DGMP guideline for medical physical aspects of intravascular brachytherapy. Part I: Guideline.
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Blood Vessels↗
Biomedical subjects
D Flühs
Publications and source records attributed to D Flühs.
[Therapy relevant weak sites in industrial quality assurance of 106Ru eye plaques].
BACKGROUND: Beta emitting 106Ru applicators manufactured by Bebig GmbH (Berlin, Germany) are widely used to treat intraocular tumors. The applicators are fixed to the bulbus and removed after several days. The following therapy relevant defects have been detected by an internal clinical acceptance test: risk of leakage and inconsistent dose-rate specifications by the manufacturer. In the meantime, components of the internal clinical acceptance test have been adopted successfully by the manufacturer of the 106Ru ophthalmic plaques. MATERIAL AND METHOD: 106Ru ophthalmic plaques were tested with the following internal clinical acceptance tests: visual inspection, surface contamination, leakage, and dose-rate verification. The surface contamination test consists of a wet wipe test at moderate pressure. For the leakage test of the 106Ru ophthalmic plaques a clinically relevant scenario was developed in which the contact of the applicator with human tissue is simulated. In the course of it the applicator is inserted into Ringer's solution for several days. The certified energy dose-rate statements of the manufacturer are examined with a 1 mm3 plastic scintillator for consistency. RESULTS: During the internal clinically acceptance tests of 106Ru ophthalmic plaques of different size the following results were obtained: The leakage test was performed with seven applicators and yielded measurements for two 106Ru ophthalmic plaques that were significantly higher than those of a dummy sample. The highest value of a wipe test was 57 Bq (Figure 1). The highest value in Ringer's solution was 520 Bq (Figure 2). During the dosimetry consistency checks of the certified dose-rate specifications for 14 applicators, six applicators were in good agreement with a variation coefficient of 2.6%. For the other eight applicators the deviations were between -37% and +74% (Figure 3), i.e. the range of the unaccepted applicators amounts to 111%. The results were representatively verified through external assessment. CONCLUSION: Grave therapy relevant shortcomings of the industrial quality assurance of ophthalmic plaques were uncovered by experimental cross-checks. It is necessary that every radioactive device is internally examined before its use. The internal clinical acceptance test of the 106Ru ophthalmic plaques can easily be adopted by other hospitals.
Brachytherapy↗
Dosimetry of beta-ray ophthalmic applicators: comparison of different measurement methods.
An international intercomparison of the dosimetry of three beta particle emitting ophthalmic applicators was performed, which involved measurements with radiochromic film, thermoluminescence dosimeters (TLDs), alanine pellets, plastic scintillators, extrapolation ionization chambers, a small fixed-volume ionization chambers, a diode detector and a diamond detector. The sources studied were planar applicators of 90Sr-90Y and 106Ru-106Rh, and a concave applicator of 106Ru-106Rh. Comparisons were made of absolute dosimetry determined at 1 mm from the source surface in water or water-equivalent plastic, and relative dosimetry along and perpendicular to the source axes. The results of the intercomparison indicate that the various methods yield consistent absolute dosimetry results at the level of 10%-14% (one standard deviation) depending on the source. For relative dosimetry along the source axis at depths of 5 mm or less, the agreement was 3%-9% (one standard deviation) depending on the source and the depth. Crucial to the proper interpretation of the measurement results is an accurate knowledge of the detector geometry, i.e., sensitive volume and amount of insensitive covering material. From the results of these measurements, functions which describe the relative dose rate along and perpendicular to the source axes are suggested.
Alanine↗
Determination of surgeon's absorbed dose in iodine 125 and ruthenium 106 ophthalmic plaque surgery.
OBJECTIVE: Validation of dosimetry and exposition time to an ophthalmic surgeon during radioactive plaque operations. DESIGN: Experimental study in which videotaped operations and dosimetric measurements were used to model dosimetry. METHODS: We used thermoluminescence detectors for high sensitivity readings in radiation fields. Typical intersurgical mobility was videotaped and distances to the plaque was evaluated. MAIN OUTCOME MEASURE: Estimated radiation received by surgeons. RESULTS: All simulated plaque operations have a maximum dose rate of 6 mGy per minute (value in the inner eyeball). Mean dose rate is 2 mGy per minute (average of approximately all measurements). The surgeon's fingers receive a dose from 2 to 6 mSv from plaque operation. CONCLUSIONS: Results suggest that radioactive plaque operations are safe for the surgeon but that the time for plaque handling should be minimized. A surgeon should not exceed 100 to 200 operations per year.
Brachytherapy↗
A high-precision, high-resolution and fast dosimetry system for beta sources applied in cardiovascular brachytherapy.
A fast dosimetry system based on plastic scintillator detectors has been developed which allows three-dimensional measurement of the radiation field in water of beta-sources appropriate for application in cardiovascular brachytherapy. This system fulfills the AAPM Task Group 60 recommendations for dosimetry of cardiovascular brachytherapy sources. To demonstrate the use of the system, measurements have been performed with an 90Y-wire source. The dose distribution was determined with a spatial resolution of better than 0.2 mm, with only a few minutes needed per scan. The scintillator dosemeter was absolutely calibrated in terms of absorbed dose to water with a precision of +/-7.5%. The relative precision achievable is +/-2.5%. The response of the system is linear within +/-2% for dose rates from 0.5 mGy s(-1) to 500 mGy s(-1).
Beta Particles↗
Fluorescence 125I eye applicator.
