Ophthalmic Applicators Research Articles

Ophthalmic applicator displacement as a method of treating large diffuse uveal melanomas.

The presentation of results of an ophthalmic plaque displacement as a brachytherapy treatment method of large diffuse uveal melanomas. This was a retrospective analysis of treatment results of 9 patients with large diffuse uveal melanomas using ophthalmic plaque displacement. Patients were treated with this method in our center between 2012 and 2021 (last follow-up visit in 2023). To achieve appropriate radiation dose distribution for large tumors with a base greater than 18 mm, brachytherapy (106Ru in 7 patients and 125I in 2 patients) with applicator displacement was used as primary treatment. Median follow-up was 2.9 years, and for patients with positive primary treatment results, it was 1.7 months. Median time to local relapse was 2.3 years. In 5 patients, a positive result of local treatment was obtained, out of whom, one patient underwent enucleation due to complications. In the next 4 cases, local recurrence developed. In all tumors, the use of applicator displacement method caused that planning target volume (PTV) was effectively covered with treatment isodose. Brachytherapy with ocular applicator displacement allows for the treatment of tumors with base measurements larger than 18 mm. The application of this method may be considered as an alternative for eye enucleation in particular cases of large diffuse tumors, such as a neoplasm of the eye with vison, or when a patient does not consent to enucleation.

Yttrium-90 (90Y) Brachytherapy for Small Iridociliary Melanomas

<h3>Purpose/Objective(s)</h3> Beta irradiation has been useful in treating numerous ocular tumors and benign growths. However, strontium-90 applicators are no longer supported and ruthenium-106 is not available for high dose rate (HDR) brachytherapy. Herein we present the first clinical use of a new HDR ⁹⁰Y brachytherapy source that is FDA 510(k) cleared for the treatment of ocular tumors and benign growths. <h3>Materials/Methods</h3> The iWand A® is a new single-use ophthalmic hand-held brachytherapy applicator, with a surface contact diameter of 10 mm. In addition, the applicator's translucent polymer backing both attenuates radiation exposure towards the surgeon and ancillary staff and allows visualization of the disc-shaped ⁹⁰Y source during treatment. A well-shaped recess on the anterior surface of the applicator accommodates a 6-mm disc-shaped source, where it is flush-mounted and affixed by biocompatible adhesive. The titanium shell of the source provides rigid encapsulation of the radioactive ⁹⁰Y source. Though the LV Y-90 Disc is FDA cleared to be utilized at up to 20 millicuries (mCi); the activity used for these 2 treatments was mean 12.4 mCi. For example, a 20 mCi LV ⁹⁰Y Disc which decays by β-emission with an end point energy of 2.28 MeV (0.98 MeV average), yields 30.0, 21.6, 16.2, and 4.8 Gy/minute at depths of 0.0, 0.6, 1.0, and 2.6 mm, respectively. While planning tool simulations were used to demonstrate the treatment volume and penumbra characteristics of the ⁹⁰Y disc, NIST-traceable preoperative calibrations were performed by an independent authorized medical physicist. <h3>Results</h3> Two patients (mean age=74 years) were diagnosed with AJCC 8^th edition T1-sized, biopsy-proven iridociliary melanoma. High-frequency ultrasound was used to measure tumor size, basal dimensions and distance from the overlying sclera. Measurements revealed a mean maximum tumor thickness of 0.7 mm (0.6-0.8) and a mean maximum largest tumor basal diameter of 3.0 mm (2.9-3.1). Surgery required a minor conjunctival recession to expose the episcleral target zone. The 10 mm application site was marked with tissue dye on the cornea and sclera. Then the ⁹⁰Y source, affixed within the iWand A® applicator, was applied to deliver HDR episcleral brachytherapy to doses of 25 - 30 Gy to a 2.5-mm depth. Treatment durations ranged from 5 to 13 minutes. During treatment, the acrylic of the iWand A® applicator was found capable of shielding the patient, surgeon and operating-room personnel. No acute or post-operative ⁹⁰Y-radiation-related complications were noted. The ⁹⁰Y source's 64-hour half-life allowed for single-use, decay in storage, and return for disposal. <h3>Conclusion</h3> A novel, FDA-cleared, HDR ⁹⁰Y beta source was used to treat 2 patients with uveal melanoma. It was affixed within a hand-held, single-use applicator that aids guidance, targeting and facilitates radiation safety (as measured during both surgeries). Future research is needed to explore additional applications for this novel ⁹⁰Y HDR brachytherapy source.

