Modification proposed for the AECL Theratron-80 cobalt 60 teletherapy unit.

The Purpose of this paper is to alert radiation therapists to the possibility of progressive source misalignment in certain types of Co60 teletherapy units, to discuss its effects on dose distribution, and to suggest several simple and practicable technics for its early detection. Such misalignment is especially insidious, as the machine shows no obvious signs of malfunction, even though the radiation pattern may be grossly distorted. The present discussion applies primarily to teletherapy units which have the source attached to a wheel that rotates 180 degrees to carry the source from the “off” to the “on” position. The wheel is brought to the “on” position by a motor-driven gear train and to the “off” position by a coiled steel spring. As long as no current flows through the motor, the source is held securely in the “off” position by the spring tension. When the motor is energized, the wheel is rotated half a revolution, its motion being arrested by a lug on the wheel striking an adjustable stop fastene...

60Co teletherapy units featuring 100 cm source-to-axis distances and with nominal source activities of 481 TBq (13,000 Ci) are available as replacements for older model 80 cm source-to-axis teletherapy units that generally have source activities of less than 370 TBq (10,000 Ci). We have redesigned and renovated two vaults--one of which required supplemental shielding--designed for older 80 cm source-to-axis units with 333 TBq (9,000 Ci) sources and installed modern 100 cm source-to-axis units with 481 TBq (13,000 Ci) sources. Renovation costs (in 1991 U.S. dollars) were about $40,000 and $160,000; the latter, including shielding costs, was about two-thirds of projected costs for installation of a 6 MV electron beam linear accelerator (linac). We have designed the treatment heads of these 100 cm 60Co units to accept the secondary field shaping blocks used on 100 cm source-to-axis linacs, allowing the 60Co units to be used as emergency back-up units for linacs when they are inoperable.

An account is furnished of some modifications made on the Bryant Symons 10-gramme Radium Beam Unit. An apparatus of this type was installed at the Royal Cancer Hospital in February, 1952, containing 3·25 curies of cobalt 60. Five new uranium nozzles were added, namely two triangular fields 8 × 6 cm, two pentagonal or notched fields 8 × 5 cm and a 5 × 2 cm rectangle. By means of these additional fields it is hoped: (1) to increase the flexibility of technique; (2) to lessen the discomforts and risks of treatment; (3) to develop techniques in accord with the natural history of the disease treated. The paper also deals with some physical measurements made on a teletherapy unit having a 3·25 curie cobalt 60 source, and uranium shielding and applicators. Measurements of the distribution of radiation in a water phantom are described. A comparison is made between the isodose distributions obtained with tungsten and uranium applicators. Isodose distributions obtained with triangular and pentagonal applicators are shown and discussed. The possibility of contamination from the cobalt 60 source is discussed, and measurements of the activity of various parts of the unit due to contamination after six months' use are tabulated.

Scattered radiation from linear accelerator and cobalt-60 collimator jaws

Fractional exposure rate due to scattered radiation from a Co 60 teletherapy unit

The distribution of ionization in the first few millimeters of tissue-like material was studied with a cobalt-60 teletherapy unit (1, 2). It was found that for short cone-to-skin distance (C.S.D.) the effect of electrons from the collimating system could be reduced appreciably by thin filters which did not noticeably affect the gamma-ray dosage pattern. Optimum results were obtained with the filter mounted over the lower end of the treatment cone. With this arrangement, however, the filter obscured the beam of light from the light localizer unless it was removed with each use. The interference of a filter with light localization is not encountered with x-ray generators in which the filter employed to harden the beam is located above the mirror of the localizer. Below the collimating system of an x-ray generator, filters to reduce electron contamination are generally not needed, for several reasons. For units operating below the supervoltage region, the average energy of secondary electrons is low, and they are removed from the beam through air scatter even for short diaphragm-skin distances. Further, the focal spot of an x-ray generator is usually small in comparison with the size of a teletherapy source. Therefore, for a given focal skin distance, long diaphragm-skin distances can be used without resulting in wide penumbras. Filters to reduce electron contamination are not needed when the diaphragm-skin distance is large. The low-activity sources employed in some teletherapy units necessitate treatment with short source-to-skin distances (S.S.D.) if the treatment time is to be kept within reasonable limits. If the penumbra width is to be kept small, this requires treatment at a short cone-to-skin distance, for which the electron contamination is appreciable. To minimize the skin dose, it was felt advisable to use an electron filter for treatment dose to the cone. It was also considered desirable to retain the light localizer without having to remove and replaces the filter with each use. Since the purpose of a light localizer is to mark the outer extremities of the field, it was found possible to leave the filter attached to the cone without hindering this function of the localizer. In fact, the method developed is believed to have improved light localization. Method of Mounting Filters and Results A Lucite cap, with bottom and walls of 1.5 mm. thickness, was constructed to fit over the end of the cone (Fig. 1). A sheet of cadmium, 0.25 mm, thick, was then attached to the Lucite so as to cover the opening of the cone except for a narrow slit (about 1 mm.) around the edges. With this arrangement, the filter can easily be removed if desired. The light pattern from the localizer is shown in Figure 2. This pattern was made with the light from the bulb of the light localizer collimated so that its image in the mirror reproduced the source in both shape and position.

