EyeDose: An open-source tool for using published Monte Carlo results to estimate the radiation dose delivered to the tumor and critical ocular structures for 125I Collaborative Ocular Melanoma Study eye plaques

A practical method of estimating medium-heterogeneity corrected dose without a Monte Carlo calculation in ocular brachytherapy using 125I COMS plaques

PURPOSE

To provide a practical method of estimating medium-heterogeneity corrected dose without a Monte Carlo (MC) calculation in ocular brachytherapy using 125I Collaborative Ocular Melanoma Study (COMS) plaques.

METHODS AND MATERIALS

Using egs_brachy, MC simulations (1) under task group-43 assumptions with fully loaded seed configurations in water (HOMO) and (2) with effects of plaque backing, insert and inter-seed interactions (HETERO) were performed for seven 125I COMS plaques (10 mm-22 mm in diameter), and homogeneous dose (DHOMO) and heterogeneous dose (DHETERO) for central-axis and off-axis points were determined. For DHOMO, 85 Gy was normalized to a depth of 5 mm. Central-axis heterogeneity correction factors (HCFs) from a depth of 0 mm (inner sclera) to 22 mm (opposite retina) were derived from a ratio of DHETERO to DHOMO. Off-axis HCFs for optic disc/macula and lens as a function of distance from optic disc/macula (DT/MT) for various basal dimensions of tumor (BD/BM) were derived from DHETERO/DHOMO.

RESULTS

Central-axis HCF varied with a dose reduction of 10.3-19.8% by heterogeneity. Off-axis HCF for optic disc/macula varied significantly depending on DT/MT and BD/BM with a dose reduction of 11.3-38.3%. Off-axis HCF for lens had a dependence on MT and BM with its variation of 11.0-19.0%. A clinical example of using HCFs to estimate DHETERO was presented.

CONCLUSIONS

The practical method of using depth-dependent central-axis HCF and DT/MT- and BD/BM-dependent off-axis HCF provided in this study will facilitate a heterogeneous dose estimate for 125I COMS plaques without MC calculations.

Central subfield thickness predicts visual acuity outcomes in plaque-irradiated eyes with choroidal melanoma

OBJECTIVE

To determine the association between pre-operative central subfield thickness (CST) and post-radiotherapy visual acuity (VA), cystoid macular edema (CME), and intravitreal anti-vascular endothelial growth factor (VEGF) requirement.

DESIGN

Single-center retrospective study.

PARTICIPANTS

Patients with plaque-irradiated extramacular choroidal melanoma treated between 11/11/2011 and 4/30/2021. Pre-operative CST difference between the affected and unaffected eye was used. Kaplan-Meier analysis and hazard ratios were calculated.

RESULTS

Of 85 patients, pre-operative CST was greater in the melanoma-affected eye (vs. fellow eye) by mean of 20.4 μm (median 14.0, range - 60.0-182.0). Greater CST at presentation (vs. fellow eye) was associated with larger tumor diameter (p = 0.02), greater tumor thickness (p < 0.001), and more frequent tumor-related Bruch's membrane rupture (p = 0.006). On univariate analysis of outcome data, greater CST at presentation (vs. fellow eye) was associated with higher 5-year risk (1.09 [1.02-1.17], p = 0.02) of VA 20/200 or worse and increased (1.10 [1.01-1.20], p = 0.03) likelihood for anti-VEGF injections after plaque irradiation. There was no significant association with CME. The association between CST and VA outcome remained significant on multivariate analysis accounting for impact of tumor thickness and radiation dose to optic disc, while tumor distance to fovea was the only significant factor on multivariate analysis for anti-VEGF injections.

CONCLUSION

Greater CST at presentation (vs. fellow eye) was associated with worse VA outcome following plaque radiotherapy for choroidal melanoma. Large-sized tumors may contribute to a higher intraocular VEGF burden, potentially leading to greater preoperative CST, which correlates with poor VA outcome post-plaque radiotherapy.

Current and Emerging Radiotherapy Options for Uveal Melanoma

What treatment options are there for patients having uveal melanoma? A randomized, prospective, multi-institutional clinical trial (COMS) showed no difference in survival between brachytherapy and enucleation for medium-sized lesions. With the obvious benefit of retaining the eye, brachytherapy has flourished and many different approaches have been developed such as low-dose-rate sources using alternate low-energy photon-emitting radionuclides, different plaque designs and seed-loading techniques, high-dose-rate brachytherapy sources and applicators, and low- and high-dose-rate beta-emitting sources and applicators. There also have been developments of other radiation modalities like external-beam radiotherapy using linear accelerators with high-energy photons, particle accelerators for protons, and gamma stereotactic radiosurgery. This article examines the dosimetric properties, targeting capabilities, and outcomes of these approaches. The several modalities examined herein have differing attributes and it may be that no single approach would be considered optimal for all patients and all lesion characteristics.

How to design, fabricate, and validate a customized COMS-style eye plaque: Illustrated with a narrow-slotted plaque example

PURPOSE

A customized Collaborative Ocular Melanoma Study (COMS)-style eye plaque may provide superior dosimetric coverage compared with standard models for certain intraocular tumor locations and shapes. This work provides a recipe for developing and validating such customized plaques.

METHODS AND MATERIALS

The concept-into-clinical treatment process for a customized COMS-style eye plaque begins with a CAD model design that meets the specifications of the radiation oncologist and surgeon based on magnetic resonance, ultrasound, and clinical measurements, as well as a TG-43 hybrid heterogeneity-corrected dose prediction to model the dose distribution. Next, a 3D printed plastic prototype is created and reviewed. After design approval, a Modulay plaque is commercially fabricated. Quality assurance (QA) is subsequently performed to verify the physical measurements of the Modulay and Silastic and also includes dosimetric measurement of the calibration, depth dose, and dose profiles. Sterilization instructions are provided by the commercial fabricator. This customization procedure and QA methodology is demonstrated with a narrow-slotted plaque that was recently constructed for the treatment of a circumpapillary (e.g., surrounding the optic disk) ocular tumor.

RESULTS

The production of a customized COMS-style eye plaque is a multistep process. Dosimetric modeling is recommended to ensure that the design will meet the patient's needs, and QA is essential to confirm that the plaque has the proper dimensions and dose distribution. The customized narrow-slotted plaque presented herein was successfully implemented in the clinic, and provided superior dose coverage of juxtapapillary and circumpapillary tumors compared with standard or notched COMS-style plaques. Plaque development required approximately 30 h of physicist time and a fabrication cost of $1500.

CONCLUSION

Customized eye plaques may be used to treat intraocular tumors that cannot be adequately managed with standard models. The procedure by which a customized COMS-style plaque may be designed, fabricated, and validated was presented along with a clinical example.