Deposition of Ruthenium-106 on a Concave Metal Surface of a Substrate of an Ophthalmic Applicator—a Closed Source of Beta Radiation

Deposition of Ruthenium-106 on a Concave Metal Surface of a Substrate of an Ophthalmic Applicator—a Closed Source of Beta Radiation

Brachytherapy in organ-preserving treatment of choroidal melanoma: complications and the possibility of their prediction

This review analyzed the domestic and foreign literature on brachytherapy of choroidal melanoma using ruthenium ophthalmic applicators. The review highlights the historical aspects of radiation treatment, from the first experience of using ionizing radiation in the treatment of malignant neoplasms to modern methods of brachytherapy; presents the radiobiological foundations of radiation therapy; considers the issues of radiation pathomorphosis, reflecting the nature of pathological changes in the choroidal melanoma tissue during brachytherapy; shows the dependence of the effect of exposure ionizing radiation from the phase of the cycle of cell division; and also describes the presence of changes characteristic of the response to ionizing radiation in unirradiated tissues. The analysis of various post-radiation complications, both early and late, was carried out in some detail, with emphasis on the possibility of predicting and preventing them in real clinical practice. A comparison is made in terms of the frequency of development of various post-radiation complications in the works of domestic and foreign authors, as well as a comparison with the effect of ionizing radiation from other radioactive isotopes. Recommendations of experts are given regarding the correct calculation of the dose to the sclera and medication support, based on many years of experience in the use of ruthenium ophthalmic applicators for brachytherapy of choroidal melanoma. The risks of developing such late complications as radiation maculopathy and radiation neuropathy have been demonstrated, especially in pre-equatorial tumor localization. The possibilities of modern methods of instrumental diagnostics for studying the processes occurring in the area of the tumor, as well as changes in the surrounding tissues, are shown, which determines the feasibility and importance of further study of this issue.

Brachytherapy for retinoblastoma: a 13 year experience

Brachytherapy (BT) is a method of radiation therapy with radioactive source contacting the tumor. It was proposed by P. Moore and H. Stallard in 1929. Despite those 50 years of experience with the use of BT in ophthalmic oncology, there are only a few studies on the use of Ru-106 BT for retinoblastoma (RB), and no publications on the use of Sr-90 BT have been found.Purpose. To present our own experience with the use of ruthenium and strontium ophthalmic applicators for BT in retinoblastoma.Materials and methods. 120 patients (137 eyes and 194 RB foci) received BT as a local treatment in the period from 2007 to 2020. At the time of treatment the age of the patients varied from 4 to 109 months (mean age 26 months). In 32% of cases (44 eyes) there were monofocal lesions, and in 68% of cases (93 eyes) — multifocal. In 36 cases (30%) BT was performed in the single eye. 79 patients (87 eyes) were treated with the use of ruthenium ophthalmic applicators (OAs), 25 patients (26 eyes) — with the use of strontium OAs, and for the treatment of 16 patients (24 eyes) both ruthenium and strontium OAs were used.Results. Clinically complete tumor regression was achieved in 62 % of cases (120 foci), partial tumor regression — in 31% of cases (60 foci). In 6% of cases (12 foci) continuous tumor growth was observed, and tumor recurrence occurred in 1% of cases (2 foci) within 4 to 6 months after BT. Local tumor control was achieved in 93% of cases.The single eyes were preserved in 92% of cases. BT complications of different intensity were reported in 38% of cases (46 patients — 49 eyes) with the mean follow-up duration of 55 months (3 to 157 months). In 92 % of cases (42 patients — 45 eyes) complications were associated with the use of ruthenium OAs, and only in 8% of cases (4 patients — 4 eyes) — with the use of strontium OAs. Risk factors for radiation-induced complications were identified: focus size (height more than 2.5 mm [P =0.0005], extension more than 7.3 mm [P &lt;0,0001]), sclera dose more than 626 Gr (P = 0,0002), and the central localization of the tumor (P &lt;0.0001).Conclusions. Ruthenium-106 and strontium-90 brachytherapy is a highly effective treatment modality for the management of RB.

