Scatter Contribution Research Articles

Solid-state dosimeters: a new approach for mammography measurements.

To compare responses of modern commercially available solid-state dosimeters (SStDs) used in mammography medical physics surveys for two major vendors of current digital mammography units. To compare differences in dose estimates among SStD responses with ionization chamber (IC) measurements for several target/filter (TF) combinations and report their characteristics. To review scientific bases for measurements of quantities required for mammography for traditional measurement procedures and SStDs. SStDs designed for use with modern digital mammography units were acquired for evaluation from four manufacturers. Each instrument was evaluated under similar conditions with the available mammography beams provided by two modern full-field digital mammography units in clinical use: a GE Healthcare Senographe Essential (Essential) and a Hologic Selenia Dimensions 5000 (Dimensions), with TFs of Mo/Mo, Mo/Rh; and Rh/Rh and W/Rh, W/Ag, and W/Al, respectively. Measurements were compared among the instruments for the TFs over their respective clinical ranges of peak tube potentials for kVp and half-value layer (HVL) measurements. Comparisons for air kerma (AK) and their associated relative calculated average glandular doses (AGDs), i.e., using fixed mAs, were evaluated over the limited range of 28-30 kVp. Measurements were compared with reference IC measurements for AK, reference HVLs and calculated AGD, for two compression paddle heights for AK, to evaluate scatter effects from compression paddles. SStDs may require different positioning from current mammography measurement protocols. Measurements of kVp were accurate in general for the SStDs (within -1.2 and +1.1 kVp) for all instruments over a wide range of set kVp's and TFs and most accurate for Mo/Mo and W/Rh. Discrepancies between measurements and reference values were greater for HVL and AK. Measured HVL values differed from reference values by -6.5% to +3.5% depending on the SStD and TF. AK measurements over limited (28-30) kVp's ranged from -6% to +7% for SStDs, compared with IC reference values. Relative AGDs for each SStD using its associated measurements of kVp, HVL and AK underestimated AGD in nearly all cases, compared with reference IC values, with discrepancies of <-1% to ∼-10%. Some differences in AGD were related to differences in contributions of compression paddle scatter to AK measurements made by ICs. Applying measured factors for scatter effects in AK measurements for three SStDs reduced discrepancies between -6.2% and +1.3%, shifting AGDs from SStDs closer to IC AGDs. This study revealed that SStD measurements yielded good agreement with set kVp, poor agreement with standard HVL determinations, and AK measurements that were substantially different from IC measurements. Discrepancies are partly related to the scattered radiation measured by ICs in determining AK. As a result, IC measurements required for AGD, using currently accepted methodology, typically result in higher AGDs than SStDs, because current methodologies do not account for differing instrument responses to scatter. HVLs reported by SStDs contribute to discrepancies in calculated AGD that depend on kVp and TF. Medical physicists are encouraged to compare their results for SStD instruments using a similar methodology for potential discrepancies with their traditional instruments.

ИССЛЕДОВАНИЕ ВКЛАДОВ РАССЕЯНИЯ И ПОГЛОЩЕНИЯ СВЕТА ВКЛЮЧЕНИЯМИ НАНОЧАСТИЦ АЛЮМИНИЯ В ТЭНЕ

ИССЛЕДОВАНИЕ ВКЛАДОВ РАССЕЯНИЯ И ПОГЛОЩЕНИЯ СВЕТА ВКЛЮЧЕНИЯМИ НАНОЧАСТИЦ АЛЮМИНИЯ В ТЭНЕ

Extraction of absorption and scattering contribution of metallic nanoparticles toward rational synthesis and application.

