SEARCH · PubMed Health

Results for “IRIDIUM, RADIOACTIVE”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

196 records · Page 11Linked to original sources

PubMedDate not supplied

Dose mapping of porcine coronary arteries using an optical fiber dosimeter.

BACKGROUND: This study is about the measurement of radiation dose contribution to the coronary arteries during intravascular brachytherapy with beta and gamma emitters utilizing in vivo optical fiber dosimeters. METHODS AND MATERIALS: Domestic pigs were used. With each measurement, catheters were introduced into two different coronary arteries, including the left circumflex (LCX), the left anterior descending (LAD), the first diagonal, and/or the right coronary artery (RCA). A radioactive source (192Ir, 90Sr/Y, or 32P) and the dosimeter were loaded in each of these catheters. Data were collected as the dosimeter was being retracted at a constant rate via computer control. RESULTS: The radiation dose was normalized to 100% at a 2-mm radial distance from the source. When radiating a branching artery, the dose to the bifurcation at 5 mm from the source was 35%, 10%, and 3% for the 192Ir (10 seeds), 90Sr/Y (40 mm), and 32P sources, respectively. When utilizing a 23-seed 192Ir source, the dose is 40% at a 5-mm distance. However, radiation of the RCA did not result in dosing to the LAD or LCX using any source. CONCLUSIONS: The dose to adjacent artery segments is less with beta than with gamma emitters. Significant dose exposition is noted when using gamma emitters at a distance of 5 mm. The results can serve as a guideline for establishing prescription doses and safety margins for the treatment of bifurcation lesions and retreatment of the arteries.

Animals↗

PubMed2000

Estimation of genome damage after exposure to ionizing radiation and ultrasound used in industry.

The application of ionizing radiation in industry for nondestructive testing entails a specific framework of working conditions that include field work, facilities with different radioactive sources, maintenance thereof without halting production, use of nonionizing radiation, and exposure to chemical agents. The present study gives an estimation of recent genome damage in two groups of subjects using chromosome aberration assay and micronucleus assay. The first group was exposed to (192)Ir and the second was simultaneously exposed to (192)Ir and ultrasound. The results show that both groups had higher values of chromosome aberrations and micronucleus frequency than controls. The group of examinees exposed both to (192)Ir and ultrasound had significantly more chromatid breaks, acentric fragments, and dicentric chromosomes, and had a significantly higher frequency of micronuclei than subjects exposed to (192)Ir only. The study suggests that the detected differences in the genome damage may be attributed to the action of ultrasound. This study confirms the dosimetry data for ionizing radiation, which indicate that the methods used in industrial radiography and the usage of nonionizing radiation entail an increased health risk. In the absence of personal dosimeters for nonionizing radiation and chemical agents, biomonitoring provides reliable parameters for estimation of genome damage and may lead to improvements in working conditions and radiation safety programs.

Adult↗

PubMed2000

Verification of the dose distribution for 192Ir mould treatments using radiochromic film and LiF:Mg,Cu,P TLDs.

Radioactive moulds are an effective way of treating skin lesions. The aim of the study was to verify the dose distribution in a low dose rate 192Ir hand mould treatment using radiochromic film and LiF:Mg,Cu,P TLDs. Measurements were compared with two computerised treatment planning systems--Theraplan VO5B and ADAC Pinnacle3 V4.0b. Radiochromic film measured doses that were typically 25-30% lower than the TLD and planning computer doses (which agreed within +/- 5%). However, radiochromic film provided a two-dimensional map, which is particularly useful for dose distributions that are difficult to predict. This was demonstrated in the effects of adding thumb shielding to the hand mould. TLD results provided only point dose verification. Dose rates to the inner surface of the thumb were reduced from 15-20 cGy/hr to 2-4 cGy/hr by using 7.5 mm lead shielding. This is consistent with three half value layer reductions. For unshielded treatments, TLD results agreed with the treatment planning computers all within +/- 13%, including an uncertainty of +/- 10% on the source strength certificate for the activity. Due to the detector's sensitivity, miniaturisation would be the next approach for further more accurate verification with LiF:Mg,Cu,P TLDs.

Brachytherapy↗

PubMed2004

Dosimetric characterization of radioactive sources employed in prostate cancer therapy.

