Critical Organ Doses Research Articles

Determination of the Appropriate Fraction Number and Size of the HDR Brachytherapy for Cervical Cancer

Based on the linear–quadratic model, we have made two isoeffect tables for transforming the traditional low dose rate (LDR) point A doses at 20, 30, 40, 50, 60, and 70 Gy to those of the high dose rate (HDR) dose per fraction. HDR fractions ranged from 1 to 12, with corresponding sizes for each fraction. We also propose the therapeutic gain ratio (TGR) method for determining the appropriate fraction number of HDR brachytherapy in cervical cancer. TGR is defined as addition of the calculated biological therapeutic difference with the supposed physical therapeutic difference of HDR brachytherapy. Through the TGR method, we predicted that after 2 to 3, 2 to 4, and 4 to 7 fractions of HDR treatments, the tumor control rate and complication rate would be equivalent to those of LDR point A doses of 30, 40, and 70 Gy, respectively. The TGR is affected by many factors, such as the equivalent total dose of LDR, dose rate of LDR, HDR fraction number,T1/2, and differences between LDR and HDR in the dose in critical organs. The TGR method might explain why a low fraction number of HDR can be used in clinical practice. We may use this principle to replace the traditional trial-and-error method for transcribing the relationship between LDR and HDR treatments.

Pharmacokinetics and dose estimates following intrathecal administration of 131I-monoclonal antibodies for the treatment of central nervous system malignancies

Treatment of malignant disease in the central nervous system (CNS) with systemic radiolabeled monoclonal antibodies (MoAbs) is compromised by poor penetration into the cerebrospinal fluid (CSF), limited diffusion into solid tumors, and the generation of anti-mouse antibodies. To attempt to avoid these problems we have treated patients with diffuse neoplastic meningitis with radioimmunoconjugates injected directly into the intrathecal space. Tumor-specific MoAbs were conjugated to Iodine-131 (131I) (629-3331 MBq) by the Iodogen technique, and administered via an intraventricular reservoir. A clinical response rate of approximately 33% was achieved, with better results in more radiosensitive tumors. Here, we present detailed pharmacodynamic data on patients receiving this intracompartmental targeted therapy. Elimination from the ventricular CSF appeared biphasic, with more rapid clearance occurring in the first 24 h. Radioimmunoconjugate entered the subarachnoid space and subsequently the vascular compartment. From this information, the areas under the effective activity curves for ventricular CSF, blood, and subarachnoid CSF were calculated to permit dosimetry. Critical organ doses were calculated using conventional medical internal radiation dose (MIRD) formalism. Where available, S-values were taken from standard tables. To calculate the doses to CSF, brain, and spinal cord, S-values were evaluated using the models described in the text. A marked advantage could be demonstrated for the dose delivered to tumor cells within the CSF as compared to other neural elements.

Methods of calculating radiation absorbed dose

The new tumoricidal radioactive agents being developed will require a careful estimate of radiation absorbed tumor and critical organ dose for each patient. Clinical methods will need to be developed using standard imaging or counting instruments to determine cumulated organ activities with tracer amounts before the therapeutic administration of the material. Standard MIRD dosimetry methods can then be applied.

Dosimetry of radiolabelled blood cells

Blood consists of a fluid (plasma) in which are suspended various cells which make up about 55% of the total volume. Broadly speaking these cells are of five kinds: platelets, red cells (erythrocytes) and three kinds of white cells (granulocytes, lymphocytes and monocytes). The relative sizes and numbers of these cells are shown in Table 1. Strictly speaking platelets and erythrocytes are not cells, since they have no nuclei, but that distinction is of no consequence to this paper. The ability to label these separate cellular components of blood with radionuclides is of immense value in medical research, and subsequently in the diagnosis of disease and in the assessment of therapy, especially with those radionuclides which emit y-rays so that their movement can be followed, after reinjection, by external counting systems. For example, labelled platelets can be used to detect clots in the veins or arteries, and labelled granulocytes can be used to detect deep-seated abscesses. However, when we label cells in order to study their kinetics and bio-distribution in health or disease-we must be aware of the hazards that may lead the labelled cells to behave abnormally-or die. Unfortunately, with the possible exception of the labelling of monocytes by phagocytosis, all the methods of labelling cells so far discovered are “nonspecific”; i.e. in a mixed population of cells all will be labelled, and so to label a specific kind of cell, e.g. lymphocytes, these must first be separated from all the other cells in the blood sample. This separation procedure exposes the cells to the hazard of mechanical damage, though with care and practice this can be minimised. Labelling cannot be achieved without exposing the cells to chemicals which may be toxic and again may damage them. However, this problem too can usually be overcome with care. The third possible cause of damage to labelled cells arises from the radiation absorbed within the cells following the decay of the radioactive label. Of course, if each cell were labelled with only one radioactive atom then once that atom had decayed the cell would no longer be labelled, so any abnormality in its behavior would not be detected. However, in practice (as we shall see) each cell usually contains a very large number of radioactive atoms, and so may remain detectable long after radiation damage has led to erratic behaviour. When planning investigations which use labelled cells, we must therefore give thought not only to the radiation dose to the whole body or to some critical organ (as is customary for in vim radionuclide studies) but also to the radiation dose experienced by the labelled cell itself. So far as an individual labelled cell is concerned. once it is m-injected into the blood stream it will be virtually unaffected by radiation from other cells. but will be affected by short-range radiation originating within itself. In attempting to calculate this radiation dose, we can therefore ignore all the yand Xradiation which contributes so importantly to the total body or critical organ dose, and consider only that radiation which has a range shorter than or comparable to the cell diameter. In practice this means we need consider only the Auger electrons (or, occasionally, conversion electrons of very low energy) associated with the decay process. Whilst the treatment of this subject which follows is superficial compared to that being applied to

The role of radium implant for the treatment of extensive vaginal involvement from cervical cancer: A dosimetry appraisal

skull. The midline neck dose is about 95% and the dose to the inferior portion of the spinal cord is about 105%, measured at an inferior distance from the central axis equal to the distance of the middle of the skull from the central axis. At 1 cm depth over the field the dose is about 82%. The dose over the crania-spinal axis is uniform to within -c 5%. The hair routinely regrows after a midplane dose of 4000 rad to the whole brain and 5400 rad to the posterior fossa. This method of treatment avoids the use of over-lapping fields and the subsequent potential over irradiation of the spine. Additional dosimetric details, including dose distributions measured in an anatomical phantom, and critical organ (eye, testes, ovaries) doses will be presented.

