Semiconductor Detectors
IBA Dosimetry GmbH provides five types of semiconductor detectors for field analysis:
- RFD: Reference detector with positive polarity (1)
- EFD: Field detector for electrons (2)
- PFD: Field detector for photons (3)
- RIO: Reference detector with inverted output (grey, not pictured)
- RAZOR: Field detector for stereotactic beams (4)
These field detectors allow field measurements with high spatial resolution due to the small size of the
active semiconductor chip. All field detectors are based on the 3G-pSi semiconductor chip. An important benefit of the 3G-pSi chip is the dose rate independence.
Table 3.1. Semiconductor Detectors
| Type | Nominal sensitivity (nC / Gy) | Inner diameter [mm] | Active volume [mm³] |
| EFD / PFD | 100 | 2.0 | ~ 1.6 |
| RAZOR | 100 | 0.6 | ~ 0.05 |
| RFD / RIO | 100 | 2.5 | ~ 2.0 |
Field Detector for Electrons
The EFD detector should be used for measurements in electron fields, where it produces a signal proportional to the absorbed dose in water, without any need for corrections.
Field Detector for Photons
The PFD detector is specially designed for measurements in photon fields. The detector has a built-in
compensation for the energy dependence of Si.
When irradiated in the axial direction the photon field detector gives a uniform resolution. The detector type is recommended for use in photon fields larger than 10 x 10 cm.
Field Detector for Stereotactic Applications
The RAZOR detector is specially designed for measurements in photon fields, for field sizes less than 10 x 10 cm. The spatial resolution of this detector is only 0.6 mm; it is therefore the choice in small fields or sharp gradient regions. The detector can also be used in electron fields if the integration time is increased.
Reference Detector
The RFD and RIO detector is specially designed to achieve a stable reference signal in both photon and
electron beams. By detecting fluctuations in the beam, the inaccuracy of the relative measurement due to
varying accelerator output is reduced.
IMPORTANT NOTICE: REFERENCE DIODE
There are two types of reference diodes:
RFD, 3G-pSi reference detector (black colored) with normal polarity, TNC, can be used in combination with other detectors and the CCU.
RIO, 3G-pSi reference detector (grey colored) with inverted polarity, BNC (as a part of the LDA-99 SC /emXX equipment), can be used in combination with the LDA-99 SC only and will be connected directly to the emXX.
The Stealth Chamber is also designed as reference detector for small filed sizes up to 20 x 20 cm. Section
3.2.5 for details.
Ionization Chambers
Ionization chambers are recommended for absolute dosimetry and used in relative dosimetry for the
measurement of profiles and depth doses in photon and electron beams. For continuous scanning, they are usually used in pairs (one field chamber, one reference chamber).
The chambers are connected via chamber extension cables to the CCU. The CCU provides a bias voltage
supply, which is controlled by the myQA Accept software.
Each chamber is calibrated and delivered with an individual calibration certificate and waterproof without
any additional accessory.
More detailed specific information about the IBA chambers is provided within the dedicated Instructions for Use.
Compact Cylindrical Chambers (CC)
CC13
Table 3.2. Compact Chambers
| Type | Nominal sensitivity (nC/Gy) | Inner diameter [mm] | Active volume [cm³] |
| RAZOR Chamber | 0.3 | 2.0 | 0.01 |
| CC04 | 1.1 | 4.0 | 0.04 |
| Type | Nominal sensitivity (nC/Gy) | Inner diameter [mm] | Active volume [cm³] |
| CC13 | 3.8 | 6.0 | 0.13 |
Plane Parallel Chambers (PPC)
PPC40
Table 3.3. Plane Parallel Chambers
| Type | Nominal sensitivity (nC / Gy) | Inner diameter [mm] | Active volume [cm³] |
| PPC05 | 2 | 9.9 | 0.046 |
| PPC40 | 12 | 16.0 | 0.40 |
The plane parallel ionization chambers are intended for the following applications:
- PPC05: The conventional ionization chamber for electron dosimetry, used in water phantoms, solid
phantoms and in air (with build-up cap) - PPC40: Fast measurements and easy data evaluation for dose determination in electron and proton
beams
Farmer Type Chambers (FC)
FC65-P
Table 3.4. Farmer Type Chamber
| Type | Nominal sensitivity (nC / Gy) |
Inner diameter [mm] | Active volume [cm³] | Wall material |
| FC23-C | 7 | 6.2 | 0.23 | Shonka C 552 |
| FC65-G | 21 | 6.2 | 0.65 | Graphite |
| FC65-P | 21 | 6.2 | 0.65 | POM (Delrin) |
The Farmer type cylindrical ionization chambers are intended for absolute dosimetry in water phantoms,
solid phantoms and in air (with build-up cap). Due to the robust wall material, the FC65-P is especially
useful for all routine applications.
