Extrapolation Chamber Research Articles

Development and performance testing of a chamber for absorbed dose in water absolute measurement for 125I brachytherapy seeds

The application of more and more low-energy, low-dose-rate photon radiation seeds in brachytherapy. According to the TG43 report and TG43-U1 report issued by the American Association of Physicists in Medicine, both apparent activity and air kerma strength are physical characterization parameters of brachytherapy seed strength,which are needed to convert into water absorbed dose at the depth of 1 cm. At present, the method of obtaining the water absorbed dose is to convert the air kerma strength, the uncertainty of results exceeds 5% (k = 1), which could reduce the cure rate of the treatment. In order to address this issue ,the China Institute of Atomic Energy has designed a device that can directly replicate the water absorbed dose of 125I brachytherapy seeds,which is an extrapolation chamber embedded with water equivalent material. In order to evaluate the performance of the extrapolation chamber, a series of experiments were carried out, including partial pressure test, leakage current, saturation curve, response linearity, collection area and zero point position. The test results show that the performance parameters of the extrapolation chamber meet the relevant requirements.

Characterization of a segmented printed circuit board (PCB) as a standard for absorbed dose to water from alpha-emitting radionuclides.

Our previous work introduced and evaluated a standard for surface absorbed dose rate per unit radioactivity to water from unsealed alpha-emitting radionuclides used in targeted radionuclide therapy (TRT). An overall uncertainty over 4.0% at k=1 was reported for the absorbed dose to air measurements, which was partially attributed to the rotational alignment uncertainty in the geometrical setup. A printed circuit board (PCB) with a segmented guard was constructed to align the extrapolation chamber (EC) and the source plates using a differential capacitance technique. The PCB EC aimed to enhance the repeatability of the ionization current measurements. The PCB EC was evaluated using a thin film 210Po source. The measured absorbed dose to air cavity was compared with the Monte Carlo (MC) calculations. Using the extrapolation method, the surface absorbed dose rate to water was calculated. The PCB EC was constructed with a 4.50mm diameter collector surrounded by four sectors and a guard electrode. The sectors were isolated for rotational alignment and later connected to the guard for ionization current measurements. A bridge circuit measured differential capacitance between opposing sectors, and a hexapod motion stage rotated the source substrate to minimize the differential capacitance. The EC was evaluated using a 210Po source with a 3.20mm diameter and 1.253 Ci radioactivity. MC simulations were performed to calculate the , , and correction factors. Ionization current measurements were performed for air gaps in the 0.3-0.525mm range and surface absorbed dose rate to water was calculated. Rotational offsets of up to 3.0° were found and the current repeatability was found to increase with the absorbed dose to air uncertainty calculated to be ∼2.0%. Using the capacitance method, the effective EC diameter was measured to be 4.53mm. The recombination, polarity, and electrometer corrections were reported to be within 1.00% across all measurement trials. The MC-calculated correction factors were calculated to be much larger than the recombination and polarity correction factors. The average , , and corrections were calculated to be 1.063, 0.9402, and 2.136, respectively. The MC-calculated absorbed dose to air was found to overestimate the absorbed dose by over 4.00% when compared with the measured absorbed dose to air. The surface absorbed dose rate to water was calculated to be Gy/s/Bq with an overall uncertainty of 4.07%. The constructed PCB EC was deemed suitable as an absorbed dose standard. A repeatable rotational alignment was achieved using the differential capacitance technique. The metal electrodes on the PCB made a difference of<1.00% on the backscatter correction when compared to the EC comprised of polystyrene-equivalent collector. A 20% difference in the surface absorbed dose rate to water was found between the two ECs, which is attributed to the cavity diameter differences leading to different magnitudes of dose fall-off along the lateral direction.

