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PubMed2001

Dosimetric effects of contrast media for catheter-based intravascular brachytherapy.

The purpose of this work is to calculate the dose perturbations due to the presence of iodine contrast media in catheter-based intravascular brachytherapy (IVBT). The EGSnrc Monte Carlo system was used to perform the calculation for the two most commonly used beta and gamma sources (90Sr and 192Ir as well as for a variety of monoenergetic photon and electron sources. Various contrast media with cylindrical-shell shapes were considered. The dose perturbations due to the presence of iodine contrast media were found to be significant for IVBT. In the region outside of the contrast media (usually the treatment target region for IVBT), the dose is generally increased for the gamma source, while it is decreased for the beta source. In the presence of a 1.0-mm-thick common clinical contrast medium, the dose enhancement can be as high as 30% for the 192Ir source, while the dose can be reduced by up to 25% for the 90Sr source. The dose enhancement region for the gamma source extends approximately 1.0 mm away from the contrast medium, while the dose reduction for the beta source affects the entire target region. The dose perturbation depends on (1) the volume (thickness) of the contrast medium, (2) the iodine concentration in contrast media, and (3) the type and energy of radioactive source. The dose effects due to the contrast medium as well as the differences between beta and gamma sources, revealed in this study, should be recognized and may be considered in the dose prescription for intravascular brachytherapy. These effects should also be taken into account in analyzing the treatment outcome for those IVBT clinical trials involving a contrast medium.

Algorithms↗

PubMed1994

Brachytherapy for lower lip epidermoid cancer: tumoral and treatment factors influencing recurrences and complications.

From 1972 to 1991, 237 patients with squamous cell carcinoma of the lower lip were treated by exclusive LDR brachytherapy (192Ir). There were 158 T1, 61 T2, 17 T3 and 1 T4 with 231 N0, 3 N1 and 3 N2 patients. The actuarial values at 5 years for local and regional controls, overall and specific survivals were 95%, 91%, 74% and 91%. Salvage treatment increased local control up to 99% and regional control to 94%. No heterolabial recurrence has been observed since the entire lip is treated, even for small tumors. The regional control depends closely on the thickness of the labial tumor (> or = 1 cm, p < 0.0001). The healing of treatment-induced mucositis is sometimes delayed for thick tumors (> or = 1 cm, p = 0.015). Late complications are not related to tumoral thickness but to the treated thickness (> 1.4 cm, p = 0.018) and particularly to the thickness of normal tissue included in the 85% isodose (treated thickness - tumoral thickness > 0.4 cm, p = 0.025). The use of a leaded protection and low linear radioactivity wires (< 2 mCi/cm, < 8.6 muGy/h.m2/cm) especially for large target volumes is required to lessen late complications. Based on this review, we advocate exclusive brachytherapy for small and intermediate tumors, with elective bilateral submaxillary and submental dissection for thick, high grade or commissure tumors. Simple recommendations are made to assure quality of the brachytherapy treatment.

Actuarial Analysis↗

PubMed2000

Plaque radiotherapy for uveal melanoma: long-term visual outcome in 1106 consecutive patients.

OBJECTIVE: To identify clinical predictive factors for visual outcome in a large series of patients who underwent plaque radiotherapy for uveal melanoma. DESIGN: Clinical factors, including patient data, tumor features, and radiation variables, were analyzed for their impact on visual acuity using Cox proportional hazards regression models. PARTICIPANTS: Patients with uveal melanoma and initial visual acuity of 20/100 or better in the affected eye who were treated with plaque radiotherapy between July 1976 and June 1992. MAIN OUTCOME MEASURES: Two end points were used to evaluate posttreatment visual acuity: (1) final visual acuity (good [20/20-20/100] vs poor [20/200 to no light perception]) and (2) loss of visual acuity (minimal [<5 lines Snellen visual acuity] vs moderate [> or = 5 lines Snellen visual acuity]). RESULTS: Of 1300 consecutive patients with uveal melanoma treated by plaque radiotherapy, 1106 had a visual acuity of 20/100 or better at the time of treatment. In this group, poor visual acuity was found in 34% at 5 years and 68% at 10 years of follow-up. From multivariable analysis, clinical factors that best predicted poor visual acuity were increasing tumor thickness, proximity to foveola of less than 5 mm, notched plaque shape, tumor recurrence, patient age 60 years or older, subretinal fluid, cobalt isotope, anterior tumor margin posterior to equator, and worse initial visual acuity. Moderate loss of visual acuity of 5 Snellen lines or more was found in 33% at 5 years and 69% at 10 years of follow-up. From multivariable analysis, clinical factors that best predicted moderate visual acuity loss included increasing tumor thickness, worse initial visual acuity, notched plaque shape, tumor recurrence, proximity to foveola of less than 5 mm, patient age of 60 years or older, subretinal fluid, and diabetes mellitus or hypertension. When analyzing visual outcome with regard to tumor thickness, ultimate poor visual acuity of 20/200 or worse at 5 years was found in 24% with a small melanoma (< or = 3.0 mm), 30% with a medium melanoma (3.1-8.0 mm), and 64% with a large melanoma (>8.0 mm). When analyzing visual outcome with regard to tumor proximity to visually important structures, tumors less than 5 mm from the optic disc or foveola demonstrated poor visual acuity in 35% at 5 years, whereas those 5 mm or more from the optic disc and foveola showed poor visual acuity in 25% at 5 years. CONCLUSIONS: Ultimate visual acuity after plaque radiotherapy for uveal melanoma depends on many factors, including patient age and general health, initial visual acuity, tumor location and size, subretinal fluid, radioactive isotope, and final tumor control. At 10 years' follow-up, 68% of patients demonstrate poor visual acuity. Visual acuity is most effectively preserved in eyes with small tumors outside a radius of 5 mm from the optic disc and foveola. Arch Ophthalmol. 2000;118:1219-1228

