Ophthalmic Plaque Research Articles

Palladium-103 plaque radiotherapy for choroidal melanoma: an 11-year study

Purpose: To describe 11 years of experience with 103Pd ophthalmic plaque brachytherapy for intraocular melanoma.Methods and Materials: Since 1990, 152 patients have been diagnosed with uveal melanoma, found to be negative for metastatic disease, and treated with 103Pd radioactive plaque radiotherapy. This study presents the first 100 patients treated with 103Pd and followed for ≥2 years. Plaques were sewn to the episclera to cover the base of the intraocular tumor. Treatment involved delivery of a mean apical radiation dose of 80.5 Gy during 5–7 days’ continuous treatment. Patients were evaluated for local tumor control, visual acuity, radiation damage (retinopathy, optic neuropathy, cataract), and metastatic disease.Results: Patients in this series were followed for a mean of 4.6 years (55.4 months). 103Pd seeds were found to be equivalent to 125I with respect to plaque manufacture and ease of dosimetric calculations. We noted a local control rate of 96% and six secondary enucleations. Including the enucleated patients, the visual acuity evaluations revealed that 35% lost six or more lines of vision and 73% had vision of 20/200 or better.Conclusion: Long-term results now exist describing the use of 103Pd plaque radiotherapy for uveal (iris, ciliary body, and choroidal) melanoma. Compared with the results from centers using 125I, patients in this series experienced equivalent local control rates and better visual function.

Plaque radiation therapy for malignant melanoma of the iris and ciliary body

PURPOSE: To report on plaque radiation therapy for malignant melanomas involving the iris and ciliary body. METHODS: Twenty-two eyes (22 patients) with anterior uveal melanomas were treated with 103Pd ophthalmic plaque radiation therapy. Transillumination and ultrasonography were used to evaluate ciliary body involvement and posterior iris extension. Plaques were placed onto the cornea to treat the anterior tumor margins. The targeted-zone included the tumor and a 2 to 3 mm tumor-free margin. After plaque removal, patients were examined at 1 day, 7 days, 4 weeks, and then every 3 to 6 months thereafter. Systemic evaluations for possible metastatic disease were performed every 6 months. RESULTS: After plaque radiation therapy, the melanomas decreased in thickness (mean 47%) in all 22 eyes, and no secondary enucleation was performed. One patient died of metastatic melanoma 5 years after radiation therapy. Despite anterior plaque placement that covered portions of the cornea, no epiphora, eyelash loss, or visually significant corneal opacities were noted. Whereas 15 of 21 phakic eyes (71%) developed secondary cataract, no eyes developed ischemic or neovascular radiation maculopathy. Four eyes were noted to have glaucoma before treatment, and two developed it after irradiation. Twenty of 22 eyes (91%) were within 2 lines of their pretreatment visual acuity. After radiation, the mean ± SD follow-up was 56 ± 34.4 months (range, 9 to 117 months). CONCLUSIONS: Plaque radiotherapy of melanomas involving the iris and ciliary body resulted in excellent local control with preservation of vision. Although there was high incidence of secondary cataracts, 103Pd plaque radiation therapy resulted in no visually significant corneal opacity or radiation retinopathy.

Determination of surgeon’s absorbed dose in iodine 125 and ruthenium 106 ophthalmic plaque surgery

ObjectiveValidation of dosimetry and exposition time to an ophthalmic surgeon during radioactive plaque operations. DesignExperimental study in which videotaped operations and dosimetric measurements were used to model dosimetry. MethodsWe used thermoluminescence detectors for high sensitivity readings in radiation fields. Typical intersurgical mobility was videotaped and distances to the plaque was evaluated. Main outcome measureEstimated radiation received by surgeons. ResultsAll 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. ConclusionsResults 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.