Development of a motorized system for the characterization of the RQR reference x-ray beams at the KFSHRC's SSDL using an extrapolation chamber

An extrapolation chamber of type Böhm 23392, used for the dosimetry of RQR beam qualities at the Secondary Standard Dosimetry Laboratory of King Faisal Specialist Hospital, is presented. A computer-based motorized system consisting of a stepping motor coupled to the chamber's built-in micrometer screw was designed to expedite the measurements process, giving a linear relationship between the number of motor steps and the chamber depth with a Coefficient of Determination (COD) equal to 0.9990. The extrapolation chamber along with the motorized system was used to determine the extrapolation curves. The slope of the extrapolation curves, measured for the eight RQR beam qualities with a relative uncertainty between 0.17% and 0.58%, varies linearly with the beam quality expressed in terms of HVL, with a COD between 0.9995 and 1.0000.

Monte Carlo study of the BSS2 calibration system using the PTW 23392 extrapolation chamber

The objective of the present work was to develop and validate a computational model of the Beta Secondary Standard type 2 (BSS2) system, with sources, filters and the PTW 23392 extrapolation chamber using MCNPx code. Simulations were performed to calculate the absorbed dose rate to tissue at null depth and 0.07 mm for the 85Kr, 90Sr/90Y and 147Pm beta radiation sources. The response curve was calculated by computing the energy deposited, at different depths, to the sensitive volume of the chamber. The deviations in the absorbed dose rate obtained using the MCNPx code compared to the calibration certificate data were found to be up to 2 %. Deviations up to 10 % were observed for the transmission factor calculated for all three beta sources. This work describes in detail the main parameters and common issues seeing when modelling an extrapolation chamber and three different beta standard sources.

Performance evaluation of a homemade extrapolation chamber in low energy radiation field

Extrapolation chambers are widely used to detect the weakly-penetrating types of radiation beams. Normally, the sensitive volume of them is limited, only a few cubic centimeters. Their collecting electrodes use sheet structure, which lead to more backscattering photons. In this work, a large volume extrapolation chamber with (235–1413) cm3 was designed for the absolute measurement of air kerma strength of 125I brachytherapy seeds. The developed chamber has the following innovation: large sensitive volume and the Aluminized Polyethylene terephthalate (PET) collecting electrode foil. In order to give a more comprehensive performance evaluation for the designed chamber, a series of experiments were conducted. Evaluation parameters include leakage current, saturation curve, polarity effect, ion collecting efficiency, linearity of response, collecting area and zero point. Those tests were measured in the standard X-ray radiation field. A comparative experiment with the primary standard free air chamber (FAC) was performed. Moreover, extrapolation curve was measured in 125I radiation field. Evaluation results show a good behavior of the extrapolation chamber. The Al-coated PET collecting electrode influence the response of the chamber to 0.07% with the simulation of MCNP5 Monte Carlo. All the results indicate the usefulness of the extrapolation chamber for the absolute measurement for 125I seeds.

Temperature dependence of effective area and depth of extrapolation chamber in dosimetry

The variation of the effective area and zero-offset of an extrapolation chamber used for beta-ray and low-energy x-ray dosimetry was measured as a function of temperature in the range 19 °C to 25 °C. The effective area and zero-offset were determined from the capacitance of the extrapolation chamber measured with the chamber depths in the range up to 1.4 mm. The extrapolation chamber was put in a precision thermostatic air bath with a programmable temperature regulator to evaluate the influence of temperature on it. At room temperature we found the thermal expansion coefficients to be (8.55 ± 0.57) × 10−5 K−1 for the effective area and (2.83 ± 0.03) µm K−1 for the depth of the extrapolation chamber. The influence of thermal expansion of the extrapolation chamber on the ionization current measurement was estimated to be about 3 × 10−3 K−1 when the measurement depth was 1 mm.