Dosimetry of ruthenium-106 ophthalmic applicators with thin layer thermoluminescence dosimeters - Clinical quality control

Ruthenium-106 ophthalmic applicators have proven to be effective when using beta emitters in brachytherapy. For dose calculations , typically, the dosimetric reference data given by the manufacturer are used. An additional check of the applicators is usually not provided. However, the medical physicist is responsible for correct dosimetry in the clinic; therefore dosimetric verification is desirable. Despite the fact that the use of beta-ray emitting sealed brachytherapy sources is a safe treatment method, errors can occur (Kaulich et al., 2004). Hence, a method for absolute dose measurements based on the use of thin layer MCP-N-thermoluminescence detectors (TLD Poland, Krakow, Poland) is described in this study. A custom-made polymethyl methacrylate (PMMA)- based phantom was developed for this study. The surface of the phantom was designed to fit with spherical shells of ruthenium-106 ophthalmic applicators (e.g. applicator type CCA, CCB and CIA by Eckert & Ziegler BEBIG GmbH, Berlin, Germany) studied in this work. To verify the reference data from the source certificates, absolute point dose values were measured at different phantom depths with the thermoluminescence detectors and compared to the certificate values.Calibrations of the thermoluminescence detectors were performed in a water phantom with a 6 MV CLINAC (Artiste, Siemens Medical, Erlangen, Germany) before. A comparison with scintillator measurement results given by the manufacturer in the applicator certificate shows the measurement series of absolute dose using MCP-N thin layer detectors being in good accordance with the values of the applicator certificate. The dose values calculated with the source certificate can be confirmed with a maximum deviation of 6.5%. Further, it can be shown that compared to TLD-100, the use of MCP-N thermoluminescence detectors is an advantage, when calibrating with 6 MV photons. The phantom measuring procedure presented in this study provides a practice-oriented realization for quality control of ruthenium-106 ophthalmic applicators in clinical routine The phantom seems capable of performing periodic system tests, as well as controlling the introduction of new applicators delivered by the manufacturer.

Effectiveness of brachytherapy in the combination treatment of retinoblastoma

Background: Retinoblastoma is a malignant tumor of the eye retina that occurs mostly in children. In the absence of treatment, the disease leads not only to vision loss, but also to death of the child. At present, combined organ-preserving methods of treatment are preferred. These include polychemotherapy and a local intervention on the tumor, the "golden standard" of which being brachytherapy. Aim: To study the effectiveness of brachytherapy against the background polychemotherapy. Materials and methods : We analyzed retrospectively medical files of 104 children with retinoblastoma aged from 5 months to 5 years (mean age 21 months), who underwent brachytherapy as a local component of management from 2010 to 2015 in the Moscow Helmholtz Research Institute of Eye Diseases. Multifocal lesions were identified in 43 cases and bilateral tumors in 87 children. In 33 cases, the worst eye was removed. Endophytic and mixed forms of tumors growth were most prevalent. Before the brachytherapy, all children received polychemotherapy (2 to 3 courses). The average tumor thickness was 2.74 mm (from 1 to 6.4 mm); its mean maximal transverse dimension was 6.27 mm. Indigenous ophthalmic applicators with isotopes 90 Sr + 90 Y and 106 Ru + 106 Rh were used. The average dose on the tumor apex with the strontium applicator was 142.1 (120–170) Gy, with ruthenic one, 107.4 (69–168) Gy; the scleral doses were 751.3 и 504.4 Gy, respectively. The median follow-up was 51 months. The patients were assessed every 3 to 4 months with ophthalmoscopy and ultrasound examination. The following effectiveness criteria were used: complete resorption, the tumor cannot be identified; partial resorption, a decrease in the initial tumor size by at least 50%; no effect, a decrease in the initial tumor size by less than 50% or an increase in the size of the tumor. Results: Complete resorption of the tumor occurred in 60.6% (n = 63) of the patients at 3 months and in additional 24% (n = 25) at 6 months. During the first year after the radiation, complete resorption of retinoblastoma was achieved 93.3% (n = 97) of the children. All children are alive, no distant metastases have been found. Early complications after brachytherapy were noted in 3 children: hemophthalmia, in 1, retinal detachment, in 1, hemophthalmia with retinal detachment, in 1, when the radiation dose on the sclera exceeded 1000 Gy. Continued tumor growth or relapses were detected in 7 (6.7%) patients. The reason to enucleate two eyes was the tumor invasion into the orbit (1.9%). Visual functions are preserved in 85 (81.7%) children, with a high visual acuity (0.9–1.0) in 21 children, and 0.1–0.8 in 21 children, as well. Conclusion : Brachytherapy is a highly effective method of local destruction of retinoblastoma, which, in the vast majority of cases, allows for complete resorption of the irradiated tumor and for maintenance of high visual acuity in almost half of patients.

