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PubMed1996

Verification and implementation of dynamic wedge calculations in a treatment planning system based on a dose-to-energy-fluence formalism.

The use of dynamic movements on linear accelerators during irradiation has found a revised interest lately due to the integration of computers to control the accelerator. In this paper, dynamic wedge fields that are produced by moving one of the collimator blocks during irradiation are studied. Since these wedge fields differ from those of mechanical wedges, certain requirements are to be met on the treatment planning system. A pencil-beam-based treatment planning system that uses the resultant energy fluence distribution from the dynamic collimator movement has been extensively reviewed. In calculations, the system treats the dynamic collimated field as a single, modulated field that yields calculation times close to those for open beams. Details are given on the theoretical model used for the calculation of dynamically generated dose distributions. Measurements of depth doses, profiles, and output factors in dynamic wedge fields indicate that calculations accurately predict the outcome from dynamic wedges without any additional measurements other than those used for characterization of static open beams.

Biophysical Phenomena↗

PubMedDate not supplied

[The lethal and mutagenic actions of radiations with different LETs on mammalian cells].

Inactivation and induction of mutations in the HGPRT locus in Chinese hamster cells after irradiation with accelerated heavy ions in the LET range of 20 to 367 keV/micron were studied. In both cases, inactivation and induction of mutations, the LET dependence of RBE is described by a curve with a local maximum in the range of 80 to 100 keV/micron. The maximum RBE value for the mutagenic action is almost twice as high as that for inactivation. However, the RBE coefficients of the mutation induction criterion for a certain level of cell-survival is lower significantly and tend to decrease with an increase in inactivation. The obtained data show that the mutagenic effects, induction of chromosome aberrations, and deaths have their origins in the same kind of primary damages, i.e., double-strand breaks of DNA.

Animals↗

PubMed1995

Analysis of mutations in the human HPRT gene induced by accelerated heavy-ion irradiation.

Multiplex PCR analysis of HPRT(-) mutations in human embryo (HE) cells induced by 230 keV/microns carbon-ion irradiation showed no large deletion around the exon regions of the locus gene in contrast to the irradiations at different LETs. To identify these mutations, the sequence alterations in a cDNA of hprt gene were determined for 18 mutant clones in this study. Missing of exon 6 was the most frequent mutational event (10 clones), and missing of both exons 6 and 8 was next most frequent event (6 clones), then base substitutions (2 clones). These characteristics were not seen in a similar analysis of spontaneous mutations, which showed base substitution (5 clones), frameshift (2 clones), missing of both exons 2 and 3 (2 clones), and a single unidentified clone. Direct sequencing and restriction enzyme digestion of the genomic DNA of the mutants which showed missing of exons 6 and 8 in the cDNA, supports the possibility that they were induced by aberrant mRNA splicing.

Base Sequence↗

PubMed1997

[A quality assurance program of simulators in radiation therapy. 2. Extent and results of long-term quality assurance test on a therapy simulator].

BACKGROUND: Since 1990 we follow a quality assurance program with periodical tests of functional performance values of a 16-year-old simulator. MATERIAL AND METHOD: For this purpose we adopted and modified German standards for quality assurance on linear accelerators and international standards elaborated for simulators (International Electrotechnical Commission). The tests are subdivided into daily visual checks (light field indication, optical distance indicator, isocentre-indicating devices, indication of gantry and collimator angles) and monthly and annually tests of relevant simulator parameters. Some important examples demonstrate the small variation of parameters over 6 years: position of the light field centre when rotating the collimator, diameter of the isocentre circle when rotating the gantry, accuracy of the isocentre indication device, and coincidence of light field and simulated radiation field. RESULTS: As an important result we can state, that by these rigid periodic tests it was possible to detect and compensate deteriorations of simulators quality rapidly. CONCLUSIONS: Technical improvements and specific calling-in of maintenance personnel whenever felt appropriate provided performance characteristics of our old simulator which are required by international recommendations as a basis for modern radiotherapy.

Germany↗

PubMed1987

Stereotactic percutaneous single dose irradiation of brain metastases with a linear accelerator.