Noble metal nanoparticles have unique localized surface plasmon resonance (LSPR), leading to their strong absorption and scattering in the visible light range. Up to date, the common practice in the selection of nanoparticles for a specific application is still based on the measured extinction spectra. This practice may be erroneous, because the extinction spectra contain both absorption and scattering contribution that may play different roles in different applications. It would be highly desirable to develop an efficient way to obtain the absorption and scattering spectra simultaneously. Herein, we develop a method to use the experimentally measured extinction and scattering signals to extract the absorption and scattering spectra that is in excellent agreement with that simulated by discrete dipole approximation (DDA). The heating curve measurement on the three types of gold nanorods, with almost the same extinction spectra but different absorption and scattering contribution, convincingly reveals an excellent correlation between the heating effect and the absorption strength rather than the extinction strength. The result demonstrates the importance to obtain the scattering and absorption spectra to predict the potential application for different types of nanoparticles, which in turn will screen efficiently nanoparticles for a specific application.

Characterization of scatter magnitude and distribution in dedicated breast computed tomography with bowtie filters.

Scatter contamination of projection images in cone-beam computed tomography (CT) degrades the image quality. The use of bowtie filters in dedicated breast CT can decrease this scatter contribution. Three bowtie filter designs that compensate for one or more aspects of the beam-modifying effects due to differences in path length in a projection were studied. These designs have been investigated in terms of their ability to reduce the scatter contamination in projection images acquired in a dedicated breast CT geometry. The scatter magnitude was measured as the scatter-to-primary ratio (SPR) using experimental and Monte Carlo techniques for various breast phantom diameters and tube voltages. The results show that a 55% reduction in the center SPR value could be obtained with the bowtie filter designs. On average, the bowtie filters reduced the center SPR by approximately 18% over all breast diameters. The distribution of the scatter was calculated at a range of different locations to produce scatter distribution maps for all three bowtie filter designs. With the inclusion of the bowtie filters, the scatter distribution was more uniform for all breast diameters. The results of this study will be useful in designing scatter correction methods and understanding the benefits of bowtie filters in dedicated breast CT.

A library least-squares approach for scatter correction in gamma-ray tomography

Abstract Scattered radiation is known to lead to distortion in reconstructed images in Computed Tomography (CT). The effects of scattered radiation are especially more pronounced in non-scanning, multiple source systems which are preferred for flow imaging where the instantaneous density distribution of the flow components is of interest. In this work, a new method based on a library least-squares (LLS) approach is proposed as a means of estimating the scatter contribution and correcting for this. The validity of the proposed method is tested using the 85-channel industrial gamma-ray tomograph previously developed at the University of Bergen (UoB). The results presented here confirm that the LLS approach can effectively estimate the amounts of transmission and scatter components in any given detector in the UoB gamma-ray tomography system.

Sci-Fri AM: Mountain - 03: Current status of the NRC primary standard for 192 Ir HDR brachytherapy sources

The Canadian primary standard for 192Ir HDR brachytherapy sources has been recently revised in a more accurate manner allowing for more realistic uncertainty estimation. Air-kerma strength Sk is derived from measurements of the source's output using a graphite-walled spherical ionization chamber (2S) at several distances. Traceability to NRC primary standards for the 192Ir calibration coefficient Nk is insured by estimating it as the inverse arithmetic mean of the inverse of the calibration coefficients for a 137Cs beam and the medium energy x-ray beam quality N250, both of which are traceable to NRC primary standards. The multiple-distance method is combined with a non-linear least squares fit to determine St, while at the same time removing the effects of room scatter and position offset. The previously used shadow-cone method for directly measuring the room scatter is found to be inadequate due to the increased scatter contribution from the lead cone itself, especially at short source-detector distances. Rather than including the reported 1% difference in source strength for 192Ir HDR sources of different construction into the total uncertainty, users are cautioned that the calibration coefficient provided by NRC is only valid for a microSelectron V2 model. A comprehensive uncertainty budged shows that the total one sigma uncertainty of the standard is actually 0.6% rather than the previously assumed 1.2%. NRC measured Sk agrees within 0.03% of the manufacturer's value.

Hadronic Light-by-Light Scattering Contributions to the Muon Anomaly

I give an overview of what we know at present about the Hadronic Ligh-by-Light Scattering Contribution to the anomalous magnetic moment of the muon in the Standard Model.

