Dose Rate Output Research Articles

Assessment of Measured and Calculated Dose Rate of Co-60 Teletherapy Machine: 06 Years’ Experience at NORIN Nawabshah, Pakistan

It is essential to determine the absolute output dose of Co-60 source in the radiation treatment periodically. It is because overdosage may cause radiation hazards whereas under dosage may lead to the unsatisfactory treatment of cancer. The current study is focused on the consistency of monthly dose output verification of the cobalt-60 Teletherapy unit which should be within ±2% as per international standards. In the present study, the measured and calculated dose rate of the Co-60 teletherapy unit at Nuclear Medicine Oncology and Radiotherapy Institute Nawabshah (NORIN) for the last 6 years is analyzed. The dose measurement was done in water phantom 30×30×30 cm3 at 80 cm Source to Surface Distance with 5cm depth by using calibrated electrometer and PTW ionization chamber. The measured output dose rate obtained by actual dosimetry is within ±2% of the dose rate calculated by the decay method and the deviation lies within the permissible limit as prescribed by International Atomic Energy Agency (IAEA), International Commission on Radiological Units and Measurement (ICRUM)and American Association of Physicists in Medicine (AAPM). The variation in measurements obtained is within the tolerable limits according to standard protocols and codes. Thus, our study shows a homogenous trend in the dose rate of the Co-60 teletherapy machine.

Parameter measurement and optimization for a 3/6 dual-energy electron linear accelerator with industrial and inspection applications

Electron linear accelerator (LINAC) is a high-energy X-ray generator with extensive industrial, inspection, and medical applications. The studied LINAC uses a 2.6 MW magnetron as its RF generator derived with a Marx modulator. An electron gun of filament voltage 6 V and current 2.2 A connected to the accelerator tube is applied to establish electron current inside the drift tube. For this purpose, 9 kV and 25 kV voltages are applied to the cathode and anode of the electron gun pulse by pulse, generating dual-energy x-ray beams as outputs. An Automatic Frequency Control (AFC) system is designed for studied LINAC so that variation of output dose rate is lower than 2% and the required time to achieve the maximum output dose rate is lower than 1 s. Optimizing the Marx modulator's switching algorithm, the ripple in the output beam has been lower than 5%. The half-value layer (HVL) of steel has been measured for high and low energies equal to 6 MeV and 3 MeV, respectively. The output pulse of the electron beam and dose rate have been measured using a linear detector array (LDA) and dosimeter, respectively, with a pulse frequency of 35–400 Hz and pulse width of 2–4 μs.

Assessing the Impact of Increased Dose Rate Output on Bladder and Rectal Quality of Life in Men Treated with Definitive SBRT for Localized Prostate Cancer

Assessing the Impact of Increased Dose Rate Output on Bladder and Rectal Quality of Life in Men Treated with Definitive SBRT for Localized Prostate Cancer

Commissioning and performance characteristics of a pre-clinical image-guided radiotherapy system

Characteristics of a small-animal radiotherapy device, the X-RAD SmART, are described following commissioning of the device for pre-clinical radiotherapy research. Performance characteristics were assessed using published standards and compared with previous results published for similar systems. Operational radiation safety was established. Device X-ray beam quality and output dose-rate were found to be consistent with those reported for similar devices. Output steadily declined over 18 months though remained within tolerance levels. There is considerable variation in output factor across the international installations for the smallest field size (varying by more than 30% for 2.5 mm diameter fields). Measured depth dose and profile data was mostly consistent with that published, with some differences in penumbrae and generally reduced flatness. Target localisation is achieved with an imaging panel and with automatic corrections for panel flex and device mechanical instability, targeting within 0.2 mm is achievable. The small-animal image-guided radiotherapy platform has been implemented and assessed and found to perform as specified. The combination of kV energy and high spatial precision make it suitable for replicating clinical dose distributions at the small-animal scale, though dosimetric uncertainties for the narrowest fields need to be acknowledged.