Late complications of choroidal melanoma brachytherapy and possibility of their prevention

to examine the frequency of complications, the characteristics of their development after choroidal melanoma (CM) brachytherapy with ruthenium ophthalmic applicators (OA) during long-term follow-up and determine the possibility of their prevention. Characteristics of postradiation period after BT were studied in 200 patients with CM (200 eyes). Among them, 127 patients were treated by authors of this study, 73 were provided treatment by other specialized medical facilities in Moscow. The study involved 84 male and 116 female patients aged 56.14±12.8 in average. The follow-up periods spanned 2 to 39 years (mean length 9.84±6.16 years). BT was done only with ruthenium OA (beta radiation) manufactured in Russian. Follow-up period after BT for 83% of patients was 5 years. Complications occurred in 68.5% of patients. Complications were found in 74.63% of patients with CM localized pre-equatorially and in 65.4% of patients with CM localized in the posterior part of the eye. Complications associated with radiation-induced injuries in crystalline lens, retina and choroidal blood vessels were more frequent. The frequency of complications depends on the size of CM and its localization. Complications were the least frequent in patients with CM thickness of 5 mm or less.

Роль брахитерапии в лечении капиллярных гемангиом сетчатки

Purpose: to evaluate the efficiency of brachytherapy treatment in capillary retinal hemangioma and the emerging complications. Material and methods. Between 2005 and 2014, 18 patients with capillary hemangioma of the retina (11 females and 7 males, mean age 29 ± 13.9 years) were treated, 8 patients had monocular and 10 patients had binocular lesion. In 12 cases, capillary hemangioma of the retina was associated with Hippel - Lindau disease, in 6 cases a sporadic tumor appeared. 90Sr and 106Ru ophthalmic applicators were used. In 7 eyes, brachytherapy was preceded by laser coagulation. After local irradiation, the patients were followed up for 1 month to 3 years. Results. The pathological process was stabilized in 13 eyes. 5 eyes, no later than 3 months after the procedure, developed a severe radiation reaction, total retinal detachment, and recurrent hemophthalmos, which later, after 6 months or more, led to the development of neovascular glaucoma. In one case, the eye had to be enucleated due to terminal painful glaucoma. In 3 eyes despite tumor regression, retinal detachment persisted over the follow-up period, although the macular area remained unaffected. Complicated cataract (12 eyes), neuroretinopathy (2 eyes), appearance of new capillary hemangiomas (1 eye), increased epiretinal fibrosis (4 eyes), and secondary central chorioretinal dystrophy (2 eyes) were observed over the period of up to 2 years. Conclusion. In most cases, brachytherapy of retinal capillary brings about a satisfactory anatomical result. However, in order to reduce postoperative complications and improve the functional result, a thorough preoperative selection of patients is needed, which should take into account the initial retinal status. For citation: Neroev V.V., Saakyan S.V., Ilyukhin P.A., Valskiy V.V., Ryabina M.V., Novikova A.Yu. The role of brachytherapy in the treatment of retinal capillary hemangiomas. Russian ophthalmological journal. 2018; 11 (3): 5-10 (In Russian). doi: 10.21516/2072-0076-2018-11-3-5-10

