Time requirements in conformal radiotherapy treatment planning.
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Humans↗
Biomedical subjects
H K Leetz
Publications and source records attributed to H K Leetz.
[Radiation exposure in abdominal radiography with digital luminescence radiography and conventional screen-film system: an experimental animal study].
PURPOSE: To determine and compare the minimum required radiation exposure for a.-p. abdominal radiographs with digital luminescence radiography (DLR) and a screen-film system (SFS) providing adequate image quality in clinical routine. MATERIAL AND METHOD: Abdominal radiographs a.-p. of a pig were produced with DLR and SFS systematically varying the tube current-time product. The image quality was assessed by eight experienced radiologists according to the criteria of visual resolution, mean optical density, perceptibility of the lateral edge of the psoas, the caudal edge of the liver, bone structures and intestinal wall. RESULTS: The image quality of the digital radiographs was better for each criterion except visual resolution if the same current-time product was used for both techniques. From the minimum tube current-time products providing an adequate image quality it follows that a dose reduction of 57% can be achieved by applying DLR instead of speed class 200 SFS. CONCLUSION: The recently published guide-lines for quality assurance in x-ray diagnostics issued by the German Federal Board of Physicians recommend using speed class 400 SFS. Since in that case an approximately halved radiation dose is necessary, dose reduction is hardly to be expected with DLR.
Animals↗
A study of dose reduction using digital luminescence radiography for lateral skull radiography.
For lateral skull radiography the minimum required radiation patient exposure to ensure adequate image quality was determined for digital luminescence radiography (DLR) in comparison with a screen-film system (speed class 200). Radiographs were produced with a grid technique on conventional X-ray equipment. A real prepared female head including a true fracture above the pars petrosa ossis temporalis was imaged. The tube current-time product (mAs), and thus the surface entrance dose, was varied systematically. Surface entrance dose was measured with TLD-100 rods. Image quality was judged by experienced radiologists according to the criteria: visual resolution, mean optical density, contrast and perceptibility of specific bone structures. Surface entrance dose was reduced from 0.46 to 0.20 mGy by application of DLR instead of speed class 200 screen-film system without loss of diagnostic information in clinical routine. This corresponds to a dose reduction potential of 57% showing a good agreement with the dose reduction potential of 52% obtained in a previous study using the Alderson head phantom.
Female↗
[The personnel needs of health physics in radiotherapy].
METHODS AND RESULTS: Using a questionnaire, mean occupation time values for the different medical physics activities were derived in 1992; they formed the basis for recommendations of minimum physics staffing levels in radiotherapy. The recommended staffing levels were compared with the actual staffing levels and to other national and international recommendations.
Germany↗
[The personnel requirements of medical radiation physics in radiotherapy. Additions and comments on the paper by P. Schneider et al.: Strahlentherap. Onkol. 172 (1996), 148-153].
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Health Physics↗
The radiation exposure of the patient from stable-xenon computed tomography.
For stable-xenon computed tomography (CT), an X-ray examination for measurement of cerebral blood circulation in the brain, the radiation exposure of the patient was determined in order to estimate the risk of inducing cancer. Organ doses of brain, eyelenses, thyroid and gonads have been calculated using the measured air kerma free-in-air on the axis of rotation and organ-specific conversion factors calculated with the Monte Carlo method. Dose measurements with TLD-100 rods using a humanoid Alderson phantom were carried out for verification of the calculated organ doses. In the case of brain partially located in the region of primary radiation a mean organ dose of 39 mSv was calculated. The dose measurements showed dose equivalents between 6 and 68 mSv in different regions of the brain and consequently an inhomogeneous dose distribution. From an estimation of the radiation-induced risk using the effective dose of 1.6 mSv it follows that one additional fatal cancer per 12,500 stable-xenon CT examinations has to be expected. The organ doses of eyelenses and thyroid located in the region of scattered radiation are so low that biological effects are hardly to be expected. The calculated dose equivalents of 6.5 mSv and 0.5 mSv, respectively, are in good agreement with measurements. The organ dose of gonads amounted to less than 0.07 mSv.
Brain↗
[Radiation exposure of the patient exemplified by lateral cranial image in digital luminescence radiography in comparison with the film-screen system].
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Body Burden↗
[The determination of the ovarian dosage in defecography on a digital C-arm unit].
