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Title: Evaluation of a diode array for QA measurements on a helical tomotherapy unit

Abstract

A helical tomotherapy system is used in our clinic to deliver intensity-modulated radiation therapy (IMRT) treatments. Since this machine is designed to deliver IMRT treatments, the traditional field flatness requirements are no longer applicable. This allows the unit to operate without a field flatness filter and consequently the 400 mm wide fan beam is highly inhomogeneous in intensity. The shape of this beam profile is mapped during machine commissioning and for quality assurance purposes the shape of the beam profile needs to be monitored. The use of a commercial diode array for quality assurance measurements is investigated. Central axis beam profiles were acquired at different depths using solid water built-up material. These profiles were compared with ion chamber scans taken in a water tank to test the accuracy of the diode array measurements. The sensitivity of the diode array to variations in the beam profile was checked. Over a seven week period, beam profiles were repeatedly measured. The observed variations are compared with those observed with an on-board beam profile monitor. The diode measurements were in agreement with the ion chamber scans. In the high dose, low gradient region the average ratio between the diode and ion chamber readings wasmore » 1.000{+-}0.005 ({+-}1 standard deviation). In the penumbra region the agreement was poorer but all diodes passed the distance to agreement (DTA) requirement of 2 mm. The trend in the beam profile variations that was measured with the diode array device was in agreement with the on-board monitor. While the calculated amount of variation differs between the devices, both were sensitive to subtle variations in the beam profile. The diode array is a valuable tool to quickly and accurately monitor the beam profile on a helical tomotherapy unit.« less

Authors:
; ; ; ; ; ; ; ;  [1];  [2]
  1. Department of Radiation Oncology, M.D. Anderson Cancer Center Orlando, Orlando, Florida (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20726906
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 32; Journal Issue: 11; Other Information: DOI: 10.1118/1.2089547; (c) 2005 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; ACCURACY; BEAM PROFILES; CALIBRATION STANDARDS; COMMISSIONING; COMPUTERIZED TOMOGRAPHY; IONIZATION CHAMBERS; QUALITY ASSURANCE; RADIATION DOSES; RADIOTHERAPY; SENSITIVITY

Citation Formats

Langen, K.M., Meeks, S.L., Poole, D.O., Wagner, T.H., Willoughby, T.R., Zeidan, O.A., Kupelian, P.A., Ruchala, K.J., Olivera, G.H., and TomoTherapy Inc., Madison, Wisconsin. Evaluation of a diode array for QA measurements on a helical tomotherapy unit. United States: N. p., 2005. Web. doi:10.1118/1.2089547.
Langen, K.M., Meeks, S.L., Poole, D.O., Wagner, T.H., Willoughby, T.R., Zeidan, O.A., Kupelian, P.A., Ruchala, K.J., Olivera, G.H., & TomoTherapy Inc., Madison, Wisconsin. Evaluation of a diode array for QA measurements on a helical tomotherapy unit. United States. doi:10.1118/1.2089547.
Langen, K.M., Meeks, S.L., Poole, D.O., Wagner, T.H., Willoughby, T.R., Zeidan, O.A., Kupelian, P.A., Ruchala, K.J., Olivera, G.H., and TomoTherapy Inc., Madison, Wisconsin. Tue . "Evaluation of a diode array for QA measurements on a helical tomotherapy unit". United States. doi:10.1118/1.2089547.
@article{osti_20726906,
title = {Evaluation of a diode array for QA measurements on a helical tomotherapy unit},
author = {Langen, K.M. and Meeks, S.L. and Poole, D.O. and Wagner, T.H. and Willoughby, T.R. and Zeidan, O.A. and Kupelian, P.A. and Ruchala, K.J. and Olivera, G.H. and TomoTherapy Inc., Madison, Wisconsin},
abstractNote = {A helical tomotherapy system is used in our clinic to deliver intensity-modulated radiation therapy (IMRT) treatments. Since this machine is designed to deliver IMRT treatments, the traditional field flatness requirements are no longer applicable. This allows the unit to operate without a field flatness filter and consequently the 400 mm wide fan beam is highly inhomogeneous in intensity. The shape of this beam profile is mapped during machine commissioning and for quality assurance purposes the shape of the beam profile needs to be monitored. The use of a commercial diode array for quality assurance measurements is investigated. Central axis beam profiles were acquired at different depths using solid water built-up material. These profiles were compared with ion chamber scans taken in a water tank to test the accuracy of the diode array measurements. The sensitivity of the diode array to variations in the beam profile was checked. Over a seven week period, beam profiles were repeatedly measured. The observed variations are compared with those observed with an on-board beam profile monitor. The diode measurements were in agreement with the ion chamber scans. In the high dose, low gradient region the average ratio between the diode and ion chamber readings was 1.000{+-}0.005 ({+-}1 standard deviation). In the penumbra region the agreement was poorer but all diodes passed the distance to agreement (DTA) requirement of 2 mm. The trend in the beam profile variations that was measured with the diode array device was in agreement with the on-board monitor. While the calculated amount of variation differs between the devices, both were sensitive to subtle variations in the beam profile. The diode array is a valuable tool to quickly and accurately monitor the beam profile on a helical tomotherapy unit.},
doi = {10.1118/1.2089547},
journal = {Medical Physics},
number = 11,
volume = 32,
place = {United States},
year = {Tue Nov 15 00:00:00 EST 2005},
month = {Tue Nov 15 00:00:00 EST 2005}
}