The objective of the present study is to establish radiation standards for absorbed doses, for clinical high energy linear accelerator beams. In the nonavailability of a cobalt-60 beam for arriving at Nd, water values for thimble chambers, we investigated the efficacy of perspex mounted extrapolation chamber (EC) used earlier for low energy x-rays and beta dosimetry. Extrapolation chamber with facility for achieving variable electrode separations 10.5mm to 0.5mm using micrometer screw was used for calibrations. Photon beams 6 MV and 15 MV and electron beams 6 MeV and 15 MeV from Varian Clinac linacs were calibrated. Absorbed Dose estimates to Perspex were converted into dose to solid water for comparison with FC 65 ionisation chamber measurements in water. Measurements made during the period December 2006 to June 2008 are considered for evaluation. Uncorrected ionization readings of EC for all the radiation beams over the entire period were within 2% showing the consistency of measurements. Absorbed doses estimated by EC were in good agreement with in-water calibrations within 2% for photons and electron beams. The present results suggest that extrapolation chambers can be considered as an independent measuring system for absorbed dose in addition to Farmer type ion chambers. In the absence of standard beam quality (Co-60 radiations as reference Quality for Nd,water) the possibility of keeping EC as Primary Standards for absorbed dose calibrations in high energy radiation beams from linacs should be explored. As there are neither Standard Laboratories nor SSDL available in our country, we look forward to keep EC as Local Standard for hospital chamber calibrations. We are also participating in the IAEA mailed TLD intercomparison programme for quality audit of existing status of radiation dosimetry in high energy linac beams. The performance of EC has to be confirmed with cobalt-60 beams by a separate study, as linacs are susceptible for minor variations in dose output on different days.

[ABSTRACT]  [FULL TEXT]  [PDF]  [PubMed]

A self-shielded medical cyclotron (11 MeV) was commissioned at our center, to produce positron emitters, namely, ¹⁸ F, ¹⁵ O, ¹³ N and ¹¹ C for positron emission tomography (PET) imaging. Presently the cyclotron has been exclusively used for the production of ¹⁸ F ^- for ¹⁸ F-FDG imaging. The operational parameters which influence the yield of ¹⁸ F ^- production were monitored. The radiation levels in the cyclotron and radiochemistry laboratory were also monitored to assess the radiation safety status in the facility. The target material, ¹⁸ O water, is bombarded with proton beam from the cyclotron to produce ¹⁸ F ^- ion that is used for the synthesis of ¹⁸ F-FDG. The operational parameters which influence the yield of ¹⁸ F ^- were observed during 292 production runs out of a total of more than 400 runs. The radiation dose levels were also measured in the facility at various locations during cyclotron production runs and in the radiochemistry laboratory during ¹⁸ F-FDG syntheses. It was observed that rinsing the target after delivery increased the number of production runs in a given target, as well as resulted in a better correlation between the duration of bombardment and the end of bombardment ¹⁸ F ^- activity with absolutely clean target after being rebuilt. The radiation levels in the cyclotron and radiochemistry laboratory were observed to be well within prescribed limits with safe work practice.

[ABSTRACT]  [FULL TEXT]  [PDF] [CITATIONS]  [PubMed]

