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PubMed2002

Preoperative hypoxyradiotherapy of colorectal carcinoma.

AIM: The article focuses on the radioprotective effect of acute hypoxia on healthy tissues during preoperative accelerated hypoxyradiotherapy of colorectal carcinoma performed as locoregional irradiation including the common iliac lymph nodes. Analysis of early and late side effects and complications. PATIENTS AND METHODS: In this prospective study, early and late complications were assessed in 50 patients as a function of hypoxyradiotherapeutic dose increase. The preliminary treatment results of this radiotherapeutic modification were evaluated after a median follow-up of 48 months using Kaplen-Meier analysis. Between April 1991 and February 1997, 50 patients (36 men and 14 women) with colorectal carcinoma were treated preoperatively with locoregional accelerated hypofractionated hypoxyradiotherapy. The extent of disease was classified according to Dukes' criteria (A: four patients, B. 28 patients, C: 18 patients). We used a 20-MeV linear accelerator with two parallel opposed fields. Hypoxyradiotherapy was performed extending from the perineum to the L4 region. Acute hypoxia was induced during irradiation by ventilation of a hypoxic gas mixture containing 7.8-8.0% oxygen. Total doses of 24 Gy/8 days, 28 Gy/9 days, and 32 Gy/10 days were applied in five, 20, and 25 patients, respectively. Low anterior resection or abdominoperineal amputation of the rectum was performed the day after completion of preoperative hypoxyradiotherapy. The early reactions after irradiation were evaluated according to the Common Toxicity Criteria of the National Cancer Institute (CTC-NCI). RESULTS: Early postirradiation proctitis was documented in three and early radiation-induced cystitis in two patients only. Neither early nor late radiation-associated complications were observed in any of the three hypoxyradiotherapy schedules during the follow-up period of 6-105 months. Based on Kaplan-Meier analysis (median 48 months), a 5-year overall survival rate of 61.5% and a local relapse-free survival rate of 84.2% can be expected. Treatment failures were predominantly systemic. CONCLUSION: We believe it can be concluded that acute hypoxia has a radioprotective effect on normal tissues during accelerated hypoxyradiotherapy of colorectal carcinoma. Hypoxyradiotherapy permits safe administration of doses higher than those tolerated by normoxic, noncanceorus tissue, resulting in the amplification of the biological effect of radiation on tumor tissue and contributing to an improved outcome after combined radiosurgical treatment of colorectal carcinoma.

Adult↗

PubMed1991

A non-invasive, relocatable stereotactic frame for fractionated radiotherapy and multiple imaging.

A non-invasive relocatable stereotactic frame has been developed for fractionated stereotactic external beam radiotherapy (SRT) by linear accelerator. Fixation is via the upper dentition and tests of repositioning have shown mean antero-posterior and lateral displacements of 1.0 mm. The relocatable frame allows accurate 3-dimensional target localisation by CT, MRI, PET and cerebral angiography and precise isocentric positioning for radiotherapy. This method of immobilisation is ideal for fractionated SRT as well as for other techniques requiring high precision localisation and treatment delivery.

Animals↗

PubMed1998

The state of positron emitting radionuclide production in 1997.

Thirty years ago Michel M. Ter-Pogossian and Henry N. Wagner, Jr. wrote an article that was published in Nucleonics on the cyclotron production of isotopes for biomedical research. In this report we use the Nucleonics paper as the framework to relate their predictions to the current state of the art, we have broken this into four key areas; commercially available cyclotrons, costs of operating cyclotron facilities, the emergence of compact accelerators, and the cyclotron production of long-lived radionuclides for therapeutic applications. Companies producing cyclotrons commercially are; General Electric Medical Systems, CTI Cyclotron Systems, EBCO, IBA, NNK/Oxford Instruments, and Japan Steel Works. The majority of these machines are now negative ion systems, which allows the option of dual irradiation of two targets. All have a modular design, which allows the system to be customed to a particular facility's need. Cyclotron facility costs have increased dramatically since 1966. We have determined that the bulk of the increase lies in the costs to establish and staff the facility. Increased regulation by Federal and State organizations has severely impacted operational expenses. The growing demand for PET radiopharmaceuticals in the clinical arena has increased the staffing requirements of the facility. Surprisingly, the costs of cyclotrons have not increased (in terms of real dollars) especially when one considers the much greater sophistication in target design, automation, and computer control that has occurred during this time. Innovative approaches are being taken to develop low energy accelerators that are capable of producing PET isotopes. These are easier to operate and less expensive than commercially available cyclotrons. Although many of these systems have been developed, none have as yet gained commercial recognition. A number of groups have begun to address the production of longer lived isotopes on biomedical cyclotrons. Development of this technology may well help to further progress in targeted radiotherapy. We present an overview of potentially useful isotopes.