PURPOSE: Three types of radiation sources are employed currently in the radiation treatment of prostate cancer, namely, external, implant, and high-dose-rate (HDR) sources using an afterloader method. The present article provides a detailed dosimetric characterization of several commercially available implant sources and an HDR source employing the same stochastic code and dataset. METHODS AND MATERIALS: The radioactive implants considered are (125)I seeds: models 6701, 6702 and 6711, (103)Pd seed: model 200, and a high-dose-rate (192)Ir source: microSelectron-HDR model V7.0x. Detailed modeling of the sources and their associated X-rays and gamma rays has been carried out using the stochastic code MCNP4C. A sensitivity study has been conducted to quantify effects of varying the composition and density of the tissue equivalent material, and a dosimetric comparison is made for different media (tissue equivalent, solid-water, water, and air). Furthermore, a set of measurements using thermoluminescent dosimeters has been done to provide experimental validation of some of the calculational results obtained. RESULTS: Effectively, high-precision dosimetric values (Monte-Carlo statistical 1-sigma error <1%) are provided in tabulated form over a wide range to enable therapy planning as well as to check numerical values calculated by other methods. A subset of calculated dosimetric values has been experimentally validated by using thermoluminescent dosimeters. CONCLUSIONS: A detailed comparison of results obtained for the radial dose distribution function, anisotropy factor, and dose rate constant as defined in the TG-43 protocol has indicated reasonable agreement with the values reported in the literature.

Brachytherapy↗

PubMed2002

Twelve versus six months of clopidogrel to reduce major cardiac events in patients undergoing gamma-radiation therapy for in-stent restenosis: Washington Radiation for In-Stent restenosis Trial (WRIST) 12 versus WRIST PLUS.

BACKGROUND: Intracoronary gamma-radiation reduces recurrent in-stent restenosis (ISR). Late thrombosis was attenuated with 6 months of aspirin and clopidogrel. We aimed to find out whether 12 months of aspirin plus clopidogrel is superior to a strategy of 6 months after radiation therapy for patients with ISR. METHODS AND RESULTS: One hundred twenty consecutive patients with diffuse ISR in native coronaries and vein grafts with lesions <80 mm in length underwent PTCA, laser ablation, or rotational atherectomy. Additional stents were placed in 39 patients (33%). After the intervention, a ribbon with different trains of radioactive 192Ir seeds was positioned to cover the treated site, and a dose of 14 Gy to 2 mm was prescribed. Patients were discharged with clopidogrel and aspirin for 12 months and followed up clinically. The cardiac clinical event rates at 15 months were compared with the gamma-treated (n=120) patients of the WRIST PLUS study (only 6 months of antiplatelet therapy). Whereas the late thrombosis rates were similar (3.3% for the group given 12 months of antiplatelet therapy versus 4.2% for the group given 6 months, P=0.72), the group treated with 12 months of antiplatelet therapy had a rate of 21% for major adverse cardiac events and 20% for target-lesion revascularization compared with 36% (P=0.01) and 35% (P=0.009), respectively, in patients who were treated with only 6 months of clopidogrel. CONCLUSIONS: Twelve months of clopidogrel is superior to 6 months in reducing overall major cardiac events and revascularization rates at 15 months for patients with ISR treated with gamma-radiation. At least 12 months of clopidogrel therapy should be recommended for patients undergoing radiation therapy for ISR.

Aspirin↗

PubMed2002

A flattening filter for brachytherapy skin irradiation.

Radioactive sources in close contact offer an alternative to superficial radiation in the treatment of skin lesions. A flattening filter was designed for a lead surface applicator to improve the skin dose distribution of a high dose rate (HDR) brachytherapy unit (Nucletron). At three heights from the opening (10, 15 and 25 mm) of the cylindrical applicator, the 192Ir source can be driven into the centre of the applicator. Thin sheets of lead foil (0.2 mm) were cut into circular shapes and placed in the opening to build a cylindrical cone that acts as a flattening filter. The shape of the cone was optimized in an iterative process using a spreadsheet and the resulting dose distribution under the applicator was determined using radiosensitive film. The use of the filter improved the dose distribution in a plane perpendicular to the beam axis to be within +/- 5% of the central axis dose. The present applicator and flattening filter together with an HDR brachytherapy unit offer an alternative for skin irradiation where a superficial unit is not available or will be replaced with a more flexible device. As the depth dose characteristics can be modified using different source-to-surface distances, the dose throughout the patient's skin can be shaped as desired by the radiation oncologist using a compensator design type approach.