Discussion by Paul T. Finger, MD,1,2 Andrzej Szechter, PhD,2 Anthony M. Berson, MD1,2

Ophthalmic plaque radiation therapy continues to offer patients an eye- and vision-sparing alternative to enucleation. Pioneers of this technique first used high-energy plaques that incorporated cobalt 60 (60Co).1 Since that time ruthenium 106 (106Ru) largely replaced Co60 in Europe, as did low-energy iodine 125 (125I) in North America.1–5 Plaque radiotherapy with these new radionuclides (isotopes) delivers less unwanted radiation to the patient, the surgeon, and health care personnel.

Diode-light transillumination for ophthalmic plaque localization around juxtapapillary choroidal melanomas

Purpose: An evaluation of plaque-mounted diode-light transillumination (DLT) for localization of episcleral plaques beneath juxtapapillary tumors. Methods and materials: Two patients scheduled for radiotherapy for juxtapapillary melanomas were offered DLT as an additional method of ophthalmic plaque localization. Plaques were constructed by affixing 4 non-heat producing, light-emitting diodes with their apertures flush with the episcleral outer surface of the plaque’s rim. Bio-implantable epoxy was used to encapsulate the electronic components. Then the plaques were loaded with 103Pd seeds. After the eye-plaques were sewn to the episclera covering the base of the intraocular tumors; the diode-lights were illuminated, viewed and recorded. Photodocumentation of the relative position of the 4 lights around tumor’s base was obtained in both cases. Results: Digital images of plaque-mounted diode retro-transillumination were obtained. No evidence of diode-light toxicity was noted. Both tumors were found to be covered by the ophthalmic plaques. Conclusion: Juxtapapillary tumors are often difficult or impossible to visualize with standard transillumination techniques and have been associated with poor local control rates. We have developed plaque-mounted DLT in an effort to improve ophthalmic plaque localization. Retrobulbar transillumination was viewed by indirect ophthalmoscopy and recorded with video-imaging. This technique provides unique photographic documentation of episcleral plaque localization beneath juxtapapillary tumors.

Palladium-103 plaque radiotherapy for choroidal melanoma: Results of a 7-year study

ObjectiveTo describe the first clinical experience with palladium-103 (103Pd) ophthalmic plaque radiotherapy for choroidal melanoma. DesignPhase-I (nonrandomized) clinical trial. ParticipantsEighty patients with uveal melanomas were diagnosed by clinical examination, found to be negative for metastatic disease, and offered 103Pd radioactive plaque treatment. Nine patients were concurrently treated with microwave hyperthermia. InterventionPalladium-103 ophthalmic plaque radiotherapy was employed for each patient. Eye plaques were sewn to the episclera to cover the base of the intraocular tumor, radiation was continuously delivered over 5 to 7 days, and then the plaques were removed. A mean apical dose of 81 Gy was delivered. Main outcome measuresThe authors evaluated the ease of use of 103Pd seeds within standard gold eye plaques. Patient-related outcomes were control of tumor growth, change in visual acuity, the development of radiation damage (retinopathy, optic neuropathy, and cataract), and metastatic disease. ResultsFrom September 1990 to December 1997, 80 patients were treated with 103Pd and followed for an average of 38 months. Two patients were lost to follow-up. During this time, the authors found that 103Pd seeds were equivalent to iodine-125 (125I) with respect to plaque manufacture and ease of dosimetric calculations. Two patients in this series were treated for tumor recurrence after 125I plaque radiotherapy. They both failed secondary 103Pd treatment and were enucleated. When 103Pd was used as a primary treatment, it controlled the growth of 75 of 78 tumors (96%). Overall, there have been six enucleations: three failures of primary treatment, two failures of retreatment, and one for neovascular glaucoma. Visual acuity evaluations at the 36-month follow-up visit (including the enucleated patients) revealed that 38% of eyes had decreased 3 or more lines of vision, and 77% were 20/200 or better. ConclusionPalladium-103 plaque radiotherapy can be used to treat uveal melanomas. Compared with 125I, computerized dosimetry suggests a more favorable dose distribution with 103Pd. Treatment of most patients resulted in tumor shrinkage and preservation of functional vision. The authors have noted no complications that might preclude the use of 103Pd ophthalmic plaque radiotherapy for choroidal melanoma.

