The CNMC Model 206 dosimetry electrometer maintains the simplicity of classic electrometer styling while utilizing contemporary design and state-of-the-art electronics.  The Model 206 is simple to operate.  All controls are located on the front panel.  The nomenclature is clear and concise.  The value is displayed in easy-to-read 0.7-inch digits.  A tilt bail is provided for optional viewing angles.  The Model 206 has a broad range of operation and can accommodate any size of ion chamber.  The versatility of the Model 206 stems from its innovative modular design.  The amplifier feedback element is contained in an external module.  This module is removable and can be exchanged with any number of modules.  Each module changes the measurement features of the electrometer.  In this way, a single electrometer can be configured to satisfy a wide range of applications.  By pairing an ion chamber with a specific module, full calibration of all chambers on a single electrometer can be achieved.

The Model 206 is designed for long term reliability.  Leakage currents as low as 1fA are achieved by the selection of special components and the implementation of proprietary production techniques.  All feedback elements are extensively evaluated to insure long-term stability.  Standard "D" cell batteries provide both 1000 hours of continuous operation and around-the-clock power to the electrometer circuit.  The instrument chassis and case employ the simplicity of classic electrometer styling, yet are rugged enough to protect the delicate system within.  This combination of simplicity and versatility makes the Model 206 one of the most economical electrometers on the market today.

A standard 200nC feedback module with a triaxial BNC connector, optimized for beam calibrations with a 0.6cc Farmer-type ionization chamber, is supplied with each Model 206 electrometer.  It allows the Model 206 to provide readings of 00.01 to 199.99nC in high, 0.001 to 19.999nC in medium, and 0.0001 to 1.9999nC in low range, making it usable with chamber volumes 100 times smaller than 0.6cc for comparable exposures.  The standard module may be substituted with another module at no additional cost, or additional extra-cost feedback modules may be added to suit multiple applications.  The following table lists optional feedback modules.  Triaxial BNC input connector is standard. TNC is available on request.

The CNMC Model 10 Dosimeter / Electrometer offers accuracy, precision and repeatability combined with unparalleled economy.  It is designed for radiation measurements in both diagnostic radiology and radiation therapy and it meets the need for all QA constancy checks and most calibrations.

The Model 10 has a dual range and units are preset at the factory to suit the individual application.  The Model 10 is simple to operate, the control nomenclature is clear and concise, the values are displayed in easy-to-read 0.5 inch digits and a tilt bail is provided for optional viewing angles.  It features an internal static bias supply with half bias switch and operates on one easily obtainable 9-volt battery.

The combination of compact design, light weight and simplicity makes the Model 10 the most economical dosimeter/ electrometer on the market today, meaning the user only pays for those features necessary to meet the application requirements.

When combined with the Model 505A, a rugged ion chamber assembly, the Model 10 becomes an economical device for performing daily beam output constancy checks.

As such, it possesses significant advantages over single-piece devices: the electrometer part suffers no radiation damage, radiation values may be read from outside the treatment room and the electrometer itself can be diverted to other uses or simply kept on hand as a back-up electrometer.

The Model N23343 Markus^® plane-parallel ionization chamber is designed specifically for the dosimetry of electrons with energies above 100keV, according to the Bragg-Gray principle.  It is suitable for measurements in either solid or water phantoms.

The chamber consists of a cylindrical acrylic body whose measuring volume is flush to the surface to permit dose measurements at very small depths.  The entrance window is made of polyethylene (2.5mg/cm²) with a graphite conductive coating.  The ion collector is graphite-coated acrylic and is provided with a guard ring that rests at ground potential.  The low collector volume minimizes polarity effects and electrostatic charge.  The chamber is vented to the atmosphere and equilibrates through the aperture in the window ring.  The design provides for energy independence and high spatial resolution, and minimizes polarity and perturbation effects.

The Model N23343 includes a 0.87mm thick acrylic protective cap for use in a water phantom, a spacer ring for use in a solid phantom and an acrylic build-up disc.  For measurements in water phantoms, equilibration may be achieved by taking the protective cap off briefly just before the measurement is taken.