Magnetic resonance imaging (MRI) provides excellent soft tissue contrast for oncology applications. We propose to combine a MRI scanner with a helical tomotherapy (HT) system to enable daily target imaging for improved conformal radiation dose delivery to a patient. HT uses an intensity-modulated fan-beam that revolves around a patient, while the patient slowly advances through the plane of rotation, yielding a helical beam trajectory. Since the use of a linear accelerator to produce radiation may be incompatible with the pulsed radiofrequency and the high and pulsed magnetic fields required for MRI, it is proposed that a radioactive Cobalt-60 (60Co) source be used instead to provide the radiation. An open low field (0.25 T) MRI system is proposed where the tomotherapy ring gantry is located between two sets of Helmholtz coils that can generate a sufficiently homogenous main magnetic field. It is shown that the two major challenges with the design, namely acceptable radiation dose rate (and therefore treatment duration) and moving parts in strong magnetic field, can be addressed. The high dose rate desired for helical tomotherapy delivery can be achieved using two radiation sources of 220TBq (6000Ci) each on a ring gantry with a source to axis-of-rotation distance of 75 cm. In addition to this, a dual row multi-leaf collimator (MLC) system with 15 mm leaf width at isocentre and relatively large fan beam widths between 15 and 30 mm per row shall be employed. In this configuration, the unit would be well-suited for most pelvic radiotherapy applications where the soft tissue contrast of MRI will be particularly beneficial. Non-magnetic MRI compatible materials must be used for the rotating gantry. Tungsten, which is non-magnetic, can be used for primary collimation of the fan-beam as well as for the MLC, which allows intensity modulated radiation delivery. We propose to employ a low magnetic Cobalt compound, sycoporite (CoS) for the Cobalt source material itself. Rotational delivery is less susceptible to problems related to the use of a low energy megavoltage photon source while the helical delivery reduces the negative impact of the relatively large penumbra inherent in the use of Cobalt sources for radiotherapy. On the other hand, the use of a 60Co source ensures constant dose rate with gantry rotation and makes dose calculation in a magnetic field as easy as the range of secondary electrons is limited. The MR-integrated Cobalt tomotherapy unit, dubbed 'MiCoTo,' uses two independent physical principles for image acquisition and treatment delivery. It would offer excellent target definition and will allow following target motion during treatment using fast imaging techniques thus providing the best possible input for adaptive radiotherapy. As an additional bonus, quality assurance of the radiation delivery can be performed in situ using radiation sensitive gels imaged by MRI.

[ABSTRACT]  [FULL TEXT]  [PDF] [CITATIONS]  [PubMed]

To evaluate the utility of Dynalog file information for planar dose verification in IMRT QA, a program is developed to convert Dynalog file data to DMLC field files. For this study, five predefined fluencies are planned and delivered using Varian, Eclipse 3D planning system and 6MV photon beam of Varian, Clinac DMX linear accelerator. To measure planar dose distribution, Kodak, EDR2 films are exposed in similar setup as planning setup. Dynalog files are recorded for each delivery and converted into DMLC field files using in-house program. Delivered dose distributions are calculated using DMLC field files from Dynalog files. Planned, Measured and Delivered dose distributions are compared using gamma evaluation in Scanditronix, Omni Pro IMRT software. The Planned and Delivered planar dose distributions agree within 2% dose difference and 2 mm DTA. Measured dose distributions agree within 4% dose difference and 4 mm DTA with Planned dose distribution. Our results show Dynalog file as a promising tool for dynamic IMRT QA.

[ABSTRACT]  [FULL TEXT]  [PDF] [CITATIONS]  [PubMed]

The objective of developing this software is to achieve auto-segmentation and tissue characterization. Therefore, the present algorithm has been designed and developed for analysis of medical images based on hybridization of syntactic and statistical approaches, using artificial neural network (ANN). This algorithm performs segmentation and classification as is done in human vision system, which recognizes objects; perceives depth; identifies different textures, curved surfaces, or a surface inclination by texture information and brightness. The analysis of medical image is directly based on four steps: 1) image filtering, 2) segmentation, 3) feature extraction, and 4) analysis of extracted features by pattern recognition system or classifier. In this paper, an attempt has been made to present an approach for soft tissue characterization utilizing texture-primitive features with ANN as segmentation and classifier tool. The present approach directly combines second, third, and fourth steps into one algorithm. This is a semisupervised approach in which supervision is involved only at the level of defining texture-primitive cell; afterwards, algorithm itself scans the whole image and performs the segmentation and classification in unsupervised mode. The algorithm was first tested on Markov textures, and the success rate achieved in classification was 100%; further, the algorithm was able to give results on the test images impregnated with distorted Markov texture cell. In addition to this, the output also indicated the level of distortion in distorted Markov texture cell as compared to standard Markov texture cell. Finally, algorithm was applied to selected medical images for segmentation and classification. Results were in agreement with those with manual segmentation and were clinically correlated.

