18 research outputs found
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Determination of the quality factor through the utilization of a balanced, tissue equivalent, ionization chamber
Accelerator dosimetry tends toward either specifying the field by way of its components or using a tissue equivalent chamber with a failsafe Quality Factor (QF). This investigation attempts a third approach, the determination of QF directly.
A Lucite, three-parallel plate ionization chamber was constructed with a common center electrode and two independent outer electrodes. This configuration allows the position of the center electrode to be manually adjusted to effect first order balance; vernier balance is obtained electronically through adjustment of one of the paired electrometers. The chamber can be pressurized to at least 17 atm with a tissue equivalent gas mixture and, therefore, approximates tissue rad response.
This ionization chamber is capable of detecting differences in LET of any radiation by operating on the principle of columnar recombination. The previous investigators use either a single ion chamber or operate their respective systems in the general recombination mode. This technique requires low polarizing voltages and, therefore, is useful only for low dose rates. Both the single chamber and the general recombination system are limited in accelerator dosimetry applications. Very high instantaneous dose rates and extreme variability of sources dictate a balanced ionization chamber system that utilizes columnar recombination.
In the present instrument, one of the chambers is operated at low polarizing potential while the other is variable. The difference current between the two chambers is adjusted to zero for background levels and when sensing radiation this difference current is a measure of QF.
In operation, the slope, with voltage, of the difference current is proportional to the QF of the radiation. This proportionality is apparently linear at 10 atm over a range of QF from one to at least 7.5. This response has been shown to be dose-rate independent. The directional dependence and pressure dependence of this chamber have been studied and will be reported
The Essential Role of External Beam Radiation Therapy in the Management of Advanced-Stage Retinoblastoma
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2196 A trial comparing hyperfractionated prophylactic cranial irradiation versus no prophylactic cranial irradiation in patients with limited stage small cell lung cancer with complete response to chemotherapy and consolidative radiotherapy
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Dosimetric Comparison of COMS and Circular Eye Physics Plaques to Treat Uveal Melanoma
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International Pediatric Oncology Patient Access to Treatment in a South Florida Health Network from 2007-2016
Comparison of Toxicity and Tumor Response in Early Glottic Cancer Treated With Conventionally Fractionated (CRT) Versus Hypofractionated Radiation Therapy (HRT): Retrospective Analysis of a Single-Institution Experience
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l Physics Contribution A QUANTITATIVE ASSESSMENT OF STANDARD VS. CUSTOMBlED MIDLINE SHIELD CONSTRUCTION FOR INVASIVE CERVICAL CARCINOMA
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Outcomes of Breast Conserving Therapy for DCIS in a Minority Population at University of Miami
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Gamma Knife Radiosurgery for Large Volume Brain Tumors: An Analysis of Acute and Chronic Toxicity
Gamma Knife radiosurgery is often used to treat intracranial tumors <4 cm (approximately 13.5 cm3) in mean diameter. Larger lesions are rarely treated because of the expectation that increasing target volume will increase toxicity. We retrospectively analyzed 35 patients with primary or metastatic brain tumors of more than 13.5 cm3 treated with the Gamma Knife. Only 3 (8.5%) patients developed acute clinical toxicity. Nine (25%) patients developed post-Gamma Knife radionecrosis based on imaging studies, with only 3 of these patients (9% of the study population) having clinical progression of symptoms. Necrosis was not found to be related to prescribed dose, treatment volume or number of treated isocenters. We found no undue toxicity from the treatment of large brain tumors with the Gamma Knife
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