FAQ

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Why is OCTAVIUS 4D a "4D" system?

OCTAVIUS 4D measures the dose in a volume and is therefore a true 3D measurement system. The dose is measured as a function of time or gantry angle, which is usually called the 4th dimension. As a 4D system, OCTAVIUS 4D makes it possible to analyze dose planes for any arbitrary angle segment, e.g., for the different control points of your delivery.

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Can OCTAVIUS 4D be used for all all treatment and delivery techniques?

OCTAVIUS 4D is an independent 4D dosimetry system, specially designed for the verification of standard IMRT, IGRT, IMAT, VMAT, RapidArc and SRS/SBRT treatment plans. The current version does not support TomoTherapy or Cyberknife treatment deliveries. The same applies to non-coplanar measurements where the patient is not aligned to the rotation axis of the gantry. The best solution for these applications is OCTAVIUS II.

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Does OCTAVIUS 4D need a connection to the LINAC?

OCTAVIUS 4D is a true independent verification system which does not require trigger information from the LINAC for operation. Contrary to other 4D dosimetry systems, it operates independently and measures the dose without connection to the LINAC or TPS. 

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Does OCTAVIUS 4D need TPS data for measurement and dose calculation?

As a truly independent verification system, OCTAVIUS 4D measures the dose without connection to a TPS and without modifying or correcting TPS data. The OCTAVIUS 4D algorithm is based on PDD curves measured for four different field sizes for the accelerator and energy in use.

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Does OCTAVIUS 4D show any angular dependence?

OCTAVIUS 4D always measures in a plane perpendicular to the incident beam as it rotates the detector with the gantry, thus eliminating any angular dependence of the detector response (Fig. 1). Its unique rotating phantom offers perfect isotropic measurement geometry, with orthogonal incidence of the radiation beam on the detector surface.


Fig. 1: Detector always perpendicular to incident beam
Unlike other dosimetry systems where inclined beam vectors result in a varying angular response of the diodes (left, center), the OCTAVIUS detector always remains perpendicular to the beam, providing truly isotropic, angle-independent dose measurements.

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How many measurement points are acquired with OCTAVIUS 4D during a measurement?

OCTAVIUS 4D rotates synchronously with the gantry, measuring a dose plane for each gantry angle, thus covering the complete volume of the phantom. The maximum number of measurement points that can be achieved depends on the treatment plan and detector used. For a typical RapidArc plan with a single 360 rotation at a speed of 6 per second, OCTAVIUS 4D allows to acquire e.g. up to 800,000 measurement points when used in combination with the OCTAVIUS 1500 detector array as the OCTAVIUS detector performs up to five measurements per second for each of its 1405 detectors.

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Do I need to calibrate the system?

OCTAVIUS 4D comes with a detector-to-detector dose calibration. As the OCTAVIUS detector array uses long-term stable PTW ionization chambers, this calibration is not subject to changes upon time or absorbed dose. For absolute dose measurements, the OCTAVIUS detector can be cross-calibrated.

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Do I need special software for OCTAVIUS 4D?

OCTAVIUS 4D requires VeriSoft 5.0 (or higher), which is used for data acquisition and dose analysis for all OCTAVIUS systems. It is already included in the package or available as an upgrade.

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What base data must be collected for installing OCTAVIUS 4D?

OCTAVIUS 4D requires the import of PDD curves for four different field sizes for the accelerator and energy in use.

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What is the difference between OCTAVIUS II and OCTAVIUS 4D which are both suitable for rotational dosimetry?

OCTAVIUS II is a 2D dosimetry system for patient plan QA. It uses a stationary octagonal phantom which allows to measure the dose in one plane only and analyze it in a coronal or sagittal direction depending on the measurement setup.
OCTAVIUS 4D uses a cylindrical phantom which rotates synchronously with the gantry, always aligning the detector perpendicular to the beam and measuring the complete volume. It is a true 4D dosimetry system as it measures the dose as a function of time or gantry angle. As a 4D system, it allows to extract multiple planes in coronal, sagittal and transverse direction, thus providing much more information based upon the same measurement time. Dose planes can also be analyzed for any arbitrary angle segment, e.g. for the different control points of your delivery.