Layout optimization method to equalize the best-focus position of different patterns

In optical lithography for microchip manufacturing, it is important that the focal ranges of all patterns in the layout be closely aligned in order to maximize a common process window. In practice, large pattern-dependent variations in the position of the best focus are observed, which have been traced back to phase errors induced on the image-forming beams by scattering from mask topography. We show that this degradation mechanism can be exploited as a source of corrective phase shift, allowing pattern-dependent focus shifts to be controlled purely by changing the details of the mask layout, without requiring a significant change in the mask-making process. Phase distortions in the imaging beams are corrected by the optimized insertion of orthogonally oriented subresolution jogs into existing edges in the layout, thereby introducing a tailored scatter contribution whose quadrature component has the opposite sign from that of the primary edge.

SU-C-12A-01: Primary Vs. Scatter Contribution to Body CTDI: Experiment Results

Purpose: To quantify experimentally scatter contribution to CTDI in center and peripheral holes of the body (32-cm) phantom. Methods: All experiments were performed in Service Mode of 750CT-Discovery with both tube and table were in stationary position, and with large filter and 40- mm collimation. First, transmission through acrylic was measured using acrylic rods of various lengths (1-cm to 33-cm), at 80, 120, and 140 kVp. These data were utilized to obtain dose from primary beam at different depths of acrylic. Thus, scatter-to-primary ratio (SPR) was determined for center-hole by measuring exposure with a pencil chamber. For peripheral hole SPR, dose was measured at eight different tube angles from 0° to 180°. Change in primary dose with tube angle due to both shape of bowtie filter and distance from tube was measured in air; hence, dose from primary from each of the 8 phantom measurements was determined and SPR was calculated by integrating the fitted models for primary and scatter distributions as a function of distance from tube. Also, scatter contribution from different segments of phantom to center-hole dose was measured using a custom-built acrylic phantom, which had similar SPR at the center-hole to that of standard body phantom. Results: After correcting for stray radiation (off-focus, scatter from collimators, etc.) for primary measurements, preliminary results of SPRs in center-hole dose of the body phantom for 80, 120, and 140 kVp were 6.8, 6.2, and 6.0, respectively, and for peripheral hole were 1.45, 1.44, and 1.39. Forward-scatter and backscatter contributions to center dose, at any point during tube rotation, were respectively, 62% and 38% with 80 kVp, and 60% and 40% with 120 and 140 kVp. Conclusion: SPR in both center and peripheral holes of body CTDI phantom was determined experimentally. Also, distribution of contributing scatter to center hole was estimated.

Enhancement and validation of Geant4 Brachytherapy application on clinical HDR 192Ir source

The Geant4 Monte Carlo MC associated Brachytherapy example was adapted, enhanced and several analysis techniques have been developed. The simulation studies the isodose distribution of the total, primary and scattered doses around a Nucletron microSelectron 192Ir source. Different phantom materials were used (water, tissue and bone) and the calculation was conducted at various depths and planes. The work provides an early estimate of the required number of primary events to ultimately achieve a given uncertainty at a given distance, in the otherwise CPU and time consuming clinical MC calculation. The adaptation of the Geant4 toolkit and the enhancements introduced to the code are all validated including the comprehensive decay of the 192Ir source, the materials used to build the geometry, the geometry itself and the calculated scatter to primary dose ratio. The simulation quantitatively illustrates that the scattered dose in the bone medium is larger than its value in water and tissue. As the distance away from the source increases, scatter contribution to dose becomes more significant as the primary dose decreases. The developed code could be viewed as a platform that contains detailed dose calculation model for clinical application of HDR 192Ir in Brachytherapy.

Scatter reduction for high resolution image detectors with a region of interest attenuator.