The Model N34045 Advanced Markus^® chamber is the latest development in electron chambers, with improved performance compared to the well-known Markus^® chamber.  The chamber features a flat energy response within the nominal useful range from 2MeV to 45MeV.

The Model N34045’s design is similar to the Markus^® chamber, having the same external dimensions.  This allows it to fit into existing solid phantom cavities made for the Markus^® chamber.  The internal dimensions are similar to the Markus^®, with the exception of an improved guard ring design and 1mm electrode spacing. The high degree of guarding greatly reduces the influence of scattered radiation from the housing and makes it possible to perform absolute electron dosimetry without perturbation effects.  The small sensitive volume makes the chamber ideal for dose distribution measurements in water phantoms, giving a good spatial resolution.  The entrance window material is polyethylene of 0.03mm thickness.

The Model N34045 comes with a protective acrylic cover, 0.87mm thick, for use in water.  The chamber is vented to the atmosphere, therefore density correction must be made for each measurement.  It is supplied with a 1m cable, choice of connectors and foam-padded case.

The Model PPC05 is the latest development of an electron chamber, with improved performance compared to the well-known Markus^® chamber.  The chamber features flat energy response within the nominal useful range from 2MeV to 45MeV.

The PPC05 design is similar to the Markus^® chamber, having the same external dimensions that allow it to fit into existing solid phantom cavities made for the Markus^® chamber.  Although the sensitive volume is the same, it is achieved with a 9.9mm diameter collector and 0.6mm electrode spacing.  The wide guard ring greatly reduces the influence of scattered radiation from the housing and makes it possible to perform absolute electron dosimetry with negligible perturbation and polarity effects.  The entrance window material is 1mm thick C552 Shonka air-equivalent conductive plastic.  The relatively thick window prevents sensitivity changes due to window distortion under water, as the chamber is watertight without the use of a protective cap.

The Model PPC05 is vented to the atmosphere, therefore density correction must be made for each measurement.  It is supplied with a 1m cable, choice of connectors, protective cap, build-up cap and spacer ring, plus a foam-padded case.

The Model A10 is a vented, waterproof, plane-parallel ionization chamber designed specifically for the dosimetry of electrons with energies above 100keV, according to the Bragg-Gray principle.

The A10 design is similar to the Markus^® chamber, having the same external dimensions that allow it to fit into existing solid phantom cavities made for the Markus^® chamber.  The collector diameter and electrode gap are the same as found in the Markus^®, therefore the collecting volume and calibration factor will be very similar.  A significant improvement was made in the width of the guard ring that greatly reduces perturbation and polarity effects.  The electrode materials are made of conductive plastics for electrical continuity, eliminating troublesome conductive coatings.

The A10 can be operated submerged in water with the waterproofing/calibration cover attached.  The chamber is supplied with your choice of connectors and has a handsome, padded wooden case.

This plane-parallel ionization chamber was developed for use as a reference chamber for electron dosimetry.  The Roos^® chamber has a wide guard ring to exclude any perturbation effect, even at low electron energies.  The polarity effect is also negligible (less than 0.5% at 10MeV between 0% and 5% half value depth).

The energy dependence of the Roos^® chamber is only influenced by the stopping power correction; a type-dependent correction is not necessary.  The chamber is watertight for use in water phantoms.  The measuring volume is vented to the atmosphere through the connecting cable sheath.  The entrance window of the Roos^® chamber is flush with the surface so that it can be used with solid phantoms.

The Model N34001 chamber is built to exacting standards by PTW-Freiburg.  It features a 1 meter cable and can be delivered with either a triaxial BNC or TNC connector.

The Model PPC40 plane-parallel ionization chamber is similar to one developed by Dr. Roos for use as a reference chamber for electron dosimetry.  The outstanding feature of this chamber is a wide guard ring to exclude any perturbation effect even at low electron energies.  The polarity effect also is negligible: less than 1% for all usable energies, field sizes and depths.  The energy dependence is only influenced by the stopping power correction; a type-dependent correction is not necessary.

The chamber is watertight for use in water phantoms.  The measuring volume is vented to the atmosphere through the connecting cable sheath.  The entrance window is flush with the surface so that it can be used with solid phantoms.  The external dimensions conform to the Roos^® design.