Brachytherapy↗

PubMed1996

The Sievert integral revisited: evaluation and extension to 125I, 169Yb, and 192Ir brachytherapy sources.

PURPOSE: The goal of this study is to assess the accuracy of the Sievert integral dose calculation model for medium and low-energy brachytherapy sources (photon energy: 25-500 keV). A simple modification of the basic model, the isotropic scattering correction, is proposed that significantly improves its accuracy. METHODS AND MATERIALS: Both the classical model and revised Sievert algorithms were tested against 2D dose distributions derived from Monte Carlo photon transport (MCPT) calculations for the following sources: a 169Yb interstitial source, pulsed and high dose rate 192Ir sources and the model 6702 125I source. The Sievert model was implemented as a 3D numerical integral over the radioactivity distribution and included photon attenuation and scattering by the surrounding medium. The Sievert filtration coefficients were approximated by linear energy absorption coefficients, parameters of best fit, and curve fits to simulated open-air transmission measurements. The revised model consists of using the Sievert integral only to calculate the primary dose distribution using contact absorber filtration coefficients. The dose component due to photon scattering in the medium is assumed to be isotropically distributed and is modeled by point-source scatter-to-primary dose ratios. RESULTS: The classical Sievert integral produces maximum and RMS average dose-calculation errors ranging from -53 to -20% and 3 to 19%, respectively. In contrast, the revised model reproduces the MCPT dose distribution with maximum and RMS mean errors ranging from 5 to 13% and 1 to 6%, respectively. CONCLUSIONS: The classical Sievert model fails to accurately describe brachytherapy dose distributions around heavily filtered sources emitting photons with average energies of 28 to 400 keV. The revised Sievert model accurately models single-source dose distributions for a wide range of sources, using well-defined filtration coefficients and scatter ratios that can be measured or calculated without knowledge of the final dose distribution. The model is potentially useful as a single-source dose-array generator for clinical treatment planning in the low energy domain.

Algorithms↗

PubMed1985

[Cancer of the prostate: technics of curietherapy. Review of the literature and experience at the Institut Gustave-Roussy].

Pasteau and Degrais in Paris used radium to treat prostatic cancer in 1907, radium was further used with different techniques including radium needles and radon seeds during twenty years. In 1951, Flock advocated colloidal radioactive gold with interesting palliative results. Permanent gold seeds implant was also used. But until 1970 with the appearance of Iodine 125 grain, brachytherapy was not widely employed. Hilaris and Whitmore treated almost 1000 cases until now, with few immediate complications. Survivals at 5 years are T1 96%, T2 76%, T3 69%. Conservation of potency and absence of late complications are the main benefits. However, the technique is a somewhat complex surgical procedure and the cases have to be carefully selected. Many others centers used iodine technique and Holm recently proposed an ingenious per-operative echography to improve the safety and accuracy of the permanent implantation. Removable implants with 192Ir wire (or nylon ribbon seeds) are obviously simpler and safer to implant through perineal route. For us, flexible plastic tubes is the technique of choice. In ten cases irradiated at 70 Gy level, no recurrences and no complications except one pulmonary embolism, but the patients were highly selected. For Syed rigid needles through perineal template is the technique of choice. External radiation is added after the implant, which delivered a dose of about 30 Gy. The results are satisfactory in the first 100 cases, but with a high level of complication. Comparative series and more follow-up are evidently requested, to know the exact place of brachytherapy in the treatment of prostatic adenocarcinoma.

Adenocarcinoma↗

PubMed1986

Dosimetry of CT-guided volumetric IR-192 brain implant.

Over the past 2 years, an afterloading technique has been developed and refined to implant radioactive Ir-192 sources into brain tumors. The implantation procedure integrates a stereotaxic system with computerized tomography (CT), which provides tumor position, volume, and guides the placement of catheters. A radiolucent ring-frame immobilizes the head as holes are made at 1 cm intervals with the aid of a template. Catheters containing dummy sources 1 cm apart are then inserted to the desired depth, and their position verified in three dimensions to insure complete coverage of visible tumor volume as defined by contrast enhancement. Once catheters are secured, the anesthetized patient is moved to the intensive care unit where the dummy sources are replaced by ribbons of Ir-192 seeds (specific activity 0.6-1.0 mg Ra eq). CT scans with the dummy sources in place are used to designate spatial coordinates of the active sources. A computer program converts position data and source strength into isodose contours in any plane. The implant duration (70-100 hours) for the desired dose to the tumor periphery (60-120 Gy) is then calculated. Dose rate contours are superimposed on preimplant CT scans. Maximum and minimum doses are determined in each of the various planes. Verification dosimetry has been carried out with thermoluminescent dosimeters placed in a catheter located in a plane along the tumor periphery. In vivo isodose values compared to idealized plans agree within +/-5%-10%.