NACP Chamber
NACP chamber
Table 3.5. NACP chambers
| Nominal sensitivity [nC/Gy] | Active area [mm] | Active volume [cm³] |
| 2 | 10.0 | 0.16 |
The NACP chamber is a sealed plane-parallel ionization chamber built to the specifications of the Nordic
Association of Clinical Physicists (NACP). It is especially suited for measurements in low-energy electron beams.
The NACP chamber features a thin front window, which allows shallow measurements, a small cavity
minimizing field perturbation, low polarity effect and high stability of detector response.
Stealth Chamber
The Stealth Chamber is a large transmission ionization chamber intended to be used as reference chamber in relative dosimetry of photon and electron beams in radiotherapy for clinical use in water phantom scanning systems. It is used for PDD and profiles measurements in small fields. Since the perturbation due to the presence of the chamber in the field is minimal and the chamber can be considered invisible to the beam. It is available in round or square shapes respectively.
IMPORTANT NOTICE: STEALTH CHAMBER AS REFERENCE DETECTOR
The Stealth Chamber can only be used as reference detector for small fields up to a field size of 20 cm × 20 cm.
It can be used in combination with any suitable field detector.
Table 3.6. Stealth Chamber Detectors
| Type |
Nominal sensitivity [nC/Gy3] |
Active area [mm] | Active volume [cm³] | Transparent material |
| Square | 30 | 219 × 219 | 588 | Polycarbonate |
| Round | 30 | 65 (Active diameter: 91) | 114 | Polycarbonate |
Left: Square Stealth Chamber; Right: Round Stealth Chamber
With a dedicated holder, the Square Stealth Chamber can be mounted on the top of a water phantom. See the Stealth Chamber Instructions for Use for mounting instruction.
LDA-99 SC Linear Detector Array and emXX Electrometer
The LDA-99 SC consists of 99 semiconductor detectors, produced by IBA Dosimetry GmbH, arranged in a linear holder. The LDA-99 SC provides fast and reliable measurements in dynamic fields.
The detectors used in LDA-99 SC are energy compensated 3G-pSi detectors; do have excellent spatial
resolution and a well-defined depth of measurement, independent of energy.
The high spatial resolution permits even a very steep penumbra to be reconstructed by the measurement.
Hot spots are displayed as they are, and not smoothened out as when using larger detectors, like ionization chambers.
The LDA-99 SC is designed for profile measurements in water and in air. For in-air measurements, LDA-99
SC is fitted with a specially designed build-up cap and installed on a tabletop holder or an empty water phantom.
The LDA-99 SC is used in conjunction with a 99 + 1 channel electrometer, called emXX. For measurements
with the LDA-99 SC, the control unit CCU, and a reference detector with inverted output signal (RIO) are also required.
IMPORTANT NOTICE: REFERENCE DIODE
RIO, 3G-pSi reference detector with inverted polarity (grey colored), BNC (as a part of the LDA-99 SC / emXX equipment), can be used in combination with the LDA-99 SC only and will be connected directly to the emXX.
Additional informaiton, including interconnections for measurements with LDA-99 SC, can be found in the
LDA-99 SC Instructions for Use.
LDA-99 SC system