When using defaecography as a radiological tool for diagnosing the anorectal function in female patients, the ovaries are inevitably directly exposed. With the aim of minimising the ovarian dose applied both the area-dose product and the surface dose above the ovaries were measured during investigations of female patients with a digital C-arm unit. These values were converted into ovarian doses using tissue-air ratios. From the surface dose measured with TLD-100 a mean ovarian dose of 15.6 +/- 8.6 mGy was derived. The contributions of screening and film exposures were similar. A reduction of screening time by 10 seconds or omission of 60 film exposures results in a decrease of ovarian dose by values between 0.7 and 2 mGy. Employing a greater focus-skin distance during defaecography, however, made it possible to reduce the ovarian dose by 26%.
Anal Canal↗
[Computer-assisted dosimetry system for the monitor calibration of accelerators].
PURPOSE: A computerized dosimetry system for calibration of the dose monitor of a medical accelerator was developed with the aim of saving time and reducing errors during measurement and analysis of measured data. METHOD: The PC-based part of the programme system controls measurements with dosimeters of type Dosimentor using an interface IF4. After transmission of the measured data to an UNIX-network the other part of the programme system serves as a tool for analysis. That means in particular the calculation of the absorbed dose in water per monitor unit and the conversion of measured data to basic data for treatment planning. RESULTS: In the case of the compact ionization chamber M233641 the relative uncertainty of the monitor calibration amounts to 3.5% and 3.3% for photons and electrons, respectively. Using the flat ionization chamber of Markus type M23343 for measuring electrons a relative measuring uncertainty of 2.1% results. CONCLUSIONS: For high-energy photons and electrons with energies above 10 MeV the greatest contribution to the relative uncertainty of the monitor calibration is caused by the uncertainty of the calibration factor for the compact ionization chamber M233641. If it is possible to reduce this error to a value of 2% the relative measuring uncertainty would be smaller than 3%. In the case of high-energy electrons it can be concluded that the precision of the monitor calibration is higher with a flat ionization chamber of Markus type M23343 than with a compact ionization chamber M233641.
Calibration↗
[A mathematical description of the relative dosage distributions of stereotactic collimator tubes in 6-MV photon radiation].
The relative dose distributions of small circular fields for 6 MV photons may be calculated using a simple mathematical model. This model has been developed for stereotactic collimators with cylindrical cross section and diameters between 5 mm and 30 mm. The model consists of the description of depth dose curves and off-axis dose distributions. The function for off-axis dose distributions is calculated by convolution of a simple profile function with a constant function. The width of the constant function is defined by beam geometry. In the result of integration only the width of the profile function is unknown, but it can be iteratively calculated. The agreement between measured and calculated dose distributions was tested at 5 cm and 20 cm depth in water and 100 cm source-to-surface distance using thermoluminescent dosimetry (TLD) and films, giving a resolution of 1 mm. The depth dose curve is described using the inverse square law and two exponential functions. The first of these functions contains the effective attenuation coefficient in the argument, the second describes the build-up. The increase of irradiated volume with increase of field diameter is accounted for using scatter-air ratios. The calculations were compared with TLD and ion-chamber measurements.
Electrons↗
[Monte Carlo calculations and TLD measurements to determine the two-dimensional dosage distribution of 125-iodine seed, Model 6702].
The angular and radial dose distribution around a type 6702 125-Iodine-seed was measured in water and air using thermoluminescence dosimetry. The radial distribution could be confirmed using Monte Carlo simulation techniques. The simulation produced enough data to allow the derivation of a new analytical function describing the radial dose distribution.
Computer Simulation↗
[Uncertainties in the localization of radiation sources in brachytherapy].
While investigating ways to solve the problem of locating radiation sources applied in brachytherapy a device was constructed which enables a precise assessment of their or their applicators' position from two only roughly positioned orthogonal radiographs. The overall accuracy (including exposure and evaluation) achieved is +/- 1 mm. The constructional elements and the evaluation algorithm are described and the influence of the location uncertainty on the uncertainty of the dose applied are discussed.
Algorithms↗
Plastic material used to optimize radiotherapy of head and neck tumors and the mammary carcinoma.
In order to improve head and neck tumor therapy, face masks were developed. The physical and mechanical properties of 11 apparently suitable materials were tested using a phantom. According to our studies "HEXCELITE" (supplied by Medimex, Hamburg, F.R.G.) proved to be the best material. Plastic breast molds were made to optimize the dose distribution for radiation therapy with fast electrons of post-mastectomy breast tumors. Here too the mechanical and physical properties of nine different materials were tested. The most suitable of these proved to be the gel mat "PRIMAMED" (supplied by Schülke and Mayr, Norderstedt, F.R.G.). The two materials mentioned have been well tolerated by more than 200 patients.