Adolescent↗

PubMed1995

Quantitative verification of 192Ir PDR and HDR source structure by pin-hole autoradiography.

For precise localization of the center and determination of the dimensions of the radioactive material within the capsule of brachytherapy sources, we have developed a method based on simultaneous pin-hole autoradiography of two sources. We constructed a variable magnification pin-hole camera consisting of two telescopically fitted Plexiglas cylinders which can accommodate two radioactive sources on the plate covering the top cylinder. The 192Ir pulsed and high dose-rate sources were studied and an 192Ir seed was used as a reference source. The magnification factor was determined from the dimensions of the 192Ir seed image, which was geometrically well defined by a separate transmission radiography experiment. The observed position for the center of radioactivity in the PDR and the HDR source capsules are in agreement with the vendor specifications. The distance from the tip of the PDR capsule to its center of radioactivity was found in this way to be 0.79 +/- 0.21 mm, which agrees with the position (0.85 mm) of the pellet situated closer to the tip as specified by the vendor. Quantitative verification of the internal source structure using this method enhances the accuracy with which the dose distribution near brachytherapy sources can be predicted by three-dimensional Monte Carlo calculations.

Autoradiography↗

PubMed1980

Development of 132 Ir sources for brachytherapy.

Techniques for the production of three kinds of 192Ir sources, i.e. hairpin, single-pin and seed, for brachytherapy were developed in Japan Atomic Energy Research Institute. Platinumiridium, alloy wire sheathed with platinum tube in advance were irradiated by the JRR-2 or JRR-3 reactor. The platinum tube cuts off beta-rays so as to minimize unnecessary radiation exposure to patients. Irradiation conditions were determined to obtain the radioactivity of 0.74 GBq (20 mCi) for a hairpin, 0.37 GBq (10 mCi) for a single-pin and 0.37 X 10(-1) GBq (1 mCi) for a seed, respectively, at the end of irradiation. Fluctuation in the linear distribution of the radioactivity along the hairpin source or the single-pin source was small enough on the viewpoint of its application. No significant impurity or surface contamination was observed in the source produced with pre-encapsulation. Seed targets were loaded in a polyethylene tube so as to be suitable for the new treatment technique of tumor. Irradiation of seed targets, packed alternately with nylon spacers in a polyethylene tube, was found to be satisfactory for preparing ribbon sources.

Brachytherapy↗

PubMed1996

Dosimetric considerations for catheter-based beta and gamma emitters in the therapy of neointimal hyperplasia in human coronary arteries.