PurposeThis study aimed to evaluate the clinical infrastructure and utilization of radiotherapy (RT) services in Korea between 2017 and 2019. Materials and MethodsWe extracted the data of patients who underwent RT between 2017 and 2019 from the Health Insurance Review and Assessment Service. We further analyzed this data according to the diagnosis and treatment modalities of patients diagnosed with International Classification of Disease 10 (ICD-10) diagnostic codes C00–C97 and D00–D48. In addition, we collected statistics on RT facilities in Korea using a nationwide survey.ResultsThe total number of patients who received RT in 2017, 2018, and 2019 were 77,901, 81,849, and 87,460, respectively. The number of patients diagnosed with ICD 10 C- and D-codes in 2019 was 86,339, of whom 39,467 were men and 46,872 women. The rate of utilization of RT among cancer patients was 30.4% in 2017 and 2018 and 30.9% in 2019. In 2019, the most common types of cancers treated with RT were breast, lung, prostate, colorectal, and liver cancers. Regarding the RT infrastructure in Korea, there were 95 radiation oncology centers, 237 megavoltage (MV) teletherapy units, 35 brachytherapy units, and two proton accelerators in 2019. There were 4.5 MV teletherapy machines per million.ConclusionThe number of patients treated with RT has increased consistently from 2017 to 2019. As the number of patients with cancer increases, it is expected that the RT infrastructure will be further expanded in Korea.

The power in the gamma -ray beam from a Cs137 teletherapy unit has been measured with a calorimeter. Comparison with ionization measurements gives a conversion factor of 2959 plus or minus 44 ergs/cm2r, and combining this result with the calculated absorption coefficient gives a value for W of 33.9 plus or minus 0.5 ev/ion pair.

The evolution of radiation therapy in Uganda has been a journey marked by significant milestones and persistent challenges. Since the inception of radiotherapy services in 1988-1989, there has been a concerted effort to enhance cancer treatment services. The early years were characterized by foundational developments, such as the installation of the first teletherapy units, low-dose-rate brachytherapy units, and conventional simulators, and the recognition of radiation oncologists and medical physicist professionals laid the groundwork for radiotherapy treatment modalities. With more support from the International Atomic Energy Agency, the acquisition of dosimetry equipment, treatment planning systems, and additional professional training signaled a new era in the fight against cancer. As we entered the second decade of the millennium, the Uganda Cancer Institute (UCI) witnessed a progression in sophisticated radiotherapy services, including high-dose-rate brachytherapy, initiation of intensity modulated radiation therapy (IMRT)/volumetric modulated arc therapy (VMAT), and use of artificial intelligence. These advancements improved the efficiency/precision of treatments and the time patients spent undergoing therapy. Around the second decade of radiotherapy services, about 600 new patients with cancer were annually treated compared with about 2,600 in 2023. Currently, an average of 1,440 brachytherapy insertions are done annually compared with 300 insertions for the first 20 years. Despite the technological strides, the UCI faced numerous obstacles, including limited equipment, knowledge gaps in appropriate tumor/organs at risk segmentations, treatment planning, and protocols. However, international support and collaboration efforts have led to significant improvement in the precision and effectiveness of treatments. Currently, about 51% of all patients are treated with image-guided techniques-IMRT/VMAT (42%) and three-dimensional conformal radiation treatment (10%). The Government has commenced the decentralization of radiotherapy services to other regions. This review can be a learning lesson for the more than 25 countries in Africa and other low-middle-income countries globally that do not have access to radiotherapy and/or are in the process of starting such facilities.