Compton scatter is the main interaction of x-rays with objects undergoing radiographic and fluoroscopic imaging procedures. Such scatter is responsible for reducing image signal to noise ratio which can negatively impact object detection especially for low contrast objects. To reduce scatter, possible methods are smaller fields-of-view, larger air gaps and the use of an anti-scatter grid. Smaller fields of view may not be acceptable and scanned-beam radiography is not practical for real-time imaging. Air gaps can increase geometric unsharpness and thus degrade image resolution. Deployment of an anti-scatter grid is not well suited for high resolution imagers due to the unavailability of high line density grids needed to prevent grid-line artifacts. However, region of interest (ROI) imaging can be used not only for dose reduction but also for scatter reduction in the ROI. The ROI region receives unattenuated x-rays while the peripheral region receives x-rays reduced in intensity by an ROI attenuator. The scatter within the ROI part of the image originates from both the unattenuated ROI and the attenuated peripheral region. The scatter contribution from the periphery is reduced in intensity because of the reduced primary x-rays in that region and the scatter fraction in the ROI is thus reduced. In this study, the scatter fraction for various kVp's, air-gaps and field sizes was measured for a uniform head equivalent phantom. The scatter fraction in the ROI was calculated using a derived scatter fraction formula, which was validated with experimental measurements. It is shown that use of a ROI attenuator can be an effective way to reduce both scatter and patient dose while maintaining the superior image quality of high resolution detectors.

ITAR: A modified TAR method to determine depth dose distribution for an ophthalmic device that performs kilovoltage x‐ray pencil‐beam stereotaxy

New technology has been developed to treat age-related macular degeneration (AMD) using 100 kVp pencil-beams that enter the patient through the radio-resistant sclera with a depth of interest between 1.6 and 2.6 cm. Measurement of reference and relative dose in a kilovoltage x-ray beam with a 0.42 cm diameter field size and a 15 cm source to axis distance (SAD) is a challenge that is not fully addressed in current guidelines to medical physicists. AAPM's TG-61 gives dosimetry recommendations for low and medium energy x-rays, but not all of them are feasible to follow for this modality. An investigation was conducted to select appropriate equipment for the application. PTW's Type 34013 Soft X-Ray Chamber (Freiburg, Germany) and CIRS's Plastic Water LR (Norfolk, VA) were found to be the best available options. Attenuation curves were measured with minimal scatter contribution and thus called Low Scatter Tissue Air Ratio (LSTAR). A scatter conversion coefficient (C(scat)) was derived through Monte Carlo radiation transport simulation using MCNPX (LANL, Los Alamos, NM) to quantify the difference between a traditional TAR curve and the LSTAR curve. A material conversion coefficient (C(mat)) was determined through experimentation to evaluate the difference in attenuation properties between water and Plastic Water LR. Validity of performing direct dosimetry measurements with a source to detector distance other than the treatment distance, and therefore a different field size due to a fixed collimator, was explored. A method--Integrated Tissue Air Ratio (ITAR)--has been developed that isolates each of the three main radiological effects (distance from source, attenuation, and scatter) during measurement, and integrates them to determine the dose rate to the macula during treatment. LSTAR curves were determined to be field size independent within the range explored, indicating that direct dosimetry measurements may be performed with a source to detector distance of 20 cm even though the SAD is 15 cm during treatment. C(scat) varied from 1.102 to 1.106 within the range of depths of interest. The experimental variance among repeated measurements of C(mat) was larger than depth dependence, so C(mat) was estimated as1.019 for all depths of interest. Equipment selection, measurement techniques, and formalism for the determination of dose rate to the macula during stereotaxy for AMD have been determined and are strongly recommended by the authors of this paper to be used by clinical medical physicists.

