Ionization Chambers

TRADEMARKS - Validity of Dosimetry Data

The terms Roos® and Markus® are registered trademarks of PTW-Freiburg and PTW-New York. These chambers have been manufactured by PTW-Freiburg for many years under the PTW type numbers 34001 and 23343. Dosimetry data published in scientific papers and various dosimetry protocols refer to chambers manufactured by PTW-Freiburg. Published data may not be valid for chambers manufactured by other companies, even if they are sold as "Roos" or "Markus" type chambers. Since Roos and Markus type chambers manufactured by PTW-Freiburg are available via different channels, buyers should carefully check whether they are purchasing an original Roos® or Markus® or an imitation for which no dosimetry data are available.

Roos® Chamber, 0.35 cm³		Type 34001
		The Roos electron chamber, developed in cooperation with Dr. Roos, PTB-Braunschweig (National Laboratory of Germany), is used as a reference electron chamber. It is recommended by the IAEA for high precision electron dosimetry in radiation therapy. The chamber has a 4 mm wide guard ring to exclude any perturbation effect even at low electron energies. The polarity effect is negligible (< 0.5 % at 10 MeV).

The energy response is only influenced by the stopping power ratios. The chamber is waterproof for absolute dose and depth dose measurements in a water phantom. The acrylic entrance window has a thickness of 1 mm. The nominal useful energy range is from 2 MeV to 45 MeV. A calibration certificate with a Co-60 calibration factor given in absorbed dose to water is included. Air density correction is required for each measurement. A radioactive check device with adapter is available as an option. The chamber cable length is 1.08 m

See also the note on Validity of Dosimetry Data.

Features:

Precision plane-parallel reference chamber for absolute dosimetry of high-energy electron radiation
Vented sensitive volume of 0.35 cm³
Perturbation-free design and minimal polarity effect
Suitable for use in water and in solid state phantoms

Markus® Chamber, 0.055 cm³		Type 23343
		The Markus chamber is the well-known electron chamber with widespread use throughout the world. Developed by Prof. Markus at Göttingen University, Germany, it was the first high-performance ionization chamber for precise dose measurements of high-energy electron beams in radiation therapy. Its small sensitive volume and its waterproof construction make this chamber suitable for dose distribution measurements in a water phantom.

It also can be used in solid state phantoms. The nominal useful electron energy range is from 2 MeV to 45 MeV. The membrane material is polyethylene of 0.03 mm thickness. The guard ring borders the measuring volume. The Markus chamber comes with a protective acrylic cover of 0.87 mm thickness (1 mm water equivalence) for use in water. A calibration certificate with a Co-60 calibration factor given in absorbed dose to water is included. Air density correction is required for each measurement. A radioactive check device is available as an option. The chamber cable length is 1.05 m.

See also the note on Validity of Dosimetry Data.

Features:

Plane-parallel chamber for high-energy electron measurements in water and solid state phantoms
Vented sensitive volume of 0.055 cm³
Commonly used electron chamber in the world
Very thin entrance window for use in solid state phantoms
The chamber is waterproof when used with protective cap

Advanced Markus® Chamber, 0.02 cm³		Type 34045
		The Advanced Markus chamber, developed in cooperation with Prof. Rosenow, Göttingen University, Germany, is the newest development of an electron chamber, combining advantages of both Roos and Markus chamber types. Since the outer shape is identical to the Markus chamber, all existing Markus chamber phantom plates and adapters can be used with the Advanced Markus chamber.

The small sensitive volume makes the chamber ideal for dose distribution measurements in a water phantom, giving a good spatial resolution. An improved design of the guard ring reduces the influence of scattered radiation from the housing and makes it possible to perform absolute electron dosimetry without perturbation effects. The chamber features a flat energy response within the nominal useful range from 4 MeV to 45 MeV. The membrane material is polyethylene of 0.03 mm thickness. The Advanced Markus chamber comes with a protective acrylic cover of 0.87 mm thickness (1 mm water equivalence) for use in water. A calibration certificate with a Co-60 calibration factor given in absorbed dose to water is included. Air density correction is required for each measurement. A radioactive check device is available as an option. The chamber cable length is 1.05 m.