Ophthalmic plaque radiotherapy for age-related macular degeneration associated with subretinal neovascularization

PURPOSE: To evaluate ophthalmic plaque radiotherapy for the treatment of subretinal neovascularization associated with age-related macular degeneration.METHODS: In a prospective phase I clinical trial, we treated 23 patients (23 eyes) with ophthalmic plaque radiotherapy for subfoveal exudative macular degeneration. Palladium 103 ophthalmic plaque brachytherapy was delivered to a retinal apex dose of 1,250 to 2,362 cGy (rad). Early Treatment Diabetic Retinopathy Study type visual acuity determinations, ophthalmic examinations, and angiography were performed before and after treatment. Clinical evaluations were performed in a nonrandomized and unmasked fashion.RESULTS: Patients were followed up for a mean (±SD) of 19 ± 10.7 months (range, 3 to 37 months). Six months after radiation therapy, three (16%) of 19 eyes had lost 3 or more lines of best-corrected visual acuity; 12 months after radiation therapy, four eyes (31% of 13 eyes), and 24 months after radiation therapy, only two (22% of nine eyes) lost 3 or more lines of visual acuity. No eye suffered sudden irreversible loss of central vision. No radiation retinopathy, optic neuropathy, or cataract could be attributed to radiotherapy within this follow-up period.CONCLUSION: Ophthalmic plaque radiotherapy can be used to treat neovascular age-related macular degeneration. In contrast to external beam radiotherapy, ophthalmic plaque radiotherapy is a unilateral treatment, which allows a larger dose to be delivered to the macula with less irradiation of normal ocular structures. We have found no sight-limiting complications at the doses, dose rates, and follow-up evaluated in this study.

Chemotherapy for retinoblastoma: a current topic.

Retinoblastoma is the most common primary intraocular tumour in children, with an incidence of 1 in 15,000 live births. Treatment strategies for retinoblastoma have gradually evolved over the past few decades. There has been a trend away from enucleation (removal of the eye) and external beam radiation therapy toward focal 'conservative' treatments. Every effort has been made to save the child's life with preservation of eye and sight, if possible. Primary enucleation continues to be the commonly used method of treatment for retinoblastoma. It is employed in situations where eyes contain large tumours, long standing retinal detachments, neovascular glaucoma and suspicion of optic nerve invasion or extrascleral extension. Most of these eyes either have or are expected to have no useful vision. Radiation therapy continues to be an effective treatment option for retinoblastoma. However, external beam radiotherapy has unfortunately been associated with secondary non-ocular cancers in the field of radiation (primarily in children carrying the RB-1 germline mutation). Ophthalmic plaque brachytherapy has a more focal and shielded radiation field, and may carry less risk. Unfortunately, its applicability is limited to small to medium-sized retinoblastomas in accessible locations. Cryotherapy and transpupillary thermotherapy (TTT) have been used to provide control of selected small tumours. TTT is an advanced laser system adapted to the indirect ophthalmoscope which provides flexible nonsurgical treatment for small retinoblastomas. Recent research in the treatment of retinoblastoma has concentrated on methods of combining chemotherapy with other local treatment modalities (TTT, radiotherapy, cryotherapy). This approach combines the principle of chemotherapeutic debulking in paediatric oncology with conservative focal therapies in ophthalmology. Termed chemoreduction, intravenous or subconjunctival chemotherapy is used to debulk the initial tumour volume and allow for local treatment with TTT, cryotherapy and plaque radiotherapy. Cyclosporin has been added to the chemotherapy regimen in several centres. Other clinical settings where chemotherapy is considered are situations where the histopathology suggests a high risk for metastatic disease and where there is extraocular extension. There is no consensus that chemotherapy is needed when choroidal invasion is observed on histopathology. However, in patients where the retinoblastoma is noted beyond the cut end of the optic nerve or if there is disruption of the sclera with microscopic invasion of the orbital tissue, treatment has been helpful. Systemic and intrathecal chemotherapy with local and cranial radiotherapy has improved the survival of these patients. Most recently, the use of new chemotherapy modalities with haematopoietic stem cell rescue or local radiotherapy has increased the survival of patients with distant metastasis. Nevertheless, the prognosis of patients with central nervous system involvement is still poor.

