23-mm iodine-125 plaque for uveal melanoma: benefit of vitrectomy and silicone oil on visual acuity

Wolfram-silicone implants as effective radiation shielding for ocular brachytherapy: dosimetric features and in vivo animal study on biocompatibility

OBJECTIVE

To evaluate wolfram as a photon and beta absorber in the management of uveal melanoma with radiotherapy, examining its potential ocular adverse effects and physiologic tolerance using an in vivo rabbit ocular model.

METHODS

A method of manufacturing implants from mixtures of wolfram and silicone was developed. Their shielding effect on the radiation of sources used in ocular brachytherapy was investigated by dosimetric measurement in an eye phantom as well as numerical simulations. Different wolfram implantation techniques, such as extraocular fixation of a wolfram-silicone implant (n = 1), vitrectomy with silicone oil and intravitreal injection of a wolfram-silicone oil suspension (n = 2), and concurrent attachment of a wolfram implant onto the sclera (n = 2), were tested to investigate the long-term effects of wolfram. A vitrectomy with silicone oil without wolfram implantation was carried out in 2 rabbits (n = 2), constituting the control group. The eyes were enucleated after 3 months for histologic analysis.

RESULTS

Wolfram-silicone mixtures have been dosimetrically proven to be very effective radiation absorbers for use in ocular brachytherapy. Severe complications, such as endophthalmitis, secondary glaucoma, cornea decompensation, and vessel occlusion, were not documented in the tested rabbit eyes after the application of wolfram. Histologic examination of the bulbi after enucleation showed epiretinal gliosis without further pathologic findings in all eyes after vitrectomy.

CONCLUSIONS

The results of this study show that wolfram and wolfram-silicone implants constitute a promising candidate as potential radiation shielding substrates.

Ocular Brachytherapy (Interventional Radiotherapy): Preserving the Vision

Uveal melanoma represents the most common intraocular neoplasia among adults. Brachytherapy (interventional radiotherapy; IRT) has a great advantage, when compared with enucleation, both in terms of organ and function sparing. The Collaborative Ocular Melanoma Study introduced into clinical practice a standardised procedure that allowed the equivalence of IRT with enucleation in terms of overall survival to be demonstrated. IRT is carried out by placing a plaque in direct contact with the sclera under the uveal melanoma. Several radioactive sources may be used, including 106-ruthenium, 125-iodine, 103-palladium and 90-strontium. It is a multidisciplinary procedure requiring the collaboration of interventional radiation oncologists and ophthalmologists in the operating theatre and medical physicists for an accurate treatment time calculation. It also relies on ultrasound imaging to identify the lesion and verifiy the correct plaque placement. An emerging tool of paramount importance could be the use of artificial intelligence and predictive models to identify those patients at higher risk of developing late side-effects and therefore who may deserve preventive and supportive therapies.

Radiobiological evaluation of organs at risk for electronic high-dose-rate brachytherapy in uveal melanoma: a radiobiological modeling study

Purpose

The objective of this study was to examine feasibility of single- or hypo-fraction of high-dose-rate (HDR) electronic brachytherapy (eBT) in uveal melanoma treatment.

Material and methods

Biologically effective doses (BED) of organs at risk (OARs) were compared to those of iodine-125-based eye plaque low-dose-rate brachytherapy (¹²⁵I LDR-BT) with vitreous replacement (VR). Single- or hypo-fractionated equivalent physical doses (SFEDs or HFEDs) for tumor were calculated from tumor BED of ¹²⁵I LDR-BT using linear-quadratic (LQ) and universal survival curve (USC) models. BED OARs doses to retina opposite the implant, macula, optic disc, and lens were calculated and compared among SFED, HFED, and ¹²⁵I LDR-BT. Electronic BT of 50 kVp was considered assuming dose fall-off as clinically equivalent to ¹²⁵I LDR-BT. All OARs BEDs were analyzed with and without silicone oil VR.

Results

For a single-fraction incorporating VR, the median/interquartile range of LQ (USC)-based BED doses of the retina opposite the implant, macula, optic disc, and lens were 16%/1.2% (33%/4%), 35%/19.5% (64%/17.7%), 37%/19% (75%/17.8%), and 27%/7.9% (68%/23.2%) of those for ¹²⁵I LDR-BT, respectively. SFED tumor values were 29.8/0.2 Gy and 51.7/0.5 Gy when using LQ and USC models, respectively, which could be delivered within 1 hour. SFED can be delivered within 1 hour using a high-dose-rate eBT. Even four-fraction delivery of HFED without VR resulted in higher OARs doses in the macula, optic disc, and lens (135 ~ 159%) than when using ¹²⁵I LDR-BT technique. A maximum p-value of 0.005 was observed for these distributions.

Conclusions

The simulation of single-fraction eBT, including vitreous replacement, resulted in significantly reduced OARs doses (16 ~ 75%) of that achieved with ¹²⁵I LDR-BT.