PURPOSE: Recent data indicate that intraluminal irradiation of coronary arteries following balloon angioplasty reduces proliferation of smooth muscle cells, neointima formation, and restenosis. We present calculations for various isotopes and geometries in an attempt to identify suitable source designs for such treatments. METHODS AND MATERIALS: Analytical calculations of dose distributions and dose rates are presented for 192Ir, 125I, 103Pd, 32P, and 90Sr for use in intracoronary irradiation. The effects of source geometry and positioning accuracy are studied. RESULTS: Accurate source centering, high dose rate, well-defined treatment volume, and radiation safety are all of concern; 15-20 Gy are required to a length of 2-3 cm of vessel wall (2-4 mm diameter). Dose must be confined to the region of the angioplasty, with reduced doses to normal tissues. Beta emitters have radiation safety advantages, but may not have suitable ranges for treating large diameter vessels. Gamma emitters deliver larger doses to normal tissues and to staff. Low energy x-ray emitters such as 125I and 103Pd reduce these risks but are not available at high enough activities. The feasibility of injecting a radioactive liquid directly into the angioplasty balloon is also explored. CONCLUSIONS: Accurate source centering is found to be of great importance. If this can be accomplished, then high energy beta emitters such as 90Sr would be ideal sources. Otherwise, gamma emitters such as 192Ir may be optimal. A liquid beta source would have optimal geometry and dose distribution, but available sources, such as 32P are unsafe for use with available balloon catheters.

Brachytherapy↗

PubMed1997

Testing shields in the Argonne National Laboratory fuel conditioning facility support areas.

Testing has been completed for two lightly shielded areas that support operations in the Fuel Conditioning Facility at the Argonne National Laboratory site at the Idaho National Engineering Laboratory. Operational requirements dictated the use of a radiography source containing 0.44 TBq (12 Ci) of 192Ir to challenge reinforced concrete and steel shields that surround a decontamination, maintenance, and repair area for contaminated equipment used in hot cell operations. A more intense source containing 0.89 TBq (24 Ci) of 192Ir was used to test lead shot and steel shields around tanks in a radioactive liquid waste system and the boundaries of the room that contained it. Measurement procedures were developed to find design flaws and construction deficiencies while minimizing radiation exposure to test participants. While the shields are adequate to limit gamma ray deep dose equivalents to 10 mSv y(-1) (1 rem y(-1)) or less to facility personnel, several modifications were necessary to assure that the attenuation is adequate to keep dose rates less than 5 microSv h(-1) (0.5 mrem h(-1)) in normally occupied areas.

Decontamination↗

PubMed1980

Computation of dose distributions for radioactive seed implants.

An interactive treatment planning program for the computation of dose distributions for 125I and 192Ir seed implants of up to 300 sources is described. The seed coordinates are entered using either the keyboard or a sonic digitizer from either orthogonal or stereo films. The program produces a dose matrix which can be displayed and plotted directly or combined with the putput of other treatment planning programs to provide composite plans for treatments using multiple modalities. Seeds of different activities can be combined within a single plan. The program uses two-letter mnemonics for specifying the available options, among which are commands for choosing standard antero-posterior, lateral, and transverse plans.

Brachytherapy↗

PubMed1996

A nondivergent specification of the mean treatment dose in interstitial brachytherapy.

The harmonic mean formalism is investigated as a nondivergent specification of the mean treatment dose in three distinct applications of interstitial brachytherapy: (a) permanent 125I prostate implant; (b) double plane 192Ir linear source array; and (c) multiple catheter optimized high dose rate implant. In each case the harmonic treatment dose (HTD) can be calculated in regions that contain radioactive sources or otherwise high dose gradient, to yield objective and consistent results with little computational effort. The need to identify local dose minima, geometric centers, or seed planes is largely avoided, which makes the formalism suitable for automated computation. Dose distribution uniformity is analyzed in terms of the fractional spread for the HTD and, where the periphery of the target volume is delineated, the uniformity number and the peripheral uniformity number. It is shown that the harmonic mean dose formalism is a practical alternative to the ICRU dose specification parameters in certain areas of brachytherapy.

Biometry↗

PubMed1994

Imaging of HDR brachytherapy dose distributions using NMR Fricke-gelatin dosimetry.

The application of NMR Fricke-gelatin dosimetry to the imaging of dose distributions around high dose rate (HDR) radioactive Ir-192 seeds in brachytherapy is presented. The duration of the irradiations required to give changes of the Fricke-gelatin NMR characteristics, which were readily detected by the magnetic resonance imager, typically ranged from 4 to 25 min for single source and multiple source (33 source positions distributed among three catheters) geometries, respectively. A fast approach for determining radiation dose from MR image intensity using a calibration curve is described. NMR Fricke-gel dosimetry is shown to be a viable means of verifying the dose distributions from brachytherapy sources.

Brachytherapy↗

PubMed2001

192Ir endovascular irradiation prevents restenosis after balloon angioplasty in rabbit.

