéty, Katalin; Dérczy, Katalin; Mangel, László

doi:10.1016/j.meddos.2010.04.002

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Volume 36, Issue 3 , Pages 250-254, Autumn 2011

A Pelvic Phantom for Modeling Internal Organ Motions

Péter Kovács, M.Sc.
- Institute of Oncotherapy, University of Pécs, Pécs, Hungary
- Reprint requests to: Péter Kovács, M.Sc., Institute of Oncotherapy, University of Pécs, Édesanyák útja 17, H-7624, Pécs, Hungary
Zsolt Sebestyén, M.Sc.
- Institute of Oncotherapy, University of Pécs, Pécs, Hungary
Róbert Farkas, M.D.
- Institute of Oncotherapy, University of Pécs, Pécs, Hungary
Szabolcs Bellyei, M.D., Ph.D.
- Institute of Oncotherapy, University of Pécs, Pécs, Hungary
András Szigeti, M.D., Ph.D.
- Institute of Oncotherapy, University of Pécs, Pécs, Hungary
Gábor Liposits, M.D.
- Institute of Oncotherapy, University of Pécs, Pécs, Hungary
Katalin Hideghéty, M.D., Ph.D.
- Oncotherapy Clinic, University of Szeged, Szeged, Hungary
Katalin Dérczy, M.D.
- Department of Radiology, University of Pécs, Pécs, Hungary
László Mangel, M.D., Ph.D.
- Institute of Oncotherapy, University of Pécs, Pécs, Hungary

Received 5 October 2009; accepted 19 April 2010. published online 21 June 2010.

Abstract

A pelvic phantom was developed for use in testing image-guided radiation therapy (IGRT) and adaptive applications in radiation therapy (ART) with simulating the anterior-posterior internal organ motions during prostate radiotherapy. Measurements could be done with an ionization chamber (IC) in the simulated prostate. The rectum was simulated by air-equivalent material (AEM). The volume superior to the IC placement was considered as the bladder. The extension of AEM volume could be varied. The vertical position of the IC placement could be shifted by ±1 cm to simulate the prostate motion parallel to the changes in bladder volume. The reality of the simulation was inspected. Three-millimeter-slice-increment computed tomography (CT) scans were taken for irradiation planning. The structure set was adapted to the phantom from a treated patient. Planning target volume was delineated according to the RTOG 0126 study. IMRT and 3D conformal radiation therapy (3D-CRT) plans were made. Prostate motion and rectum volume changes were simulated in the phantom. IC displacement was corrected by phantom shifting. The delivered dose was measured with IC in 7 cases using intensity-modulated radiation therapy (IMRT) and 3D-CRT fractions, and single square-shaped beams: anteroposterior (AP), posteroanterior (PA), and lateral (LAT). Variations from the calculated doses were slightly below 1% at IMRT and around 1% at 3D-CRT; below 4.5% at square AP beam; up to 9% at square PA beam; and around 0.5% at square LAT beam. Other authors have already shown that by using planning systems and ultrasonic and cone beam CT guidance, correction of organ motions in a real patient during prostate cancer IGRT does not have a significant dosimetric effect. The inspection of our phantom—as described here—ended with similar results. Our team suggested that our model is sufficiently realistic and can be used for IGRT and ART testing.

Key Words: Pelvic phantom, Conformal radiotherapy, IMRT, IGRT