Three-dimensional ultrasonography of choroidal melanoma: localization of radioactive eye plaques.

To evaluate the use of 3-dimensional (3D) ultrasonography for the localization of episcleral eye plaques during the treatment of choroidal melanomas. A series of 13 patients with choroidal melanoma were treated with radioactive palladium 103 seeds affixed into gold eye plaques. During surgery, 3D ultrasonography was performed with a commercially available system to evaluate the relative position of radioactive plaques secured beneath their intraocular tumors. This system consists of an automated, rotating, handheld, B-scan ultrasonographic probe operating at 10 MHz, a personal computer, and 3D imaging software. We measured the margins of the plaque extending beyond the tumor and the distance between the radioactive seeds and the tumor apex. We also evaluated the relationship between the plaque edge, the episclera, and the tumor's edges. While the plaques were well centered over the tumor in all cases, the plaque margins around the tumor were found to be variably sized. When comparing measurements taken at the time of plaque insertion with those taken at the time of plaque removal, we noted changes in the apical tumor height and in plaque centration. In the 1 patient with a juxtapapillary tumor, the posterior margin of the plaque was found to be displaced away from the sclera, or "tilted." Three-dimensional ultrasonography offers a new method for ophthalmic plaque localization. Unique perspectives can be visualized through the use of computer-aided 3D reconstructions that permit the assessment of the relative position of the plaque to the optic nerve and the measurement of the distance between the in vivo radioactive seed and the tumor apex. Our experience suggests that when compared with 2-dimensional ultrasonography, 3D ultrasonography offers new capabilities that can be used to improve plaque placement and radiation dose calculations.

Microwave Thermoradiotherapy for Uveal Melanoma: Results of a 10-year Study

Objective: The purpose of the study is to evaluate clinically the use of microwaveheating (hyperthermia) as an adjuvant to ophthalmic plaque irradiation for treatment of patients with uveal melanoma. Hyperthermia was also used as a radiation sensitizer, allowing for significant dose reductions during ophthalmic plaque radiation therapy.Participants: In this case series, 48 patients were treated with microwave plaque thermotherapy for uveal melanoma.Intervention: Microwave treatment, which involved affixing a miniature microwave dish antenna on the sclera beneath the tumor after completion of plaque brachytherapy, was performed. During hyperthermia treatment, the tumor's apex was targeted to receive a minimum of 42 °C for a 45-minute duration. A subset of 38 (79%) were given reduced apical doses of ophthalmic plaque radiation (radioactive isotope of iodine [125I] or palladium-103 [103Pd]) to an average of 52.6 Gy.Main Outcome Parameters: Patients were evaluated for visual function, microwave toxicity, radiation oculopathy, eye retention, local tumor control, and metastatic disease.Results: Patients have been observed for up to 10 years and for an average of 60 months (5 years). To date, there have been 3 cases of postoperative tumor enlargement (growth) for a 93.8% local control rate. Two patients were lost to followup. Seven eyes have been enucleated: three due to neovascular glaucoma, one due to uveitic neovascular glaucoma, and three due to progressive tumor enlargement. Although 15 patients have died, only 4 deaths were because of metastatic choroidal melanoma. Of the original 48 patients, 33 (69%) have maintained within 2 lines or have better than their preoperative visual acuity. Side effects attributable to heating have included decreased intraocular pressure without hypotony as well as chorioretinal scar formation within and around the targeted zone.Conclusions: The results of this series suggest that adjuvant microwave thermotherapy can be used with reduced doses of ophthalmic plaque radiation therapy to control the growth of uveal melanomas. Although the incidence of neovascular glaucoma, enucleation, and tumor regrowth is comparable to that of other series evaluating radiation alone, the visual acuities of microwave plaque the rmotherapy-treated eyes were found to be superior.