Brachytherapy↗

PubMed2002

Recommendations for implementation of high dose rate 192Ir brachytherapy in developing countries by the Advisory Group of International Atomic Energy Agency.

PURPOSE: To provide recommendations for the implementation of high dose rate (HDR) 192Ir brachytherapy technology in developing countries. METHODS: An Advisory Group Meeting of the International Atomic Energy Agency (IAEA) met to address the implementation of HDR 192Ir brachytherapy technology in developing countries. These recommendations reflect only the personal opinions of the authors and do not necessarily represent the opinion of the IAEA. RESULTS: An HDR treatment system should be purchased as a complete unit that includes the 192Ir radioactive source, source loading unit, applicators, treatment planning system, and control console. Infrastructure support may require additional or improved buildings and procurement of or access to new imaging facilities. A supportive budget is needed for quarterly source replacement and the annual maintenance necessary to keep the system operational. The radiation oncologist, medical physicist, and technologist should be specially trained before HDR can be introduced. Training for the oncologist and medical physicist is an ongoing process as new techniques or sites of treatment are introduced. Procedures for quality assurance (QA) of patient treatment, and the planning system must be introduced. Emergency procedures with adequate training of all associated personnel must be in place. CONCLUSIONS: The decision to select HDR in preference to alternate methods of brachytherapy is influenced by the ability of the machine to treat a wide variety of clinical sites. In departments with personnel and budgetary resources to support this equipment appropriately, economic advantage becomes evident only if large numbers of patients are treated. Intangible benefits of source safety, personnel safety, and easy adaptation to fluctuating demand for treatments also require consideration when evaluating the need to introduce this treatment system.

Brachytherapy↗

PubMedDate not supplied

[Stereotaxic biopsy and 192Ir implant in intracranial tumors. A review of 7 years of experience].

INTRODUCTION: The combination of stereotaxic techniques, advances in neuroimaging and the creation of continually improving software has permitted stereotaxic biopsy of cerebral lesions at the most varied sites. Improvement in the method of permanent interstitial radiation (brachytherapy) improves the precision with which the radioactive sources may be inserted, releasing a maximum dose of radiation to the tumour with minimum radiation to the surrounding tissue. PATIENTS AND METHODS: We treated 237 patients (aged 1 to 78 years) with intracranial lesions, all included in the protocol of our centre. Stereotaxic systems of Leksell, Riechert-Mundinger, Micromar and Estereoflex were used. The procedure was in three stages: acquisition of the image, surgical planning and surgical operation. The imaging guide was the computerized axial tomography (CAT). RESULTS: Stereotaxic biopsy guided by CAT images was done in 153 patients. These were divided into three groups, taking the biopsy findings as the reference: group A (primary tumors, 128), group B (metastatic tumors, 15) and group C (non-malignant lesions, 10). Ninety six permanent implants of 192Ir were inserted, with a low dose of 4-7 cGy/h and a total dose of 80-120 Gy. CONCLUSIONS: Stereotaxic biopsy is a very effective procedure with a significantly low range of complications. The permanent implant with a low dose rate, well situated and using a source of 192Ir is a safe, simple, effective method for the treatment of primary and recurrent glial tumours, and non-glial tumours which fulfil criteria for this type of brachytherapy.

Adolescent↗

PubMed1996

Plaque radiotherapy for juxtapapillary choroidal melanoma. Visual acuity and survival outcome.