RETRACTED: Surface dose rate variations in planar and curved geometries of 106Ru/106Rh plaque sources for ocular tumors

Investigation of surface dose rate variation with respect to the source configuration of 106Ru/106Rh eye plaque. To explore an alternate way to determine activity of brachytherapy plaques.The surface dose rates of 106Ru/106Rh plaque developed indigenously were measured by extrapolation chamber. To rule out possibility of any error in the activity distribution and quantity, same source was used in two different configurations namely planar and curved. EBT3 Gafchromic film was used for determination of uniformity in activity. Monte Carlo-based Codes EGSnrc and FLUKA were used to calculate dose rate in tissue, percentage depth dose and for determination of activity. Parameters and correction factors were estimated using simulations.The measured reference absorbed dose rates for planar and curved 106Ru/106Rh eye plaques are found to be 589 ± 29 mGy/h and 560 ± 28 mGy/h, respectively. The difference in the reference absorbed dose rate of curved eye plaque is about ~5% as compared to planar configuration. The FLUKA-calculated dose values are almost independent of cavity length of the extrapolation chamber for both eye plaques. The FLUKA-based dose rates per μCi 106Ru/106Rh are about 17.28 ± 0.08 mGy/h and 16.48 ± 0.06 mGy/h, respectively for planar and curved eye plaques which match well with the measurements. The calculated activities for planar and curved eye plaques are 34.08 μCi and 33.98 μCi, respectively.Surface dose rates for a prototype 106Ru/106Rh eye plaque with different configurations were estimated using simulations and measured experimentally. An alternate way to determine activity of beta-gamma brachytherapy plaque has been proposed.

Performance comparison of an extrapolation chamber in computed tomography standard beams of two laboratories

The doses received by the patients during the computed tomography (CT) exams are the highest when compared to other diagnostic radiology procedures. This fact makes it so important to keep the quality control using the correct instrument. For dosimetry in CT, a pencil type ionization chamber is usually utilized with a sensitive volume length of 10 cm. A comparison of the performance of an extrapolation chamber in two different laboratories, at the Instrument Calibration Laboratory (LCI) from Instituto de Pesquisas Energéticas e Nucleares (IPEN, Brazil) and at the National Physical Laboratory (NPL, UK) was undertaken. Two chamber characteristics were determined (zero depth and extrapolation curve), and the main recommended characterization tests were performed (stabilization time, saturation curve, polarity effect, ion collection efficiency, linearity of response, and variation of response with source-detector distance). This extrapolation chamber was calibrated using the standard system of NPL laboratory, and the energy dependence was determined. The results obtained were within the international recommendations of IEC 61674, except for the energy dependence, as already expected. This study also established a reference system for the LCI of the IPEN, using a homemade extrapolation chamber for X-ray CT beams. Using the extrapolation curves obtained in the characterization tests and the correction factors of ionic recombination, and scattering and fluorescence, the air kerma rates were obtained, as a reference system in standard laboratory computed tomography beams. The last correction factor was obtained using computer simulations by the MCNP5 code (Monte Carlo). Moreover, two pencil type ionization chambers were calibrated using the replacement method in relation to the extrapolation chamber.

Dosimetric tests of an extrapolation chamber in standard computed tomography beams

Computed tomography (CT) diagnostic exams are responsible for the highest dose values to the patients. Therefore, the radiation doses in this procedure must be accurate. For the dosimetry of CT beams, the radiation detector is usually a pencil-type ionization chamber. This type of dosimeter presents a uniform response to the incident radiation beam from all angles, which makes it suitable for such equipment since the X-ray tube executes a circular movement around the table during irradiation. However, there is no primary standard system for this kind of radiation beam yet. In order to search for a CT primary standard, an extrapolation chamber built at the Calibration Laboratory (LCI) of the Instituto de Pesquisas Energéticas e Nucleares (IPEN) was tested. An extrapolation chamber is a parallel-plate ionization chamber that allows the variation of its sensitive air volume. This chamber was used previously for low-energy radiation beams and showed results within the international recommended limits. The aim of this work is to perform some characterization tests (saturation curve, polarity effect, ion collection efficiency and linearity of response) considering the chamber depth of 1.25 mm in the radiation qualities for computed tomography beams at the LCI. The results showed to be within the international recommended limits.