Ultra-Fast Hybrid CPU–GPU Multiple Scatter Simulation for 3-D PET

Scatter correction is very important in 3-D PET reconstruction due to a large scatter contribution in measurements. Currently, one of the most popular methods is the so-called single scatter simulation (SSS), which considers single Compton scattering contributions from many randomly distributed scatter points. The SSS enables a fast calculation of scattering with a relatively high accuracy; however, the accuracy of SSS is dependent on the accuracy of tail fitting to find a correct scaling factor, which is often difficult in low photon count measurements. To overcome this drawback as well as to improve accuracy of scatter estimation by incorporating multiple scattering contribution, we propose a multiple scatter simulation (MSS) based on a simplified Monte Carlo (MC) simulation that considers photon migration and interactions due to photoelectric absorption and Compton scattering. Unlike the SSS, the MSS calculates a scaling factor by comparing simulated prompt data with the measured data in the whole volume, which enables a more robust estimation of a scaling factor. Even though the proposed MSS is based on MC, a significant acceleration of the computational time is possible by using a virtual detector array with a larger pitch by exploiting that the scatter distribution varies slowly in spatial domain. Furthermore, our MSS implementation is nicely fit to a parallel implementation using graphic processor unit (GPU). In particular, we exploit a hybrid CPU-GPU technique using the open multiprocessing and the compute unified device architecture, which results in 128.3times faster than using a single CPU. Overall, the computational time of MSS is 9.4s for a high-resolution research tomograph (HRRT) system. The performance of the proposed MSS is validated through actual experiments using an HRRT.

A study on the use of Gafchromic™ EBT3 film for output factor measurements in kilovoltage X-ray beams

Relative output factors are used in radiation therapy for treatment planning purposes including treatments using kilovoltage X-ray beams. The output factor is the relative dose output for a particular applicator relative to a reference applicator. Due to the differences in the scatter contribution from the inside of an applicator, it is more accurate if output factors are measured for all combinations of X-ray beam energy and applicator. Previously published papers and various kilovoltage X-ray beam dosimetry protocols have discussed the validity of using various cylindrical and parallel plate ionization chambers for relative output factor measurements. In this work, we evaluated the suitability of Gafchromic™ EBT3 film for the determination of output factors for kilovoltage X-ray beams. Output factors were measured with Gafchromic™ EBT3 film for beam qualities of 50, 75, 100 and 125kVp and applicator sizes of 2, 3, 4cm diameter, 8×8 and 12×12cm(2) square applicators. The film read out was performed with a flatbed EPSON Expression10000XL scanner. The measured data was compared with benchmark data from measurements using an Advanced Markus ionisation chamber as well as comparing with ratios of published backscatter factor values. The agreement between output factors measured with EBT3 film and the ionisation chamber was generally better than 2%, with the largest difference of 3.3% occurring for the 2cm diameter field with the 50kVp X-ray beam. These differences were consistent with the estimated total uncertainty in the measurements as calculated by the ISO GUM. The agreement between the output factors measured with film and the published BSFs was generally better than 5% but differences of up to 12% occurred for the smallest field size. The results demonstrate that Gafchromic™ EBT3 film is a suitable dosimeter for output factor measurements of kilovoltage X-ray beams.

Volume scattering and reverberation in shallow water: A simplified modeling approach

A simplified physics-based approach is described that allows significantly faster yet reasonably accurate estimations of volume reverberation in complex shallow water environments. An integral expression is presented for scattering intensity with a factorized integrand comprised of two kernels, the double propagator and local volume scattering coefficient. The propagator describes the local intensity and can be calculated using available models, such as PE, normal modes, or ray approximations. The scattering kernel can be specified using available volume scattering models for continuous or discrete heterogeneity of sea-water column and seabed caused by spatial fluctuations of compressibility and density, or randomly distributed discrete targets, such as bubbles, fish, shells, and others. The approach is more general than and can be used for verification of existing reverberation models. For instance, calculation of bottom reverberation is not based on using the equivalent surface scattering strength (although considers it as a particular case). Numerical examples for shallow water reverberation time series, based on a PE propagation model, are presented to estimate potential contributions of different mechanisms of scattering. The estimations provide a comparison of relative contributions of scatterers with the same scattering strengths but located at different depths in water column or in the sediment. [Work supported by the US Office of Naval Research.]

Analytical approach for determining beam profiles in water phantom of symmetric and asymmetric fields of wedged, blocked, and open photon beams.