OBJECTIVE: To examine the effect of endovascular irradiation on restenosis after balloon angioplasty in rabbit. METHODS: After the establishment of rabbit iliac atherosclerosis model, balloon angioplasty was performed at the lesion segment of the iliac artery. Rabbits were randomly divided into three groups: control group, 10 Gy irradiated group and 18 Gy irradiated group. Endovascular irradiation was performed for irradiated groups at the dilated sites by introducing the 192Ir radioactive guidewire through a catheter. After four weeks, the animals were killed and the target segments were cut down. Histopathologic and morphometric analyses were carried out. RESULTS: The mean final lumen area in the 18 Gy group was larger than that in the control or 10 Gy group (P < 0.05). The intimal area in the 18 Gy group was smaller (P < 0.05). CONCLUSIONS: 192Ir endovascular irradiation may prevent restenosis after balloon angioplasty. The effect is related to the delivered dose. The mechanism is involved in inhibition of neointimal proliferation.

Angioplasty, Balloon↗

PubMed1997

Tumor bed brachytherapy with a mesh template: an accessible alternative to intraoperative radiotherapy.

BACKGROUND AND OBJECTIVES: Locally advanced and recurrent malignancies often require adjuvant radiotherapy to achieve tumor control. We report our experience with a technique that uses an intraoperatively placed mesh template for the delivery of radiotherapy. METHODS: from 1988 to 1996, 14 patients were treated with tumor bed brachytherapy using this mesh technique. Sites of involvement included the head and neck region (n = 6), abdomen/pelvis (n = 4), retroperitoneum (n = 3), and the lower extremity (n = 1). During surgery, plastic catheters were evenly placed within a mesh template (Vicryl or Marlex), which was positioned in the tumor bed. The catheters were afterloaded with radioactive sources once the final pathology had been determined and the patient required limited nursing care. Radiation dose was titrated to the surgico-pathologic findings (e.g., margin status). RESULTS: All of the patients tolerated the procedure without experiencing acute or chronic sequelae. The median survival time was 13 months. Local control was achieved in 11 of 13 evaluable patients, with an actuarial local control of 82% at 6 months. CONCLUSION: Tumor bed brachytherapy with a mesh implant is a practical technique to improve tumor control and warrants further investigation.

Abdominal Neoplasms↗

PubMed1993

An afterloading 192Ir surface mold.

Patients with basal cell skin cancer can be treated with afterloading 192Ir surface molds constructed from dental wax. High activity 192Ir seeds in ribbons are distributed in the mold to uniformly irradiate the target volume. The treatment is preplanned with a treatment planning system to achieve a uniform dose distribution in the planned target volume. The implant parameters optimized include the seed strength and number of seeds, inter- and intracatheter spacing between 192Ir seeds, and the distance between the implant and treatment planes. The radioactive 192Ir strands are afterloaded in the catheters embedded in the wax mold and the position secured with buttons. The treatment area drawn on the patient surface is visually overlapped with the uniformly irradiated area sketched on the mold surface. The mold is taped to the head to secure this position. The dose rate on the surface of the mold in contact with the patient skin is measured with calibrated LiF TLD chips and is within +/- 5% of the computer preplanned dose rate value. This technique is a viable alternative to external beam treatments when daily treatments are not feasible and a dose distribution conforming to the treatment area is desirable.

Brachytherapy↗

PubMed2002

A Monte Carlo approach to calculate dose distribution around the lineal brachytherapy sources.

Monte Carlo means the statistical methods used to solve stochastic or deterministic physical or mathematical problems. The use of this technique for solving deterministic problems is indicated whenever there is no analytical solution for the problem or when this solution is very difficult or when the use of numerical methods requires an excessive amount of CPU-time. This paper describes the application of Monte Carlo methods using a computer program, called ISODOSE, which calculates isodose curves around linear radioactive sources to be used in brachytherapy treatment-planning. Brachytherapy is a special form of cancer treatment in which the radioactive source is placed near or inside the tumor, in order to produce cancer tissue necrosis. The program is written in C language, and the results will be compared to similar data obtained from a commercially available program at Hospital do Cancer de Recife (Brazil), radiation therapy institute. The use of Monte Carlo techniques in the ISODOSE program allows for plotting isodose curves around linear sources, and it is especially more precise near the borders of the source (singularities), taking less time than it would be possible by using deterministic methods. The ISODOSE program can be used for brachytherapy planning in small clinics in Recife and adjacent areas.

Algorithms↗

PubMed1993

Brachytherapy--interstitial implant radiosurgery.