Corrections for photons attenuation and scattering for the extrapolation chamber for measurement of air-kerma strength of 125I brachytherapy source

A type of extrapolation chamber was designed in China Institute of Atomic Energy, CIAE. The chamber was used for the measurement of the air-kerma strength of the medical radiation 125I source on primary standard level. In order to obtain the air-krema strength with a low uncertainty, some correction factors such as photon attenuation and scattering are needed to calculate. Correction factors for different types of 125I seeds were estimated with increasing chamber depth. Based on the relation between ionization current and average photon fluence, attenuation correction factors were calculated with the analytical solution. Additionally, the scattering correction factors were estimated by a suitable method of Monte Carlo simulation. Photon attenuation includes four components. katt-volume, katt-foil, katt-sf, and katt-Al. The differences of correction factors are concerned, mainly due to the variation of chamer depths and 125I seed types. katt-volume increases from 1.001 to 1.005. katt-foil varies between 1.0012 and 1.0014. katt-sf changes from 1.015 to 1.018. katt-Al varies between 1.038 and 1.048, which largely depend on the photon spectrum from the source. Meanwhile, the geometric dimension of the ionization chamber has a great influence on the scattering correction factors. The ksca values vary from 0.9960 to 0.9964 with different chamber depths, which only has 0.04% fluctuation.

Performance of an extrapolation chamber in computed tomography standard beams

Among the medical uses of ionizing radiations, the computed tomography (CT) diagnostic exams are responsible for the highest dose values to the patients. The dosimetry procedure in CT scanner beams makes use of pencil ionization chambers with sensitive volume lengths of 10 cm. The aim of its calibration is to compare the values that are obtained with the instrument to be calibrated and a standard reference system. However, there is no primary standard system for this kind of radiation beam. Therefore, an extrapolation ionization chamber, built at the Calibration Laboratory (LCI), was used to establish a CT primary standard. The objective of this work was to perform some characterization tests (short- and medium-term stabilities, saturation curve, polarity effect and ion collection efficiency) in the standard X-ray beams established for computed tomography at the LCI.

Impact of air gap, range shifter, and delivery technique on skin dose in proton therapy.

Side effects of radiation therapy may include skin damage. The surface dose is of great interest and contains the buildup effect. In particular, the proton therapy community requires further experimental data to quantify doses in the surface region. This specification includes the skin dose, which is defined according to ICRU Report No. 39 at 70μm water equivalent depth. The aim of this study is to gather more knowledge of the skin dose by varying key parameters defined by the patient treatment plan. This consists of clinical aspects such as the influence of the air gap, the application of a range shifter (RS), or the proton delivery technique. Skin doses were determined with a PTW 23391 extrapolation chamber with three thin Kapton® entrance windows operated as a conventional ionization chamber. The impact on the skin dose for quasi-monoenergetic pencil beam scanning (PBS) proton beams was evaluated for clinical air gaps between 3.5 and 51.1cm. The differences in skin dose were assessed by irradiating equivalent fields with an RS of 51mm water equivalent thickness (RS51) and without. Furthermore, the delivery techniques PBS, uniform scanning (US), and double scattering (DS) were compared by defining a spread-out Bragg peak (SOBP). TOPAS (V.3.1.2) was used to model an IBA nozzle with PBS and to score dose to water at the surface of a water phantom. For the monoenergetic fields without the application of the RS the skin dose was constant down to an air gap of 6.2cm. A lower air gap of 3.5cm showed a variation in skin dose by up to 2.4% compared to the results obtained with larger air gaps. With the inserted RS51 an increase in the skin dose was found for air gaps smaller than 11.3cm. Experimentally, a dose difference of 1.4% was recorded for an air gap of 6.2cm by inserting an RS and none. With the Monte Carlo calculations the largest dose increase was observed at the air gap of 3.5cm with 1.7% and 4.0% relative to the skin dose results without the RS and to the largest evaluated air gap of 51.1cm, respectively. The SOBP comparison of the beam modalities at the measuring plane at the isocenter revealed higher skin doses without RS (including RS) by up to +1.9% (+1.5%) for DS and +1.3% (+1.1%) for US compared to PBS. For all three techniques an approx. 2% rise in skin dose was observed for the largest evaluated air gap of 37.7cm to an air gap of 6.2cm when using an RS51. The study investigated aspects of skin dose of a water equivalent phantom by varying key parameters of a proton treatment plan. Parameters like the RS, the air gap, and the delivery modality have an impact on the order of 4.0% for the skin dose at the depth of 70μm. The increases in skin dose are the effects of the contribution of the increased electron fluence at small air gaps and the emitted hadronic particles produced by the RS.

