Air Kerma Rate Research Articles

Geometrical model for calculating the effect of surface morphology on total x-ray output of medical x-ray tubes.

PurposeCorrelation of characteristic surface appearance and surface roughness with measured air kerma (kinetic energy released in air) reduction of tungsten‐rhenium (WRe) stationary anode surfaces.MethodsA stationary anode test system was developed and used to alter nine initially ground sample surfaces through thermal cycling at high temperatures. A geometrical model based on high resolution surface data was implemented to correlate the measured reduction of the air kerma rate with the changing surface appearance of the samples. In addition to the nine thermally cycled samples, three samples received synthetic surface structuring to prove the applicability of the model to nonconventional surface alterations. Representative surface data and surface roughness values were acquired by laser scanning confocal microscopy.ResultsAfter thermal cycling in the stationary anode test system, the samples showed surface features comparable to rotating anodes after long‐time operation. The established model enables the appearance of characteristic surface features like crack networks, pitting, and local melting to be linked to the local x‐ray output at 100 kV tube voltage ,10° anode take off angle and 2 mm of added Al filtration. The results from the conducted air kerma measurements were compared to the predicted total x‐ray output reduction from the geometrical model and show, on average, less than 10 % error within the 12 tested samples. In certain boundaries, the calculated surface roughness Ra showed a linear correlation with the measured air kerma reduction when samples were having comparable damaging characteristics and similar operation parameters. The orientation of the surface features had a strong impact on the measured air kerma rate which was shown by testing synthetically structured surfaces.ConclusionsThe geometrical model used herein considers and describes the effect of individual surface features on the x‐ray output. In close boundaries arithmetic surface roughness Ra was found to be a useful characteristic value on estimating the effect of surface damage on total x‐ray output.

Analysis of Long-Term Quality Control Data for a 137Cs Dosimetry Calibration Source.

Strict quality assurance programs are required for many radiological applications, but these seldom exist for verifying dosimetry calibration sources. After initial characterization of a dosimetry calibration facility, quality control procedures are recommended to ensure the early detection of any changes or malfunctions. These also result in refined knowledge about average dose rate and experimental variations in dose delivery. This paper describes the implementation of a phase I quality control protocol for a 137Cs dosimetry calibration source and includes an analysis of the resulting data collected over a 24-mo period. During this time, substantial data was collected to establish trial control limits. Air kerma rate measurements were obtained using an ion chamber and were adjusted for decay, corrected for ambient temperature, pressure and humidity, and then analyzed using quality control charts. Three variations of rational subgrouping methods were used in order to find assignable causes of error, and Nelson's Rules were followed to detect any non-random statistical variations. Measurements were subgrouped according to same-day measurements in order to detect positional errors as well as atmospheric correction errors. Additionally, measurements were subgrouped according to analogous experimental setups in order to detect failure in equipment or incorrect settings. Both were analyzed using the X-bar and R chart method. Similarly, individuals and moving ranges charts were used to carefully examine each position in order to observe any situational errors that may occur which include timing, positional, or interference errors. Each method was successful in identifying unique out-of-control data points that occurred during the phase I application of forming control limits. Over the 24-mo period, enough data points were deemed in-control to establish reliable trial limits. Future experiments will include the phase II application of gaining more reliable measurements in order to fine-tune the limits, as well as performing a designed experiment, where variables are purposefully changed in order to test the variation of the data.

APMP Key comparison report of reference air kerma rate for HDR 192Ir brachytherapy sources (BIPM KCDB: APMP.RI(I)-K8)

Main textThe APMP/TCRI Dosimetry Working Group performed the APMP.RI(I)-K8 key comparison of the reference air kerma rate for high-dose-rate (HDR) 192Ir brachytherapy sources between 2016 and 2018. Eight laboratories, including seven national metrology institutes (NMIs), took part in the comparison. Two commercial well-type chambers were used as transfer instruments and circulated among the participants. The results showed that the maximum difference between the participants and the BIPM, evaluated using the comparison data of the linking laboratories NMIJ and NRC, was less than 4%. The degrees of equivalence for the participants were calculated, so that results for the six non-linking laboratories may be included in the Key Comparison Database (KCDB).To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Establishment and Dissemination of Radiological Standards in the Field of Diagnostic Radiology in India.