Features (also see Markus chamber):

Plane-parallel chamber for relative and absolute dosimetry of high-energy electrons in water and solid state phantoms
Vented sensitive volume of 0.02 cm³
Same dimensions as the Markus chamber
Very thin entrance window
The chamber is waterproof when used with protective cap

Type 30011 with graphite wall and graphite electrode is used for therapy dosimetry, where a completely graphite-built chamber is required. The nominal useful energy range is from 140 keV to 50 MeV.

Type 30012 is used for therapy dosimetry, where a chamber with graphite wall and Al electrode is required. The nominal useful energy range is from 60 keV to 50 MeV.

Type 30013 is the waterproof standard chamber for absolute photon and electron dosimetry. The nominal useful energy range is from 30 keV to 50 MeV. This chamber type is of rugged construction, since the wall material is graphite with a protective acrylic cover and the electrode is made of aluminum.

The guard rings of all chamber types border the measuring volume. An acrylic build-up cap for in-air measurement in Co-60 beams is included (chambers 30010/11/12), as well as a calibration certificate.

Features:

Thimble chambers for measuring high-energy photon and electron radiation in air (type 30013 in water) or in phantom material
Vented sensitive volumes of 0.6 cm³
Flat energy response
A variety of different versions is available
Type 30013 is waterproof

PinPoint® Chambers, 0.015 cm³, 0.03cm³		Type 31006, 31009, 31014, 31015, 31016
		The waterproof PinPoint chambers have been specially designed for relative beam profile measurements in a motorized water phantom for characterization of LINAC radiation fields where superior spatial resolution is desired. The PinPoint chambers are ideally suited for this purpose with their inner diameters of only 2 mm (models 31006/31014) and 2.9 mm (models 31009/31015).

The chamber models 31006/31009 are used for the evaluation of stereotactic and IMRT photon beams, while the chamber models 31014/31015 can also be used for analyses of larger photon and electron fields. The chamber model 31016 shows a flat angular response, since the measuring volume is approximately spherical. When calibrated against a PTW Farmer chamber, the PinPoint chambers can be used for depth dose and absolute dose measurements. The sensitive volume is vented. The wall material is graphite with a protective acrylic cover. The chambers are fully guarded up to the measuring volume. The nominal energy ranges are Co-60 up to 50 MV photons and 6 MeV to 50 MeV electrons. The chambers have a short stem for mounting and a flexible connection cable. They can be supplied with different connector types.

Features:

Vented sensitive volumes of 0.015 cm³ and 0.03 cm³
Suitable for dose scanning in radiotherapy beams with a superior spatial resolution
Suitable for use in water

The wall material is graphite with a protective acrylic cover. The guard ring borders the measuring volume. An acrylic build-up cap for in-air measurement in Co-60 beams is included with each chamber, as well as a calibration certificate for calibration in absorbed dose to water or in air kerma. Air density correction is required for each measurement, and a radioactive check device is available as an option. Both chambers are shaped cylindrically with an inner diameter of 5.5 mm; they differ only in the length of the measuring volume. The 0.125 cm³ chamber is ideal for 3D dosimetry in a water phantom, since the measuring volume is approximately spherical resulting in a flat angular response over an angle of ± 160° and a uniform spatial resolution along all three axes of a water phantom.

Features:

Waterproof thimble chambers for measuring high-energy photon and electron radiation in air, water and phantom material
Vented sensitive volumes of 0.125 cm³ and 0.3 cm³
Flat energy response within a wide energy range

Sealed Ionization Chambers		Type 23322, 23323
		The flexible 0.1 cm³ chambers are to be used in environments with varying temperature without the necessity of air density correction. The sensitive volume is sealed to prevent entry of the surrounding air according to IEC 60731. Therefore, the chambers are ideal for in-vivo measurements during gynecological afterloading therapy.