The PPC40 features a 1.4 meter cable and can be delivered with either a triaxial BNC or TNC connector.

The Model P11 plane-parallel ion chamber is recommended for routine electron beam measurements and for depth dose studies in electron, photon, proton and neutron beams.

The sensitive region of the chamber is defined by a wide guard ring for negligible perturbation in field lines and polarity effect.  The collecting volume is thus precisely defined and independent of operating conditions.

The exceptional shielding provided by the cable and the complete guarding combine to eliminate stem and soakage effects.  Ionization currents may therefore be read immediately upon the application and reversal of the polarizing potential.

The P11’s rigid stem allows accurate positioning.  No stem effects are present.  The chamber is vented through a flexible tube that surrounds the cable.  The vent tube is sealed to the chamber body and open near the connector.

The Model P11 is made from a polystyrene-equivalent plastic, which is a mixture of polyethylene, polystyrene and carbon black, with a density of 1.1g/cm³ and electrical resistivity in the range of 0.01 to 1 Ohm-meters.

Designed primarily for calibrating the X-ray output of therapy superficial machines and stereotactic dosimetry, this chamber is also suitable for measuring buildup in solid phantoms.  The acrylic chamber body has backscatter properties similar to skin, and the thin window permits accurate measurements of soft X-ray radiation.  The energy response is exceptionally flat over the 10kV to 100kV range.

Depth dose may be obtained by using a specially-machined phantom section which positions the chamber at the beam central axis with its window level with the surface.  This then becomes part of a phantom assembly and the desired buildup thickness may be added.  Depth buildup may also be accomplished by placing a special cylindrical water phantom over the chamber and adding water as necessary.

PTW Farmer^® ionization chambers conform to the physical dimensions and meet or exceed the performance standards of the original Farmer^® design.  They are available from CNMC in several configurations.  All chambers feature a new, low-noise triaxial cable with radiation resistant insulation.  Each chamber is supplied with an integral 1 meter cable, male triax BNC connector with cap & chain, an acrylic ⁶⁰Co buildup cap and a foam-lined case.

Model N30010 (formerly N30001, formerly N23333) with a sensitive volume of 0.6cm³, features a thimble with internal 0.09mm thick graphite layer, protected by a 0.335mm acrylic exterior wall.  This combination makes the N30010 essentially air-equivalent with all the ruggedness of an acrylic thimble.

Model N30012 (formerly N30004) has a sensitive volume of 0.6cm³, with a thimble that is made entirely of graphite, but with an aluminum central electrode for enhanced low-energy response uniformity.

Model N30012.2 (formerly Model N30004.2) is a CNMC version of the model N30004 with a sensitive volume of 0.2cm³ for greater spatial resolution, an all-graphite thimble and aluminum central electrode.  It is supplied with an appropriate acrylic ⁶⁰Co buildup cap.  Optional 15mm long acrylic spacers to take up the extra space within a solid phantom drilled for 0.6cm³ chambers are available.

The Model N30013 (formerly N30006) is an ionization chamber of the classic Farmer design, intended for absolute dosimetry, but featuring waterproof construction.  Similarities to the PTW N30010 include a sensitive volume of 0.6cm³, guarding up to the measuring volume, atmospheric communication and a thimble with internal 0.09mm thick graphite layer protected by a 0.335mm acrylic exterior wall.  This thimble material combination makes the N30013 essentially air-equivalent with all the ruggedness of an acrylic thimble.

As with all PTW Farmer^® ionization chambers, the N30013 conforms to external physical dimensions and meets or exceeds performance standards of the original Farmer design.  It features a low-noise triaxial cable with radiation resistant insulation.  Each chamber is supplied with an integral 1 meter cable, male triax BNC connector with dust cap and chain, an acrylic ⁶⁰Co build-up cap, a foam-lined case and QA checkout at CNMC.