Background:The increased use of ionizing radiation for diagnostic purpose has resulted in an increase in the world population dose. Patient dosimetry in X-ray diagnostic radiology is required to establish diagnostic reference levels (DRLs) and to assess the average dose received by organs and tissues. International bodies have recommended DRLs to be based on dosimetric quantities.Aim:To cater to the increased requirement for dosimetry in diagnostic radiology, international guidelines are provided to establish and disseminate traceable calibration for dosimeters used in X-ray diagnostic radiology. X-ray diagnostic beams established are standardized using a diagnostic range free-air ionization chamber (DFAIC) (20-150 kV).Materials and Methods:Characterization of the DFAIC and determination of the correction factors for the air kerma measurements were evaluated experimentally and by theoretical calculations.Results:The paper details the establishment of 18 diagnostic beam qualities using DFAIC along with the associated uncertainties. The overall uncertainty for the air kerma measurements was within ±0.5% at 1 sigma level. Eight diagnostic range air kerma measurements using DFAIC were compared with the medium energy primary standard FAIC (50–300 kV) maintained in the laboratory.Conclusion:The air kerma rates agreed within ±1% and are within the overall standard uncertainty of both the chambers at the time of the comparison. Dissemination to the users in the field of diagnostic radiology in the country has been carried out by calibrating their ionization chambers and solid-state detector-based instruments against the DFAIC. The methodology followed to standardize the beams using DFAIC and calibration of dosimeters is presented in this work.

Radioactivity of building materials in Mahallat, Iran – an area exposed to a high level of natural background radiation – attenuation of external radiation doses

In this study, mass activity of naturally occurring radioactive materials were measured in twenty-three building material samples, use extensively in the area exposed to a high level of natural background radiation (Mahallat, Iran), to determine the radioactivity index and changes to the level of indoor gamma radiation. The mass activity of 232Th, 226Ra and 40K were within the ranges from 18 ± 3 to 44 ± 10 Bq/kg (average of 27 ± 6 Bq/kg), 22 ± 5 to 53 ± 14 Bq/kg (average of 34 ± 6 Bq/kg) and 82 ± 18 to 428 ± 79 Bq/kg (average of 276 ± 58 Bq/kg), respectively. The gamma dose rates for population were estimated between 48 ± 9 and 111 ± 26 nGy/h with exception of radon exhalation from building materials. Since the air kerma rate in the town varies from 0.8 to 4 μGy/h, the attenuation coefficient was calculated for buildings made of the aforementioned materials. Additionally, the annual gamma radiation doses for inhabitants were calculated based on time spent outdoors and indoors.

Response of 4H-SiC Detectors to Ionizing Particles

We report the response of newly designed 4H-SiC Schottky barrier diode (SBD) detector prototype to alpha and gamma radiation. We studied detectors of three different active area sizes (1 × 1, 2 × 2 and 3 × 3 mm2), while all detectors had the same 4H-SiC epi-layer thickness of approximately µm, sufficient to stop alpha particles up to 6.8 MeV, which have been used in this study. The detector response to the various alpha emitters in the 3.27 MeV to 8.79 MeV energy range clearly demonstrates the excellent linear response to alpha emissions of the detectors with the increasing active area. The detector response in gamma radiation field of Co-60 and Cs-137 sources showed a linear response to air kerma and to different air kerma rates as well, up to 4.49 Gy/h. The detector response is not in saturation for the dose rates lower than 15.3 mGy/min and that its measuring range for gamma radiation with energies of 662 keV, 1.17 MeV and 1.33 MeV is from 0.5 mGy/h–917 mGy/h. No changes to electrical properties of pristine and tested 4H-SiC SBD detectors, supported by a negligible change in carbon vacancy defect density and no creation of other deep levels, demonstrates the radiation hardness of these 4H-SiC detectors.