A new approach to optimize curative eye plaque brachytherapy is presented. The application of ophthalmic plaques is a common therapy modality for small and medium sized intraocular tumors. At Essen University Hospital eye applicators with photon emitting 125I seeds are used for the treatment of tumors with a thickness from 5 to 10 mm. Our clinical experiences indicate that the dose distributions of these applicators-used so far worldwide-are not optimal. A steeper dose falloff would meet the radiobiological requirements better, to provide the eradication of all tumor cells as well as sufficient occlusion of tumor supplying blood vessels. Our investigations for eye plaque optimization are based both on measurements and Monte Carlo simulation. For fast dosimetric measurements we have built a computer controlled device which allows reading out, directly and simultaneously, 16 1 mm3 scintillators. For the numerical simulations of the dose distribution of 125I eye plaques we have adapted a Monte Carlo program originally developed to calculate the synchrotron radiation in particle physics. We have investigated the influence of geometrical as well as physical eye plaque parameters on the dose distribution: Shielding of the primary radiation, penumbra modification, and energy conversion by exploiting fluorescence x-radiation have been considered. New types of fluorescence eye applicators have been designed which are more suitable for the prevention of radiopathic effects on structures at risk.
Brachytherapy↗
Endovascular brachytherapy--treatment planning and radiation protection.
The risk of restenosis, main late effect limiting the success of percutaneous transluminal coronary artery angioplasty, can be reduced significantly by vascular radiotherapy, subsequent to PTCA. This discovery lead to the development of new irradiation techniques. Endovascular brachytherapy is the choice in treatment of coronary artery stenosis. Successful irradiation, however, requires precise treatment planning. This review addresses the physical possibilities and problems of intravascular brachytherapy planning, and the radiobiologically based definition of the target volume and of structures at risk. Recommendations for dose specification, recording and reporting are given. The criteria for selecting a vascular radiotherapy technique are discussed as well as the possibilities of dosimetric treatment planning and quality assurance based on precise plastic scintillator dosimetry and intravascular ultrasound. Radiation protection and safety must be reconsidered prior to the usage of therapeutic radiation sources in the catheter laboratory and for the decision about emergency plans. Finally, the design of clinical trials, the role of medical physicists, and the future of irradiation treatment of stenosis is discussed.
Angioplasty, Balloon, Coronary↗
Primary conjunctival rhabdomyosarcoma: 2.5 years' follow-up after combined chemotherapy and brachytherapy.
BACKGROUND: The 2.5-year outcome of a 3-year-old girl with a primary intraconjunctival rhabdomyosarcoma treated by biopsy-controlled combined chemo- and brachytherapy is reported. METHODS: The patient presented with a conjunctival dermoid-like lesion which showed modest growth on 1-month follow-up. The first biopsy appointment was missed because of a viral illness. When she showed up 3 months later a further increase in size was obvious and several incisional biopsies were taken immediately. RESULTS: Light microscopy revealed an undifferentiated subepithelial small cell tumour. On immunohistochemistry the tumour reacted with vimentin and desmin antibodies. Thus, the diagnosis of an embryonal rhabdomyosarcoma was made. The patient underwent 9 cycles of polychemotherapy and the tumour mass disappeared macroscopically. However, immunohistochemistry of incisional biopsies showed residual tumour cells. The latter were eradicated by an individually shaped strontium-90 applicator. CONCLUSION: At 2.5 years after biopsy-controlled combined chemotherapy and brachytherapy the patient is free of tumour at a manageable level of complications. This new approach appears to be a good alternative in the treatment of primary conjunctival rhabdomyosarcomas since it takes advantage of the unique location of this rare tumour and avoids hemifacial retardation, known to be induced by external beam radiation.
Antineoplastic Combined Chemotherapy Protocols↗
Dosimetry and design of radioactive eye plaques.
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Brachytherapy↗
Direct reading measurement of absorbed dose with plastic scintillators--the general concept and applications to ophthalmic plaque dosimetry.
We have developed dosemeters based on plastic scintillators for a variety of applications in radiation therapy. The dosemeters consist basically of a tissue-substituting scintillator probe, an optical fiber light guide, and a photomultiplier tube. The background light generated in the light guide can be compensated by a simultaneous measurement of the light from a blind fiber. Plastic scintillator dosemeters combine several advantageous properties which render them superior to other dosemeter types for many applications: minimal disturbance of the radiation field because of the homogeneous detector volume and the approximate water equivalence; no dependence on temperature and pressure (under standard clinical conditions) and angle of radiation incidence; no high voltage in the probe; high spatial resolution due to small detector volumes; direct reading of absorbed doses; and a large dynamical range. The high spatial resolution together with direct reading make these detectors suitable for real-time 3-D dosimetry using multi-channel detector systems. Such a system has been developed for eye plaque dosimetry and successfully employed for dosimetric treatment optimization. The plaque optimization can be performed by dosimetric measurements for the individual patient ("dosimetric treatment planning"). The time consumption for this procedure is less than for a physically correct computer-based therapy planning, e.g., by means of a Monte Carlo simulation.
Biophysical Phenomena↗
The influence of guiding equipment and stents on the beta dose distribution in the brachytherapy of in-stent restenosis.
BACKGROUND: Intracoronary devices such as stents or guide wires may disturb the dose distribution of beta sources in cardiovascular brachytherapy. As clinical observations indicate that underdosage increases the risk of restenosis, accurate measurements are mandatory to investigate these effects. METHODS AND RESULTS: Dose perturbation effects of different interventional equipment were systematically determined. Dose distributions of 90Sr-beta line sources were measured by means of a special set-up employing plastic scintillator dosimeters in a water phantom. Shielding effects were found to be 2-5% for single stents and 5-10% for graft stents, stent-in-stent geometries, and guiding catheters. Guide wires close to the source reduced the dose by 25-30%. CONCLUSIONS: Beta dose perturbation effects of typical stent types are almost negligible and can be corrected by an increased source dwell time if necessary. Guide wires produce effects which are clinically much more important and should therefore be retracted from the irradiation area.
Brachytherapy↗