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Diffusion spectroscopy, imaging and particularly diffusion tensor imaging have become popular thanks to their numerous clinical and research applications which span from brain stroke evaluation to fiber tracking. With a few exceptions, these methods are rooted in the classic Stejskal-Tanner formula for the diffusion-attenuated signal, usually obtained by solving the Bloch-Torrey partial differential equations. Here we derive the Stejskal-Tanner formula in the simplest possible manner, avoiding integrals and differential equations. This approach makes it easy to understand the origin of the diffusion signal attenuation, the effects of various diffusion sequence parameters, and also the numerous important pitfalls, which are discussed in the last section.

[ABSTRACT]  [FULL TEXT]  [PDF] [CITATIONS]  [PubMed]

This work was undertaken with the intention of investigating the possibility of clinical use of commercially available self-developing radiochromic film - Gafchromic EBT film - for IMRT dose verification. The dose response curves were generated for the films using VXR-16 film scanner. The results obtained with EBT films were compared with the results of Kodak EDR2 films. It was found that the EBT film has a linear response between the dose ranges of 0 and 600 cGy. The dose-related characteristics of the EBT film, like post-irradiation color growth with time, film uniformity and effect of scanning orientation, were studied. There is up to 8.6% increase in the color density between 2 and 40 h after irradiation. There was a considerable variation, up to 8.5%, in the film uniformity over its sensitive region. The quantitative difference between calculated and measured dose distributions was analyzed using Gamma index with the tolerance of 3% dose difference and 3 mm distance agreement. EDR2 films showed good and consistent results with the calculated dose distribution, whereas the results obtained using EBT were inconsistent. The variation in the film uniformity limits the use of EBT film for conventional large field IMRT verification. For IMRT of smaller field size (4.5 x 4.5 cm), the results obtained with EBT were comparable with results of EDR2 films.

[ABSTRACT]  [FULL TEXT]  [PDF] [CITATIONS]  [PubMed]

Total Body Irradiation (TBI) is one main component in the interdisciplinary treatment of widely disseminated malignancies predominantly of haematopoietic diseases. Combined with intensive chemotherapy, TBI enables myeloablative high dose therapy and immuno­ablative conditioning treatment prior to subsequent transplantation of haematopoietic stem cells: bone marrow stem cells or peripheral blood progenitor stem cells. Jointly prepared by DEGRO and DGMP, the German Society of Radio-Oncology, and the German Association of Medical Physicists, this DEGRO/DGMP-Leitlinie Ganzkoerper-Strahlenbehandlung - DEGRO/DGMP Guideline Whole Body Radiotherapy, summarises the concepts, principles, facts and common methods of Total Body Irradiation and poses a set of recommendations for reliable and successful application of high dose large-field radiotherapy as essential part of this interdisciplinary, multi­modality treatment concept. The guideline is geared towards radio-oncologists, medical physicists, haematooncolo­gists, and all contributing to Whole Body Radiotherapy. To guide centres intending to start or actualise TBI criteria are included. The relevant treatment parameters are defined and a sample of a form is given for reporting TBI to international registries.

[ABSTRACT]  [FULL TEXT]  [PDF] [CITATIONS]  [PubMed]

The advances in modern radiation therapy with techniques such as intensity-modulated radiation therapy and image-guid­ed radiation therapy (IMRT and IGRT) have been limited almost exclusively to linear accel­erators. Investigations of modern Cobalt-60 (Co-60) radiation delivery in the context of IMRT and IGRT have been very sparse, and have been limited mainly to computer-modeling and treatment-planning exercises. In this paper, we report on the results of experiments using a tomotherapy benchtop apparatus attached to a conventional Co-60 unit. We show that conformal dose delivery is possible and also that Co-60 can be used as the radiation source in megavoltage computed tomography imaging. These results complement our modeling studies of Co-60 tomotherapy and provide a strong motivation for continuing development of modern Cobalt-60 treatment devices.