Benchmarking FLUKA Monte Carlo code with international measurement standard for air kerma

Various Monte Carlo codes have been used for a long time in gamma ray calibration. However, to the best of our knowledge, no studies have employed the FLUKA MC code for the simulation of photon transport in an accredited calibration laboratory. This study aimed to model the benchmark of the international standard of the air kerma rate and the air kerma rates calculated by FLUKA simulation. As a comparative analysis tool, the linear regression equation used in the accredited calibration laboratory was used. After normalizing the measured and simulated values, a deviation of up to 1.0% was observed, and all the calculated air kerma rates were consistent within the uncertainty. In the analysis using the linear regression equation, the slope and interpolation uncertainty were consistent. Furthermore, the regression error was extremely small, and excellent linearity was observed. Thus, the coefficient of determination was calculated to be five or more. Since calibration sets the standard of every measurement, our study will encourage the application of FLUKA for simulations in various fields involving photons.

New S-chamber Mid-Term electrets: Experimental characterization and uncertainty evaluation

Electret ion chambers are widely used passive detectors, employed for measurements of radon activity concentration in air. These devices are made of a Teflon electret coupled to an interchangeable ion chamber. A new type of electret produced by Rad Elec Inc., named Mid-Term, is used together with the S-type (200cm3) chamber. It is designed to be operated in an intermediate range with respect to the standard Short-Term and Long-Term electrets. This work describes the complete characterization of such device, performed according to the ISO guidelines. The characterization was carried out in the secondary standard calibration laboratory of Politecnico di Milano Italy, and with a traceable radon chamber. The coefficients and equations presented can be used by operators to assess both the radon activity concentration and the related uncertainty, with the only requirement of the knowledge of the background gamma air kerma rate of the specific measurement site and its related uncertainty.

A study of the impact of x-ray tube performance on angiography system imaging efficiency

This work compared the impact of x-ray tube performance and automatic dose rate control (ADRC) parameter selection on system imaging efficiency of two Siemens angiography systems: a Siemens Megalix x-ray tube installed on an Artis Zee system (denoted ‘MEGALIX’) and a newer generation Gigalix x-ray tube installed on an Artis Q (denoted ‘GIGALIX’). A method was used that accounted for two potential sources of bias in this comparison: differences in radiation output between the x-ray tubes and differences between the x-ray detectors on the two systems. First, ADRC x-ray factors (tube voltage, tube current, pulse length, focus size, spectral prefilter) and radiation output were recorded as a function of poly(methyl) methacrylate (PMMA) thickness on the MEGALIX unit. These factors were then applied manually on the GIGALIX system and incident air kerma rate (IAKR) and signal difference to noise ratio (SDNR) were measured. Second, the ADRC on the GIGALIX system was used to give the x-ray factors and both IAKR and SDNR relevant to the GIGALIX based system directly. This method enabled the SDNR to be measured from images acquired on the same x-ray detector. SDNR and IAKR were measured on both systems using a PMMA phantom covering thicknesses from 6 cm to 40 cm. A small 0.3 mm iron insert was used to measure SDNR, which was then multiplied by modulation transfer function based weighting factors for focal spot blurring and motion blurring. These factors were evaluated for an object motion of 25 mm s−1 and at a spatial frequency of 1.4 mm−1 in the object plane, relevant to interventional cardiology, giving a spatial frequency dependent SDNR(u). In the second phase of the study, a technical figure of merit (FOM) was used to express imaging performance of both systems, calculated as SDNR2(u)/IAKR. Averaged over all phantom thicknesses, the FOM of the GIGALIX-based system was 42% and 73% higher compared to that of the MEGALIX based system, for fluoroscopy and acquisition mode respectively. The results indicate that increased x-ray tube power and smaller foci can improve overall system efficiency and reduce doses.

End-to-end dosimetric audit: A novel procedure developed for Irish HDR brachytherapy centres.

