Use Of Linear Accelerator Research Articles

Potato sprout inhibition and tuber quality after treatment with high-energy ionizing radiation

The use of industrial-type linear accelerators may be an alternative treatment for controlling sprouts in potatoes during long-term storage. The technical aspect of treatment has been described and may include largescale treatment of bulk potatoes as they are moving along a system of conveyors either to or from storage. The objective of the study was to evaluate the use of a linear accelerator for long-term sprout control under commercial storage conditions and the effects on tuber quality. An 18-MeV linear accelerator was used to provide sprout-inhibiting irradiation to various lots of ‘Russet Burbank’ potatoes. Successful sprout suppression was achieved with doses of 40 to 50 Gy (0 g sprout weight after 9 months of storage at 7.2 C) while higher doses caused undesirable increases in reducing sugars in the tubers. Glucose concentrations of treated tubers (0.25% fresh tuber weight) were higher after treatment than the untreated controls (0.08%), but returned to control levels after 2 to 6 months in storage. Glucose concentrations in treated tubers were significantly reduced with storage management for reconditioning by increasing the storage temperature for one month (from 7.2 C to 14.4 C) resulting in glucose concentrations near control concentrations. By increasing the dose-rate from the accelerator, recovery of tuber glucose concentration due to radiation treatments was significantly faster than when the dose was given more slowly. Potato tubers irradiated with high rates (100 Gy) of high-energy electrons exhibited an increase in soft rot and dry rot incidence in storage. Disease development in potatoes treated with sprout inhibiting doses of radiation (50 Gy) increased in lots with a high rot potential. Treated lots with low rot potential were successfully stored for 8 months or more without an increase in rot potential or shrinkage. Selection of lots for irradiation treatment should include some preliminary evaluation for development of disease in long-term storage.

Linear accelerator surgery for meningiomas

In this paper the authors review the results of a single-center experience in the use of linear accelerator (LINAC) surgery for radiosurgical treatment of meningiomas. A retrospective analysis of all patients treated with LINAC surgery for meningiomas between May 1989 and December 2001 was performed. All patients participated in follow-up review for a minimum of 2 years, and no patients were excluded. Two hundred ten patients were treated during the study interval. The actuarial local control rate for benign tumors was 100% at both 1 and 2 years, and 96% at 5 years. The actuarial local control rate for atypical tumors was 100% at 1 year, 92% at 2 years, and 77% at 5 years; and that for malignant tumors was 100% at both 1 and 2 years, and only 19% at 5 years. Of the 210 patients 13 (6.2%) experienced temporary radiation-induced complications, and only five (2.3%) experienced permanent complications. In all patients with a permanent complication the histological characteristics of the meningioma were malignant. Linear accelerator surgery produced high local control rates and very low rates of permanent morbidity in patients harboring benign meningiomas.

Radiosurgery for pituitary adenomas

Radiosurgery for pituitary adenomas

Stereotactic one-time irradiation (radiosurgery). The methods, indications and results

Stereotaxy is a method to determine a point in the patient's body by an external coordinate system which is attached to the patient. Radiosurgery uses this method for precise delivery of a high single radiation dose to the patient. The aim is to destroy the tissue in the target and to spare surrounding unaffected normal tissue by a steep dose gradient. Three techniques of percutaneous radiosurgery are available: radiosurgery with ion beams with a cyclotron, spherical arrangement of cobalt-60 sources, the so-called gamma knife, and an adapted linear accelerator. The availability and the good clinical experience lead to a wide spread use of linear accelerator for radiosurgery in recent years. A subsequent development is fractionated stereotactic radiotherapy which combines the precision of radiosurgery with the radiobiological advantage of fractionation. Only a few indications for radiosurgery are proven by statistically valid studies. One of these is the treatment of small arteriovenous malformation, where obliteration rates of 80% to 100% are reported with only minor toxicity. However, the obliteration rate is reduced significantly in large arteriovenous malformations. A local control rate of 90% is obtained after radiosurgery of brain metastases which is comparable to the results of microsurgical resection followed by adjuvant whole brain radiotherapy. An ongoing EORTC study evaluates the role of adjuvant whole brain radiotherapy after radiosurgery. The survival of the patients with brain metastases is limited by the existence of progressive extracerebral disease. The role of radiosurgery in the treatment of benign tumors is currently evaluated in clinical studies which include: vestibular schwannomas, meningiomas, chordomas and chondrosarcomas and pituitary adenomas. Most of the published studies include only small tumors because radiosurgery is limited by the risk of radionecrosis of adjacent normal tissue, which shows a steep dose volume response relationship. Recent developments of stereotactic radiotherapy include the use of mini-multileaf-collimators and clinical studies on stereotactic radiotherapy of extracranial targets. Stereotactic irradiation is a well established treatment technique for intracranial tumors and arteriovenous malformations. Methods are available that allow optimization of dose distributions to irregularly shaped tumors for single dose as well as fractionated stereotactic irradiations by linear accelerator. Therefore the therapeutic potential of this technique has increased and enables also the extracerebral application in controlled clinical studies.