We describe the commissioning of the first dedicated commercial total body irradiation (TBI) unit in clinical operation. The Best Theratronics GammaBeam 500 is a Co‐60 teletherapy unit with extended field size and imaging capabilities. Radiation safety, mechanical and imaging systems, and radiation output are characterized. Beam data collection, calibration, and external dosimetric validation are described. All radiation safety and mechanical tests satisfied relevant requirements and measured dose distributions meet recommendations of American Association of Physicists in Medicine (AAPM) Report #17. At a typical treatment distance, the dose rate in free space per unit source activity using the thick flattening filter is 1.53 × 10−3 cGy*min−1*Ci−1. With a 14,000 Ci source, the resulting dose rate at the midplane of a typical patient is approximately 17 and 30 cGy/min using the thick and thin flattening filters, respectively, using the maximum source to couch distance. The maximum useful field size, defined by the 90% isodose line, at this location is 225 × 78 cm with field flatness within 5% over the central 178 × 73 cm. Measured output agreed with external validation within 0.5%. End‐to‐end testing was performed in a modified Rando phantom. In‐house MATLAB software was developed to calculate patient‐specific dose distributions using DOSXYZnrc, and fabricate custom 3D‐printed forms for creating patient‐specific lung blocks. End‐to‐end OSLD and diode measurements both with and without lung blocks agreed with Monte Carlo calculated doses to within 5% and in‐phantom film measurements validated dose distribution uniformity. Custom lung block transmission measurements agree well with design criteria and provide clinically favorable dose distributions within the lungs. Block placement is easily facilitated using the flat panel imaging system with an exposure time of 0.01 min. In conclusion, a novel dedicated TBI unit has been commissioned and clinically implemented. Its mechanical, dosimetric, and imaging capabilities are suitable to provide state‐of‐the‐art TBI for patients as large as 220 cm in height and 78 cm in width.

Many designs of radiation therapy rooms miss the correct shielding requirements due to improperly selected equipment or incorrectly chosen design. These designs may have been established based on the most common devices in the market at design time or based on previous work or experiences. Furthermore, the device upgrading from low energy to high energy or from cobalt tele-therapy gamma-ray units to linear accelerator may result in an imperfect shielding. Through implementation, problems may be faced to keep the required safety levels, furthermore, to satisfy the needed protection. In this paper, we illustrate through selected case studies, some of the problems faced and how it could be overcome in order to reach the required protection levels. This study includes seven bunkers at different places whose designs prevented to establish a linear accelerator due to room areas, room surrounding spaces or type of existing shielding: wall or layers thickness and material. Three rooms were predesigned for a cobalt tele-therapy system with an overall wall thickness of 70 cm; two rooms were inadequately designed with irregular walls of 1 m thickness, and the other two rooms were designed for low energy devices and are to be upgraded to high energy, in-addition to different inadequate conditions surrounding these bunkers. Combined solutions were used to overcome the faced problems. The presented solutions incorporate using other shielding materials than concrete as lead, borated polyethylene, gamma-600 together with changing and/ or controlling the obliquity factor (changing the incident angle of radiation). The existing shielding may be also be modified by adding an internal/external layer of lead. Moreover, the position of the device inside the room was re-allocated with a certain angle to the incident rays in order to reduce leakage radiation. The resulting design solutions were validated via the atomic energy commission at those countries.

Thermoluminescence Dosimeter (TLD) is used as an ionizing radiation detector in the field of clinical radiotherapy, diagnostic radiology, personal radiation monitoring as well as in environmental radiation dosimetry. The sensitivity of all the TLDs is not the same even though the manufacturer produced them in the same batch. The response of TLD at various doses is also not always linear. In the present study fifty-seven rod shaped LiF TLDs had been irradiated by doses of 50cGy, 100cGy, 150cGy and 200cGy using 60Co teletherapy unit of Dhaka Medical College (Alcyon II, CGR, McV, France). The TLDs were placed in the grooves of a slab phantom and then covered by a 0.5cm thick plexiglass sheet. The phantom was then irradiated in the reference condition (10x10cm2 field size, 80cm SSD). After irradiation, readout of TLDs was done using a Harshaw TLD reader (Model 3500). Measurements were performed three times for each dose value and their average was taken. For convenience all fifty-seven TLDs were divided into nineteen groups. Grouping was done according to the response of the TLDs for a fixed dose value. In a particular group of TLDs, variation of the response of the dosimeters is the smallest one. The dose (cGy) – response (nC) linearity curve of TLDs for each of the nineteen groups showed to be very close to unity.Bangladesh Journal of Medical Physics Vol.8 No.1 2015 14-21

Two of the three methods most commonly employed for the measurement of teletherapy unit timer errors were unreliable when using Victoreen R-meters, due to their nonlinear exposure response. The third technique, although eliminating gross errors, was inherently inaccurate, even with linear exposure meters. A fourth method was devised by which the resultant degree of accuracy could be readily controlled and was independent of exposure-meter linearity.

Optically stimulated Al2O3:C luminescence dosimeters for teletherapy: Hp(10) performance evaluation

The influence of field size, treatment modality, commissure involvement and histology in the treatment of early vocal cord cancer with irradiation