Costs and Cost Analysis↗

PubMed2004

Liquid chromatographic aqueous product characterization of high-energy electron beam irradiated 2-chlorobiphenyl solutions.

Polychlorinated biphenyls (PCBs) are of environmental concern due to their toxic nature. Ionizing radiation has been suggested as a means to remediate PCB-contaminated samples in complex matrices. A set of experiments was performed to qualitatively and quantitatively determine the aromatic degradation products of 2-monochlorobiphenyl (2-MCB) in an aqueous system exposed to ionizing radiation. The degradation of 2-MCB was observed in aqueous samples that were exposed to radiation from a linear accelerator electron beam source. Analytical measurements performed by liquid chromatography (LC) equipped with an ultraviolet (UV) detector revealed that biphenyl, o-hydroxybiphenyl, p-hydroxybiphenyl, phenol, chlorobenzene, and other unidentified products were created after 2-MCB irradiation. These results suggest that sensitive and selective analytical methods will be required to account for all degradation products during ionizing radiation of aqueous PCB-contaminated samples.

Biphenyl Compounds↗

PubMed2003

Infrastructure of radiotherapy in the Netherlands: evaluation of prognoses and introduction of a new model for determining the needs.

BACKGROUND AND PURPOSE: In the Netherlands, the radiotherapy infrastructure is regulated by a Governmental license system. This requires timely and realistic prognostication of the needs for radiotherapy. In the present study, the latest prognoses (1993) and the realized changes in infrastructure are evaluated and a new prognosis for the period until 2010, which has been calculated using a new model, is presented. MATERIALS AND METHODS: Data on cancer incidence and use of radiotherapy were obtained from various published national reports and from a survey of all radiotherapy departments. RESULTS: The cancer incidence over the period 1993-1997 was about 10% higher than predicted. In 1996 and 1997, the percentage of new cancer patients treated with radiotherapy was 45.6 and 48.2%, respectively. The absolute number of newly irradiated patients was about 10% higher than foreseen in the prognosis. The needs for radiotherapy infrastructure not only depend on epidemiological data and changes in indications for radiotherapy, but also on changes in types of treatment with different workloads. A new model, which uses four categories for teletherapy and four categories for brachytherapy is described and a new prognosis for the required number of linear accelerators and staff up to the year 2010 is presented. CONCLUSION: The original prognosis on cancer incidence and radiotherapy patients underestimated the actual figures considerably. The new prognosis, based on a model, which not only accounts for an increase in number of patients, but also for changes in treatment techniques, is expected to more accurately predict and acquire the required radiotherapy capacity.

Aged↗

PubMedDate not supplied

Dosimetry of wedged fields with asymmetric collimation.

Shaping of wedged fields with asymmetric collimators (independent jaws) produces dosimetric effects which need to be taken into account when calculating isodose distributions and accelerator monitor units. These effects were studied using ion chamber dosimetry in a water phantom. Wedged fields of 30 degrees to 60 degrees wedge angles were shaped by an asymmetric collimator. A system of dose calculation was developed to take into account the changes in dose in the open portion of the field. The formalism utilizes regular symmetric field parameters (e.g., Sc, Sp, and TPR). Calculated point doses and profiles agreed well with the measured data.

Biophysical Phenomena↗

PubMedDate not supplied

Recombination correction factors for an ionization chamber exposed to discrete patterned pulsed swept beams.

An equation for a recombination correction factor for a pulsed swept beam of electrons was derived by Boag. This equation is based on an integration technique, which assumes that a large number of spot beams cover the radiation field, that the field size is much larger than the spot beam size, and that the spot beam size is much larger than the chamber size. However, for computer-controlled pulsed swept beams of electrons, the spot beam pattern can be altered, may not cover all of the field area, and the locations are reproducible. In this report, a summation method is proposed for this type of beam. Calculations for two such beams are demonstrated with the chamber located in the center of the field, and with the chamber half-way to and at the edge of the field for a linear accelerator. The results lie between the integration pulsed swept and pulsed beam curves. Moving the ionization chamber from the center toward the edge of the field produces curves closer to the pulsed swept beam curve. Increasing spot beam size produces curves closer to the pulsed beam curves. It is therefore concluded that the pulsed swept beam cannot be characterized by a single recombination correction factor curve. The actual curve will be bounded by the integration pulsed swept and pulsed beam curves.

Electrons↗

PubMed1995

A scintillating fiber beam-energy monitor for electron beam therapy.