Over 20 years of progress in radiation oncology: Cervical cancer

Carcinoma of the cervix remains of special interest to the Patterns of Care Study (PCS) because of the prominent role that radiotherapy plays in the definitive management of all stages and extents of disease. Five PCS surveys have been conducted for squamous cell cancer of the uterine cervix beginning in 1973 and repeated thereafter at 5-year intervals. The records of over 2,700 women have been reviewed for these surveys. Changes in the pretreatment investigations of cervical cancer patients have occurred during these years, with an increase in the use of computed tomography (CT) and a decrease in the use of intravenous pyelography and cystoscopy. A marked increase in the use of linear accelerators has also occurred, with 98% of all facilities having a linear accelerator as the highest energy treatment machine in the 1988 survey. There has been a change in brachytherapy prescription over the time of the surveys, with most institutions reporting point dose calculations and dose distributions instead of milligram hours. Mean point A dose has increased to approximately 80 cGy, reflecting the PCS recommendations of dose intensity to the paracentral point through use of brachytherapy. The outcome for stage I and II cervical cancer has remained stable over the time of the surveys, while the results have improved for stage III disease. This improvement in survival and local control for stage III cervical cancer corresponds to an increased use of brachytherapy. The change in outcome for stage III cervical cancer is due in part to the PCS, which has developed standards of treatment with the goal of radiation dose intensity. A number of patient, tumor, and treatment factors significant in multivariate analysis have been described by the PCS with large cohorts of patients. The most important treatment factors associated with a decrease in pelvic failure and improved survival are the use of brachytherapy and higher paracentral dose. A significant dose response has been described for stage III cervical cancer and optimal pelvic control has been demonstrated with point A doses above 8,500 cGy. Other treatment factors associated with improved outcome include the reduction of overall treatment time, particularly for stage III cervical cancer, and the adequacy of an intracavitary placement. The rate and time course of major complications associated with radiation for cervix cancer has been described by the PCS. An increase in complicaitons was seen for young patients and those with a history of abdominal surgery. Treatment factors that increased the risk of complications included a fraction size greater than 200 cGy, a paracentral dose greater than 7,500 cGy, and the use of staging laparotomy via a transperitoneal approach. Through the findings of the PCS, national averages of the process and outcome of radiation for cervical cancer as well as the important patient, tumor, and treatment factors that affect outcome have been reported. These results have positively affected routine clinical practice. Greater emphasis is placed on the use of intracavitary radiation therapy (RT) and dose escalation, as well as on a reduction in overall treatment time for cervical cancer. Future research will focus on the use of new technologies, such as high-dose rate brachytherapy and the impact of CT-and magnetic resonance imaging-directed treatment planning on local tumor control and survival. It will specifically evaluate the radiation treatment and outcome of minority populations. It will also measure the adoption of the results of positive clinical trials and the findings from previous PCS analyses into the national practice of radiation oncology