Combined TDF values from external beam and brachytherapy to interpret critical organ and tumor dose

Combined TDF values from external beam and brachytherapy to interpret critical organ and tumor dose

Plutonium--health implications in man. The concepts of critical organ and radiation dose as applied to plutonium.

Plutonium--health implications in man. The concepts of critical organ and radiation dose as applied to plutonium.

Physical dose estimates for A-bomb survivors. Studies at Chiba, Japan.

In-air tissue absorbed doses** from the primary and scattered radiations of the Hiroshima and Nagasaki atomic bombs, without shielding, were estimated as function of distance from the hypocenters. Gamma-ray dose was determined from the thermoluminescence in bricks and tiles; neutron dose, from 60Co activity induced in concrete-imbedded iron of buildings. The ratio of the absorbed dose in critical organs to the in-air tissue absorbed dose was determined by phantom measurements using simulated radiation sources for the atomic bombs. The absorbed doses in the thyroid gland, the gonads, and the fetus in utero were thus estimated as a function of distance from the hypocenters.

Secondary Radiation Associated with Diagnostic X-Ray Tube Collimators

Diagnostic x-ray tube housings must be shielded sufficiently to assure an exposure of less than 100 mR∕hr. at 1 m from the target under maximum operating conditions. Manufacturers generally meet this standard by providing a tube housing with adequate primary shielding. The attached collimation system must conform to this specification. Ionization chamber measurements, corroborated by spectral data, show that the secondary-radiation level increases as a result of the inclusion of transparent plastic primary beam definers in the collimator. This significantly higher, avoidable dose level is discussed with respect to patient critical organ dose.

Glass Dosimeter for Measuring the Apsorped Dose in Critical Orgons

Glass dosimeter developed by Piesch for measuring the absorbed dose in critical organs, in which only one FD-P8-1 glass was encased in asuitable badge case, was examined for the case of FD-3 glass, FGD-6 type Fluorimeter, standard Japanese man phantom, and a badge case manufactured by us.This experiment confirmed the same validity for this case as well as the case of FD-1 glass, FGD-3B type Fluorimeter and Alderson man phantom which were used used by Piesch.The merits of this glass dosimeter against other dosimeters are discussed from the view point of the personnel dosimetry for radiation protection.

The indication of adsorbed dose in critical organs by energy independent personnel dosimeters.

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Image contrast and radiation protection: a figure of merit. I. Narrow beams.

The beneficial and adverse effects of hardening the bean on protection and contrast are discussed and merit figure established inside and outside the beam for parts of various thickness. By the merit figure of a technique, the beneficial effect on exit dose related to critical-organ dose is balanced against the adverse effect on perceptible thickness difference Merit inside the beam, high for thin parts, decreases with hardening of the beam and increases for thick parts. The importance of the interpretation of merit is emphasised. The effect of added filters on merit on account of prolongation of exposure is considered and some suggestion on the desirable filtration are made. Outside-beam meri depends little on added filtration but decreases markedly with increasing tube tension at greater depths. Direct and scatter dose to the critical organ referred to contrast and primary exit dose, i.e. merit, decreases rapidly with th proximity of the organ to the exit side. The connection of the authors' findings wi...

FOUR CASES OF THOROTRAST INJURY AND ESTIMATION OF ABSORBED TISSUE DOSE IN CRITICAL ORGANS.

Four autopsy cases of thorotrast injury were presented, in which one case of liver cirrhosis and three cases of malignant tumors were included. The malignant tumors were diagnosed as cholangiocarcinoma, hemangioendothelioma and osteosarcoma, respectively. The dose delivered to critical organs, liver and the spleen, were measured spectrometrically and calculated using the method developed by Rundo, on the autopsy specimens. Several correction factors were introduced to obtain the final estimation of the dose. They are related to the equilibrium state of the thorotrast samples used, biological half life of 228Ra, distribution of thorotrast granules in the tissue and reduction of the critical organ weight, etc.. Average tissue doses delivered were estimated as 0.58 to 2.6 rad per week for the liver and 0.92 to 5.6 rad for the spleen. Possible relationship between corrected tissue dose and pathological findings was discussed.

Bone-marrow dose produced by radioactive isotopes.

This report describes the design and construction features of a realistic phantom and dose-measuring system which make feasible experimental determination of the radiation dose distribution through-out the body, produced by internally located radioactive isotopes. The application of this system to the determination of the bone-marrow dose throughout the skeleton, from radium applicators in the cervix, is also presented. The method is being employed to ascertain the bone-marrow and other critical organ doses produced by a variety of radioactive isotopes either mechanically or metabolically located in the body. When radiation is used therapeutically, the maximum absorbed tissue dose can be produced in the “target volume,” with proper care and adequate technological facilities. Other healthy body tissues, however, are usually unavoidably irradiated during the course of treatment. This is particularly true when gamma-ray-emitting isotopes are employed internally. In such instances, where there is appreciable ...