Design of Band-Pass Filters by Experimental and Simulation Methods at the range of 100-125 keV of X-ray in Fluoroscopy

The determination of filters that remove low-energy and attenuate high-energy spectra does not essentially influence image quality, so it can reduce the absorbed patient dose. This work examines the impacts of thickness and filter material on contrast, resolution, absorbed patient dose and image quality. Based on the attenuation curves of elements and taking into account the cost-effectiveness and availability factors, four elements including tin, tungsten, lead and copper in different thicknesses was studied at the range of 100-125 keV. The simulations were executed using MCNPX code with an error less than 1% that represented the accuracy. Experimental data were obtained based on the results of calculations and simulations using fluoroscopy equipment. The results showed that applying the filters caused improving the resolution and image quality, and also remarkable reduction in output dose rate. In conclusion, the 0.1 mm thick lead element was taken as the most appropriate element in filtration.

P250] National survey of kilovoltage radiotherapy equipment in Denmark

Purpose The purpose of this study was to compare dosimetry specifications between kilovoltage (kV) radiotherapy units available at Danish radiotherapy departments. Methods A survey was conducted to gather information about the kV radiotherapy units in Danish radiotherapy departments, i.e. which dosimetry protocols each centre followed, the dosimeters used for calibration, kVp of the clinically used energies, measured half-value layer (HVL), dose rate, output factors, and depth dose measurements. Results Six of the seven Danish radiotherapy departments offer kV radiotherapy, and all six centres contributed data to the study. All kV units are from the same manufacturer, and all centres use clinical energies up to 100 kVp. Beam quality as measured by the HVL ranges from 0.9 to 4.2 mm aluminium, and all centres offer at least two different beam qualities. Dose rate output varies between 3.8 and 7.5 Gy/minute for a 4 cm diameter field, depending on the beam quality and kVp. Different protocols for the determination of absorbed dose are used, with 3 centres following the IPEMB protocol (Phys Med Biol 1996, pp2602-25), 2 centres following the IAEA TRS 277 protocol, and 1 centre following the AAPM protocol (Med Phys 2001, pp868-93). 4 centres use Farmer type cylindrical ion chambers for absolute dosimetry, while 2 centres use plane-parallel chambers. Comparing the data across the departments revealed no systematic differences based on the absorbed dose protocol each department followed. There may be a slight difference in the determination of relative output of the different applicators depending on the ion chamber used for output factor measurements, but with limited data available this remains inconclusive. The 90% and 85% dose to water range of x-rays agree between the departments within 1 mm for similar beam qualities, even though different methods were used to determine the depth dose deposition. Conclusions A national comparison of kV radiotherapy units was conducted, and overall the units were found very similar. No systematic differences were observed based on the calibration protocol, but the available data hint that the choice of ion chamber for calibration measurements may have a small effect on the determination of output factors.

Abstract 4153: Commissioning and radiobiological verification of the small animal radiotherapy research platform (SARRP)

Abstract Preclinical radiation biology has become increasingly sophisticated due to the implementation of advanced small animal image guided radiation platforms into laboratory investigation. Small animal radiotherapy devices enable state-of-the-art image guided therapy (IGRT) research to be performed in small animal cancer models by combining high-resolution cone beam computed tomography (CBCT) imaging with an isocentric irradiation system. The technological evolution from simple, broad field irradiation configurations, to more sophisticated dose deliveries for preclinical radiobiology experiments has introduced new dosimetry challenges for preclinical small animal cancer research. Because of this, robust QA and dosimetry techniques are a key part of using novel treatment platforms using very small irradiation fields. In this study, we present a dosimetric study of the small animal radiotherapy research platform (SARRP, Xstrahl Inc.) focusing on the small field dosimetry. Physical dosimetry was assessed using ion chambers and radiochromic film, investigating the impact the beam focus size has on the dose rate output as well as beam characteristics (beam shape and penumbra variations). Two film reading modalities have been used to assess the dose output using the 0.5 mm diameter aperture. This study establishes that FilmQA Pro is a suitable tool for small field dosimetry, with a sufficiently small sampling area (0.1 mm) to ensure an accurate measurement. Furthermore, all small field dosimetry data generated in this study are equally comparable with our Monte Carlo simulations for both focal spot sizes. Overall, it was observed that the small focal spot, while having a lower dose-rate output was shown to produce a more stable and homogenous beam with minimum penumbra over time when compared to the larger focal spot. These findings suggest that when preclinical stereotactic irradiation fields are used, a practical compromise (time to deliver a desired dose and field homogeneity) needs to be considered when deciding the optimum treatment plan and beam configuration used. Citation Format: Jonathan L. Kane. Commissioning and radiobiological verification of the small animal radiotherapy research platform (SARRP) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4153.