[ABSTRACT]  [FULL TEXT]  [PDF] [CITATIONS]  [PubMed]

Stereotactic radiosurgery (SRS) is a special radiotherapy technique used to irradiate intracranial lesions by 3-D arrangements of narrow photon beams eliminating the needs of invasive surgery. Three different tertiary collimators, namely BrainLab and Radionics circular cones and BrainLab micro multileaf collimator (mMLC), are used for linear accelerator-based SRS systems (X-Knife). Output factor (St), tissue maximum ratio (TMR) and off axis ratio (OAR) of these three SRS systems were measured using CC01 (Scanditronix/ Welhofer) and Pinpoint (PTW) cylindrical and Markus plane parallel ionization chambers as well as TLD and radiochromic film. Measurement results of CC01 and Pinpoint chambers were very close to each other which indicate that further reduction in volume and physical dimensions of cylindrical ionization chamber is not necessary for SRS/SRT dosimetry. Output factors of BrainLab and Radionics SRS cones were very close to each other while output factors of equivalent diameter mMLC field were different from SRS circular cones. TMR of the three SRS systems compared were very close to one another. OAR of Radionics cone and BrainLab mMLC were very close to each other, within 2%. However, OARs of BrainLab cone were found comparable to OARs of Radionics cone and BrainLab mMLC within maximum variation of 4%. In addition, user-measured similar data of other three mMLC X-Knives were compared with the mMLC X-Knife data measured in this work and found comparable. The concept of switching over to mMLC-based SRS/SRT is thus validated from dosimetric characteristics as well.

[ABSTRACT]  [FULL TEXT]  [PDF] [CITATIONS]  [PubMed]

For the determination of the absorbed dose to water for high-energy photon and electron beams the IAEA code of practice TRS-398 (2000) is applied internationally. In Germany, the German dosimetry protocol DIN 6800-2 (1997) is used. Recently, the DIN standard has been revised and published as Draft National Standard DIN 6800-2 (2006). It has adopted widely the methodology and dosimetric data of the code of practice. This paper compares these three dosimetry protocols systematically and identifies similarities as well as differences. The investigation was done with 6 and 18 MV photon as well as 5 to 21 MeV electron beams. While only cylindrical chambers were used for photon beams, measurements of electron beams were performed using cylindrical as well as plane-parallel chambers. The discrepancies in the determination of absorbed dose to water between the three protocols were 0.4% for photon beams and 1.5% for electron beams. Comparative measurements showed a deviation of less than 0.5% between our measurements following protocol DIN 6800-2 (2006) and TLD inter-comparison procedure in an external audit.

[ABSTRACT]  [FULL TEXT]  [PDF]  [PubMed]

Multiple fields in IMRT and optimization allow conformal dose to the target and reduced dose to the surroundings and the regions of interest. Thus we can escalate the dose to the target to achieve better tumor control with low morbidity. Orientation of multiple beams can be achieved by i) different gantry angles, ii) rotating patient's couch isocentrically. In doing so, one or more beam may pass through different materials like the treatment couch, immobilization cast fixation plate, head and neck rest or any other supportive device. Our observations for 6MV photon beam on PRIMUS-KXE2 with MED-TEC carbon fiber tabletop and 10 x 10 cm2 field size reveals that the maximum dose attenuation by the couch was of the order of 2.96% from gantry angle 120-160°. Attenuation due to cast fixation base plate of PMMA alone was of the order of 5.8-10.55% at gantry angle between 0 and 90°. Attenuation due to carbon fiber base plate alone was 3.8-7.98%. Attenuation coefficient of carbon fiber and PMMA was evaluated and was of the order of 0.082 cm-1 and 0.064 cm-1 respectively. Most of the TPS are configured for direct beam incidence attenuation correction factors only. Whereas when the beam is obliquely incident on the couch, base plate, headrest and any other immobilization device get attenuated more than the direct beam incidence. The correction factors for oblique incidence beam attenuation are not configured in most of the commercially available treatment planning systems. Therefore, such high variations in dose delivery could lead to under-dosage to the target volume for treatments requiring multiple fields in IMRT and 3D-CRT and need to be corrected for monitor unit calculations.