Correction factors for primary beta dosimetry

Several correction factors for primary beta dosimetry in radiation protection have been determined by means of measurements and simulations for both the well-known Böhm primary standard extrapolation chamber developed at PTB (which has been commercially available for a long time) and a new primary standard extrapolation chamber also developed at PTB. The correction factors kel for electrostatic attraction of the entrance window due to the collecting voltage and ksat for ionisation collection losses due to ionic recombination have been measured. The following correction factors have been determined by simulations for normal (0°) as well as oblique (15°, 30°, 45° and 60°) radiation incidence: kba for backscatter from the collecting electrode, kpe for perturbation by the chamber’s side walls, and kra, kac and kdi for inhomogeneity inside the collecting volume. The latter three have been combined to kih. Six more correction factors adopted from the literature are described to complete the necessary corrections. A comparison with values given in ISO 6980-2:2004 (for 0°), all determined at that time by means of measurements, is shown as well as the application of the new factors to measured data. The newly determined correction factors are ready to be implemented in an updated version of ISO 6980-2.

Some characterization tests for an extrapolation chamber in CT standard beams in a specific chamber depth

The use of Computed Tomography (CT) for diagnostic images has been growing due to technological advances of this equipment. Therefore, there is a concern regarding the dose received by the patients undergoing this procedure, and this procedure needs to be performed with the highest precision and accuracy possible.The radiation detector used for CT beams is a pencil-type ionization chamber. However, there is no primary standard system for this kind of radiation beam. In this work a homemade extrapolation chamber was used to establish a CT primary standard [1]. This detector was tested for low-energy radiation beams and showing results within the internationally acceptable limits [2].This work had the objective to study the response stability of an extrapolation chamber, as well as obtaining the energy dependence and the angular dependence in standard CT beams of the Calibration Laboratory of IPEN (LCI).

Determination of surface dose in pencil beam scanning proton therapy.

Quantification of surface dose within the first few hundred water equivalent µm is challenging. Nevertheless, it is of large interest for the proton therapy community to study dose effects in the skin. The experimental determination is affected by the detector properties, such as the detector volume and material. TheInternational Commission on Radiation Units and Measurements in its report 39 recommends assessing the skin dose at a depth of 0.07mm. The aim of this study is the estimation of the absorbed dose at and around a depth of 70µm. We used various dosimetric approaches in conjunction with proton pencil beam scanning delivery to determine the skin dose in a clinical setting. Five different detectors were tested for determining the surface dose in water: EBT3 and HD-V2 GAFCHROMIC™ radiochromic film, LiF:Mg,Ti thermoluminescent dosimeter, IBA PPC05 plane-parallel ionization chamber, and PTW 23391 extrapolation chamber. The irradiation setup consisted of quasi-monoenergetic scanned proton pencil beams with kinetic energies of 100, 150, and 226.7MeV, respectively. Radiochromic films were placed within a vertical stack and in wedge geometry and were analyzed with FilmQA Pro™ adopting triple channel dosimetry. The extrapolation chamber PTW 23391, which served as a reference in the current work, was used in a conventional ionization chamber setup with a fixed electrode gap of 2mm. Three Kapton® entrance windows with thicknesses of 25, 50, and 75µm were employed. Thermoluminescent dosimeters were provided as powder and were pressed onto a sheet of aluminum. Furthermore,the Monte Carlo code TOol for PArticle Simulation (TOPAS) in version 3.1.p2 was used to model an IBA pencil beam scanning nozzle and score dose to water in a water phantom. The resulting depth dose curves were normalized to their 100% dose at the reference depth of 3cm. We obtained the skin doses with the extrapolation chamber and with TOPAS. For the experimental approach this resulted in 79.7±0.3%, 86.0±0.6%, and 87.1±0.1% for the proton energies 100, 150, and 226.7MeV, respectively. The results for TOPAS were 80.1±0.2% (100MeV), 87.1±0.5% (150MeV), and 86.9±0.4% (226.7MeV), respectively. Based on the experimental results of the skin dose, we provided a clinically relevant surface extrapolation factor for the common measurement methods. This allows the result of the first measurement depth of a detector to be scaled to the dose at the skin depth. Most practical would be the use of the surface extrapolation factor for the PPC05 chamber, due to its direct reading, the wide availability in clinics and the low uncertainties. The calculated factors were 0.986±0.004 for 100MeV, 0.961±0.008 for 150MeV, and 0.963±0.003 for 226.7MeV. In this study, dissimilar experimental approaches were evaluated with respect to measurements at depths close to the surface. The experimental depth dose curves are in good agreement with the simulation with TOPAS Monte Carlo. To the author's knowledge this was the first experimental determination of the skin dose according to the International Commission on Radiation Units and Measurements 39 definition in proton pencil beam scanning.