The FC series are ionization chambers of a classic Farmer design, intended for absolute dosimetry, that meet or exceed performance standards of the original Farmer design.  Similarities to the original Farmer include conformity to all external physical dimensions, a choice of thimble materials (graphite or robust), sensitive volumes of 0.65cm³ and 0.23cm³, and atmospheric communication.  Additional features not shared with the original Farmer include guarding up to the measuring volume and waterproof construction.

The low-noise 3.3mm diameter triaxial cable is sheathed along the entire 1.5m length and terminated with a male triax BNC connector with dust cap & chain (TNC connector is optional).  Each chamber includes a Delrin ⁶⁰Co buildup cap, a padded storage case and QA checkout at CNMC.

Graphite thimble, aluminum electrode – The Model FC65-G is a direct replacement for the NE 2571A.  It features a thin-walled graphite thimble, an aluminum center electrode and a sensitive volume of 0.65cm³.

Delrin thimble, aluminum electrode – The Model FC65-P most closely resembles the NE 2581A, in that it has a rugged thimble made of Delrin (POM, poly-oxy-methylate), an aluminum center electrode and a sensitive volume of 0.65cm³.

AE Thimble and electrode – The Model FC23-C offers improved spatial resolution for greater precision in the measurements of beam profiles and isodose contours.  It most closely resembles the NE 2577C but features a conductive C552 air equivalent thimble, C552 center electrode and a volume of 0.23cm³.

These precision ion chambers from PTW have been designed specifically for beam scanning applications of photon and electron beams in water phantoms.

The Model N31010 (formerly N31002) has a nominal volume of 0.125cc for increased spatial resolution along the axis, which allows scanning in all directions without repositioning the chamber.  The internal dimensions of 5.5mm diameter and 6.5mm length makes the sensitive volume almost spherical.

The Model N31013 (formerly N31003) has a nominal volume of 0.3cc for improved signal-to-noise and leakage current ratio.

Both chambers have a rigid stem with a nominal outside diameter of 7mm that allows convenient mounting in most water phantom chamber holders.

Although these ion chambers can be safely inserted and used in water, it is a matter of good practice to limit the immersion time to the actual duration of measurements.  The chambers should be removed from the water, dried and stored shortly after completion of scanning studies.

Both chambers are supplied with an acrylic ⁶⁰Co build-up cap, 1 meter of cable terminated with triax BNC with cap & chain, and a foam-lined case.

Model N31014, 0.015 cc
Model N31015, 0.03 cc
Model N31016, 0.015 cc spherical

PTW 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, and for evaluation of stereotactic and IMRT small radiation fields.

The Model N31016 distinguishes itself in having a flat angular response due to its sensitive volume being nearly spherical.

When calibrated, the Pinpoint chambers can be used for depth dose and absolute dose measurements.  The sensitive volume is vented, requiring air density correction.  The wall material is graphite with a protective acrylic cover.  The chambers are fully guarded up to the sensitive volume.  The nominal energy ranges are ⁶⁰Co up to 50MV photons and 6 to 50MeV electrons.  The chambers have a 28mm long aluminum stem for mounting and a 1.3m cable with choice of connector.

The Model N23323 is specially designed for use in intracavitary applications.  It is watertight and equipped with a flexible stem so it can be inserted in the patient’s rectum during afterloading treatment.  It features a one-piece waterproof sleeve, and all external parts are free of high voltage.

Although the measuring volume of the chamber is closed to the atmosphere, the seal is maintained for a limited time.  Typically, the internal air density will equilibrate after approximately eight hours.  This feature prevents a sudden sensitivity change when the chamber is brought into contact with the patient’s body.

No air density corrections due to temperature or barometric pressure changes are necessary if the measurement is made within a few hours of calibrating the chamber.  This is also true when the chamber is used in water, making the Model N23323 especially suitable for use in water phantom scanning applications.

Wellhöfer compact ionization chambers are designed for scanning applications in computerized water phantom systems.  They feature high spatial resolution and a Shonka air-equivalent C552 thimble & electrode.  Venting is accomplished through the waterproofing sheath and the chamber connector.

Although these ion chambers can be safely inserted and used in water, it is a matter of good practice to limit the immersion time to the actual duration of measurements.  The chambers should be removed from water, dried and stored shortly after completion of the scanning studies.