Small field dosimetry for the small animal radiotherapy research platform (SARRP)

BackgroundPreclinical radiation biology has become increasingly sophisticated due to the implementation of advanced small animal image guided radiation platforms into laboratory investigation. These small animal radiotherapy devices enable state-of-the-art image guided therapy (IGRT) research to be performed by combining high-resolution cone beam computed tomography (CBCT) imaging with an isocentric irradiation system. Such platforms are capable of replicating modern clinical systems similar to those that integrate a linear accelerator with on-board CBCT image guidance.MethodsIn this study, we present a dosimetric evaluation of the small animal radiotherapy research platform (SARRP, Xstrahl Inc.) focusing on small field dosimetry. Physical dosimetry was assessed using ion chamber for calibration and radiochromic film, investigating the impact of beam focus size on the dose rate output as well as beam characteristics (beam shape and penumbra). Two film analysis tools) have been used to assess the dose output using the 0.5 mm diameter aperture.ResultsGood agreement (between 1.7–3%) was found between the measured physical doses and the data provided by Xstrahl for all apertures used. Furthermore, all small field dosimetry data are in good agreement for both film reading methods and with our Monte Carlo simulations for both focal spot sizes. Furthermore, the small focal spot has been shown to produce a more homogenous beam with more stable penumbra over time.ConclusionsFilmQA Pro is a suitable tool for small field dosimetry, with a sufficiently small sampling area (0.1 mm) to ensure an accurate measurement. The electron beam focus should be chosen with care as this can potentially impact on beam stability and reproducibility.

Quality Assurance with Dosimetric Consistency of a Co-60 Teletherapy Unit

<p class="Default">It is essential to know the standard dose rate, output of Co-60 source in the radiation treatment periodically. It is because the over dosage may cause radiation hazards where as under dosage may lead to unsatisfactory treatment of cancer. Present study focused on the radiation standards and dosimetry for the assurance of the quality and verify that the output of the ionizing radiation emitting medical instruments such as Teletherapy Unit (TTU) which should be within ±2% of the stated one. Present study was done as a part of the regularity of quality assurance (QA) of telecobalt radiotherapy unit that includes the dosimetric measurements of Co-60 TTU at Bhaktapur Cancer Hospital (BCH), Bhaktapur per each month from 29 March 2012 to 29 December 2014. The radionuclide source is Co-60 which has been incorporated in TTU, BCH for the purpose of therapeutic treatment of cancer. The Co-60 source decays continuously to Ni-60 (half-life of 5.27 years) with the decrease in its activity and hence the output dose rate. The calculations of actual dose rate of Co-60 TTU were done by the source to surface distance (SSD) technique. It has been concluded that there is a quality assurance management in Co-60 TTU, BCH with the consistency in the average output dose rate obtained by the actual dosimetry values and the expected output values obtained by decay method. The values obtained by actual dosimetry are within ±2% of the expected values so that the deviation of the actual output dose rate from the expected output data lies within the permissible limit as prescribed by International Atomic Energy Agency (IAEA) and International Commission on Radiation Units and Measurement (ICRUM). In conclusion, our study shows a trend towards uniform and better dose delivery from Co-60 TTU, BCH, Nepal</p><p><strong>Journal of Nepal Physical Society</strong><em><br /></em>Volume 4, Issue 1, February 2017, Page: 88-92</p>