Microwave thermoradiotherapy for intraocular melanoma

We evaluated the use of microwave hyperthermia as an adjuvant to ophthalmic plaque radiotherapy for patients with intraocular tumors. Forty-eight patients were offered combined microwave plaque thermoradiotherapy (TRT) as a primary treatment for their uveal melanomas. A dish-shaped microwave antenna was placed on the sclera beneath the tumor at the time of plaque brachytherapy. While temperatures were measured at the sclera, the tumor's apex was targeted to receive a minimum of 42 degrees C for a 45-min duration. Patients were also given full or reduced doses of plaque radiotherapy (125I or 103Pd). We reduced the minimum tumor radiation dose (apex dose) for 42 (88%) of our patients to <70 Gy (mean, 52.5 Gy). The 48 TRT patients were followed for < or =8 years (average, 45 months). To date, there has been one documented postoperative tumor enlargement, for a 97.2% local control rate. Two patients were lost to follow-up. Four eyes have been enucleated: two due to neovascular glaucoma, one to glaucoma secondary to intraocular inflammation, and one for progressive tumor enlargement. Although 13 patients have died, only four deaths were due to metastatic melanoma. Thirty-five patients (73%) have maintained within two lines or had better than their preoperative visual acuity. Side effects attributable to heating included chorioretinal scar formation within and around the targeted zone and decreased intraocular pressures without hypotony. Our experience with this heat delivery system suggests that adjuvant microwave thermotherapy can be used with plaque radiotherapy for the treatment of uveal melanoma.

Radiation Therapy for Subretinal Neovascularizadon

Purpose: To evaluate low-dose external beam irradiation and plaque radiotherapy for the treatment of subretinal neovascularization.Methods: The authors treated 137 patients with radiation therapy for subretinal neovascularization. Herein, they examine a subset of 75 patients with exudative age-related macular degeneration who were treated with (4- or 6-MV photons) external beam irradiation at a dose of 1200 to 1500 cGy to the affected macula. In addition, six patients were treated with palladium 103 ophthalmic plaque brachytherapy to an equivalent retinal apex dose of 1200 to 1500 cGy. The authors compared the intralesional, intraocular, and intracranial radiation dose distributions of each treatment modality. Early Treatment Diabetic Retinopathy Study-type visual acuity determinations, ophthalmic examinations, and angiography were performed before and after treatment. Clinical evaluations were performed in a nonrandomized and unmasked fashion.Results: Episcleral plaque brachytherapy was found to provide a higher average radiation dose within the neovascular tissues while delivering less radiation to most normal ocular (both eyes) and all intracranial structures. Both forms of radiotherapy were associated with decreased hemorrhages, exudates, and leakage of neovascular membranes. Ten (13%) patients receiving external beam radiotherapy had transient epiphora and ocular irritation.Conclusion: Observation and laser photocoagulation of subfoveal neovascularization have been associated with poor visual outcomes. Pilot experience suggests that low-dose radiotherapy offers a method to treat subretinal neovascularization without destroying the overlying retina. Although the authors' radiation distribution studies favored plaque radiotherapy, additional factors such as relative efficacy, expense, convenience, and safety must be investigated.