Windowless extrapolation chamber measurement of surface dose rate from a 90Sr/90Y ophthalmic applicator

In this study, a planar extrapolation chamber without an entrance window was tested through measurements of a 90Sr/90Y ophthalmic applicator that had been previously calibrated at the National Institute of Standards and Technology (NIST). This work was performed as part of a larger aim to determine surface dose rate from curved 106Ru/106Rh plaques using a convex windowless extrapolation chamber. Capacitance measurements were carried out to assess the initial air gap width between the source face and collecting electrode. The EGSnrc DOSRZnrc Monte Carlo user code was used to determine correction factors for backscatter, divergence, and attenuation caused by the aluminized Mylar® entrance window in the NIST extrapolation chamber. Measured surface dose rate values were compared with the expected result from the NIST source calibration, and the average observed difference was +4.1% with a standard deviation of ±0.6%. The dose rate from each measurement trial was within the estimated combined uncertainty in the reference source calibration of ±7.0% (k = 2) given by NIST. The experiment results suggest that an entrance window is not needed to achieve accurate dose rate measurements for a beta-emitting source with a planar extrapolation chamber, as long as the collecting electrode diameter is small compared to the source diameter. Therefore, a convex extrapolation chamber without an entrance window is proposed for the calibration of concave 106Ru/106Rh episcleral plaques.

Inhibiting the effect of (90)Sr-(90)Y ophthalmic applicators on rat corneal neovascularization induced by sutures.

To investigate a practical technique used to inhibit corneal angiogenesis with a (90)Sr-(90)Y ophthalmic applicator. A (90)Sr-(90)Y ophthalmic applicator was detected with a radioactive nuclide application treatment healthy protection standard. The applicator used was produced through medical dosimetry research; it had a concave applicator add measured the applicator temperature, serviceable humidity range, applicator appearance status, applicator radiation homogeneity, radioautography, and radiological safety of the original applicator surface. A vessel model was established using newborn rats, with sutures around the corneal limbus. Corneal neovascularization (CNV) were observed with a slit lamp. The new vessel length and response area were measured. Low-dose radiation can inhibit CNV after corneal sutures. The absorbed dose of the applicator (0.046 Gy/s) was safe for the treatment of it. The lengths of new vessels and the areas of new vessels were lower than the new born vessel rat group (P<0.01). The optimal radiation dose emitting from the applicator can be safe and potentially used in humans.

Comparison between beta radiation dose distribution due to LDR and HDR ocular brachytherapy applicators using GATE Monte Carlo platform

Eye applicators with 90Sr/90Y and 106Ru/106Rh beta-ray sources are generally used in brachytherapy for the treatment of eye diseases as uveal melanoma. Whenever, radiation is used in treatment, dosimetry is essential. However, knowledge of the exact dose distribution is a critical decision-making to the outcome of the treatment. The Monte Carlo technique provides a powerful tool for calculation of the dose and dose distributions which helps to predict and determine the doses from different shapes of various types of eye applicators more accurately. The aim of this work consisted in using the Monte Carlo GATE platform to calculate the 3D dose distribution on a mathematical model of the human eye according to international recommendations. Mathematical models were developed for four ophthalmic applicators, two HDR 90Sr applicators SIA.20 and SIA.6, and two LDR 106Ru applicators, a concave CCB model and a flat CCB model. In present work, considering a heterogeneous eye phantom and the chosen tumor, obtained results with the use of GATE for mean doses distributions in a phantom and according to international recommendations show a discrepancy with respect to those specified by the manufacturers. The QC of dosimetric parameters shows that contrarily to the other applicators, the SIA.20 applicator is consistent with recommendations. The GATE platform show that the SIA.20 applicator present better results, namely the dose delivered to critical structures were lower compared to those obtained for the other applicators, and the SIA.6 applicator, simulated with MCNPX generates higher lens doses than those generated by GATE.

