Why PTW ionization chambers are
the right choice for IMRT QA

  • The Gold Standard
    Ionization chambers are considered the gold standard and method of choice for accurate clinical dosimetry as specified in national and international dosimetry protocols, such as AAPM TG-51 or IAEA 398. They are known for their excellent stability and low energy, field size, dose rate or dose per pulse dependency. Their quality is guaranteed by performance standards [1].
  • Superior directional response
    OCTAVIUS systems use long-term stable ionization chambers as detectors which are known to show a significantly lower angular dependence compared to silicon diodes. As a consequence, they do not require any numerical corrections of the measured data as a function of the gantry angle.
    OCTAVIUS 4D always measures in a plane perpendicular to the incident beam as it rotates with the gantry, thus eliminating any angular dependence of the detectors (Fig. 1).
  • Measurements inside volume of interest
    The aim of IMRT plan verification is to precisely measure dose in regions that are characteristic for the target volume and the adjacent healthy tissue. Flat-panel detectors which are positioned in patient-like phantoms at a relevant depth measure a plane intersecting the clinically relevant volume. As it rotates with the gantry, OCTAVIUS 4D is the only system that verifies the dose inside the entire phantom volume, including the clinically relevant target volume around the isocenter (Fig. 2). 
  • Largest field coverage - better detection of hot spots
    In IMRT QA, field coverage is of greater importance than detector size. With their high detector density and unique detector layout, OCTAVIUS detectors offer the best field coverage of available arrays in the market, increasing the chance to measure dose at steep gradients or at hot spots (Fig. 3).
[1] Indra J Das et al; Accelerator beam data commissioning equipment and procedures: Report of the TG-106 of the Therapy Physics Committee of the AAPM, Med. Phys. 35 (9), 09/2009
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Fig.2: Always perpendicular to the beam
OCTAVIUS 4D (right) compared to other dosimetry systems (left, center) where inclined beam vectors result in a varying angular response of the diodes.
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Fig. 2: Always inside volume of interest
Simplified illustration showing measurement positions (blue) obtained with OCTAVIUS 4D (right) compared to other dosimetry systems which measure either outside the target volume in the low dose area (left) or far fewer measurement planes (center)
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Fig. 3: Impact of field coverage on hot spot detection
Simplified illustration showing maximum field coverage achieved by OCTAVIUS 1500 with a single measurement (Fig. 1) or two measurements (Fig. 2) compared to diode array of the same detector spacing (Fig. 3).

What Users Say

"My staff at Advanced Radiation Centers of New York relies on PTW for all of our QA and dosimetry needs. We prefer PTW ion chambers for our daily, monthly and annual Beam and Linac QA. The equipment is easy to set-up and the analysis software is comprehensive and reliable. The robust ion chambers nullify the detector radiation damage and energy dependence seen with diodes."

John Keane, MS
Advanced Radiation Centers
of New York
A Division of Integrated
Medical Professionals
Plainview, NY, USA