A dosimetric audit of Ir-192 high dose rate (HDR) brachytherapy remote after-loading units was carried out in 2019. All six brachytherapy departments on the island of Ireland participated in an end-to-end test and in a review of local HDR dosimetry procedures. A 3D-printed customised phantom was created to position the following detectors at known distances from the HDR source: a Farmer ionization chamber, GafChromic film and thermoluminescent dosimeters (TLDs). Dedicated HDR applicator needles were used to position an Ir-192 source at 2cm distance from these detectors. The end-to-end dosimetry audit pathway was performed at each host site and included the stages of imaging, applicator reconstruction, treatment planning and delivery. Deviations between planned and measured dose distributions were quantified using gamma analysis methods. Local procedures were also discussed between auditors and hosts. The mean difference between Reference Air Kerma Rate (RAKR) measured during the audit and RAKR specified by the vendor source certificate was 1.3%. The results of end-to-end tests showed a mean difference between calculated and measured dose of 2.5% with TLDs and less than 0.5% with Farmer chamber measurements. GafChromic films showed a mean gamma passing rates of >95% for plastic and metal applicators with 2%/1 mm global tolerance criteria. The results of this audit indicate dosimetric consistency between centres. The 'end to end' dosimetry audit methodology for HDR brachytherapy has been successfully implemented in a multicentre environment, which included different models of Ir-192 sources and different treatment planning systems. The ability to create a 3D-printed water-equivalent phantom customised to accurately position all three detector types simultaneously at controlled distances from the Ir-192 source under evaluation gives good reproducibility for end-to-end methodology.

Feasibility of dosimetric measurements using Al2O3:C OSL dosimeter during fluoroscopy-guided procedures

This study investigated the feasibility of dosimetric measurements using Al2O3:C optically stimulated luminescence (OSL) dosimeters during fluoroscopy-guided procedures. The linearity and energy dependence of Al2O3:C OSL dosimeters were evaluated, and the air kerma rate at the operator’s position was measured. The response of Al2O3:C OSL dosimeters to short, repetitive irradiations was compared to that of long uninterrupted irradiation. The change in response of the Al2O3:C OSL dosimeter under automatic exposure rate control (AERC) was evaluated with the use of various thicknesses of polymethyl-methacrylate (PMMA) plates (15–30 cm). The Al2O3:C OSL dosimeters could detect 5 µGy and showed good linearity in doses of ≥10 µGy (R2: 0.997–0.999, p < 0.001). The relative response of the Al2O3:C OSL dosimeter normalised to that of 36.8 keV was 0.828–1.101 at the energies investigated (30.6–46.0 keV). The air kerma rate at the operator’s position was estimated to be 2.61–7.17 µGy min−1 depending on the heights representing different body parts. Repetitive short irradiations had no significant impact on the relative response of the Al2O3:C OSL dosimeters (p > 0.05). Despite a high energy dependence on the low energy beam used in fluoroscopy, the change in relative response of the Al2O3:C OSL dosimeter under AERC was within 5.7% depending on the thickness of the PMMA plates. Dosimetric measurement using Al2O3:C OSL dosimeters for patients and operators is feasible. However, one should be cautious about high standard deviations when measuring small doses of ≤20 µGy using Al2O3:C OSL dosimeters. It is essential to perform intensive bleaching before measuring very small doses to minimise pre-irradiation counts.

GET 8–2019 State Primary Standard of Units of Air Kerma, Air Kerma Rate, Exposure, Exposure Rate, and Energy Flux of X-Radiation and Gamma Radiation

Results of studies designed to improve GET 8–2011, the State Primary Standard of the units of air kerma, air kerma rate, exposure, exposure rate, and energy flux of x-radiation and gamma radiation, are described. The studies are performed in 2019 to implement the recommendations of Report No. 90, Key Data for Dosimetry of Ionizing Radiation: Standards and Applications, International Commission on Radiation Units and Measurements. The following changes are introduced into the equation for reproduction of the units of quantities in GET 8–2019: in the field of x-radiation, new correction factors for free-air ionization chambers are introduced and the value of the relative standard uncertainty of the mean ionization energy is changed; in the field of gamma radiation, the values of the product of the mean ionization energy and ratio of the mass stopping powers of graphite to air in measurements with cavity ionization chambers are changed. More accurate values of the units of quantities reproduced by GET 8–2019 are obtained.