Measurement of Energy Parameters for Electron Gun Heater Currents and Output Dose Rate for Electron Beams from a Prototype Linac

The dosimetric characteristics were experimentally evaluated for electron beams from the prototype linac developed for radiotherapy units. This paper focuses on the electron beam output and energy variations as a function of electron gun heater current. The electron energy was derived from its mean and most probable energies measured by film dosimetry. The electron beam output at the maximum electron energy was measured with the plane parallel ionization chamber in water using TRS-398 dosimetry protocol. The mean energy and the most probable energy of the electron beam were 6.54∼3.31 MeV and 5.94∼2.80 MeV at electron gun current of 2.02∼2.50 A respectively. The output dose rate for an electron beam of mean energy 6.54 MeV was 5.41 Gy/min ±1.5% at the reference depth in water.

SU-GG-T-43: Physics Commissioning in Xoft Axxent® Electronic Brachytherapy (eBx) for the Primary Treatment of Non-Melanoma Skin Cancer

Purpose: The Xoft Axxent® X‐ray source has been used for treating non‐melanoma skin cancer since the surface applicators became clinically available in the summer of 2009. We report a comprehensive quality assurance (QA) procedure for the commissioning of the Electronic Brachytherapy (eBx) system with the Xoft surface applicators. Materials and methods: The Xoft miniature tube (model S700) generates 50kVp low‐energy x‐rays. The new surface applicators used with this device have four available sizes of 10mm, 20mm, 35mm, and 50mm in diameter. Our tests include dose‐rate measurement, air‐gap factor, output stability, energy verification, beam flatness and symmetry, timer linearity and treatment planning with patientspecific cutout factors. TG‐61 in‐air method was used as a guideline for acquiring nominal dose rate output at the skin surface. Soft x‐ray parallel plate chamber (PTW T34013) and electrometer was used for the output commissioning. Gafchromic(R) EBT films were used for testing the properties of the treatment fields with the skin applicators. Solid water slabs were used to verify the source energy and measure cutout factors. Results: The average nominal dose‐rate output at the skin surface for the 35mm applicator is 1.35 Gy/min with ±5% variation for fifteen sources. For the same source, the output variation is within 2%. The effective SSD was also calculated based on the air‐gap measurements for four applicator sizes. The field flatness and symmetry are well within 5%. Treatment duration is calculated based on the nominal dose‐rate, the prescription fraction size, the depth dose percentage, and the cutout factor. Conclusion: Together with TG‐61, our methodology provides a comprehensive commissioning procedure for medical physicists in using the Xoft eBx system and skin applicators for the treatment of non‐melanoma skin cancer.

SU-GG-T-234: Time Resolved Output Measurements as a Linear Accelerator Quality Assurance Tool

Purpose: An elegant method of time‐resolved output (cGy/min) measurements, or TROM, is presented as a unique quality assurance tool. This temporal sampling technique of the dose rate allows for visual investigation of the output under a variety of circumstances. Method and Materials: An available tool has been implemented to monitor time‐resolved accelerator output for quality assurance. Tomotherapy Inc. provides an electrometer and software package (Tomoelectrometer and TEMS) that can sample charge readings from multiple ionization chambers at rates of 0.1 – 1.0 Hz. The Tomoelectrometer is interfaced to a computer running the TEMSsoftware by RS232 connector. An ionization chamber inserted in the phantom is connected to the Tomoelectrometer. The measured charge is converted to the dose rate using the chamber calibration factor and an atmospheric correction. Static measurements have been performed using an SAD setup at 1.5 cm depth in a solid water phantom. TROM were performed on 2 helical Tomotherapy HiART II systems and a Varian EXd linear accelerator for “beam on” times in excess of 10 minutes. Results: The output dose rate is plotted against time for Varian and Tomotherapy accelerators. Rise times were < 1 second for all accelerators. TROM show variations on the order of ±1% for the Varian accelerator. Tomotherapy units showed greater variation. Peak values for both machines have been found to be 3.5% above the “average” value. Conclusion: Both types of machines exhibit a similar overshoot phenomenon at the onset, but the Tomotherapy unit(s) showed larger variation for some measurements. Temporal measurements of the output allow one to examine the inter‐ and intra‐ fractional dose rate variations, provides insight into other prolonged beam measurements, and may be a useful tool for troubleshooting.