OBJECTIVES: To assess the effect of plaque radiotherapy on the visual acuity of patients with juxtapapillary choroidal melanoma and to determine the clinical predictive factors for radiation retinopathy, radiation papillopathy, local tumor recurrence, and distant metastasis. DESIGN: A retrospective review of the medical records of 93 patients with juxtapapillary choroidal melanoma who were treated initially with plaque radiotherapy. RESULTS: During a mean follow-up of 78 months, radiation retinopathy developed in 81 patients (87%) and radiation papillopathy developed in 48 patients (52%) after a mean interval of 21 and 27 months, respectively. The univariate variables that were significant predictors of radiation retinopathy were history of diabetes mellitus (P = .05) and use of a notched radioactive plaque (P = .04). The factors predictive of radiation papillopathy were age (> 45 years; P = .01), history of diabetes mellitus (P = .05), mushroom-shaped tumor configuration (P = .006), and nasal location of the tumor (P = .04). By using Kaplan-Meier survival curves, we found that the proportion of the 93 patients with radiation retinopathy was 87 (94%) at 5 years and with radiation papillopathy was 53 (57%) at 5 years. By using life-table analysis, we found that the proportion of the 93 patients who experienced a decrement of at least 3 lines of visual acuity was 67 (72%) by 50 to 60 months. Local tumor recurrence was documented in 14 patients (15%) after a mean interval of 41 months. The age of the patient (< 35 years; P = .02) and the superior (P = .004) and inferior (P = .05) locations of the tumor were predictive of local tumor recurrence. Distant metastasis developed in 11 patients (12%) after a mean interval of 44 months. The factors predictive of distant metastasis were a tumor with a basal diameter larger than 6.0 mm (P = .05), the superior location of the tumor (P = .01), and local tumor recurrence (P < .001). CONCLUSION: Based on these observations, plaque radiotherapy remains a potential option vs enucleation for the management of juxtapapillary choroidal melanoma.

Brachytherapy↗

PubMed2004

Treatment planning dosimetric parameters for 192Ir seed at short distances: effects of air channels and neighboring seeds based on Monte Carlo study.

The dose distributions around two different arrangements of a single radioactive 192Ir seed in water, (1) with air channels at the ends, and (2) surrounded by two nonactive ("dummy") seeds on both longitudinal ends, were calculated using MCNP4C Monte Carlo simulations at distances up to 1 cm. The contributions from beta particles and electrons emitted by 192Ir were included in the calculations. The effects of (a) the air channels at the seed ends and (b) the interference effect of the dummy seeds on the dose distribution were quantified and compared. It was found that the dummy seeds do not cause significant dose reduction for radial distances beyond 0.05 cm from the seed center. It is decided to report the dose rate values and the dosimetric parameters in TG43 format for a single seed with air channels for use in treatment planning computer systems. The dose rate constant (at 1 cm) of 192Ir seed, lambda, is 1.108 cGyU(-1) h(-1). The values of radial dose function, g(r), are within 1% from the TG43 recommended polynomial fit, except for distances within 0.08 cm. The anisotropy function, F(r, theta), attains large values near the seed ends and shallow angles (up to 8), as well as many values greater than 2 at the 20 degrees polar angle. Treatment planning systems involving intravascular brachytherapy do not compromise the accuracy for dosimetry of multiple seed trains by summing single seed values in water.

Air↗

PubMed2002

Dosimetric effects of source-offset in intravascular brachytherapy.

In intravascular brachytherapy (IVBT), radioactive sources can be displaced (offset) laterally from the center of the lumen and/or longitudinally from the desired location due to the cardiac motion and/or the absence of a source-centering device. The purpose of this work is to study the dosimetric impact of such a source offset. Dose effects of both lateral and longitudinal source offsets with or without the presence of a calcified plaque or a metallic stent are calculated for the three most commonly used sources (32P, 90Sr/90Y, and 192Ir). The MCNP Monte Carlo code is used in the calculation. Static and random source offsets are considered. The major results include that (a) dose can be changed significantly (by a factor of up to 4) due to a static lateral source offset; (b) this dose variation is reduced if the lateral source offset is considered as random moving within the vessel (the dose at the 2 mm reference radial distance is increased by 5-15% for the three sources in the case of the 2D random offset studied); (c) the presence of a calcified plaque and/or a metallic stent worsens the dosimetric effects; (d) the longitudinal random source offset results in a reduction (15-18%) in the effective treatment length; (e) the dose effects of source offsets for the beta source are higher than those for the gamma source. The data presented in this paper may be used for IVBT treatment planning or for dosimetric analysis of treatment outcome. The dose change due to the source offset should be considered in dose prescription. The reduction of effective treatment length should be taken into account in selection of a proper source length to ensure an adequate coverage of the treatment target.

Blood Vessels↗

PubMed1990

Episcleral radioactive plaque therapy: initial clinical experience with 56 patients.

