Treatment plan optimization and robustness of 106 Ru eye plaque brachytherapy using a novel software tool

Apical dose versus volume dose of Ruthenium-106 brachytherapy for uveal melanoma

OBJECTIVE

Ruthenium-106 brachytherapy is commonly used to treat uveal melanomas. Most centres prescribe a radiation dose to the tumour apex that is calculated with the tumour located in the centre of the plaque. Recent work suggests that D99%-the minimum radiation dose delivered to 99% of tumour volume-may be a better predictor of tumour control than apex dose. Both dosing regimens may be affected by tumour and treatment variables differently. We explored the effect of differences in these variables on volume and apex dose using a 3-dimensional planning model.

METHODS

The time required to deliver 100 Gy to the tumour apices of representative tumours ranging from 2- to 6-mm thickness with central plaque positioning was calculated in Plaque Simulator™. This treatment time was used for further calculations, including D99% with central plaque placement, and apical and tumour volume doses when tumour and plaque characteristics were altered, including eccentric plaque placement, either away from (tilt) or along (offset) scleral surface, tumour shape, and plaque type.

RESULTS

D99% was always greater than the apex dose when plaques were placed centrally, and the difference increased with tumour thickness. Increasing degrees of tumour offset reduced apical dose and D99%, with a greater effect on apical dose for thicker and D99% for thinner tumours, respectively. Differences in tumour shape and plaque type had idiosyncratic effects on apical and volume dosing.

CONCLUSION

D99% and apex dose are affected by tumour and treatment characteristics in different ways, highlighting the complexity of radiation delivery to uveal tumours.

GEC-ESTRO survey of 106Ru eye applicator practice for ocular melanoma - Physicist survey

AIM

106Ru eye plaque brachytherapy (BT, interventional radiotherapy) is an eye-preserving treatment for uveal melanoma performed in about 100 clinics worldwide. Despite this relatively low number, there is a considerable variation in clinical practice. In 2022, the BRAPHYQS and Head & Neck and Skin GEC-ESTRO working groups conducted a survey to map the current clinical practice. The survey consisted of a physicist and a physician part. This paper describes the physicist results. However, three physician questions with overlapping interest are included here as well.

MATERIALS AND METHODS

The survey questions pertained to commissioning and quality control (QC) of the plaques, treatment planning, radiobiological correction, as well as more general questions on practice improvement. The questions overlapping with the physician survey were related to dose prescription and margins.

RESULTS

Sixty-five physicist responses were included. A majority of the centres do not perform an independent measurement of the absorbed dose at reference depth, percentage depth dose (PDD) and off-axis data. A lack of calibration services and suitable equipment are the main reasons. About one third of the centres indicated that they do image based treatment planning. The use of margins and dose prescription showed a large variability, despite the availability of guidelines [1]. Many respondents expressed a strong wish for improvement in a wide range of aspects of clinical practice.

CONCLUSION

The physics survey showed a wide variability regarding quality control of the 106Ru sources and treatment planning practice.

Brachytherapy With 15- Versus 20-mm Ruthenium 106 Plaques Without Verification of Plaque Position Is Associated With Local Tumor Recurrence and Death in Posterior Uveal Melanoma

PURPOSE

Brachytherapy with episcleral plaques is the most common primary tumor treatment for uveal melanoma. This study aimed to compare the risk of tumor recurrence and metastatic death between 2 frequently used ruthenium 106 plaque designs: CCB (20.2 mm) and CCA (15.3 mm).

METHODS AND MATERIALS

Data were obtained from 1387 consecutive patients treated at St. Erik Eye Hospital, Stockholm, Sweden between 1981 and 2022 (439 with CCA and 948 with CCB plaques). During the period, scleral transillumination was performed to delineate tumor margins before plaque insertion, but accurate plaque positioning was not verified after scleral attachment, and no minimum scleral dose was used.

RESULTS

Patients treated with CCA plaques had smaller tumors than those treated with CCB plaques (mean diameter, 8.6 vs 10.5 mm; P < .001). There were no differences in patient sex, age, tumor distance to the optic disc, tumor apex dose, dose rate, or in rates of ciliary body involvement, eccentric plaque placement, or adjunct transpupillary thermotherapy (TTT). The average difference between plaque and tumor diameter was greater with the CCB plaque, and a smaller difference was an independent predictor of tumor recurrence. The 15-year incidence of tumor recurrence was 28% and 15% after treatment with CCA and CCB plaques, respectively (competing risk analysis, P < .001). Multivariate Cox regression analysis revealed a lower risk for tumor recurrence with CCB plaques (hazard ratio, 0.50). Similarly, patients treated with CCB plaques had a lower risk for uveal melanoma-related mortality (hazard ratio, 0.77). The risk for either outcome was not lower for patients treated with adjunct TTT. Uni- and multivariate time-dependent Cox regressions demonstrated that tumor recurrence was associated with uveal melanoma-related and all-cause mortality.