With both surgery and radiosurgery a selective destruction and removal of a lesion is undertaken. Using interstitial irradiation a calculated volume of necrosis is induced, which is subsequently removed by macrophage activity. Interstitial irradiation is therefore considered a radiosurgical method. To better understand the side effects of radiosurgical lesions in the brain, we studied the effects of three physically distinct gamma emitters iridium-192, gold-198 and iodine-125 with respect to the morphological development of radionecroses and the consecutive vasogenic oedema using different dose rates and application times. Experimental dose effects on normal brain (beagle dogs) revealed that depending on the energy range, application time and dose rate, calcified or liquified necroses develop from the center around the seed into the periphery. These well-defined radionecroses are surrounded by reactive glia and, temporarily, by fibrinoid necrosis of endothelial cells. In contrast to permanent implants, effects of temporary implants on tissue are characterised in the early stages of oedema, in later stages by progressive resorption of necrotic tissue and less permanent damage. Dose rate and energy range determine the volume of the necroses and the magnitude of vasogenic oedema. It is the vasogenic oedema which primarily determines the extent of demyelination and reactive glioses in the vicinity of the radionecrosis. Toxic side effects of interstitial implant radiosurgery can be minimised by using temporary implants with moderate dose rates, in which case repair processes are free to take place after removal of the radioactive source from the brain. Based on experimental and clinical findings a biological dosimetry has evolved which favours temporary implants of iodine-125 with dose rates of 10 cGy/h.

Blood-Brain Barrier↗

PubMed2005

Neutron-activation revisited: the depletion and depletion-activation models.

The growth of a radioactive daughter in neutron activation is commonly described with the saturation model that ignores the consumption of parent nuclei during the radio-activation process. This approach is not valid when radioactive sources with high specific activities are produced or when the particle fluence rates used are very high. Assuming a constant neutron fluence rate throughout the activation target, a neutron-activation model that accounts for the depletion in parent nuclei is introduced. This depletion model is governed by relationships similar to those describing the parent-daughter-granddaughter decay series, and, in contrast to the saturation model, correctly predicts the practical limit of the daughter specific activity, irrespective of the particle fluence rate. Also introduced is a neutron-activation model that in addition to parent depletion accounts for the neutron activation of daughter nuclei in situations where the cross section for this effect is high. The model is referred to as the depletion-activation model and it provides the most realistic description for the daughter specific activity in neutron activation. Three specific neutron activation examples of interest to medical physics are presented: activation of molybdenum-98 into molybdenum-99 described by the saturation model; activation of cobalt-59 into cobalt-60 described by the depletion model; and activation of iridium-191 into iridium-192 described by the depletion-activation model.

Cobalt Radioisotopes↗

PubMed1987

Choice of radioisotope in stereotactic interstitial radiotherapy of small brain tumors.

In stereotactic interstitial radiotherapy, small radioactive sources are placed within the brain tumor to deliver locally high radiation doses. The choice of the radioisotope depends upon the dose distribution around the isotope, energy of the emitted radiation, relative biological effectiveness, and finally, the cost and availability of the isotope. We have analyzed 198gold, 125iodine and 192iridium in terms of these four factors. Our results have shown that 125I is superior to the other two isotopes due to its soft X-rays and dosimetric as well as radiobiological properties. Unfortunately, it is the most expensive of these radioisotopes, and can be difficult to obtain in specific activities.

Brachytherapy↗

PubMed1999

Combined use of transverse and scout computed tomography scans to localize radioactive seeds in an interstitial brachytherapy implant.

Various techniques have been developed to localize radioactive sources in brachytherapy implants. The most common methods include the orthogonal film method, the stereo-shift film method, and recently, direct localization from a series of contiguous CT transverse images. The major advantage of the CT method is that it provides the seed locations relative to anatomic structures. However, it is often the case that accurate identification and localization of the sources become difficult because of partial source artifacts in more than one transverse cut and other artifacts on CT images. A new algorithm has been developed to combine the advantages of using a pair of orthogonal scout views with the advantages of using a stack of transverse cuts. In the new algorithm, a common reference point is used to correlate CT transverse images and two orthogonal scout CT scans (AP and lateral). The radioactive sources are localized on CT transverse images. At the same time, the sources are displayed automatically on the two CT scout scans. In this way, the individual sources can be clearly distinguished and ambiguities arising from partial source artifacts are resolved immediately. Because of the finite slice thickness of transverse cuts, the longitudinal coordinates are more accurately obtained from the scout views. Therefore, the longitudinal coordinates of seeds localized on the transverse cuts are adjusted so that they match the position of the seeds on scout views. The algorithm has been tested on clinical cases and has proved to be a time saving and accurate method.

Adult↗