Microwave Thermoradiotherapy for Intraocular Melanoma

We evaluated the use of microwave hyperthermia as an adjuvant to ophthalmic plaque radiotherapy for patients with intraocular tumors. Forty-eight patients were offered combined microwave plaque thermoradiotherapy (TRT) as a primary treatment for their uveal melanomas. A dish-shaped microwave antenna was placed on the sclera beneath the tumor at the time of plaque brachytherapy. While temperatures were measured at the sclera, the tumor's apex was targeted to receive a minimum of 42 degrees C for a 45-min duration. Patients were also given full or reduced doses of plaque radiotherapy (125I or 103Pd). We reduced the minimum tumor radiation dose (apex dose) for 42 (88%) of our patients to <70 Gy (mean, 52.5 Gy). The 48 TRT patients were followed for < or =8 years (average, 45 months). To date, there has been one documented postoperative tumor enlargement, for a 97.2% local control rate. Two patients were lost to follow-up. Four eyes have been enucleated: two due to neovascular glaucoma, one to glaucoma secondary to intraocular inflammation, and one for progressive tumor enlargement. Although 13 patients have died, only four deaths were due to metastatic melanoma. Thirty-five patients (73%) have maintained within two lines or had better than their preoperative visual acuity. Side effects attributable to heating included chorioretinal scar formation within and around the targeted zone and decreased intraocular pressures without hypotony. Our experience with this heat delivery system suggests that adjuvant microwave thermotherapy can be used with plaque radiotherapy for the treatment of uveal melanoma.

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.

Health checks in general practice

<b>Aim:</b> To report 7 year results of ophthalmic plaque radiotherapy for exudative macular degeneration. <b>Methods:</b> In a phase I clinical trial, 30 patients (31 eyes) were treated with ophthalmic plaque irradiation for subfoveal exudative macular degeneration. Radiation was delivered to a mean 2 mm from the inner sclera (range 1.2–2.4) prescription point calculated along the central axis of the plaque. The mean prescription dose was 17.62 Gy (range 12.5–24) delivered over 34 hours (range 18–65). Early Treatment Diabetic Retinopathy Study (ETDRS) type standardised visual acuity determinations, ophthalmic examinations, and angiography were performed before and after treatment. Clinical evaluations were performed in a non-randomised and unmasked fashion. <b>Results:</b> At 33.3 months (range 3–4), 17 of 31 (55%) eyes had lost 3 or more lines of vision on the ETDRS chart, five (16%) had improved 3 or more lines, and the remaining nine (29%) were within 2 lines of their pretreatment visual acuity measurement. Overall, 45% of patients were within or improved more than 2 lines of their initial visual acuity. Five eyes developed macular scars, eight developed subsequent neovascularisation or haemorrhage, and three progressed through therapy. Two patients were lost to follow up. The most common finding of patients followed for 6 or more months (n = 18 of 29 (62%)) was regression or stabilisation of the exudative process. No radiation retinopathy, optic neuropathy, or cataracts could be attributed to irradiation. <b>Conclusion:</b> Ophthalmic plaque radiation can be used to treat exudative macular degeneration. At the dose and dose rates employed, most patients experienced decreased exudation or stabilisation of their maculas. No sight limiting radiation complications were noted during 7 year follow up. Owing to the variable natural course of this disease, a prospective randomised clinical trial should be performed to evaluate the efficacy of plaque radiation therapy for exudative macular degeneration.

Palladium 103 Plaque Radiotherapy for Uveal Melanoma: Clinical Experience

To evaluate the effect of palladium 103(103Pd) ophthalmic plaque brachytherapy on patients with uveal melanoma. Radioactive 103Pd seeds have become available for plaque brachytherapy, and computer-aided simulations have compared the intraocular dose distribution of 103Pd versus iodine 125 (125I) plaques in patients with uveal melanoma. The use of the lower-energy radionuclide 103Pd increased the radiation to the tumors and decreases irradiation of most normal ocular structures. The authors have begun a phase 1 clinical trial evaluating the effect of 103Pd ophthalmic plaque radiotherapy on intraocular tumors. Uveal melanoma was diagnosed, and the patients were found to be negative for metastatic disease. All patients were given one 103Pd radioactive plaque treatment, and six patients also were given adjuvant microwave hyperthermia. Palladium 103 ophthalmic plaque radiotherapy was used to treat 23 patients with uveal melanoma. Patients were followed for up to 27 months (mean, 13.5 months). One eye was enucleated for progressive tumor enlargement (4 months after treatment). One patient died (of metastatic melanoma). Eight patients have lost greater than two lines of visual acuity, one has gained more than two lines. Fifteen patients (65%) were within two lines or had better than their preoperative visual acuity. Relating to the effect of treatment on visual acuity, 15 (65%) tumors were located equal to or less than 2 mm from the fovea. Palladium 103 ophthalmic plaque radiotherapy was noted to control the growth of uveal melanomas. Compared with other forms of plaque radiotherapy at this follow-up interval, the authors have noted no new complications, no difference in local control, and/or changes in tumor response to treatment. More long-term follow-up will be required to demonstrate differences between 125I and 103Pd ophthalmic plaque brachytherapy.