The effectivity of stereotactic percutaneous single dose irradiations in the treatment of solitary brain metastases has been assessed in a series of 12 consecutive patients. Only radioresistant deeply localized metastases have been treated. Photon-irradiation was carried out with the convergent beam technique using stereotactic localization methods, in a linear accelerator facility. In 11 of the 12 patients no side effects occurred. The first 7 patients, who could be observed 3 months or longer, have been studied in detail. In each of these cases single dose irradiation with 20-30 Gy yielded arrest of tumor growth. In one case a marked decrease in contrast enhancement and in four cases shrinkage of the metastasis as well as a marked decrease of the edema occurred. In every patient a marked, sometimes dramatic improvement of the clinical condition was achieved, beginning a few days after irradiation. Stereotactic radiosurgery is a valuable tool in the treatment of inoperable, radioresistant brain metastases, the major advantage being high efficacy and smoothness of the procedure, as well as extremely short hospitalization times (2-3 days).

Adult↗

PubMed2006

Radiation therapy facilities in the United States.

PURPOSE: About half of all cancer patients in the United States receive radiation therapy as a part of their cancer treatment. Little is known, however, about the facilities that currently deliver external beam radiation. Our goal was to construct a comprehensive database of all radiation therapy facilities in the United States that can be used for future health services research in radiation oncology. METHODS AND MATERIALS: From each state's health department we obtained a list of all facilities that have a linear accelerator or provide radiation therapy. We merged these state lists with information from the American Hospital Association (AHA), as well as 2 organizations that audit the accuracy of radiation machines: the Radiologic Physics Center (RPC) and the Radiation Dosimetry Services (RDS). The comprehensive database included all unique facilities listed in 1 or more of the 4 sources. RESULTS: We identified 2,246 radiation therapy facilities operating in the United States as of 2004-2005. Of these, 448 (20%) facilities were identified through state health department records alone and were not listed in any other data source. CONCLUSIONS: Determining the location of the 2,246 radiation facilities in the United States is a first step in providing important information to radiation oncologists and policymakers concerned with access to radiation therapy services, the distribution of health care resources, and the quality of cancer care.

Health Services Accessibility↗

PubMed2004

[Five years of proton therapy of eye neoplasms at the Hahn-Meitner Institute, Berlin].

Eye tumors (choroidal melanomas, iris melanomas, and choroidal hemangiomas) are being treated with 68 MeV protons since 1998 at the Ion Beam Laboratory of the Hahn-Meitner Institute of Berlin (Germany's first proton therapy center), in cooperation with the Charité University Hospital in Berlin, Campus Benjamin Franklin. The proton beam, generated via a combination of Van de Graaff accelerator and cyclotron, is prepared by passive shaping for conformal tumor irradiation. A digital X-ray verification of the tumor location with the patient in sitting position limits the position uncertainties to a maximum of 0.3 mm. The treatment planning is performed using the program EYEPLAN. OCTOPUS, a CT-based planning program developed in cooperation with the German Cancer Research Center of Heidelberg, is under pre-clinical testing. Thus far, more than 400 patients have been irradiated. The first results are comparable to those obtained in other proton therapy centers. At the end of 2002, the University Hospital of Essen has also become a cooperation partner of the Hahn-Meitner Institute.

Academies and Institutes↗

PubMed2001

Isotropic beam bouquets for shaped beam linear accelerator radiosurgery.

In stereotactic radiosurgery and radiotherapy treatment planning, the steepest dose gradient is obtained by using beam arrangements with maximal beam separation. We propose a treatment plan optimization method that optimizes beam directions from the starting point of a set of isotropically convergent beams, as suggested by Webb. The optimization process then individually steers each beam to the best position, based on beam's-eye-view (BEV) critical structure overlaps with the target projection and the target's projected cross sectional area at each beam position. This final optimized beam arrangement maintains a large angular separation between adjacent beams while conformally avoiding critical structures. As shown by a radiosurgery plan, this optimization method improves the critical structure sparing properties of an unoptimized isotropic beam bouquet, while maintaining the same degree of dose conformity and dose gradient. This method provides a simple means of designing static beam radiosurgery plans with conformality indices that are within established guidelines for radiosurgery planning, and with dose gradients that approach those achieved in conventional radiosurgery planning.