[ABSTRACT]  [FULL TEXT]  [PDF] [CITATIONS]  [PubMed]

The rate of glucose utilization in tumor cells is significantly enhanced as compared to normal cells and this biochemical characteristic is utilized in PET imaging using FDG as a major workhorse. The PET systems as well as cyclotrons producing positron emitting radiopharmaceuticals have undergone continuous technological refinements. While PET (CT) systems enable fusion images as well as precise attenuation correction, the self-shielded cyclotrons developed provide dedicated systems for in-house production of a large number of PET radiopharmaceuticals. The application of PET images in oncology includes those of pulmonary, colorectal, breast, lymphoma, head & neck, bone, ovarian and GI cancers. The PET has been recognized as promising diagnostic tool to predict biological and physiological changes at the molecular level and hence offer a potential area for future applications including Stem Cell research.

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Comprehensive tests on single slice CT scanner was carried out using in-house fabricated phantoms/test tools following AAPM recommended methods to independently validate the auto-performance test (APT) results. Test results of all the electromechanical parameters were found within the specified limits. Radiation and sensitivity profile widths were within ± 0.05 cm of the set slice thickness. Effective energy corresponding to nominal kVp of 80, 110 and 130 were 49.99, 55.08 and 59.48 keV, respectively. Percentage noise obtained by APT was 1.32% while the independently measured value was 0.38%. Observed contrast resolutions by independent method at 0.78% and 12% contrast difference were 4 mm and 1.25 mm (= 4 lp/cm) respectively. However, high contrast resolution (limiting spatial resolution) by APT at 50, 10 and 2% MTF levels were 9, 12.5 and 14.1 lp/cm respectively. Difference in calculated and measured CT numbers of water, air, teflon, acrylic, polystyrene and polypropylene were in the range of 0 to 24 HU, while this difference was 46 and 94 HU in case of nylon and bakelite respectively. The contrast scale determined using CT linearity phantom was 1.998×10-4 cm-1/CT number. CT dose index (CTDI) and weighted CTDI (CTDIw) measured at different kVp for standard head and body phantoms were smaller than manufacturer-specified and system-calculated values and were found within the manufacturer-specified limit of ± 20%. Measured CTDIs on surface (head: 3.6 cGy and body: 2.6 cGy) and at the center (3.3 cGy, head; and 1.2 cGy, body) were comparable to reported values of other similar CT scanners and were also within the industry-quoted CTDI range. Comprehensive QA and independent validation of APT results are necessary to obtain baseline data for CT virtual simulation.

[ABSTRACT]  [FULL TEXT]  [PDF] [CITATIONS]  [PubMed]

Accurate segmentation of medical images is a key step in contouring during radiotherapy planning. Computed topography (CT) and Magnetic resonance (MR) imaging are the most widely used radiographic techniques in diagnosis, clinical studies and treatment planning. This review provides details of automated segmentation methods, specifically discussed in the context of CT and MR images. The motive is to discuss the problems encountered in segmentation of CT and MR images, and the relative merits and limitations of methods currently available for segmentation of medical images.

[ABSTRACT]  [FULL TEXT]  [PDF] [CITATIONS]  [PubMed]

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[FULL TEXT]  [PDF] [CITATIONS]  [PubMed]

In order to investigate the problems of detecting tumours by ultrasound it is very important to have a portable Doppler flow test object to use as a standardising tool. The flow Doppler test objects are intended to mimic the flow in human arteries. To make the test meaningful, the acoustic properties of the main test object components (tissue and blood mimic) should match closely the properties of the corresponding human tissues, while the tube should ideally have little influence. The blood mimic should also represent the haemodynamic properties of blood. An acceptable flow test object has been designed to closely mimic blood flow in arteries. We have evaluated the properties of three blood mimicking fluid: two have been described recently in the literature, the third is a local design. One of these has emerged as being particularly well matched to the necessary characteristics for in-vitro work.