WE‐DE‐201‐05: Evaluation of a Windowless Extrapolation Chamber Design and Monte Carlo Based Corrections for the Calibration of Ophthalmic Applicators

Purpose:To test the validity of a windowless extrapolation chamber used to measure surface dose rate from planar ophthalmic applicators and to compare different Monte Carlo based codes for deriving correction factors.Methods:Dose rate measurements were performed using a windowless, planar extrapolation chamber with a 90Sr/90Y Tracerlab RA‐1 ophthalmic applicator previously calibrated at the National Institute of Standards and Technology (NIST). Capacitance measurements were performed to estimate the initial air gap width between the source face and collecting electrode. Current was measured as a function of air gap, and Bragg‐Gray cavity theory was used to calculate the absorbed dose rate to water. To determine correction factors for backscatter, divergence, and attenuation from the Mylar entrance window found in the NIST extrapolation chamber, both EGSnrc Monte Carlo user code and Monte Carlo N‐Particle Transport Code (MCNP) were utilized. Simulation results were compared with experimental current readings from the windowless extrapolation chamber as a function of air gap. Additionally, measured dose rate values were compared with the expected result from the NIST source calibration to test the validity of the windowless chamber design.Results:Better agreement was seen between EGSnrc simulated dose results and experimental current readings at very small air gaps (&lt;100 µm) for the windowless extrapolation chamber, while MCNP results demonstrated divergence at these small gap widths. Three separate dose rate measurements were performed with the RA‐1 applicator. The average observed difference from the expected result based on the NIST calibration was −1.88% with a statistical standard deviation of 0.39% (k=1).Conclusion:EGSnrc user code will be used during future work to derive correction factors for extrapolation chamber measurements. Additionally, experiment results suggest that an entrance window is not needed in order for an extrapolation chamber to provide accurate dose rate measurements for a planar ophthalmic applicator.

Point/Counterpoint. Particle therapy is ideal for the treatment of ocular melanomas.

Point/Counterpoint. Particle therapy is ideal for the treatment of ocular melanomas.

Dose Assessment of Phosphorus-32 (32P) for the Treatment of Recurrent Pterygium

Introduction Pterygium is a wing-shaped, vascular, fleshy growth that originates from the conjunctiva and can spread into the corneal limbus and beyond. Beta irradiation after bare sclera surgery of primary pterygium is a simple, effective, and safe treatment, which reduces the risk of local recurrence. Materials and Methods Dosimetric components of strontium-90 (90Sr), phosphorous-32 (32P), and ruthenium-106 (106Ru), in form of ophthalmic applicators, were evaluated, using the Monte Carlo method. Results The obtained results indicated that 32P applicator could deliver higher doses (about 10 Gy) to a target, located within a close distance from the surface, compared to 90Sr and 106Ru; it also delivered a lower dose to normal tissues. Conclusion The risk of pterygium has increased given the geographical location and climate of Iran. Spread of dust in the country over the past few years has also contributed to the rising rate of this condition. Our results showed that using 32P applicator is a cost-effective method for pterygium treatment.

Effects of ocular surface strontium-90 beta radiotherapy in dogs latently infected with canine herpesvirus-1