Dose-Response Relationship, Radiation↗

PubMed2003

Surface and buildup dose characteristics for 6, 10, and 18 MV photons from an Elekta Precise linear accelerator.

Understanding head scatter characteristics of photon beams is vital to properly commission treatment planning (TP) algorithms. Simultaneously, having definitive surface and buildup region dosimetry is important to optimize bolus. The Elekta Precise linacs have unique beam flattening filter configurations for each photon beam (6, 10, and 18 MV) in terms of material and location. We performed a comprehensive set of surface and buildup dose measurements with a thin window parallel-plate (PP) chamber to examine effects of field size (FS), source-to-skin distance (SSD), and attenuating media. Relative ionization data were converted to fractional depth dose (FDD) after correcting for bias effects and using the Gerbi method to account for chamber characteristics. Data were compared with a similar vintage Varian linac. At short SSDs the surface and buildup dose characteristics were similar to published data for Varian and Elekta accelerators. The FDD at surface (FDD(0)) for 6, 10, and 18 MV photons was 0.171, 0.159, and 0.199, respectively, for a 15x15 cm2, 100 cm SSD field. A blocking tray increased FDD(0) to 0.200, 0.200, and 0.256, while the universal wedge decreased FDD(0) to 0.107, 0.124, and 0.176. FDD(0) increased linearly with FS (approximately 1.16%/cm). FDD(0) decreased exponentially for 10 and 18 MV with increasing SSD. However, the 6 MV FDD(0) actually increased slightly with increasing SSD. This is likely due to the unique distal flattening filter for 6 MV. The measured buildup curves have been used to optimize TP calculations and guide bolus decisions. Overall the FDD(0) and buildup doses were very similar to published data. Of interest were the relatively low 10 MV surface doses, and the 6 MV FDD(0)'s dependence on SSD.

Dose Fractionation, Radiation↗

PubMed1989

Verification of electron beam therapy with conventional and storage phosphor images: preliminary experience.

Portal verification images were generated by the photon contamination in electron beams produced by a linear accelerator during treatment of patients receiving high-energy electron radiation therapy. Both conventional and storage phosphor methods yielded projection radiographs in which anatomy of the irradiated and surrounding tissue was demonstrated. Exposed phantoms were used to confirm that the images represent a true projection of the radiation field. A preliminary series of 22 cases was evaluated by two radiotherapists and judged subjectively to be of clinical value. Geometric error, or more importantly, the lack thereof, during high-energy electron treatments was easily confirmed with this method. In three cases, the treatment protocol was corrected based on the images obtained. Because the readout process of storage phosphor images allows for gain adjustments and post-processing, the images obtained with this method were found to delineate anatomy in the treated and surrounding tissues somewhat more consistently than could conventional images.

Electrons↗

PubMed2005

The FLUKA code: new developments and application to 1 GeV/n iron beams.

The modeling of ion transport and interactions in matter is a subject of growing interest, driven by the continuous increase of possible application fields. These include hadron therapy, dosimetry, and space missions, but there are also several issues involving fundamental research, accelerator physics, and cosmic ray physics, where a reliable description of heavy ion induced cascades is important. In the present work, the capabilities of the FLUKA code for ion beams will be briefly recalled and some recent developments presented. Applications of the code to the simulation of therapeutic carbon, nitrogen and oxygen ion beams, and of iron beams, which are of direct interest for space mission related experiments, will be also presented together with interesting consideration relative to the evaluation of dosimetric quantities. Both applications involve ion beams in the AGeV range.

Carbon↗

PubMed1998

A simple oral cone attachment for the Varian linear accelerator.