Microchambers were developed specifically for the assessment of radiation fields encountered in stereotactic radiosurgery.  Their excellent spatial resolution and waterproof construction also make them well suited for other radiation beam measurements, including beam calibrations.

Microchambers were developed specifically for assessment of the radiation fields encountered in stereotactic surgery.  Outwardly, the model A14 is identical to the A1, but with a sensitive volume 5.5 times smaller; the Model A1 and A14 feature a true cylindrical chamber design, whereas the Model A14P features a true planar design with a 1.5mm collector diameter and collector gap of 1mm.

The chamber wall, collector and guard are made entirely of C552 Shonka conducting plastic, simulating air.  C552 is an air-equivalent formulation, which makes it ideally suited to the measurement of exposure.  C552 consists of polyvinylidene fluoride, carbon black and silica.  Density is 1.76 g/cm³. Electrical resistivity is on the order of 0.03 Ohm-meters.  Tissue-equivalent versions of these chambers are also available.

Slim-Line miniature chambers were developed specifically for assessment of the radiation fields encountered in stereotactic surgery where an extremely small sensing volume is needed to achieve good spatial resolution.  Slim-Line design provides compact profile, but does not allow for gas circulation through the sensing volume.

Internally, A1SL is identical to the A1 and Model A14SL is identical to Model A14.  Externally, the A1SL and the A14SL differ in having a uniform thimble and stem diameter of only 6.25mm.

To insure atmospheric equilibrium, the chambers are vented through the sheathed cable and are therefore inherently waterproof.

The chamber wall, collector and guard are made entirely of C552 conducting Shonka plastic, a highly homogenous air-equivalent formulation which makes it ideally suited to the measurement of exposure.  C552 consists of polyvinylidene fluoride matrix, in which finely divided inert powders of carbon black and silica are uniformly dispersed.  Density is 1.76 g/cm³.  Electrical resistivity is on the order of 0.03 Ohm-meters.  Carbon black is the main source of electrical conductivity.

Waterproof silicon detector for dosimetry in high-energy photon beams up to field size 40cm x 40cm

The 60016 Dosimetry Diode P is ideal for dose measurements in small photon fields as encountered in IORT, IMRT and stereotactic beams.  The excellent spatial resolution makes it possible to measure very precisely beam profiles even in the penumbra region of small fields.  The superior energy response enables the user to perform accurate percentage depth dose measurements which are field size independent up to field sizes of 40 x 40cm square.  The waterproof detector can be used in air, solid state phantoms and in water.

• Useful for measurements in small and large photon fields.
• Excellent spatial resolution.
• Minimized energy response for field size measurements up to 40cm x 40cm.

Waterproof silicon detector for dosimetry in high-energy electron and photon beams

The 60017 Dosimetry Diode E is ideal for dose measurements in small electron and photon fields as encountered in IORT, IMRT and stereotactic beams.  The excellent spatial resolution makes it possible to precisely measure beam profiles in the penumbra region of small fields.  The superior energy response enables the user to perform accurate percentage depth dose measurements which are field size independent up to field sizes of 40 x 40cm square.  The detector is waterproof and can be used in water, air and solid state phantom material.

• Useful for measurements in all electron fields and for small photon fields.
• Excellent spatial resolution.
• Minimized energy response.
• Thin entrance window for measurements in the vicinity of surfaces and interfaces.

Waterproof silicon detector for dosimetry in 6MV photon beams up to field size 10cm x 10cm

The 60018 Dosimetry Diode SRS is ideal for dose measurements in photon fields with a maximum field size of 10 x 10cm and with a maximum energy of 6 MV.  The very high response of this detector allows to measure beam profiles with a very high resolution and very short dwell time.  Typical use is beam profile measurement for stereotactic radio surgery (SRS).

• Designed for measurements in small photon fields with maximum 6 MV.
• Excellent spatial resolution.
• High response.
• Very low noise.
• Thin entrance window for measurements in the vicinity of surfaces and interfaces.