Investigating the air kerma rate constant for 241Am through first principle calculations and simulation

The air kerma rate constant is important for estimating radiation dose and shielding calculations to ensure radiation exposure is as low as reasonably achievable (ALARA). Currently, there are significant deviations in this constant reported for 241Am by various institutions. Therefore, through first principle calculations and simulation, we investigate the air kerma rate constant for 241Am based on photon energies and emission probabilities reported in literature.

Determination of the absorbed dose to water for medium-energy x-ray beams using Fricke dosimetry.

For x-ray beams in the low and medium energy range, reference dosimetry is established in terms of air kerma. Fricke dosimetry has shown great potential in the absolute measurements of the absorbed dose to water for high-energy ranges. Therefore, the main purpose of this work was to compare the absorbed dose to water for medium-energy x-ray beams obtained through Fricke dosimetry with that obtained from the air kerma rate. To determine the absorbed dose to water using Fricke dosimetry, the polyethylene bags methodology was chosen. Fricke solution was irradiated at four different beam qualities. The absorbed dose to water values obtained using Fricke dosimetry were compared to those obtained using the standard protocol, using the Z-score. Values of the Z-score were <2 for all measurements of absorbed dose to water, which means that the values obtained using Fricke dosimetry are equivalent to those obtained using the reference protocol. The combined standard uncertainty for the absorbed dose to water obtained by Fricke dosimetry was lower than that obtained with the ionization chamber. Chemical dosimetry using a standard FeSO4 solution has been demonstrated to be a potential option as a standard for the quantity absorbed dose to water for medium kV x-ray qualities.

The Measurement of the Air-Kerma Rate in Air and a Solid Phantom with Ionization Chambers for a 192Ir HDR Brachytherapy Source.

IntroductionThis study aims to measure the air-kerma rate of 192-Ir-HDR-afterloading source with an ionization chamber in air and a solid cylindrical phantom separately and to compare the dose calibration by the American Association of Physicists in Medicine (AAPM) Task Group TG-43U1 formalism with the Abacus treatment planning system (TPS).Materials and MethodsThe air-kerma rate of 192Ir source was measured by an ionization chamber in air and a solid cylindrical phantom separately. For the interesting point position P (8cm, 90°), the values of the dose were calculated with the TG-43U1 formula and compared with data from the Abacus TPS with single and multiple dwell positions, respectively.ResultsThe air-kerma rate percentage deviations between the detector measurements in air and the source certificate were −1.28%, −0.91%, −0.71%, and 0.33% at the distances of 25cm, 50cm, 75cm, and 100cm, respectively. For the measurement in solid cylindrical phantom, the percent deviation from the air-kerma rate certificate was 1.85%. The percentage deviations of the dose calibration between Abacus TPS and TG-43U1 formalism at P (8cm, 90°) were −2.30%, 1.76%, and 2.10% with different distances (between the dwell positions) of 0cm, 0.5cm, and 1cm, respectively.ConclusionThe in-air technique was a new attempt for clinic routine measurement. Further studies are still necessary. As a treatment planning system, the Abacus TPS should apply the AAPM TG-43U1 formulism for the development required in the future.