Characterization of an extrapolation chamber in beta radiation beams and Monte Carlo modelling

At the Calibration Laboratory (LCI) of the IPEN/CNEN, studies are in development on the establishment of a standard composed by the beta radiation sources for the dosimetry and calibration for personal monitoring in Brazil. For this purpose is used the Böhm extrapolation chamber (PTW model 23392). This chamber was already characterized at LCI in 90Sr/90Y beams using two different entrance windows: one of aluminized Mylar and another of PET (polyethylene terephthalate) known as Hostaphan. In this work, this extrapolation chamber was characterized in 85Kr and 147Pm beams. All tests were carried out with the reference 90Sr /90Y source, for comparison purposes. The Monte Carlo code MCNP5 code was used to obtain an extrapolation chamber and the BSS2 system sources computational model, based on the determination of the absorbed dose rate. Saturation curves, ion collection efficiency, ion recombination, polarity effect, stability of response, null depth, linearity of response, variation of response as a function of source-detector distance, extrapolation curves, correction factors and absorbed dose rates were obtained. The difference between the experimental absorbed dose rates and those obtained using the Monte Carlo model, compared to those from the calibration certificates, was less than 1.9% for the 108 histories for each BSS2 system source. All results of the performed tests are within the limits of the international recommendations. The results for the 90Sr/90Y source were in good agreement with previous works performed at LCI. These results are suitable for the establishment of a standard instrument for the dosimetry and calibration of beta radiation sources and detectors in the LCI/IPEN. This standard will allow the calibration of detectors in beta radiation beams in dosimetry services in Brazil.

Assessments of the characteristics of an extrapolation chamber for 60 to 200 kVp X-rays: Experiment and Monte Carlo simulation

According to the principles of radiation protection, the patient and personnel dose should be decreased to a reasonably achievable level. Therefore, it is essential to use reliable dosimeters in the radiation dosimetry course. One of these dosimeters is an extrapolation chamber. It is a plane-parallel ion chamber (PPIC), which its sensitive volume can be varied. In this paper, the performance of an extrapolation chamber has been evaluated in 60–200 kVp X-rays. It was submitted to several necessary tests, and also simulated with MCNP code. All of the results were within the recommendations of the International Electrotechnical Commission (IEC). The chamber responses were linear with electrode separation. The comparison between experiment and simulation agrees in an overall sense within 5.4% in the worst case. The results indicated the usefulness of the chamber in this energy range. They show that the extrapolation chamber can be also used for computed tomography (CT) beams, considering that a primary standard system doesn't exist for these beams yet.