CONCLUSIONS

Compared with 20-mm plaques, brachytherapy with 15-mm ruthenium plaques is associated with a higher risk for tumor recurrence and death. These adverse outcomes may be avoided by increasing safety margins and implementing effective methods to verify accurate plaque positioning.

Individualized dosimetry in Ru-106 ophthalmic brachytherapy based on MRI-derived ocular anatomical parameters

PURPOSE

To estimate ocular geometry-related inaccuracies of the dosimetric plan in Ru-106 ophthalmic brachytherapy.

METHODS AND MATERIALS

Thirty patients with intraocular lesions were treated with brachytherapy using a Ru-106 plaque-shell of inner radius of 12 mm. Magnetic resonance imaging was employed to determine the external scleral radius at tumor site and the tumor margins. A mathematical model was developed to determine the distance between the external sclera and the internal surface of the plaque associated with the tangential application of the plaque on the treated eye. Differences in delivered dose to the tumor apex, sclera and tumor margins as derived by considering the default eye-globe of standard size (external sclera radius = 12 mm) against the individual-specific eye globe were determined.

RESULTS

The radius of external sclera at the tumor site was found to range between 10.90 and 13.05 mm for the patient cohort studied. When the patient specific eye-globe/tumor geometry is not taken into account, the delivered dose was found to be overestimated by 8.1% ± 4.1% (max = 15.3%) at tumor apex, by 1.5% ± 2.8% (max = 5.7%) at anterior tumor margin, by 16.6% ± 7.5% (max = 36.4%) at posterior tumor margin and 8.1% ± 3.8% (max = 13.2%) at central sclera of eyes with lower than the default radius. The corresponding dose overestimations for eyes with higher than the default radius was 13.5% ± 4.3% (max = 22.3%), 1.5% ± 2.8% (max = 5.7%), 12.6% ± 4.5% (max = 20.0%), and 15.1% ± 5.0% (max = 24.4%).

CONCLUSIONS

The proposed patient-specific approach for Ru-106 brachytherapy treatment planning may improve dosimetric accuracy. Individualized treatment planning dosimetry may prevent undertreatment of intraocular tumors especially for highly myopic or hyperopic eyes.

Automatic Three-Dimensional Magnetic Resonance-based measurements of tumour prominence and basal diameter for treatment planning of uveal melanoma

Background and Purpose

Three-dimensional (3D) Magnetic Resonance Imaging (MRI) is increasingly used to complement conventional two-dimensional ultrasound in the assessment of tumour dimension measurement of uveal melanoma. However, the lack of definitions of the 3D measurements of these tumour dimensions hinders further adaptation of MRI in ocular radiotherapy planning. In this study, we composed 3D MR-based definitions of tumour prominence and basal diameter and compared them to conventional ultrasound.

Materials and methods

Tumours were delineated on 3DT2 and contrast-enhanced 3DT1 (T1gd) MRI for 25 patients. 3D definitions of tumour prominence and diameter were composed and evaluated automatically on the T1gd and T2 contours. Automatic T1gd measurements were compared to manual MRI measurements, to automatic T2 measurements and to manual ultrasound measurements.

Results

Prominence measurements were similar for all modalities (median absolute difference 0.3 mm). Automatic T1gd diameter measurements were generally larger than manual MRI, automatic T2 and manual ultrasound measurements (median absolute differences of 0.5, 1.6 and 1.1 mm respectively), mainly due to difficulty defining the axis of the largest diameter. Largest differences between ultrasound and MRI for both prominence and diameter were found in anteriorly located tumours (up to 1.6 and 4.5 mm respectively), for which the tumour extent could not entirely be visualized with ultrasound.

Conclusions

The proposed 3D definitions for tumour prominence and diameter agreed well with ultrasound measurements for tumours for which the extent was visible on ultrasound. 3D MRI measurements generally provided larger diameter measurements than ultrasound. In anteriorly located tumours, the MRI measurements were considered more accurate than conventional ultrasound.

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.

Surface dose rate variations in planar and curved geometries of 106Ru/106Rh plaque sources for ocular tumors

PURPOSE

Investigation of surface dose rate variation with respect to the source configuration of ¹⁰⁶Ru/¹⁰⁶Rh eye plaque. To explore an alternate way to determine activity of brachytherapy plaques.

METHODS

The surface dose rates of ¹⁰⁶Ru/¹⁰⁶Rh plaque developed indigenously were measured by extrapolation chamber. To rule out possibility of any error in the activity distribution and quantity, same source was used in two different configurations namely planar and curved. EBT3 Gafchromic film was used for determination of uniformity in activity. Monte Carlo-based Codes EGSnrc and FLUKA were used to calculate dose rate in tissue, percentage depth dose and for determination of activity. Parameters and correction factors were estimated using simulations.