Addressing the burden of cervical cancer through IAEA global brachytherapy initiatives

PurposeBrachytherapy (BT) is an essential component of definitive therapy for locally advanced cervical cancer. Despite the advantages of the dose distribution with BT in cervical cancer, there is paucity of specific skills required for good-quality BT applications. Furthermore, replacing BT with other modern external beam techniques as a boost can lead to suboptimal results in cervix cancer. Methods and MaterialsReview of available IAEA resources, research and cooperation programs available from the IAEA was completed. These opportunities can be used to address challenges in Brachytherapy.The International Atomic Energy Agency (IAEA) provides support for BT through various means that includes education and training, both long term, short term and continuing medical education of professionals, providing expert visits to support implementation, development of curricula for professionals, e-learning through the human health campus, contouring workshops, 2D to 3D BT training, and virtual tumor boards. In addition, the IAEA provides support for implementing quality assurance in radiotherapy to its member states and provides guidelines for comprehensive audits in radiation therapy (QUATRO), and produces safety standards and training in radiation safety. In addition, mapping BT resources, making the case for investment and support for setting up BT services and radiotherapy centers are also available. The IAEA Dosimetry Laboratory provides calibration services to Secondary Standards Dosimetry Laboratories for well chambers used to confirm the reference air kerma rate of Co60 and Ir192 high-dose-rate BT sources, as well as for Cs137 low-dose-rate sources.Furthermore, the IAEA supports research and development in radiotherapy (and BT) through coordinated research activities that include controlled randomized clinical trials, Patterns of Care studies among others. Partnerships with professional organizations and funding bodies, as well as through the United Nations Joint Global Programme on Cervical Cancer Prevention and Control support radiotherapy activities, including BT in countries worldwide. ConclusionThe IAEA supports brachytherapy implementation, training and research and provides resources to professionals in the area.

A PRELIMINARY STUDY OF RADIATION QUALITY CORRECTION FACTOR (KQ) DETERMINATION FOR WELL-TYPE IONIZATION CHAMBER

This paper deals with the determination of the radiation quality correction factor (kQ) well-type ionization chamber for the measurement of Co-60 brachytherapy. The measurement of the brachytherapy source has been done in the hospital brachytherapy facilities. The measurement of air Kerma has been done using three different ionization chambers 0.6 cm3, 30 cm3, 80 cm3, which have calibration factor traceability for Co-60 and one well-type ionization chamber which calibrated for Ir-192. The determination of the radiation quality correction factor (kQ) was determined based on the results of the air Kerma ratio between measurements using ionization chambers, which have traceability to Co-60 and Ir-192 sources. The results of the measurement of the reference air Kerma rate (RAKR) obtained from the three chambers were 21.36, 19.87, 19.34 mGy.m2.h-1, while the results of measurements with ionization chambers get a value of 19.01 mGy.m2.h-1. The kQCal results from 0.6 cm3 ionization chamber get a value of 1.07. The kQCal value was compared with the value of Andreas Schuller’s et al. kQreff of 1.05 and get a deviation of 2.2%. Implementation of the booth kQ value on the results of the RAKR from the HDR1000Plus well-type ionization chamber in the measurement of brachytherapy in two different facilities gets maximal deviation 1.7% with dose value from Treatment Planning System (TPS). The deviation was in the acceptable range of ±5%. Based on this, the use of radiation quality correction factor (kQ) value can be implemented as one method if it does not have the traceability factor calibration of the Co-60 brachytherapy source.

Study the Calibration of the High Dose Rate Brachytherapy Radioactive Source 60Co

Aim of this work is to calibrate the high dose rate (HDR) brachytherapy source 60Co. The radioactive source calibration is a very important part of the quality assurance program for dosimetry of brachytherapy source. The goal of this project is the calibration of HDR Brachytherapy source in radiation therapy is the measurement of the air kerma rate which required actual dose to deliver. The source calibration is an essential part of the quality assurance program for dosimetry of brachytherapy source. This research will help the patient who is involving brachytherapy treatment. HDR brachytherapy source 60Co is inserted directly or in close to the tumor. Most commonly using method for calibration of HDR brachytherapy source 60CO is well type ionization chamber. Calibration of the radioactive source 60Co brachytherapy source is very important for the treatment of cancer patient. We have got the variation between RAKR from TPS and measured Air Kerma Rate of 60Co brachytherapy source are 3.2% and 3.04% and which give very good agreement with the Air Kerma Rate (RAKR) is 5% (from BEBIG protocol, Germany). So, our results were satisfied for brachytherapy treatment. From these results, it must be concluded that, 60Co brachytherapy source is suitable for brachytherapy cancer treatment. It is very difficult to calculate treatment deliver dose without calibrating AKR of HDR brachytherapy source. It is very important to verify the calculated Air Kerma Rate by TPS Air Kerma Rate.

