Always One Step Ahead

Compared to other detectors, PTW ion chambers offer significant advantages for use in step & shoot as well as rotational IMRT:

• Superior directional detector response:
  
  Ion chambers are generally known to show a negligible angular dependence compared to diodes. The unique cubic design of PTW ion chambers comes close to the ideal spherical geometry, minimizing angular dependence of the detector's response (Fig. 1). OCTAVIUS systems, therefore, do not require any numerical corrections of the measured data to be applied as a function of the gantry angle. By contrast, silicon diode arrays are known to exhibit a significant angular dependence, especially if they are partially shielded in order to provide buildup or to avoid over-response at low photon energies. The inherent problem of diodes, which is their large angular dependence¹, cannot be solved with a cylindrical array design as off-axis diodes on the cylindrical array are still hit at considerable angles, many even from the back (Fig. 1).

• Higher field coverage - better detection of hot spots:
  
  In IMRT QA, field coverage is of greater importance than detector size. With its unique cubic detector and geometrically uniform matrix design, the OCTAVIUS Detector 729 provides a significantly larger field coverage compared to other detectors, increasing the chance to measure dose at steep gradients or at hot spots (Fig. 2). Detector arrays with diodes or cylindrical ion chambers cannot provide this maximum of information.

• Unrivaled accuracy & stability:
  
  Ion chambers are known for their excellent stability and low energy, field size, dose rate or dose per pulse dependency. OCTAVIUS systems come factory-calibrated at ⁶⁰Co. They require no frequent calibration or other sophisticated maintenance to ensure long-term accuracy and reproducibility.

• The Gold Standard:
  
  Ion 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.

¹ Paul A Jursinic, Ben E Nelms; A 2-D diode array and analysis software for verification of intensity modulated radiation therapy delivery, Med. Phys. 30 (5), May 2003