[ABSTRACT]  [FULL TEXT]  [PDF] [CITATIONS]  [PubMed]

The present paper illustrates our attempt to design and test the reproducibility of low-cost patient positioning devices prepared in-house in our radiotherapy department. Rigid thermocole boards with angulations, scales and support were designed as breast, pelvis and head positioning devices. Reproducibility and accuracy were tested by serial electronic portal imaging detector imaging. The positioning devices (with or without superimposed moulds) showed variations within 2-3 mm on serial treatment days which were within acceptable limits. It is therefore concluded that low-cost patient positioning devices for head, breast and pelvis (the common sites of treatments in radiotherapy) can be fabricated from available materials in-house. These have been shown to be resulting in accurate immobilization, can be customized for particular techniques and are considerably cheaper than commercially available solutions.

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Implementation of step-and-shoot intensity-modulated radiotherapy (IMRT) needs careful understanding of the accelerator start-up characteristic to ensure accurate and precise delivery of radiation dose to patient. The dosimetric characteristic of a Siemens Primus linear accelerator (LA) which delivers 6 and 18 MV x-rays at the dose rate of 300 and 500 monitor unit (MU) per minutes (min) respectively was studied under the condition of small MU ranging from 1 to 100. Dose monitor linearity was studied at different dose calibration parameter (D1_C0) by measuring ionization at 10 cm depth in a solid water phantom using a 0.6 cc ionization chamber. Monitor unit stability was studied from different intensity modulated (IM) groups comprising various combinations of MU per field and number of fields. Stability of beam flatness and symmetry was investigated under normal and IMRT mode for 20×20 cm2 field under small MU using a 2D Profiler kept isocentrically at 5 cm depth. Inter segment response was investigated form 1 to 10 MU by measuring the dose per MU from various IM groups, each consisting of four segments with inter-segment separation of 2 cm. In the range 1-4 MU, the dose linearity error was more than 5% (max -32% at 1 MU) for 6 MV x-rays at factory calibrated D1_C0 value of 6000. The dose linearity error was reduced to -10.95% at 1 MU, within -3% for 2 and 3 MU and ±1% for MU ≥4 when the D1_C0 was subsequently tuned at 4500. For 18 MV x-rays, the dose linearity error at factory calibrated D1_C0 value of 4400 was within ±1% for MU ≥ 3 with maximum of -13.5 observed at 1 MU. For both the beam energies and MU/field ≥ 4, the stability of monitor unit tested for different IM groups was within ±1% of the dose from the normal treatment field. This variation increases to -2.6% for 6 MV and -2.7% for 18 MV x-rays for 2 MU/field. No significant variation was observed in the stability of beam profile measured from normal and IMRT mode. The beam flatness was within 3% for 6 MV x-rays and more than 3% (Max 3.5%) for 18 MV x-rays at lesser irradiation time ≤ 3 MU. The beam stability improves with the increase in irradiation time. Both the beam energies show very good symmetry (≤ 2%) at all irradiation time. For all the three segment sizes studied, the nonlinearity was observed at smaller MU/segment in both the energies. When the MU/segment is ≥ 4, all segment size shows fairly linear relation with dose/MU. The smaller segment size shows larger nonlinearity at smaller MU/segment and become more linear at larger MU/segment. Based on our study, we conclude that the Primus LA from Siemens installed at our hospital is ideally suited for step-and-shoot IMRT preferably for radiation ON time ³4MU per segment.

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Impressive advances in computers and materials science have fueled a broad-based confluence of basic science breakthroughs.These advances are making us reformulate our learning, teaching and credentialing methodologies and research and development frontiers. We are now in the age of molecular medicine. In the entire field of health care, a paradigm shift from population-based solutions to individual specific care is taking place. These trends are reshaping the practice of medical physics. In this short presentation, examples are given to illustrate developments in image-guided intensity-modulated and adaptive helical tomotherapy, enhanced application of intensity modulation radiotherapy (IMRT) using adaptive radiotherapy and conformal avoidance. These advances include improved normal tissue sparing and permit dose reconstruction and verification, thereby allowing significant biologically effective dose escalation and reduced radiation toxicity. The intrinsic capability of helical TomoTherapy for megavoltage CT imaging for IMRT image-guidance is also discussed. Finally developments in motion management are described.