Nowadays, in most radiotherapy departments, the commercial treatment planning systems (TPS) used to calculate dose distributions needs to be verified; therefore, quick, easy‐to‐use, and low‐cost dose distribution algorithms are desirable to test and verify the performance of the TPS. In this paper, we put forth an analytical method to calculate the phantom scatter contribution and depth dose on the central axis based on the equivalent square concept. Then, this method was generalized to calculate the profiles at any depth and for several field shapes — regular or irregular fields—under symmetry and asymmetry photon beam conditions. Varian 2100 C/D and Siemens Primus Plus linacs with 6 and 18 MV photon beam were used for irradiations. Percentage depth doses (PDDs) were measured for a large number of square fields for both energies and for 45° wedge, which were employed to obtain the profiles in any depth. To assess the accuracy of the calculated profiles, several profile measurements were carried out for some treatment fields. The calculated and measured profiles were compared by gamma‐index calculation. All γ–index calculations were based on a 3% dose criterion and a 3 mm dose‐to‐agreement (DTA) acceptance criterion. The γ values were less than 1 at most points. However, the maximum γ observed was about 1.10 in the penumbra region in most fields and in the central area for the asymmetric fields. This analytical approach provides a generally quick and fairly accurate algorithm to calculate dose distribution for some treatment fields in conventional radiotherapy.PACS number: 87.10.Ca

A Comparison of Measurements and Calculations of the Effects of Scattered Radiation on Dosimeter Calibration in a Calibration Range.

The method presented provides an alternative to the shadow shield method for experimentally measuring the contribution due to scattering radiation in a calibration range. Scattering of 0.6616 MeV photons from a Cs irradiator in a calibration range does not only occur due to the walls and floor of the range. It also occurs due to the source material itself, its encapsulation, the brass cup that holds the source, the two stainless tubes that surround the source capsule and the brass cup, and the irradiator structure that surrounds the aforementioned objects. The shadow shield method underestimates this scattering radiation that originates in the irradiator. By measuring the uncollided effective activity using a CZT detector and a total effective activity using a survey meter, the contribution of scattered radiation (including all of the abovementioned sources of scatter) to the effective source activity is able to be measured. In this paper, the measured mean effective source activities for a Cs irradiator in a calibration range are reported for a CZT detector and a survey meter. The measured activities are compared among themselves and with the results of MCNP calculations. From these comparisons, the new alternative method for measuring the scatter contribution was validated by agreement in both the MCNP calculations and experimental measurements that scattering contributed about 28% to the overall effective activity of the range.

Scatter Characterization and Correction for Simultaneous Multiple Small-Animal PET Imaging

The rapid growth and usage of small-animal positron emission tomography (PET) in molecular imaging research has led to increased demand on PET scanner's time. One potential solution to increase throughput is to scan multiple rodents simultaneously. However, this is achieved at the expense of deterioration of image quality and loss of quantitative accuracy owing to enhanced effects of photon attenuation and Compton scattering. The purpose of this work is, first, to characterize the magnitude and spatial distribution of the scatter component in small-animal PET imaging when scanning single and multiple rodents simultaneously and, second, to assess the relevance and evaluate the performance of scatter correction under similar conditions. The LabPET™-8 scanner was modelled as realistically as possible using Geant4 Application for Tomographic Emission Monte Carlo simulation platform. Monte Carlo simulations allow the separation of unscattered and scattered coincidences and as such enable detailed assessment of the scatter component and its origin. Simple shape-based and more realistic voxel-based phantoms were used to simulate single and multiple PET imaging studies. The modelled scatter component using the single-scatter simulation technique was compared to Monte Carlo simulation results. PET images were also corrected for attenuation and the combined effect of attenuation and scatter on single and multiple small-animal PET imaging evaluated in terms of image quality and quantitative accuracy. A good agreement was observed between calculated and Monte Carlo simulated scatter profiles for single- and multiple-subject imaging. In the LabPET™-8 scanner, the detector covering material (kovar) contributed the maximum amount of scatter events while the scatter contribution due to lead shielding is negligible. The out-of field-of-view (FOV) scatter fraction (SF) is 1.70, 0.76, and 0.11% for lower energy thresholds of 250, 350, and 400 keV, respectively. The increase in SF ranged between 25 and 64% when imaging multiple subjects (three to five) of different size simultaneously in comparison to imaging a single subject. The spill-over ratio (SOR) increases with increasing the number of subjects in the FOV. Scatter correction improved the SOR for both water and air cold compartments of single and multiple imaging studies. The recovery coefficients for different body parts of the mouse whole-body and rat whole-body anatomical models were improved for multiple imaging studies following scatter correction. The magnitude and spatial distribution of the scatter component in small-animal PET imaging of single and multiple subjects simultaneously were characterized, and its impact was evaluated in different situations. Scatter correction improves PET image quality and quantitative accuracy for single rat and simultaneous multiple mice and rat imaging studies, whereas its impact is insignificant in single mouse imaging.