Latent canine herpesvirus-1 (CHV-1) infections are common in domestic dogs, but stimuli causing viral reactivation and recrudescent disease are poorly understood. Immunosuppressive pharmaceuticals are currently the only experimentally established triggers for recurrent ocular CHV-1 infection in dogs; however, ocular CHV-1 shedding has been reported clinically following strontium-90 beta radiotherapy of the ocular surface and it has been speculated that radiotherapy can directly induce viral reactivation. Strontium-90 is used as a beta radiation source for the treatment of a variety of neoplastic and immune-mediated canine ocular surface diseases. In the present study, the effects of ocular surface strontium-90 beta radiotherapy in dogs latently infected with CHV-1 were evaluated. Ten mature dogs with experimentally induced latent CHV-1 infections were randomly divided into two groups: one group received a single fraction 50Gy radiation dose in one application from a strontium-90 ophthalmic applicator and the second group received sham radiotherapy. Dogs were then monitored for 45 days for recurrent ocular CHV-1 infection using clinical and virological outcome measures. Clinical ophthalmic examinations, ocular sample CHV-1 PCR assays, and serum CHV-1 virus neutralizing antibody assays were performed at specified intervals. No abnormalities suggestive of recurrent CHV-1 ocular disease were observed on clinical examination in any dog during the study. Ocular viral shedding was not detected and CHV-1 virus neutralizing titers remained stable in all dogs. A single fraction 50Gy radiation dose administered to the ocular surface by strontium-90 beta radiotherapy did not result in detectable recurrent ocular CHV-1 infection in mature dogs with experimentally induced latent infection.

WE-A-17A-01: Absorbed Dose Rate-To-Water at the Surface of a Beta-Emitting Planar Ophthalmic Applicator with a Planar, Windowless Extrapolation Chamber

Purpose: Currently there is no primary calibration standard for determining the absorbed dose rate-to-water at the surface of β-emitting concave ophthalmic applicators and plaques. Machining tolerances involved in the design of concave window extrapolation chambers are a limiting factor for development of such a standard. Use of a windowless extrapolation chamber avoids these window-machining tolerance issues. As a windowless extrapolation chamber has never been attempted, this work focuses on proof of principle measurements with a planar, windowless extrapolation chamber to verify the accuracy in comparison to initial calibration, which could be extended to the design of a hemispherical, windowless extrapolation chamber. Methods: The window of an extrapolation chamber defines the electrical field, aids in aligning the source parallel to the collector-guard assembly, and decreases the backscatter due to attenuation of lower electron energy. To create a uniform and parallel electric field in this research, the source was made common to the collector-guard assembly. A precise positioning protocol was designed to enhance the parallelism of the source and collector-guard assembly. Additionally, MCNP5 was used to determine a backscatter correction factor to apply to the calibration. With these issues addressed, the absorbed dose rate-to-water of a Tracerlab 90Sr planar ophthalmic applicator was determined using National Institute of Standards and Technology's (NIST) calibration formalism, and the results of five trials with this source were compared to measurements at NIST with a traditional extrapolation chamber. Results: The absorbed dose rate-to-water of the planar applicator was determined to be 0.473 Gy/s ±0.6%. Comparing these results to NIST's determination of 0.474 Gy/s yields a −0.6% difference. Conclusion: The feasibility of a planar, windowless extrapolation chamber has been demonstrated. A similar principle will be applied to developing a primary calibration standard for concave applicators and plaques. This research is funded by the customers of the University of Wisconsin Accredited Dosimetry Calibration Laboratory

Assessment of ocular beta radiation dose distribution due to 106Ru/106Rh brachytherapy applicators using MCNPX Monte Carlo code