Lesions in the oral cavity are often treated with two opposed lateral fields. These include a significant amount of normal healthy tissue whose radiation tolerance is dose-limiting. The tumor dose can be boosted to tumorcidal levels by brachytherapy or by small electron fields directed straight on the lesion. We have developed a simple attachment to the standard electron applicator of the Varian Clinac 1800 that allows irradiation of small electron fields through acrylic tubes-the oral cones. These tubes have been evaluated in terms of depth dose and field profiles for 6, 9, 12, 16, and 20 MeV electrons using film for relative dosimetry. At these small field sizes there are significant changes in output factors, in the depth dose as well as in the effective size of the field, and a thorough dosimetric evaluation is imperative prior to treatment. The attachment can be manufactured locally at low cost. For reasons of patient safety the assembly is collapsible. In clinical practice the cone is directed directly on the tumor. For deep-seated lesions we use a penlight and a mirror for positioning.

Humans↗

PubMed1995

[Studies on chemical radioprotectors against X-irradiation used by soft X-ray accelerator].

This review describes the modes of mice radiation injuries induced by soft X-irradiation under various conditions and the protective effects of several kinds of substances on these injuries. The models of radiation injuries in this study were bone marrow death after lethal irradiation, skin damage induced by irradiation with long length soft X-ray and leukocytopenia in the peripheral blood after sublethal irradiation. Two bioassay methods were established for the survival effect on the lethal irradiation and protective potency on the skin damage induced by soft X-irradiation. The protective potencies of various sulfur compounds, related compounds of ferulic acid, nucleic acid constitutional compounds, crude drugs and chinese traditional medicines were determined and then many effective drugs were recognized. Effective components in the methanol extracts of Cnidii Rhizoma and Aloe arborescens recognized as radioprotectable were fractionated. As a result of these studies, it was observed that the active principles in Cnidii Rhizoma were identified as ferulic acid and adenosine. The scavenge action of active oxygens, a protective effect on the damages of deoxyribonucleic acid and superoxide dismutase by in vitro soft X-irradiation were evaluated as radiation protective mechanisms.

Animals↗

PubMed1989

Radiation therapy treatment planning in supratentorial glioblastoma multiforme: an analysis based on post mortem topographic anatomy with CT correlations.

In a previous study of the brains of 15 adults with glioblastoma multiforme who received minimal or no radiotherapy we determined the topographic distribution of tumor cells. All 15 brains had been fixed and then cut in the coronal or horizontal plane. The distribution of neoplastic cells was determined and entered onto tracings of the whole mount histologic sections. The last CT scans obtained prior to death of 11 of the patients were reviewed independently by a neuroradiologist who traced, on the CT scans, the outer edge of both the contrast-enhancing area and the peritumoral low density "edema". Presented with the neuroradiologist's assessment of the contrast enhancing rim of tumor and of the "edema", a radiotherapist and a radiation dosimetrist, in the present study, prepared treatment plans for a 6 MeV linear accelerator. In 9 of the 11 cases in which immediately antemortum CT scans were available, radiation treatment of the contrast enhancing area alone with a 1 cm margin would have missed portions of the histologically identified tumor. Treatment of the contrast enhancing area along with the peritumoral "edema", with a 1 cm margin, would have covered histologically identified tumor in six of the 11 cases. Treatment of the contrast enhancing area, all "edema", and a 3 cm margin around the "edema" would have covered histologically identified tumor in all cases. Tumors tended to track along nerve pathways. In those lesions near the midline it was common for tumor to cross the corpus callosum. We conclude that radiotherapy with fields designed to treat the contrast enhancing region alone or this region plus "edema" with a tight margin will frequently miss tumor which can be histologically identified by our technique.

Adult↗

PubMed2000

Analysis of DNA adducts by accelerator mass spectrometry in human breast tissue after administration of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and benzo[a]pyrene.