20 Years of Progress in Radiation Oncology: Prostate Cancer.

Carcinoma of the cervix remains of special interest to the Patterns of Care Study (PCS) because of the prominent role that radiotherapy plays in the definitive management of all stages and extents of disease. Five PCS surveys have been conducted for squamous cell cancer of the uterine cervix beginning in 1973 and repeated thereafter at 5-year intervals. The records of over 2,700 women have been reviewed for these surveys. Changes in the pretreatment investigations of cervical cancer patients have occurred during these years, with an increase in the use of computed tomography (CT) and a decrease in the use of intravenous pyelography and cystoscopy. A marked increase in the use of linear accelerators has also occurred, with 98% of all facilities having a linear accelerator as the highest energy treatment machine in the 1988 survey. There has been a change in brachytherapy prescription over the time of the surveys, with most institutions reporting point dose calculations and dose distributions instead of milligram hours. Mean point A dose has increased to approximately 80cGy, reflecting the PCS recommendations of dose intensity to the paracentral point through use of brachytherapy. The outcome for stage I and II cervical cancer has remained stable over the time of the surveys, while the results have improved for stage III disease. This improvement in survival and local control for stage III cervical cancer is due in part to the PCS, which has developed standards of treatment with the goal of radiation dose intensity. A number of patient, tumor, and treatment factors significant in multivariate analysis have been described by the PCS with large cohorts of patients. The most important treatment factors associated with a decrease in pelvic failure and improved survival are the use of brachytherapy and higher paracentral dose. A significant dose response has been described for stage III cervical cancer and optimal pelvic control has been demonstrated with point A doses above 8,500 cGy. Other treatment factors associated with improved outcome include the reduction of overall treatment time, particularly for stage III cervical cancer, and the adequacy of an intracavitary placement. The rate and time course of major complications associated with the radiation for cervix cancer has been described by the PCS. An increase in complications was seen for young patients and those with a history of abdominal surgery. Treatment factors that increased the risk of complications included a fraction size greater than 7,500 cGy, and the use of staging laparotomy via a transperitoneal approach. Through the findings of the PCS, national averages of the process and outcome of radiation for cervical cancer as well as the important patient, tumor, and treatment factors that affect outcome have been reported. These results have positively affected routine clinical practice. Greater emphasis is placed on the use of intracavitary radiation therapy (RT) and dose escalation, as well as on a reduction in overall treatment time for cervical cancer. Future research will focus on the use of new technologies, such as high-dose rate brachytherapy and the impact of CT- and magnetic resonance imaging-directed treatment planning on local tumor control and survival. It will specifically evaluate the radiation treatment and outcome of minority populations. It will also measure the adoption of the results of positive clinical trials and the findings from previous PCS analyses into the national practice of radiation oncology.

The irradiation of blood and blood components to prevent graft-versus-host disease: technical issues and guidelines.

In recent years, there have been several advances in blood irradiation practice. These include a better definition of the most appropriate dose level that should be used when irradiating blood components. Commercial innovation has provided the tools for a quality assurance program to assess the dose that is delivered throughout the canister in a free-standing irradiator, and, through the use of radiation-sensitive indicator labels, to confirm that the irradiation process has taken place. With the apparent increased use of linear-accelerators to irradiate blood components, appropriate quality assurance measures need to be developed. The maximum storage period for irradiated red cells should be shorter than for nonirradiated red cells if the treatment is performed early during the storage period because irradiation reduces the in vivo 24-hour red cell recovery parameter. The storage period for irradiated platelets does not need to be modified. Some questions are being raised regarding whether fresh-frozen plasma should be irradiated to inactivate a small number of immunocompetent progenitor cells that may be present. Table 4 summarizes the practices that should be followed in connection with the technical issues that have been addressed in this article. These guidelines follow the recommendations issued in July 1993 by the FDA in the United States. This article and Tables 1 and 2 contain additional guidelines.

Progress in the treatment of Hodgkin's disease in the United States, 1973 versus 1983. The Patterns of Care Study.

The prognosis for Hodgkin's disease patients has improved significantly since the early 1960s. The reasons for this improvement are multifactorial. In the Patterns of Care Study of the American College of Radiology, national surveys to examine process and outcome of patients treated for Hodgkin's disease in 1973 and 1983 were completed. Data were compared for patients who had Stage I-II Hodgkin's disease and who were treated with radiation therapy alone. Clinical characteristics of the patients in the two different treatment eras were similar. There were important differences in treatment parameters. In 1983 compared with 1973, there was more common use of a dedicated simulator, performance of routine port films, use of linear accelerators, use of individually shaped blocks, and treatment to extended fields. Adequacy of treatment fields also was judged superior in the 1983 study. There were improvements in survival and relapse-free survival for patients treated in 1983 versus 1973. Improvement in radiation therapy technique is associated with an improved outcome for patients treated for Hodgkin's disease. The national standards have improved during the time from 1973 to 1983.

Linac-accelerator-radiosurgery.

A survey is given of the actual possibilities and limitations of the use of linear accelerators (Linac radiosurgery systems) for intra = cranial radiosurgery. Depending on the collimator size, spherical fields from 5-54 mm in diameter can be irradiated with dose gradients from 10% (large fields) to 20% (small fields) per millimeter distance between surface and treatment volume. This is comparable to the possibilities of Gamma-Knife and Proton-irradiation. Optimal mechanical adjustment of gantry and linac table are necessary for the required stability of the isocenter. Mechanical inaccuracy should be smaller than 0.8 mm. Advanced computerized 3D-treatment planning systems are indispensable prerequisites for accurate treatment and use of the flexibility of the linac system. Future developments are outlined.