Purpose: Melanoma at the choroid region is the most common primary cancer that affects the eye in adult patients. Concave ophthalmic applicators with 106 Ru/ 106 Rh beta sources are the more used for treatment of these eye lesions, mainly lesions with small and medium dimensions. The available treatment planning system for 106 Ru applicators is based on dose distributions on a homogeneous water sphere eye model, resulting in a lack of data in the literature of dose distributions in the eye radiosensitive structures, information that may be crucial to improve the treatment planning process, aiming the maintenance of visual acuity. Methods : The Monte Carlo code MCNPX was used to calculate the dose distribution in a complete mathematical model of the human eye containing a choroid melanoma; considering the eye actual dimensions and its various component structures, due to an ophthalmic brachytherapy treatment, using 106 Ru/ 106 Rh beta-ray sources. Two possibilities were analyzed; a simple water eye and a heterogeneous eye considering all its structures. Two concave applicators, CCA and CCB manufactured by BEBIG and a complete mathematical model of the human eye were modeled using the MCNPX code. Results and Conclusion : For both eye models, namely water model and heterogeneous model, mean dose values simulated for the same eye regions are, in general, very similar, excepting for regions very distant from the applicator, where mean dose values are very low, uncertainties are higher and relative differences may reach 20.4%. For the tumor base and the eye structures closest to the applicator, such as sclera, choroid and retina, the maximum difference observed was 4%, presenting the heterogeneous model higher mean dose values. For the other eye regions, the higher doses were obtained when the homogeneous water eye model is taken into consideration. Mean dose distributions determined for the homogeneous water eye model are similar to those obtained for the heterogeneous eye model, indicating that the homogeneous water eye model is a reasonable one. The determined isodose curves give a good visualization of dose distributions inside the eye structures, pointing out their most exposed volume. Cite this article as: Barbosa NA, da Rosa LAR, de Menezes AF, Reis JP, Facure A, Braz D. Assessment of ocular beta radiation dose distribution due to 106Ru/106Rh brachytherapy applicators using MCNPX Monte Carlo code. Int J Cancer Ther Oncol 2014; 2 (3):02038. DOI : 10.14319/ijcto.0203.8

Calculation of dose distributions for 12 106Ru/106Rh ophthalmic applicator models with the PENELOPE Monte Carlo code

For decades, (106)Ru/(106)Rh ophthalmic applicators have been widely used to treat intraocular malignancies with good clinical outcomes. Determining the dosimetry of such applicators is challenging because of their spherical shape, the low range of emitted betas and the steep gradients involved. Furthermore, there is a lack of dose distribution data in the literature for some applicator models. It is crucial to understand the generated dose distributions to improve the treatment planning process. This study aims to calculate the dose distributions in water for 12 commercially available (106)Ru/(106)Rh ophthalmic applicators. The applicators were modeled using the Monte Carlo (MC) code PENELOPE-2008.1. A planar nonclinical applicator was also simulated. Depth-dose profiles along the central axis and lateral dose profiles at several depths were calculated and compared with the available published measured and calculated data. In the absence of published data, measurements performed by the manufacturer were used. For some applicators, the calculated results obtained in this work showed improved consistency with the available experimental data compared with previously published calculations. For others, the data calculated in this work represent the first published dose data. The MC code PENELOPE-2008.1 can accurately calculate the dose distributions for (106)Ru/(106)Rh ophthalmic applicators. The obtained set of tabulated dose distribution values may be useful for quality assurance of treatment planning systems and as a reference for comparison with future measurements and calculations.

SU‐E‐T‐355: A Novel Ophthalmic Applicator Design for Brachytherapy for Conjunctival Melanoma

Purpose: To design and construct a novel ophthalmic brachytherapy applicator for the treatment of conjunctival melanoma using I‐125 radioactive seed sources to overcome the dosimetric limitations of the commonly used standard Collaborative Ocular Melanoma Study (COMS) plaques. Methods: A commercially available polymethylmethacrylate conformer (Gulden Ophtalmics, Elkins Park, PA) was employed to hold a total of 12 low dose I‐125 seeds (model IAI‐125A, IsoAid, LLC, Port Richey, FL) distributed along the periphery of the conformer. Three dimensional dose distribution was calculated using the Plaque Simulator software (EyePhysics, LLC, Los Alamitos, CA) to optimize seed distribution pattern. The AAPM TG‐43 dose calculation formulism was utilized within the software. Results: The seed distribution pattern was designed in a way that dose would be delivered to the conjunctival tissue,while limiting the dose to the cornea and lens. Once the design was finalized, each slot for the seed was fabricated using a 6‐axis computer numerical control (CNC) machine available at our institution. The slots were milled into the convex side of the conformer to minimize any patient discomfort and to protect the cornea from direct contact with the seeds. Conclusion: The difficulty of treating conjunctival melanomas with COMS eyeplaques due to its unique anatomical distribution called for a custom design brachytherapy applicator. The applicator designed in the current study can effectively deliver radiation dose to affected area while minimizing the dose to the centrally located unaffected tissues.