Epidemiological evidence has suggested an association between meat consumption and the risk of breast cancer. 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), a heterocyclic amine found in cooked meat, has been implicated in the aetiology of breast cancer and has been shown to induce tumour formation in rodent mammary glands. In addition, polycyclic aromatic hydrocarbons, such as benzo[a]pyrene (B[a]P) which has also been shown to induce tumour formation at a number of sites in rodents including the breast, are produced during the cooking of meat through the pyrolysis of fats. The aim of this study was to examine the bioavailability of these compounds to human breast tissue and their ability to bind to DNA to form DNA adducts. Patients undergoing breast surgery at York District Hospital were orally administered prior to surgery a capsule containing 20microg of 14C PhIP (182kBq, specific activity 2.05GBq/mmol) or 5microg of 14C B[a]P (36kBq, specific activity 1.81GBq/mmol). At surgery, normal and tumour breast tissue was resected and tissue concentrations of carcinogen measured by liquid scintillation counting and DNA adduct levels by accelerator mass spectrometry (AMS) were subsequently determined. It was found that both 14C PhIP and 14C B[a]P were able to reach the target organ where they had the ability to form DNA adducts. The level of adducts ranged from 26.22-477.35 and 6.61-208. 38 adducts/10(12) nucleotides following administration of 14C PhIP and 14C B[a]P, respectively, with no significant difference observed between levels in normal or tumour tissue. In addition, the data obtained in this study were comparable to adduct levels previously found in colon samples following administration of the same compounds to individuals undergoing colorectal surgery. This is the first report that these two carcinogens bind to human breast DNA after administration of a defined low dose.

Aged↗

PubMed1998

Liquid ionization chamber measurements of dose distributions in small 6 MV photon beams.

A new liquid ionization chamber (LIC) design optimized for high spatial resolution was used for measurements of dose distributions in radiation fields intended for stereotactic radiosurgery (SRS). This work was mainly focused on the properties of this detector in radiation fields from linear accelerators for clinical radiotherapy (pulsed radiation with dose rates from approximately 0.5 to 5 Gy min-1 and beam diameters down to 8 mm). The narrow beams used in stereotactic radiosurgery require detectors with small sizes in order to provide a good spatial resolution. The LIC is investigated to see whether it can be used as a detector for dose measurements in beams currently used for stereotactic radiosurgery. Its properties are compared with those of silicon diodes. The comparisons include output factor (OF), depth dose and profile measurements in 6 MV photon fields of different sizes. For OF measurements, an NACP air ionization chamber was also used in the comparison. The dependence of the response on the detector orientation in the photon beam is also investigated for the diodes and the LIC. The results suggest that LICs can provide better properties than diodes for measuring dose distributions in narrow photon beams.

Biophysical Phenomena↗

PubMed2005

Experimental determination of electron source parameters for accurate Monte Carlo calculation of large field electron therapy.

Extensive work has been performed to validate Monte Carlo models for both photon and electron beams under standard conditions. However, for large field electron beam therapy, Monte Carlo simulations have not been able to provide good agreement when compared to the measured dose distributions. Since the accuracy of the calculation relies heavily on the geometry parameters of the linear accelerator and the characteristics of the incident electron beam, it is crucial to have a complete comprehension of these independent factors. In this work, the electron focal spot size for a CL21EX linac with various energies (6, 9, 12 and 16 MeV) was measured with a slit camera composed of alternating lead and paper sheets. For all the energies investigated, the electron focal spot is found to be elliptical and has a full width at half maximum (FWHM) ranging from 1.69 mm to 2.24 mm. A shift with respect to the crosshair was associated with each measured focal spot. In addition, we present an improved result for the large field in-air profile by utilizing a proposed divergent beam model in conjunction with the experimental focal spot dimension. This model can potentially provide a solution to the Monte Carlo validation of large field electron beam therapy.

Electrons↗

PubMed1992

Photoneutron production in the primary barriers of medical accelerator rooms.

Several radiation surveys, at medical linear accelerator facilities where lead or steel had been used with concrete to fabricate the primary barriers, revealed the existence of a sizable neutron field outside the shielding. This neutron field is produced by photoneutrons generated in the metal portion of the shield when the primary x-ray beam is aimed at the barrier. A method was developed to calculate the neutron dose-equivalent rate expected outside a primary shield when it is irradiated by a high-energy x-ray beam. It was found that the minimum photoneutron dose was produced when the metal part of the shield was positioned inside the treatment room in front of the concrete and also by using steel in place of lead. A thickness of less than or equal to 17 cm of metal on the inner surface of the shield produced only a slight increase in the neutron dose equivalent outside the barrier.

Health Facility Environment↗