A new type of beam-energy monitor is described, which has been developed to check the energies of electron beams from radiotherapy accelerators. The monitor consists of a pair of scintillating fibers and photodiode read-out circuits that measure the energy dependence of electron transmission through a wedge-shaped absorber. A linear energy response and 1% accuracy for energy constancy measurements are attained with the monitor. The monitor having advantages of simple mechanical and electronic constructions, small size, and low cost is suitable for practical use as a portable device.

Biophysical Phenomena↗

PubMed2000

Electron spectra derived from depth dose distributions.

The technique of extracting electron energy spectra from measured distributions of dose along the central axis of clinical electron beams is explored in detail. Clinical spectra measured with this simple spectroscopy tool are shown to be sufficient in accuracy and resolution for use in Monte Carlo treatment planning. A set of monoenergetic depth dose curves of appropriate energy spacing, precalculated with Monte Carlo for a simple beam model, are unfolded from the measured depth dose curve. The beam model is comprised of a point electron and photon source placed in vacuum with a source-to-surface distance of 100 cm. Systematic error introduced by this model affects the calculated depth dose curve by no more than 2%/2 mm. The component of the dose due to treatment head bremsstrahlung, subtracted prior to unfolding, is estimated from the thin-target Schiff spectrum within 0.3% of the maximum total dose (from electrons and photons) on the beam axis. Optimal unfolding parameters are chosen, based on physical principles. Unfolding is done with the public-domain code FERDO. Comparisons were made to previously published spectra measured with magnetic spectroscopy and to spectra we calculated with Monte Carlo treatment head simulation. The approach gives smooth spectra with an average resolution for the 27 beams studied of 16+/-3% of the mean peak energy. The mean peak energy of the magnetic spectrometer spectra was calculated within 2% for the AECL T20 scanning beam accelerators, 3% for the Philips SL25 scattering foil based machine. The number of low energy electrons in Monte Carlo spectra is estimated by unfolding with an accuracy of 2%, relative to the total number of electrons in the beam. Central axis depth dose curves calculated from unfolded spectra are within 0.5%/0.5 mm of measured and simulated depth dose curves, except near the practical range, where 1%/1 mm errors are evident.

Computer Simulation↗

PubMed1990

[An empirical model for calculating electron dose distributions].

Dose-distributions in radiation fields are calculated for purpose of irradiation planning from measured depth dose and cross-distributions predominantly. Especially in electron fields the measuring effort is high to this, because these distributions have to be measured for all occurring irradiation parameters and in many different tissue depths. At the very least it can be shown for the 6...10 MeV electron radiation of the linear accelerator Neptun 10p that all required distributions can be calculated from each separately measured depth dose and cross-distribution. For this depth dose distribution and the measured border decrease of cross-distribution are tabulated and the abscissas are submitted to a linear transformation x' = k.x. In case of depth dose distribution the transformation factor k is dependent on electron energy only and in cross-distribution on tissue depth and source-surface-distance additionally.

Electrons↗

PubMed1996

A study of waiting times and waiting lists for radiation therapy patients.

A simple mathematical model based on queueing theory is introduced, and used to obtain a sensitive measure of the capacity of a radiation therapy centre to provide service. The model illustrates the relationships among the relevant variables: the patient waiting time, the number on the waiting list, the rate at which requests for radiation therapy are received and the rate at which courses of treatment are commenced. In particular, the rate at which the waiting time increases is equal to the difference between the request rate and the start rate, expressed as a fraction of the start rate, and is therefore a measure of the deficiency in service capacity of a facility. A study of the records of patients treated on the linear accelerators of the Tom Baker Cancer Centre from January 1991 to June 1994 shows that this relationship holds to a high degree of accuracy for average values of the various parameters in spite of the considerable variation in these values, and particularly variation in the individual waiting times. This finding suggests that such an approach would be useful in assessing and comparing the performance of radiation therapy facilities.

Alberta↗

PubMed1996

The dependency of wedge factors on field size and depth in megavoltage beams.

