Intensity Modulated Radiation Therapy (IMRT) is a complex treatment modality that requires pre-treatment patient-specific quality control (QC) in order to assess a correct treatment delivery. The aim of this work is to investigate pre-treatment patient-specific per-field QCs performed with an on-board EPID at the gantry angle of 0° and at the treatment ones, and to asses if measurements executed at 0° are able to guarantee a correct treatment.
Ten patients with prostate cancer were evaluated. Two “verification” plans were created for each patient in order to calculate the dose at the EPID surface: one with all fields positioned at 0° and one with all fields at the actual treatment angles.
EPID’s mechanical shifts due to gravity effects were always taken into account and corrected.
0 and no-0 plans were compared using a gamma-index method (3%, 3 mm). The gamma index was found dependent on gantry angles but the difference between 0 and no-0 samples was small (−0.3% mean value) and the criteria of acceptability of the gamma method was always satisfied for every field delivered at angles different from 0.
Therefore patient-specific pre-treatment QCs should be done at treatments angles, but, if periodical quality assurance is performed on dynamic MLC for different gantry angles, this requirement was shown not strictly mandatory and pre-treatment IMRTQC can be reasonably executed at 0° angles too.
To read this article in full you will need to make a payment
Purchase one-time access:Academic & Personal: 24 hour online accessCorporate R&D Professionals: 24 hour online access
One-time access price info
- For academic or personal research use, select 'Academic and Personal'
- For corporate R&D use, select 'Corporate R&D Professionals'
Subscribe:Subscribe to Physica Medica: European Journal of Medical Physics
Already a print subscriber? Claim online access
Already an online subscriber? Sign in
Register: Create an account
Institutional Access: Sign in to ScienceDirect
- Guidance document on delivery, treatment planning, and clinical implementation of IMRT: Report of the IMRT subcommittee of the AAPM radiation therapy committee.Med Phys. 2003; 30: 2089-2115
- ICRU Report 83: Prescribing, recording and reporting photon-beam Intensity-Modulated radiation therapy (IMRT).J ICRU. 2010; 10
- A literature review of electronic portal imaging for radiotherapy dosimetry.Radiother Oncol. 2008; 88: 289-309
- Pre-treatment verification of intensity modulated radiation therapy plans using a commercial electronic portal dosimetry system.Australasian Phys Eng Sci Med. 2010; 33: 51-57
- Monte Carlo simulation of portal dosimetry on a rectilinear voxel geometry: a variable gantry angle solution.Phys Med Biol. 2003; 48: N231-N238
- Correction for dose-response variations in a scanning liquid ion chamber EPID as a function of linac gantry angle.Phys Med Biol. 2004; 48: N93-N103
- On the sensitivity of patient-specific IMRT QA to MLC positioning errors.J Appl Clin Med Phys. 2009; 10: 120-128
- Verification of dose delivery for a prostate sIMRT treatment using a SLIC– EPID.Appl Radiat Isotopes. 2008; 66: 1930-1938
- Use of an amorphous silicon EPID for measuring MLC calibration at varying gantry angle.Phys Med Biol. 2008; 53: 473-485
- Quality assurance measurements of a-si epid performance.Med Dosim. 2004; 29: 11-17
- IMRT delivery performance with Varian multileaf collimator.Int J Radiat Oncol Biol Phys. 2008; 71: S85-S88
- The use of an aSi- based EPID for routine absolute dosimetric pre-treatment verification of dynamic IMRT fields.Radiother Oncol. 2004; 71: 223-234
- Physical and dosimetric aspects of a multileaf collimation system used in the dynamic mode for implementing intensity modulated radiotherapy.Med Phys. 1998; 25: 1919-1927
- Comprehensive quality assurance for the delivery of intensity modulated radiotherapy with a multileaf collimator used in the dynamic mode.Med Phys. 2001; 28: 2209-2219
- Consequences of leaf calibration errors on IMRT delivery.Phys Med Biol. 2007; 52: 1147-1156
- Portal imaging and portal dosimetry reference Guide.Varian Medical Systems, USA2008
- Dosimetric verification of 6 and 18 MV intensity modulated photon beams using a dedicated fluoroscopic electronic portal imaging device (EPID).Radiother Oncol. 2006; 81: 88-96
- Comparison between two different methods of portal dosimetry.Radiother Oncol. 2009; 92: S211
- A technique for the quantitative evaluation of dose distributions.Med Phys. 1998; 25: 656-661
- An analytical approach to acceptance criteria for quality assurance of intensity modulated radiotherapy.Radiother Oncol. 2011; 100: 453-455
Published online: January 27, 2012
Accepted: January 12, 2012
Received in revised form: January 8, 2012
Received: February 27, 2011
© 2012 Associazione Italiana di Fisica Medica. Published by Elsevier Inc. All rights reserved.