Is the Image Quality of I-124-PET Impaired by an Automatic Correction of Prompt Gammas?

ObjectivesThe aim of this study is to evaluate the quality of I-124 PET images with and without prompt gamma compensation (PGC) by comparing the recovery coefficients (RC), the signal to noise ratios (SNR) and the contrast to F-18 and Ga-68. Furthermore, the influence of the PGC on the quantification and image quality is evaluated.MethodsFor measuring the image quality the NEMA NU2-2001 PET/SPECT-Phantom was used containing 6 spheres with a diameter between 10 mm and 37 mm placed in water with different levels of background activity. Each sphere was filled with the same activity concentration measured by an independently cross-calibrated dose calibrator. The “hot” sources were acquired with a full 3D PET/CT (Biograph mCT®, Siemens Medical USA). Acquisition times were 2 min for F-18 and Ga-68, and 10 min for I-124. For reconstruction an OSEM algorithm was applied. For I-124 the images were reconstructed with and without PGC. For the calculation of the RCs the activity concentrations in each sphere were determined; in addition, the influence of the background correction was studied.ResultsThe RCs of Ga-68 are the smallest (79%). I-124 reaches similar RCs (87% with PGC, 84% without PGC) as F-18 (84%). showing that the quantification of I-124 images is similar to F-18 and slightly better than Ga-68. With background activity the contrast of the I-124 PGC images is similar to Ga-68 and F-18 scans. There was lower background activity in the I-124 images without PGC, which probably originates from an overcorrection of the scatter contribution. Consequently, the contrast without PGC was much higher than with PGC. As a consequence PGC should be used for I-124.ConclusionsFor I-124 there is only a slight influence on the quantification depending on the use of the PGC. However, there are considerable differences with respect to I-124 image quality.

Calibration of 192Ir high dose rate brachytherapy source using different calibration procedures

AimTo calibrate Ir-192 high dose rate (HDR) brachytherapy source using different calibration methods and to determine the accuracy and suitability of each method for routine calibrations. BackgroundThe source calibration is an essential part of the quality assurance programme for dosimetry of brachytherapy sources. The clinical use of brachytherapy source requires an independent measurement of the air kerma strength according to the recommendations of medical physics societies. Materials and methodsThe Ir-192 HDR brachytherapy source from Gammamed plus machine (Varian Medical Systems, Palo Alto, CA) was calibrated using three different procedures, one using the well-type ionization chamber, second by the in-air calibration method and third using solid water phantoms. The reference air kerma rate (RAKR) of the source was determined using Deutsche Gesellschaft fur Medizinische Physik (DGMP) recommendations. ResultsThe RAKR determined using different calibration methods are in good agreement with the manufacturer stated value. The mean percentage variations of 0.21, −0.94, −0.62 and 0.58 in RAKR values with respect to the manufacturer quoted values were observed with the well-type chamber, in-air calibration, cylindrical phantom and slab phantom measurements, respectively. ConclusionMeasurements with a well-type chamber are relatively simple to perform. For in-air measurements, the indigenously designed calibration jig provides an accurate positioning of the source and chamber with minimum scatter contribution. The slab phantom system has an advantage that no additional phantom and chamber are required other than those used for external beam therapy dosimetry. All the methods of calibration discussed in this study are effective to be used for routine calibration purposes.