Chamber type 23322 is used with a catheter for measurements in the bladder, whereas chamber type 23323 is designed for measurements in the rectum, using a protective sleeve. The chambers are to be used with a radioactive check device, which is available as an option. The nominal useful energy range is from 140 keV to 50 MeV. Calibration is usually conducted at 280 kV X-rays and Cs-137. Ir-192 calibration, for example for patient dosimetry during afterloading treatment, can be obtained by interpolation. The chambers are equipped with a flexible stem. The outer diameter of the chamber type 23322 is 5.5 mm, and the diameter of chamber type 23323 is 7 mm. The chambers are supplied with a flexible cable of 1.5 m length. Different connector types are available. A calibration certificate is included with each chamber.

Features:

Waterproof and flexible therapy chambers with measuring volume of 0.1 cm³ sealed against the surrounding air
Can be used for intracavitary in-vivo measurements (in conjunction with an UNIDOS dosemeter), suitable for use in water
Comply with safety standard IEC 60601-2-9 for patient contact

See also the product section In-Vivo Dosimetry

Rigid Stem Chambers 0.3 cm³ and 1 cm³		Type 30016, 30015
		The rigid stem chambers are designed as reference chambers for absolute dosimetry to be used in radiation therapy or by secondary standard dosimetry laboratories (SSDL). The chambers have been type tested by PTB-Braunschweig, the German National Laboratory. They have very small variations of response with radiation quality from low X-ray energies up to high-energy photon and electron radiation.

The nominal useful energy range is from 30 keV to 50 MeV. Both chambers are shaped cylindrically (thimble chambers). The wall material is graphite with a protective acrylic cover. The electrodes are made of graphite-coated aluminum. The guard rings border the measuring volume. Both chambers are constructed with a long stem of approx. 25 cm length for easy mounting in the radiation beam. An acrylic build-up cap for in-air measurement in Co-60 beams is included with each chamber, as well as a calibration certificate for calibration in absorbed dose to water or in air kerma. Air density correction is required for each measurement. A radioactive check device is available as an option.

Features:

Thimble chambers for measuring high-energy photon and electron radiation in air and in phantom material
Suitable as reference chambers for use in solid phantoms
Vented sensitive volumes of 0.3 cm³ and 1 cm³
Very flat energy response within a wide range

The usual calibration of both chambers is done at 15 kV to 70 kV. The chambers have a very flat energy response in the range from 10 kV to 100 kV. The 0.0053 cm³ soft X-ray chamber type 34013 has an extremely small sensitive volume and makes it possible to measure therapeutic X-ray beams with very small field sizes or with steep fluence gradients. The calibration is typically done at 15 to 50 kV. The energy response within this range is ± 2 %. The membrane material is polyethylene of 0.03 mm thickness. The guard ring borders the measuring volume. A calibration certificate is included. Air density correction is required for each measurement. A radioactive check device is available as an option.

Features:

Plane-parallel chambers for measuring therapeutic X-rays in air and solid state phantoms
Vented sensitive volumes of 0.0053 cm³ , 0.02 cm³ and 0.20 cm³
Very thin flat entrance windows for dose measurements of low energy X-ray beams
Protective cap available

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Farmer® Chamber, 0.6 cm³		Type 30010, 30011, 30012, 30013
		The 0.6 cm³ PTW Farmer chambers are designed for absolute photon and electron dosimetry with therapy dosemeters. Type 30010 is the standard chamber. The wall material is graphite with a protective acrylic cover, and the electrode is made of Al. The nominal useful energy range is from 30 keV to 50 MeV.

Semiflex Chambers 0.125 cm³ and 0.3 cm³		Type 31010, 31013
		The semiflex chambers are designed for therapy dosimetry, mainly for dose distribution measurements in motorized water phantoms. They have a short stem for mounting and a flexible connection cable. The nominal useful energy range is from 30 keV to 50 MeV photons.

Soft X-Ray Chambers 0.0053 cm³, 0.02 cm³, 0.20 cm³		Type 34013, 23342, 23344
		The 0.02 cm³ soft X-ray chamber type 23342 is the standard ionization chamber for dose measurements in superficial radiation therapy. The 0.20 cm³ chamber type 23344 with its bigger sensitive volume is used for similar pur-poses, where a higher response is required.