Palladium-103 versus iodine-125 for ophthalmic plaque radiotherapy

Purpose : A dosimetry study comparing the use of I-125 vs. Pd-103 radioactive seeds for ophthalmic plaque brachytherapy. Methods and Materials : Palladium-103 (Pd-103) seeds in ophthalmic plaques were used to treat 15 patients with intraocular malignant melanoma. Computer-aided simulations were performed to evaluate the intraocular dose distribution of I-125 versus Pd-103 ophthalmic plaques (delivering equivalent apex doses). Seven target points were selected. Starting at the outer scleral surface, four were located along the central axis of the plaque: the 1 mm point (the inner sclera), the 6 mm point, the tumors apex, and the opposite eye wall. We also evaluated the fovea, optic nerve, and the lens because they were considered to be critical structures. Results : These studies demonstrated that the lower energy photons generated by Pd-103 seeds (average 21 KeV) in ophthalmic plaques were more rapidly absorbed in tissue than photons generated by I-125 (average 28 KeV). Therefore, during ophthalmic plaque radiotherapy, Pd-103 photons were found to be more rapidly absorbed within the tumor and less likely to reach most normal ocular structures. On average, the use of Pd-103 decreased the dose to the fovea by 5.7%, to the optic nerve by 8.4%, to the lens by 26%, and to the opposite eye wall by 38.4%. Conclusion : Palladium-103 ophthalmic plaque brachytherapy resulted in slightly more irradiation of the tumor and less radiation to most normal ocular structures.

Autoradiography for iodine-125 seeds

To study the interior design of model 6702 and 6711 iodine-125 seeds contact autoradiographs were performed using mammography film. Improved resolution was obtained using a pin-hole camera with a hole of 0.1 mm × 0.1 mm. With these techniques, qualitative determination of the relative activity distribution within each seed was possible. The number of the activated resin spheres and the positions of the centers of these spheres can be exactly determined. A model calculation shows, that variations in the arrangement of the activated spheres within a seed have a moderate influence on the dose distribution at source distances below 10 mm. Knowing the exact source configuration may be useful when comparing dose calculations with measured data for model 6702 125I seeds which are currently employed in ophthalmic plaque and implant therapy of other tumors.

Palladium-103 versus iodine-125 for ophthalmic plaque radiotherapy

Palladium-103 versus iodine-125 for ophthalmic plaque radiotherapy

Optimization of 125I Ophthalmic Plaque Brachytherapy

Episcleral plaques containing 125I sources are often used in the treatment of ocular melanoma. Within four years post-treatment, however, the majority of patients experience some visual loss due to radiation retinopathy. The high incidence of late complications suggests that careful treatment optimization may lead to improved outcome. The goal of optimization would be to reduce the magnitude of vision-limiting complications without compromising tumor control. We have developed a three-dimensional computer model for ophthalmic plaque therapy which permits us to explore the potential of various optimization strategies. One simple strategy which shows promise is to maximize the ratio of dose to the tumor apex (T) compared to dose to the macula (M). By modifying the parameters of source location, activity distribution, source orientation, and shielding we find that the calculated T:M ratio can be varied by a factor of 2 for a common plaque design and posterior tumor location. Margins and dose to the tumor volume remain essentially unchanged.