Local tumor control and treatment related toxicity after plaque brachytherapy for uveal melanoma: A systematic review and a data pooled analysis

Uveal melanoma (UM) represents the most common primary intraocular tumor, and nowadays eye plaque brachytherapy (EPB) is the most frequently used visual acuity preservation treatment option for small to medium sized UMs. The excellent local tumor control (LTC) rate achieved by EPB may be associated with severe complications and adverse events. Several dosimetric and clinical risk factors for the development of EPB-related ocular morbidity can be identified. However, morbidity predictive models specifically developed for EPB are still scarce. PRISMA methodology was used for the present systematic review of articles indexed in PubMed in the last sixteen years on EPB treatment of UM which aims at determining the major factors affecting local tumor control and ocular morbidities. To our knowledge, for the first time in EPB field, local tumor control probability (TCP) and normal tissue complication probability (NTCP) modelling on pooled clinical outcomes were performed. The analyzed literature (103 studies including 21,263 UM patients) pointed out that Ru-106 EPB provided high local control outcomes while minimizing radiation induced complications. The use of treatment planning systems (TPS) was the most influencing factor for EPB outcomes such as metastasis occurrence, enucleation, and disease specific survival, irrespective of radioactive implant type. TCP and NTCP parameters were successfully extracted for 5-year LTC, cataract and optic neuropathy. In future studies, more consistent recordings of ocular morbidities along with accurate estimation of doses through routine use of TPS are needed to expand and improve the robustness of toxicity risk prediction in EPB.

Silicone Oil and Iodine-125 Brachytherapy for Uveal Melanoma in High-Risk Patients

Purpose

Silicone oil a burgeoning adjuvant in the treatment of uveal melanoma where it is used for tissue protection during I-125 brachytherapy. While risk factors in the development of radiation retinopathy (RR) have been identified, treatment modulation for high-risk patients has largely been overlooked. We seek to expand the literature on this subject by reporting outcomes of I-125 brachytherapy with silicone oil in a high-risk population in the community setting.

Methods

Five patients with uveal melanoma and at least one risk factor for RR development underwent iodine-125 (I-125) plaque brachytherapy with concurrent pars plana vitrectomy (PPV), silicone oil administration, and fine needle aspiration biopsy (FNAB). Plaque and silicone oil removal were performed after seven days. Minimum follow-up was 12 months.

Results

Follow-up ranged from 12 to 56 months. Macular radiation doses ranged from 12.55 to 141.5 Gy; the two eyes with the largest doses developed RR at 34 and 15 months as well as neovascular glaucoma (NVG). Surgical complications included one rhegmatogenous retinal detachment (RD) and an intra-operative vitreous hemorrhage with post-operative hyphema requiring additional intervention.

Conclusion

RR may be attenuated by silicone oil administration in patients with some risk factors. In tumors farther from the macula, this benefit is more readily apparent. Tumors located more posteriorly may not benefit from silicone oil administration considering postoperative complications and operating time. Patient demographics, tumor characteristics, and anticipated macular radiation dosage may help determine which patients can benefit from silicone oil and identify patient risks for adverse outcomes.

A comparison of the shielding effectiveness of silicone oil vitreous substitutes when used with Palladium-103 and Iodine-125 eye plaques

PURPOSE

Episcleral eye plaques provide excellent local control of ocular melanoma, but vision sparing remains a significant problem with 30% or more of patients experiencing significant visual acuity degradation. The use of silicone oil shielding with Iodine-125 plaques has previously been reported to improve critical structure sparing. We hypothesized that the use of Palladium-103 would improve the shielding effectiveness of silicone oil due to the strong energy dependence of the photoelectric effect. This Monte Carlo simulation study reports a comparison of the shielding effects of silicone oil when used in conjunction with Pd-103 and with I-125 plaques.

MATERIALS AND METHODS

GEANT4 was used to simulate eye plaque treatments to an eye with either water-equivalent vitreous humor, or silicone oil in place of the vitreous humor. Two solid gold plaques, 15 and 23 mm, were simulated loaded with I-125 and with Pd-103 source seeds. Seed activity was normalized such that 85 Gy was delivered to the tumor apex in the water-equivalent cases. Tumor apex dose, central axis dose, and inner sclera dose reductions with silicone oil were evaluated.

RESULTS

Silicone oil resulted in an underdosing to the tumor apex of 6.1% and 7.5% in the 15 mm plaque for I-125 and Pd-103, respectively, and 3.4% and 4.3% in the 23 mm plaque for I-125 and Pd-103, respectively. When renormalized to 85 Gy to the tumor apex in all scenarios, silicone oil reduced the dose to the inner sclera 90° from the plaque by 19-32% for the 15 and 23 mm plaques using I-125, and by 33-65% for the 15 and 23 mm plaques using Pd-103.

CONCLUSIONS

The combination of silicone oil and Pd-103 eye plaques offers the potential for greatly improved sparing to normal structures compared to Pd-103 plaques alone or I-125 plaques with or without silicone oil.

Plaque brachytherapy for posterior uveal melanoma in 2018: improved techniques and expanded indications

PURPOSE OF REVIEW

Plaque brachytherapy remains the dominant globe-sparing therapy of uveal melanoma. This report highlights recent advances, which have expanded plaque brachytherapy's uses as well as improved the surgical technique.

RECENT FINDINGS

Plaque brachytherapy is effective for tumors that may previously have demanded enucleation. Plaque brachytherapy can be used to control large melanomas as well as melanomas touching the optic nerve. Improvements in planning and design have made plaque therapy simpler for the surgical operator and may reduce collateral radiation damage to normal ocular structures. The COMS implies a required dose of 85 Gy to the tumor apex for treatment of uveal melanoma. However, multiple reports indicate that lower doses may be equally effective for tumor control while reducing radiation dose to uninvolved structures. Vitreoretinal surgeons can be called upon safely to treat long-term side effects of radiation or tumor death such as intractable vitreous hemorrhage or inflammation. Further, vitreoretinal surgeons have employed tumor endoresection as primary local tumor control or in combination with plaque brachytherapy.

SUMMARY

Plaque brachytherapy for uveal melanoma remains highly effective for local tumor control and prevention of metastasis. Indications for plaque brachytherapy have expanded, and the technique has improved.