Bandages↗
[A simple device for positioning and fixing the head in radiotherapy of brain tumors in frontal and lateral position].
In radiotherapy of cerebral tumors in the occipital, central, and parietal area it can be favourable to fix the patient's head in frontal or lateral position. It is true that this problem can be solved by manufacturing individual face masks of PVC with the vacuum deep-drawing method, but this method is very time- and cost-consuming. The present study suggests a simplified method using the thermoplastic polyester "Orfit". Such a mask provides a good immobilization and can be manufactured in 10 to 15 minutes without bothering much the patient. Simulation and computed tomography are not substantially affected by the material.
Brain Neoplasms↗
[Systematic research on the dose distribution in mantle field irradiation with Co60 gamma radiation in the Alderson phantom].
A mantle field is localized according to the patient's data in an inhomogenous Alderson phantom. After having established the irradiation scheme, the dose distributions measured in the Alderson phantom are compared with those measured and calculated in an homogenous water phantom. The possible side effects of this irradiation technique can be assessed on the basis of the radiation exposure of heart, lung and spinal marrow. The dose differences found on the central ray are within the margin of error amounting to 5 to 10% which is indicated in the calculation program. In case of a total reference dose of 40 Gy, the radiation exposures of heart and lung do not reach the tolerance limit. A spinal marrow dose of 50 Gy is found in the upper neck marrow. In case of an exact therapy planning, a sufficient dose can be directed to the Waldeyer's tonsillar ring.
Cobalt Radioisotopes↗
[Chest wall moulages for radiotherapy of resected breast cancer with fast electrons: comparative tests of different materials].
Irradiation of the thoracic wall with high-speed electrons is one of the standard methods of prophylaxis and therapy of local recurrences and cutaneous metastases of an operated mammary carcinoma. The surface dose, however, is only 85% of the maximum dose, due to the depth dose curve of the electron beams with the preponderantly applied energy of 7MeV. This is a poor value, since most of all recurrences appear near to the surface and so the risk of giving an insufficient dose is involved. The dose distribution could be essentially improved by the use of moulages on the chest. These moulages were made of different materials which were tested and compared with respect to their suitability for radiotherapeutic purposes. The best materials proved to be "Urgo-Plastan" (manufacturer: Holphar, Sulzbach) and "Orthoplast" (manufacturer: Johnson & Johnson, Düsseldorf). Both materials are synthetic substances which after heating can easily be adapted to the body shape and which offer a good stability, little inconvenience for the patient and a relative easy handling. With these moulage materials, the surface dose is increased to 98% ("Urgo-Plastan") and 99% ("Orthoplast") of the maximum dose.
Breast Neoplasms↗
[Face masks for radiotherapy of head and neck tumors: comparative tests of different materials].
A most precise immobilisation of the patient's head is indispensable in order to reach a high degree of exactness and reproducibility in radiotherapy of malignant head and neck tumors. Face masks made of different synthetic materials have proved to be a simple and economical solution for this problem. Based on our own experiences with "Baycast Longuettes" (manufacturing firm: Johnson & Johnson, Düsseldorf), eleven substances have been tested in the phantom (compound of plaster and synthetic resin, thermoplast, polyurethane foam, compounds of cotton and synthetic resin, and fibre glass compounds). An appropriate material was "Hexcelite" (manufacturing firm: Medimex, Hamburg), a reticulated thermoplast which after warming up can be easily adapted to the patient's face and which guarantees a very good fixation of the head. As compared to solid masks, there is only a slight superposition of the depth dose of Co-60 gamma radiation by secondary electrons from the mask material, so that an increased rate of radiogenic dermatitides is not to be expected.
Casts, Surgical↗
[Calculation of the dose distribution for ultrahard X-ray bremsstrahlung].
The dose distribution of the 42 MV X-ray bremsstrahlung of the betatron is represented by reference dose, depth dose and transverse dose. The method used to determine the parameters of a system of functions to approximate reference dose and depth dose is described and the coefficient schemes of the functions are indicated. The standardized equivalent field surface and the opening ratio of the useful radiation stop of the betatron serve as variables for the approximation.
Calibration↗