[ABSTRACT]  [FULL TEXT]  [PDF]  [PubMed]

Integrated PET/CT has emerged as an integral component of oncology management because of its unique potential of providing both functional and morphological images in a single imaging session. In this work, performance of the 'bismuth germinate (BGO) crystal'-based PET of a newly installed Discovery ST PET/CT was evaluated in 2D and 3D mode for whole-body scanning using National Electrical Manufacturers Association (NEMA) NU 2-2001 protocol and the recommended phantoms. During the entire measurements, the system operates with an energy window of 375-650 keV and 11.7 ns coincidence time window. The set of tests performed were spatial resolution, sensitivity, scatter fraction (SF) and counting rate performance. The average transaxial and axial spatial resolution measured as full width at half maximum (FWHM) of the point spread function at 1 cm (and 10 cm) off-axis was 0.632 (0.691) and 0.491 (0.653) cm in 2D and 0.646 (0.682) and 0.54 (0.601) cm in 3D respectively. The average sensitivity for the two radial positions ( R = 0 cm and R = 10 cm) was 2.56 (2.63) cps/kBq in 2D and 11.85 (12.14) cps/kBq in 3D. The average scatter fraction was 19.79% in 2D and 46.19% in 3D. The peak noise equivalent counting rate (NECR) evaluated with single random subtraction was 89.41 kcps at 49 kBq/cc in 2D and 60 kcps at 12 kBq/cc in 3D acquisition mode. The NECR with delayed random subtraction was 61.47 kcps at 40.67 kBq/cc in 2D and 45.57 kcps at 16.45 kBq/cc in 3D. The performance of the PET scanner was satisfactory within the manufacturer-specified limits. The test result of PET shows excellent system sensitivity with relatively uniform resolution throughout the FOV, making this scanner highly suitable for whole-body studies.

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A mathematical model has been developed for prediction of off axis ratio (OAR), using Wood - Saxon term used to represent nuclear potential. This method has been satisfactorily applied for predicting OAR in case of ⁶⁰Co γ -rays and high energy X-rays. Investigations are considered upto a depth of 25 cm in the case of 4MV LINAC for which measurements were carried out in our laboratory using indigenously developed Radiation Field Analyzer. For 60Co γ-rays as well as 6 and 18MV LINAC beams we could get off-axis profiles only upto 20 cm. The shift δ between measured and predicted OAR is within ±2 mm except for 20 cm depth near the falling edge of the penumbra, where it is 2.80 mm. Software has been developed in Visual Basic 6 on Windows platform to plot Isodose curves, which is based on the mathematical modeling of OAR and central axis percentage depth dose.

[ABSTRACT]  [FULL TEXT]  [PDF]  [PubMed]

A new generation telecobalt unit, Theratron Equinox-80, (MDS Nordion, Canada) has been evaluated. It is equipped with a single 60-degree motorized wedge (MW), four universal wedges (UW) for 150, 300, 450 and 600. MW was configured in Eclipse (Varian, Palo Alto, USA) 3D treatment planning system (TPS). The profiles and central axis depth doses (CADD) were measured with radiation field analyzer blue water phantom for MW. These profiles and CADD for MW were compared with UW in a homogeneous phantom generated in Eclipse for various field sizes. The absolute dose was measured for a field size of 10 x 10 cm2 only in a MEDTEC water phantom at 10 cm depth with a 0.13 cc thimble ion chamber (Scanditronix Wellhofer, Uppsala, Sweden) and a NE electrometer (Nuclear Enterprises, UK). Measured dose with ion chamber was compared with the TPS predicted dose. MW angle was verified on the Equinox for four angles (15o, 30o, 45o and 60o). The variation in measured and calculated dose at 10 cm depth was within 2%. The measured and the calculated wedge angles were in well agreement within 2o. The motorized wedges were successfully configured in Eclipse for four wedge angles.

[ABSTRACT]  [FULL TEXT]  [PDF] [CITATIONS]  [PubMed]