WE-D-224C-02: High Dose Rate Mode Linear Accelerator Based Stereotactic Radiosurgery and Image Guided Radiation Therapy

Introduction: In order to improve the standard linear accelerator's ability to address the demands of intracranial and extracranial stereotactic radiosurgery as well as for image‐guided and intensity modulated radiotherapy, a high dose rate output accelerator was developed. The objective of this study was to assess the device performance and compare it to standard accelerators. Materials and Methods: The 6 MV x‐ray beam of a Siemens Oncor linac was modified by removing the flattening filter, enabling dose rates to reach 1000 MU per minute. Ion chambers, diodes, and film dosimeters were used to assess monitor chamber behavior, energy, and dose profile characteristics. Treatment time required for radiosurgerytreatments in 40 patients was measured. Results: Even at this high dose rate, the linacdosimetry system remains robust; constancy, linearity, and beam energy remain within 1% for 3 to 1000 MU. Measurements at incrementally reduced dose rates (1000 to 300 in 100 MU increments) showed the output calibration to fall from 1.000 cGy/MU to 0.994 cGy/MU, with an average value of 0.997 cGy/MU. Over this range of dose rates the beam energy held consistent, with the ratio of percent depth dose values within 0.5%. Dose profiles for larger field sizes are not flat, but they are radially symmetric and as such able to be modeled by a treatment planning system. Radiosurgerytreatment times, computed here as the beginning of x‐ray delivery until the end of treatment, were reduced to an average of 2 minutes and 18 seconds per arc, or 11 minutes 27 seconds per isocenter. Conclusions: Even at this high dose rate, the linacdosimetry system remains robust. Because stereotactic IGRT can require significantly longer times for treatment delivery, the advantages of the high dose rate design should be pursued.

Technique for routine output verification of Leipzig applicators with a well chamber

The H-type Leipzig applicators are accessories of the microSelectron-HDR system (Nucletron, Veenendaal, The Netherlands) for treatment of superficial malignancies. Recently, the dose rate distributions in liquid water for the whole set of applicators using both source models available for the microSelectron-HDR afterloaders have been obtained by means of the experimentally validated Monte Carlo (MC) code GEANT4. Also an output table (cGy/hU) at 3 mm depth on the applicator central axis was provided. The output verification of these applicators by the user, prior to their clinical use, present practical problems: small detectors such as thermoluminescent dosimeters or parallel-plate ionization chambers are not easily used for verification in a clinical environment as they require a rigid setup with the Leipzig applicator and a phantom. In contrast, well-type ionization chambers are readily available in radiotherapy departments. This study presents a technique based on the HDR1000Plus well chamber (Standar Imaging) measurements with a special insert, which allows the output verification of the H-type Leipzig applicators on a routine basis. This technique defines correspondence factors (CF) between the in water dose rate output of the Leipzig applicators (cGy/hU) obtained with MC and the reading on the well chamber with the special insert, normalized to the HDR calibration factor with the HDR insert and to the source strength. To commission the applicators (with the well chamber and the special insert used), the physicist should check if the CF value agrees with its tabulated values presented in this work. If the differences are within 5% the tabulated output values can be used in clinical dosimetry. This technique allows the output validation of the Leipzig applicators with a well chamber widely used for HDR Ir-192 source strength measurements. It can easily be adapted to other types of well chambers for HDR source output verification.