Between 1983 and 1987, 56 patients with choroidal melanoma were treated at the University of Southern California with episcleral plaque (RPT). There were 29 female and 27 male patients, with a mean age of 59 years. Tumor stage at diagnosis was T2 in 18 (32%) and T3 in 38 (68%) patients. The tumor height ranged from 2.9 to 15 mm (mean 6.8 mm). Radial dimensions ranged from 5 to 25 mm (mean 13.2 mm), and circumference ranged from 7 to 23 mm (mean 12.3 mm). Most (77%) patients had posteriorly located tumors, including 18% that were juxtapapillary. Custom-designed gold plaques were utilized in this study. Radioactive isotopes used were 125I for 26 procedures or 192Ir for 31 procedures. A total of 56 patients were treated, with one patient having two procedures. Radiation doses at the tumor apex ranged from 29.8 to 165.4 Gy (mean 94.5 Gy), with the dose at 5-mm depth ranging from 70.5 to 430 Gy (mean 161.5 Gy). Follow-up ranged from 29 to 57 months (mean 39 months). The overall 4-year survival was 96%, with a 91% incidence of free-of-disease progression at 4 years. The majority (84%) of patients experienced a decrease in tumor height, with 27 (48%) patients having greater than 50% decrease. Increase in tumor height was noted in 5 (9%) and no change in 4 (7%) patients. Useful vision (greater than 5/200) was observed in 59% of patients, including 21% who had improved vision. Metastatic tumor occurred in 5 (9%) patients, with a mean time to metastases of 14 months. There was a good correlation between radial tumor dimension and metastatic disease, p less than 0.001. Treatment complications were observed in 34 (61%) patients, with cataract and retinopathy being the most common. Enucleation was performed in 11 (20%) patients, with a mean time to enucleation of 14.5 months. Causative factors for enucleation were treatment complications in 6 and tumor progression in 5 patients. Enucleations were required primarily in patients with tumors greater than 8 mm in height (p = 0.009). Improved RPT techniques with three-dimensional dosimetry are needed to reduce the overall incidence of treatment complications. Adjuvant hyperthermia is being investigated in an attempt to improve tumor control in patients with larger tumors.

Adult↗

PubMed1993

Plaque radiotherapy in the management of retinoblastoma. Use as a primary and secondary treatment.

BACKGROUND: Radioactive episcleral plaque brachytherapy is a treatment method for selected retinoblastomas. The authors have used this technique since 1976 as both a primary and a secondary treatment method after other methods failed to achieve tumor control. METHODS: A review of the records of 400 consecutive children with retinoblastoma showed that solitary plaque radiotherapy was used as a method of management in 103 cases. The authors' overall experience was evaluated, and the results between primary and secondary plaque therapies were compared in these 103 cases. RESULTS: Of the 103 tumors, the mean basal diameter was 7 mm, and the mean thickness was 4 mm. Overlying vitreous seeds were clinically apparent in 50 cases (48%). The mean proximity of the tumor margin to the optic disc margin was 6 mm and to the foveola was 6 mm. The mean follow-up period was 40 months. In 89 cases (86%), the tumor was controlled by one plaque application, whereas in 13 cases (13%), tumor recurrence after initial tumor shrinkage necessitated subsequent treatment. Final visual outcome was good in 63 cases (62%), poor in 30 (29%), enucleation in 9 (9%), and unknown in 1 case. The poor vision was due to foveal retinoblastoma (with or without amblyopia) in 25 cases (83%). Eight of the nine enucleated eyes were treated initially with external beam radiotherapy then later with plaque radiotherapy. In 31 cases (30%), plaque radiotherapy was used as a primary treatment to the tumor, while in 72 cases (70%), it was a secondary form of management after failure of other methods to control the tumor. Statistical analysis showed that tumors treated with plaque radiotherapy as a primary measure were more likely to be larger in in base (P = 0.01) and thickness (P = 0.01) than secondary treated tumors. The secondary treated retinoblastomas were more likely to have vitreous seeds (P = 0.02) than the primary treated tumors. The rate of tumor control and patient survival was similar between the two groups. CONCLUSION: Plaque radiotherapy is very effective in treating selected retinoblastomas with a high rate of tumor control and patient survival. It can be used successfully as a primary or a secondary treatment for tumors that have not been adequately controlled by other therapeutic methods.

Brachytherapy↗