AIM: To investigate the variation of wedge factors on field size, depth on 2 types of telecobalt units and 3 types of medical linear accelerators and to make a simplified approach for day to day calculation procedure. MATERIALS AND METHODS: A 0.125 cm3 ion chamber was used to determine the wedge factors which is connected to the computer controlled radiation field analyser. The wedge factors were determined for field sizes varying from 5 x 5 cm to the maximum square field size available for each wedge angles and at multiple depths upto 25 cm of respective teletherapy units. The results obtained are fitted to a second degree polynomial function. RESULTS: There is no significant variation of wedge factor on field size for all the 3 linear accelerators. The wedge factors are found to vary mainly at larger depths and wedge angles. The variation of wedge factors for 2 types of cobalt units were similar and increase of 3%, 4% and 5.5% is observed for wedge angles 30 degrees, 45 degrees and 60 degrees respectively with respect of depth of maximum build-up. The trend was similar for linear accelerators with maximum increase in wedge factor up to 7.5% for 60 degrees wedge angle at 25 cm depth for 6 MV photon beams. DISCUSSION AND CONCLUSIONS: The determination of wedge factors at various field sizes and depths is essential to ensure accurate dose delivery. With experimental wedge data fitted with second degree polynomial function is a simplified and alternative method which can be adopted for routine dosimetric calculations.

Cobalt Radioisotopes↗

PubMed1992

Induction of SOS repair by ionizing radiation. Results from experiments at accelerators.

beta-galactosidase and alkaline phosphatase activities of Escherichia coli strain PQ37 carrying the fusion gene of sulA and lacZ treated with different types of ionizing radiation were examined. The induction factor (ratio of beta-galactosidase to alkaline phosphatase activity), reflecting the SOS-induction potency, increases significantly with radiation dose. Maximum effectiveness to induce SOS-response has been found for deuterium and helium ions in comparison to gamma-rays, carbon or krypton ions. Increased energy of helium ions leads to greater SOS-induction potency of radiation.

Dose-Response Relationship, Radiation↗

PubMedDate not supplied

On the field-size dependence of relative output from a linear accelerator.

The radiation output in air on the central axis of a linac photon beam has been modeled as the sum of two components. These are a point source representing radiation direct from the target and a distributed source representing scatter in the flattening filter and primary collimator. By fitting only two parameters, the ratio of the two components for a 20 x 20 field and a width parameter for the distributed source this semi-empirical model describes the relative outputs of square, symmetric rectangular, and asymmetric rectangular fields with an average error of 0.25% for the field sizes studied.

Particle Accelerators↗

PubMed1984

Cyclotrons, radionuclides, precursors, and demands for routine versus research compounds.

Accelerators for producing commonly used short-lived positron emitters for positron emission tomography are addressed in the context of their use for the preparation of labeled compounds for research and routine biomedical applications. Progress and direction in the preparation and use of radiotracers for studies of the brain are discussed. Advancement to complete automation is stressed as an important factor for the eventual use of positron emission tomography as a routine clinical tool in universities and major medical centers.

Drug Compounding↗

PubMed1988

Design and characteristics of a facility for total-body and large-field irradiation.

A facility for total-body X ray irradiation has been built using two 4 MV linear accelerators, one supported from the ceiling and one placed in a floor pit. The maximum distance between the sources is 410 cm. The patient lies supine on a light, movable support with a stretched-canvas top, halfway between the sources where the field size is 80 X 220 cm2. A special flattening filter maintains the doserate variation in air within +/- 3% over the central 70 X 200 cm2 of the field, but some quality variations within the beam are noticeable. The doserate at 205 cm distance from the sources is variable between 0.05 and 0.8 Gy/min (half from each source). To permit treatment of large fields at higher doserates, the accelerators can be moved vertically to place the sources at 120 cm or 160 cm from the patient's midplane. For this purpose, independently movable collimators are provided and the flattening filter is designed to provide two options, one for the large total-body field and the other with less filtration covering a smaller solid angle. At 120 cm distance, each beam can provide a doserate of up to 1.1 Gy/min.

Facility Design and Construction↗

PubMed1991

Introducing a computerized record and verify system: its impact on the reduction of treatment errors.

A survey of treatment errors has been conducted over a period of several months before and after the introduction of a CMS computerized record and verify system for radiation treatments administered on a Varian CL-1800 accelerator. It was found that treatment errors could be reduced considerably. However, some errors were also caused by wrong data entry into the system. In two instances, errors were detected only through the record and verify system; they had escaped all previous chart checks and would never have been found otherwise. The impact of the computerized record and verify system is analyzed with regard to improved treatment delivery, reception by technologists, and treatment documentation.

Humans↗

PubMed1986

The study of a swept electron beam in order to apply Boag's theory for calculation of the collection efficiency: I. Beam and swept area characteristics.

The characteristics of swept electron beams produced by Sagittaire or Saturne type accelerators were investigated by film dosimetry. Beam sections perpendicular to the beam limiting system (BLS) axis are fully described by Gaussian curves close to the centre of the field defined by the BLS, but they become more and more distorted as the elementary beam approaches the BLS. The swept area was also evaluated and was related to the magnitude of the current applied to the two orthogonal magnets of the sweeping system.

Evaluation Studies as Topic↗