Semiconductor detectors offer many practical advantages for radiation field analysis.  They are small, mechanically stable devices which deliver a high level signal output.  Bias voltages are not required, and the response is very fast and independent of pressure variations.  Their small size allows the detection area to be located very close to the surface (0.5mm) and provides excellent spatial resolution.  The sensitivity is extremely high – typically about 18,000 times that of an air-filled ionization chamber of the same volume.

The waterproof Hi-pSi semiconductor radiation field detectors are designed to meet the diverse needs of photon and electron radiation field analysis.  They are delivered preirradiated, which stabilizes sensitivity at the expense of a slight temperature coefficient.  However, for extensive water phantom measurements, detector stability with accumulated dose is a much more important consideration than variation due to temperature change.

The water/silicon mass collision stopping power of the 3G-pSi semiconductor detector is practically constant at energy levels above 5MeV.  This allows depth-ionization curves for electron beam measurements to be used as depth-dose curves without requiring correction factors.  Electron beam measurements may be made as close as 0.5mm to the phantom surface, and directional dependence is less than 2.5% for a 20 x 20cm field at 2cm depth in a 20MeV beam.

In photon beams, depth-dose percentages obtained from a semiconductor tend to be overestimated.  This tendency increases with the depth due to increased sensitivity of the semiconductor to energies below 400keV.  To prevent this, the Hi-pSi semiconductor chip is backed with a tungsten/epoxy shield to capture low-energy back-scattered photons.  The result is an energy-compensated photon detector giving precise readings from 50 to 400mm.

The very small size of the stereotactic detector, its energy independence in fields less than 10cm, and the low impact of non-electron equilibrium makes it the obvious choice for measuring output factors and depth-dose curves in stereotactic beams.

This is a relatively low-cost detector that should only be used to obtain a reference signal for relative field measurements.  By calculating the quotient of the field and reference signals, the effect of variations in dose rate from the accelerator are nulled out.  It is best not to use an ion chamber as the reference when the field detector is a diode because of signal size and the need for bias.

When a dosimetry system is purchased through CNMC, we will schedule the calibration at one of the AAPM ADCL (Accredited Dosimetry Calibration Laboratory) facilities.  This insures that your system will be delivered to you ready for use.

When your dosimetry system is being scheduled through CNMC for recalibration, we will thoroughly inspect the dosimeter and the ionization chamber and report on any conditions requiring attention.  This service is provide to you at no additional charges.

CNMC will send your equipment through on of the following Accredited Dosimetry Calibration Laboratories:

K&S Associates, Inc.

University of Texas MD Anderson Cancer Center

University of Wisconsin

Keithley 602 modifications include:

• The installation 150/300V electronic bias supply with reversible polarity.
• Replacement of the analog meter with a 4.5 digit LCD.
• Installation of a single 12V rechargeable battery with a wall-mount UL-listed transformer/charger.
• Installation of circuitry to allow bias voltage and battery condition to be read on the display.

Similarly, CNMC can modify and improve your other dosimeters, which includes replacing bias batteries with ±300V, ±150V electronic bias supply and converting the input connector to BNC or TNC.

CNMC can generally repair and significantly improve your dosimeter/electrometer regardless of its manufacturer.  Repairs at ½ the cost and/or ½ the time are common at CNMC.

Includes thimble, waterproof, plane-parallel, extrapolation and diode detectors of any manufacturer.  Modifications include:

• Conversion of any style of connector.
• Shortening the cable.
• Farmer thimble (non-waterproof) conversion from 0.6cc to 0.2cc, to acrylic, graphite or Solid Water™ chambers.

Same day repairs are possible at CNMC; typical chamber repairs include:

• Thimble replacement (non-waterproof types).
• Connector repair or replacement.
• Correcting leakage condition.
• Resheathing waterproof ion chambers.

CNMC manufactures low-noise triaxial and coaxial cables per your specifications with connectors of your choice and custom lengths.  CNMC will repair and modify your extension cable.  Repair and modification includes:

• Connector repair or replacement.
• Conversion of any style of connector (BNC, TNC, PET, PTW, MDH, etc.).
• Installation in a wind-up reel.

When scheduled through CNMC, we will thoroughly inspect dosimeter and ionization chamber and report on conditions requiring attention.