A comparison between revised Manchester Point A and ICRU-89–recommended Point A definition absorbed-dose reporting using CT images in intracavitary brachytherapy for patients with cervical carcinoma

PurposeThis study is a comparison between revised Manchester Point A and International Commission on Radiation Units and measurements (ICRU) 89 report–recommended Point A absorbed-dose reporting in intracavitary brachytherapy for patients with cervical carcinoma. Methods and MaterialsThe retrospective dosimetric study is based on the data of 32 patients with cervical carcinoma treated with high-dose-rate brachytherapy. Patients received 21 Gy in three fractions (7.0 Gy X three fractions) to Point A (Aflange, revised Manchester definition). All the patients were replanned with a new Point A (Aicru89) defined on CT images as per the American Brachytherapy Society/ICRU-89. The data collected were compared with the data obtained from Point A (Aflange). ResultsWhen using the Aflange plan normalization method, the mean dose of 0.1 cc, 1 cc, and 2 cc bladder volumes was 820.79 ± 207.47 cGy, 654.66 ± 152.69 cGy, and 588.91 ± 136.35 cGy, respectively. Likewise, when using the ICRU-89 Point Aicru89 normalization method, the mean dose of 0.1 cc, 1 cc, and 2 cc bladder volumes was 869.30 ± 224.67 cGy, 693.24 ± 166.20 cGy, and 616.61 ± 150.32 cGy, respectively. For the rectum, Point Aflange normalization plans, the mean dose of 0.1 cc, 1 cc, and 2 cc volumes was 589.37 ± 163.26 cGy, 487.51 ± 126.03 cGy, and 442.70 ± 111.43 cGy, respectively. Likewise, using the Aicru89 plan, the mean 0.1 cc, 1 cc, and 2 cc rectum volume was 625.07 ± 171.31 cGy, 517.50 ± 131.05 cGy, 464.94 ± 121.81 cGy, respectively. The statistical mean difference of Total Reference Air Kerma rate, V100 (cc), bladder, rectum and sigmoid, was found significant. ConclusionsIt has been found that the position of revised Manchester (Aflange) and ICRU-89 Point A does not match on CT images/radiograph, which resulted in variation in doses to the tumor, V100 (cc), organ at risk, and Total Reference Air Kerma.

Performance evaluation of near-real time angular tube current modulation in X-ray computed tomography using real-time dosimeter: a phantom study

In X-ray computed tomography (CT), angular tube current modulation (TCM) minimizes the unnecessary travel of X-rays in the anteroposterior direction. This study aimed to evaluate the performance of near-real time angular TCM in a CT scanner using a real-time dosimeter when different-sized elliptical phantoms were scanned. Air kerma and air kerma rate profiles of small and large elliptical phantoms were measured using a solid-state detector with a fixed tube current (FTC) and TCM with the same volume CT dose index (6.20 mGy for the small phantom and 12.32 mGy for the large phantom) displayed on the CT console. Image noises were evaluated by measuring the standard deviation of CT numbers in specific regions in the phantoms. The air kerma at the central and upper and lower peripheral holes were decreased with TCM, whereas air kerma at left and right peripheral holes were increased. With both phantom sizes, the air kerma rate profiles stabilized when TCM was used after the first two cycles. The standard deviations of CT numbers in images of the small phantom were 10.7 ± 1.3 and 10.3 ± 1.2 Hounsfield units (HU) with the FTC and TCM, respectively, and those of the large phantom were 20.6 ± 2.0 and 19.6 ± 1.7 HU, respectively. Therefore, angular TCM can adjust the tube current during each tube rotation according to the phantom’s angular attenuation profile and can decrease the image noises. It can also decrease the variance of air kerma within the in-plane direction.