RESULTS

The measured reference absorbed dose rates for planar and curved ¹⁰⁶Ru/¹⁰⁶Rh eye plaques are found to be 589 ± 29 mGy/h and 560 ± 28 mGy/h, respectively. The difference in the reference absorbed dose rate of curved eye plaque is about ~5% as compared to planar configuration. The FLUKA-calculated dose values are almost independent of cavity length of the extrapolation chamber for both eye plaques. The FLUKA-based dose rates per μCi ¹⁰⁶Ru/¹⁰⁶Rh are about 17.28 ± 0.08 mGy/h and 16.48 ± 0.06 mGy/h, respectively for planar and curved eye plaques which match well with the measurements. The calculated activities for planar and curved eye plaques are 34.08 μCi and 33.98 μCi, respectively.

CONCLUSIONS

Surface dose rates for a prototype ¹⁰⁶Ru/¹⁰⁶Rh eye plaque with different configurations were estimated using simulations and measured experimentally. An alternate way to determine activity of beta-gamma brachytherapy plaque has been proposed.

3D image-guided treatment planning for Ruthenium-106 brachytherapy of choroidal melanomas

BACKGROUND

Current standard treatment procedures for Ruthenium-106 (Ru-106) brachytherapy for choroidal melanomas do not use 3D image-guided treatment planning. We evaluated the potential impact of introducing 3D treatment planning and quantified the theoretical clinical benefits in terms of tumour control probability (TCP) and normal tissue complication probability (NTCP).

MATERIALS AND METHODS

Treatment plans for thirty-two patients were optimized using 3D image-guided treatment planning and compared to the original 2D clinical plans. Optimization of plans was done in an image-based treatment planning system by optimizing the plaque position and treatment time such that the entire tumour received the prescribed dose of 100 Gy. TCP and NTCP for 2D clinical plans and optimized 3D image-guided plans were estimated from published outcome prediction models and compared within patients using Wilcoxon signed-rank test.

RESULTS

The median minimum tumour dose (D_99% ) for 2D clinical plans was 93 Gy (range: 23-158 Gy), corresponding to 5-year TCP of 75% (IQR 61-86%), while median tumour D_99% for optimized 3D image-guided plans was 115 Gy (range 103-141 Gy), corresponding to TCP of 82% (IQR 80-84%). This was a statistically significant increase in estimated TCP (median increase in TCP 8% (IQR: -5-23, p = 0.006). While the dose to normal tissue increased somewhat, there was no significant change in NTCP.

CONCLUSION

3D treatment planning theoretically allows for improved tumour dose delivery for Ru-106 brachytherapy of choroidal melanomas, resulting in a significant increase in expected tumour control compared to traditional approaches using 2D calculations. The deliverability of optimized plans, and potential increased risk of late complications, will have to be confirmed in future clinical studies.

Tumour control probability after Ruthenium-106 brachytherapy for choroidal melanomas

Purpose: Ruthenium-106 (Ru-106) brachytherapy is a common eye-preserving treatment for choroidal melanomas. However, a dose-response model describing the relationship between the actual delivered tumour dose and tumour control has, to the best of our knowledge, not previously been quantified for Ru-106 brachytherapy; we aimed to rectify this.Material and methods: We considered consecutive patients with primary choroidal melanomas, treated with Ru-106 brachytherapy (2005-2014). Dosimetric plans were retrospectively recreated using 3D image-guided planning software. Pre-treatment fundus photographies were used to contour the tumour; post-treatment photographies to determine the accurate plaque position. Patient and tumour characteristics, treatment details, dose volume histograms, and clinical outcomes were extracted. Median follow-up was 5.0 years. The relationship between tumour dose and risk of local recurrence was examined using multivariate Cox regression modelling, with minimum physical tumour dose (D99%) as primary dose metric.Results: We included 227 patients with median tumour height and largest base dimension of 4 mm (range 1-12, IQR 3-6) and 11 mm (range 4-23, IQR 9-13). The estimated 3 year local control was 82% (95% CI 77-88). Median D99% was 105 Gy (range 6-783, IQR 65-138); this was the most significant factor associated with recurrence (p < .0001), although tumour height, combined TTT and Ru-106 brachytherapy, and sex were also significant. The hazard ratio (HR) for a 10 Gy increase in D99% was 0.87 (95% CI 0.82-0.93). Using biological effective dose in the model resulted in no substantial difference in dose dependence estimates. Robustness cheques with D1-99% showed D99% to be the most significant dose metric for local recurrence.Conclusion: The minimum tumour dose correlated strongly with risk of tumour recurrence, with 100 Gy needed to ensure at least 84% local control at 3 years.

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.