Evaluation of an extrapolation chamber for dosimetry in computed tomography beams using Monte Carlo code (MCNP5)

Computed tomography (CT) is responsible for the highest dose values to the patients during the exams. Therefore, the radiation doses in this procedure must be accurate. However, there is no primary standard system for this kind of radiation beam yet. A homemade extrapolation ionization chamber was preliminary evaluated for the establishment of a CT beam primary standard. The aim of this study was to determine the influence that the various components of the extrapolation chamber may present on the energy deposited in its sensitive volume. Different materials for its collecting electrode were also studied for this type of radiation beam. The evaluation of the homemade extrapolation chamber showed the highest influence of 25.9% for the collecting electrode, and the best material for the collecting electrode for CT radiation beams was graphite.

A convex windowless extrapolation chamber to measure surface dose rate from 106 Ru/106 Rh episcleral plaques.

A convex windowless extrapolation chamber was developed as a primary measurement device to determine surface dose rate from curved 106 Ru/106 Rh episcleral plaques. A convex extrapolation chamber without an entrance window was constructed for this work, and surface dose rate measurements were performed with two curved CCB-type 106 Ru/106 Rh plaques (S/N 2545 and 2596) manufactured by Eckert & Ziegler BEBIG. FARO Gage measurements were performed to verify the radius of curvature for the convex electrode and the concave plaque surface. Furthermore, the collecting electrode area was verified through capacitance measurements. Chamber correction factors for divergence and backscatter were generated using the EGSnrc cavity user code. For each source, surface dose rate was measured with the convex extrapolation chamber and compared with on-contact measurements made with curved un-laminated EBT3 film strips. A Monte Carlo correction was generated for radiochromic film measurements to account for volume averaging within the active layer and effects of phantom scatter. Additionally, extrapolation chamber results for each plaque were compared with scintillation detector measurements performed by the manufacturer. For the second source (S/N 2596), a comparison was also made with the Monte Carlo-corrected surface dose rate measured at the National Physical Laboratory (NPL) using cylindrical alanine pellets. Finally, source measurements were performed using conventional ionization chambers (Exradin A26, A1SL, and A20) within a custom fixture to investigate the transfer of extrapolation chamber surface dose rate to clinics. For the first 106 Ru/106 Rh plaque (S/N 2545), average surface dose rate from the convex windowless extrapolation chamber was found to be 1.5% higher than the corresponding value from curved un-laminated EBT3 film measurements and 5.6% lower than the manufacturer value. For the second source (S/N 2596), the extrapolation chamber surface dose rate was 2.5% higher than the un-laminated EBT3 film result, 4.5% lower than the manufacturer value, and 3.9% higher compared to corrected alanine measurements made at NPL. Total uncertainty in the extrapolation chamber measurement was estimated to be approximately ±7.0% (k=2). For the plaque measurements made using conventional ionization chambers with a custom fixture, surface dose rate from the transfer technique was found to agree within 3.8% with the expected convex extrapolation chamber result for S/N 2596. A convex windowless extrapolation chamber was developed as a primary measurement device for 106 Ru/106 Rh plaques. Through comparison with the extrapolation chamber, the accuracy of surface dose rate measurements from current dosimetry techniques was assessed and agreement was seen within 5.6%. Finally, it was found that conventional ionization chambers could be calibrated with a reference 106 Ru/106 Rh plaque in order to transfer the extrapolation chamber result for surface dose rate to clinics.

MEASUREMENT OF OPERATIONAL QUANTITIES Hp(0.07) AND Hp(3) FOR INDIGENOUSLY DEVELOPED 106Ru/106Rh SOURCE USING AN EXTRAPOLATION CHAMBER.

In the present study, a prototype 106Ru/106Rh source was fabricated using high level liquid waste from reactor fuel, fixed in a stainless steel housing with a window and backing made of silver. The study involves measurement of the operational quantities Hp(0.07), Hp(3) and the percentage depth dose (PDD) using an extrapolation chamber. It also involves determination of necessary correction factors to arrive at Hp(0.07) and Hp(3) following International Organisation for Standardisation (ISO) and methods suggested in literature. The study facilitates incorporation of the 106Ru/106Rh source as a beta reference source for quality assurance programme in TLD personnel monitoring as per the guidelines of ISO.