Photon Radiosurgery: A Clinical Review

The term radiosurgery has been used to describe a variety of radiotherapy techniques which deliver high doses of radiation to small, stereotactically defined intracranial targets in such a way that the dose fall-off outside the targeted volume is very sharp. Proton, charged particle, gamma unit, and linear accelerator-based techniques appear to be equivalent from the standpoint of accuracy, dose distributions, and clinical results. However, capital and operating costs associated with the use of linear accelerators in general clinical use are much lower. Radiosurgery has an established role in the treatment of arteriovenous malformations and acoustic neurinomas. Interest in these techniques is increasing in neurosurgical and radiation oncological communities, as radiosurgery is rapidly assuming a place in the management of several other conditions, including craniopharyngiomas, meningiomas, and selected malignant lesions.

Small field stereotactic external beam irradiation

Department of Radiation Oncology, University of Miami School of Medicine, Miami, FL 33101 . . Puroose/Obrectlve: While stereotactic radiosurgery has generally utilized heavy particle and high LET radiation sources, as well as convergent beam gamma units, recent interest has centered on the use of linear accelerator based systems to deliver convergent noncoplanar arc small field irradiation using stereotactic techniques. The course will deal with the history and background of stereotaxic radiosurgery, modalities and methods which have traditionally been used, and current techniques and future directions for radiosurgery. Basic concepts of localization treatment planning and delivery will be discussed. Advantages, disadvantages and limitations of various systems will be explored.

Radiosurgery with a Linear Accelerator

Based on the concepts of Leksell and on recommendations of different Swedish physicists on the use of linear accelerator for radiosurgical use, we developed a new methodology coupling the Talairach stereotactic system with a commercial linac. Anatomical facts encouraged us to use coronal angles of irradiation employing the angular displacement of the linac above the horizontal plane. Different coronal planes are obtained by rotation of the stereotactic frame. The center of the irradiated target coincides with the irradiation and rotation center of the linear accelerator. Multiple targets can be irradiated in the same session. We use as recommended a secondary collimator in heavy alloy. Special software was prepared after different dosimetric controls. The use of a PC allows us to employ 1-6 targets and different collimators to displace the isocenters in order to obtain geometrical isodose modification, and to change the value of each irradiation arc or portions of each arc in some minutes. Simple or sophisticated neurosurgical strategies can be applied in the treatment of frequently irregular shape and volume AVMs.

Patterns of change in the physics and technical support of radiation therapy in the USA 1975–1986

Information on the patterns of personnel and related equipment support and availability at various types of radiation oncology facilities are included in the Facilities Master List surveys conducted by the American College of Radiology. This paper summarizes the surveyed data obtained during 1975–1986. The data presented include the use of equipment and the degree of personnel support at government owned, hospital or university based, and freestanding facilities. There is increasing use of linear accelerators, simulators, and treatment planning computers among all types of facilities. The use of 60Co units has been progressively decreasing. Almost all types of facilities show inadequate, but slowly improving, numbers of physicians, physicists, dosimetrists, and technologists when compared with the level recommended by the Blue Book.

Equipment and Manpower Needs in Radiation Oncology Dosimetry and Treatment Delivery

Information on the patterns of personnel and equipment support at various radiation oncology facilities are included in the Facilities Master List surveys conducted by the American College of Radiology. This paper summarizes the surveyed data on equipment and dosimetrist and technologist support obtained during 1975–1986. There is increasing use of linear accelerators, simulators, and treatment planning computers but the use of 60Co units has been progressively decreasing. There are inadequate but slowly improving numbers of dosimetrists and technologists when compared with the level recommended by the Blue Book.

Current limits in linear accelerators

In recent years considerable interest has developed in the use of linear accelerators for various high-current applications (radiation testing facilities, neutron spallation sources, heavy-ion fusion, etc.). The beam dynamics and current limits in a linear accelerator are determined largely by the periodicity and phase-space acceptance of the external focusing system and the particle oscillation frequencies (or phase shifts per focusing period), both without the space-charge forces and with the space-charge forces of the particle bunch. General formulas for the transverse and longitudinal current limits in terms of these fundamental quantities are derived. The relationships with the actual accelerator and particle beam parameters are examined for strong (quadrupole) and weak focusing field configurations. As a practical illustration, the results are applied to a drift-tube linac with quadrupole focusing in the transverse direction and rf phase focusing in the longitudinal direction.

The use of linear accelerators for gamma radiography

The use of linear accelerators for radiography for ndt is still in its infancy. The author describes the operation of linear accelerators from the point of view of gamma radiography. He discusses the working parameters and limits. He describes installations in operation in France and proposes that hiring the facilities out by the beam-hour would best serve the development of this method of gamma radiography.