Delivery time comparison for intensity-modulated radiation therapy with/without flattening filter: a planning study

The treatment delivery time of intensity-modulated radiation therapy (IMRT) with a multileaf collimator (MLC) is generally longer than that of conventional radiotherapy. In theory, removing the flattening filter from the treatment head may reduce the beam-on time by enhancing the output dose rate, and then reduce the treatment delivery time. And in practice, there is a possibility of delivering the required fluence distribution by modulating the unflattened non-uniform fluence distribution. However, the reduction of beam-on time may be discounted by the increase of leaf-travel time and (or) verification-and-recording (V&R) time. Here we investigate the overall effect of flattening filter on the treatment delivery time of IMRT with MLCs implemented in the step and shoot method, as well as with compensators on six hybrid machines. We compared the treatment delivery time with/without flattening filter for ten nasopharynx cases and ten prostate cases by observing the variations of the ratio of the beam-on time, segment number, leaf-travel time and the treatment delivery time with dose rate, leaf speed and V&R time. The results show that, without the flattening filter, the beam-on time reduces for both static MLC and compensator-based techniques; the number of segments and the leaf-travel time increase slightly for the static MLC technique; the relative IMRT treatment delivery time decreases more with lower dose rate, higher leaf speed and shorter V&R overhead time. The absolute treatment delivery time reduction depends on the fraction dose. It is not clinically significant at a fraction dose of 2 Gy for the technique of removing the flattening filter, but becomes significant when the fraction dose is as high as that for radiosurgery.

A sub-standard X-ray dose-meter. 1955.

Few pages can claim to have had more impact on a speciality than the three pages reproduced this month from Volume 28 of the British Journal of Radiology. Frank Farmer moved from the Middlesex Hospital to Newcastle in 1945 and soon became involved in the design and construction of a reliable dosemeter for measuring the output dose rate of X-ray therapy equipment. Unaware of its future impact, he patiently waited to prove his design and to negotiate for its manufacture, by the Baldwin Instrument Company, before penning his opening paragraph “The instrument described below has been in use at a number of hospitals for the past four years”. 40 years later and physicists in countless hospitals around the world are familiar with, if not weaned on, the Farmer Dosemeter. Such has been its impact.

Dosimetry of an endocavitory treatment system.

The dosimetric properties of an x-ray applicator system for the treatment of rectal carcinoma by endocavitory contact therapy are discussed. Half-value layer, percent depth dose, field flatness, and output dose rate were evaluated. Film was used to evaluate field flatness and ionization chambers were used to evaluate the other quantities. The methods of measurement and their results are discussed.

Portable radiography using linear accelerators

There are numerous instances where the availability of a portable high-energy radiography machine that could be transported to the inspection site with relative ease would save time, money, and make radiography of permanent installations, such as bridges, possible. One such machine, the Minac built by Schoenberg Radiation Inc., is commercially available. It operates at 9.3 GHz, has an electron energy on target of 3.5 MeV, and an output dose rate of 100 R/min. A second portable accelerator, recently completed at the Los Alamos National Laboratory, operates at 2.998 GHz, has electron energies on target of 6, 8, and 10 MeV, and an output dose rate of 800 R/min at 8 MeV. This paper discusses the need for and applications of portable accelerators for radiography. Physical characteristics and beam parameters of both machines are examined in detail. Problems of operating at higher frequencies to further minimize size and weight are discussed.

Automatic electron dosimetry system for a microwave linear accelerator.

In the practical application of a linear accelerator as an electron source in tumor therapy, the problem of dosage control is paramount. Because of considerable fluctuation in electron-beam dosage caused by significant and rapid variations in beam current, a constant dose rate for this form of therapy cannot be anticipated. The very high dose rate output of this modality is in the range of 10,000 rads per minute, making it difficult, if not impossible, to anticipate an exact dosage in a given period of time. A search of the recent literature revealed a method of dealing with this problem, based on a tachometer principle (1), but the system is accurate for only those dose rates up to 300 rads per minute. A digital voltmeter principle is being used in the application of cobalt-60 teletherapy (2) for an automatic dosimeter. In an attempt to overcome this problem, an automatic dosimetry system for electron beam therapy which will terminate treatment at an exactly predetermined dose has been developed and is p...