Ru-106 Plaque Research Articles

Ru-106 plaque radiotherapy for vasoproliferative tumors of retina: a 15-year single-center experience.

This study evaluates the outcomes of ruthenium-106 (Ru-106) plaque brachytherapy for vasoproliferative tumors (VPTs) of the ocular fundus in a single referral ocular oncology center. The clinical charts of all patients diagnosed with VPT who underwent plaque radiotherapy from 2002 to 2017 were reviewed. Clinical features, types of treatment, outcomes and complications were evaluated. Of 46 patients with VPT diagnosis in our ocular oncology clinic, 25 (54.34%) cases were treated with Ru-106 plaque brachytherapy. Eleven patients (44%) were male, and the mean age at the time of diagnosis was 40.92 ± 13.11years. The mean follow-up time was 47.56 ± 36.87months. Inferotemporal quadrant was the most common site of the tumor (64.00%). The mean delivered apex and scleral dose was 101.56 ± 6.51 and 412.26 ± 113.66 Gray (Gy), respectively. Initial tumor length, width and thickness were 10.26 ± 3.42, 8.05 ± 2.83 and 4.27 ± 1.10mm, respectively. The mean tumor thickness decreased to 2.60 ± 0.63mm, postoperatively. Complete resolution of subretinal fluid around the tumor was achieved in 81.80% of cases. Visual acuity was more than 20/400 in 64% of patients before treatment and 60% of patients at last follow-up. Our study showed that Ru-106 plaque radiotherapy is an effective and safe method of treatment in VPTs.

Dual-energy CT imaging of orbits during episcleral brachytherapy with Ru-106 plaques: A phantom study on its potential for plaque position verification

PurposeTo investigate the potential of dual energy CT (DECT) to suppress metal artifacts and accurately depict episcleral brachytherapy Ru-106 plaques after surgical placement. MethodsAn anthropomorphic phantom simulating the adult head after surgical placement of a Ru-106 plaque was employed. Nine DECT acquisition protocols for orbital imaging were applied. Monochromatic 140 keV images were generated using iterative reconstruction and an available metal artifact reduction algorithm. Generated image datasets were graded by four observers regarding the ability to accurate demarcate the Ru-106 plaque. Objective image quality and visual grading analysis (VGA) was performed to compare different acquisition protocols. The DECT imaging protocol which allowed accurate plaque demarcation at minimum exposure was identified. The eye-lens dose from orbital DECT, with and without the use of radioprotective bismuth eye-shields, was determined using Monte Carlo methods. ResultsAll DECT acquisition protocols were judged to allow clear demarcation of the plaque borders despite some moderate streaking/shading artifacts. The differences between mean observers’ VGA scores for the 9 DECT imaging protocols were not statistically significant (p > 0.05). The eye-lens dose from the proposed low-exposure DECT protocol was found to be 20.1 and 22.8 mGy for the treated and the healthy eye, respectively. Bismuth shielding was found to accomplish >40% reduction in eye-lens dose without inducing shielding-related artifacts that obscure plaque delineation. ConclusionsDECT imaging of orbits after Ru-106 plaque positioning for ocular brachytherapy was found to allow artifact-free delineation of plaque margins at relatively low patient exposure, providing the potential for post-surgery plaque position verification.

High-dose ruthenium-106 plaque therapy for circumscribed choroidal hemangioma: a retrospective study of 25 Chinese patients.

To evaluate the efficacy and safety of ruthenium-106 (106Ru) plaque radiotherapy at a dose (>50 Gy) higher than recommended (29-50 Gy) for treatment of circumscribed choroidal hemangioma (CCH) in Chinese patients. This retrospective study included 25 symptomatic CCH patients undergoing 106Ru plaque brachytherapy involving 25 eyes between January 2005 and August 2016. Ophthalmic examination was performed at the baseline and at each post-treatment follow-up visit, using best-corrected visual acuity (BCVA), dilated fundus examination, and B-scan ultrasonography. The primary efficacy outcome measures included the changes in BCVA and hemangioma dimensions at the last followup visit from the baseline. The mean follow-up duration was 28.0±26.6 (range, 12-110)mo. All the hemangiomas were located in the posterior pole except for two involving the fovea. The mean apex dose of 106Ru plaque radiotherapy was 84.4±19.7 Gy. The mean BCVA improved from 41.4±29.3 (0-97) at the baseline to 53.0±33.8 (0-97) ETDRS letters at the last visit (P=0.01). The mean hemangioma height declined from 3.98±0.88 (2.40-5.50) mm to 0.84±1.63 (0-6.47) mm (P≤0.001), and the greatest linear diameter (GLD) reduced from 9.36±2.23 (6.80-15.00) to 7.40±2.45 (0-13.00) mm (P≤0.001). Hemangioma size increased in one (4%) eye with a worsened vision, and subretinal fluid completely resolved in all but one patient (4%). Radiation-related retinopathy was observed in two patients at post-treatment 9 and 11mo, respectively. 106Ru plaque brachytherapy at a dose (>50 Gy) higher than recommended (29-50 Gy) is an effective treatment regimen for symptomatic CCH associated with significantly improved visual acuity and a favorable safety profile in Chinese patients.

Comparison of Iodide-125 and Ruthenium-106 Brachytherapy in the Treatment of Choroidal Melanomas.

BackgroundTo compare iodine-125 (125I) with ruthenium-106 (106Ru) episcleral plaque radiation therapy in terms of the effectiveness and non-inferiority for choroidal melanoma treatment.ObjectiveTo report the non-inferiority of new made iodine-125 (125I) compared with ruthenium-106 (106Ru) episcleral plaque radiation.Patients and MethodsA retrospective, non-randomized comparative case series. In this series the patients treated with 125I and 106Ru episcleral plaques for choroidal melanoma between September 2013 and August 2017 at Farabi Hospital are compared. Local control of choroidal melanomas after 125I and 106Ru plaques implantation and vision changes are the main outcome measures.ResultsA total of 35 patients were identified (125I = 15, 106Ru = 20). No significant difference between two groups in visual acuity, diameter and thickness changes were observed after treatment. Multivariate linear regression (MLR) analysis showed that final diameter was only, independently and significantly, correlated with the pre-treatment diameter of the tumor (β = 0.59, 95% confidence interval [CI]: 0.29, 1.34, P = 0.003). The same MLR analysis for the final thickness and visual acuity, after adjusting for age and sex showed no significant difference between two groups. A single patient treated with 106Ru had local tumor recurrence with no one in the 125I group. No statistical difference in the rate of ocular complications was observed.ConclusionThe treatment with our 125I plaques is as effective as 106Ru plaques in controlling choroidal melanoma tumor and preserving the vision during the two and half year of follow-up. The complication rates are alike. It means that the effectiveness of 125I is not only comparable to 106Ru but also superior when the outcome of the interest is the thickness of the tumors.

AVATAR: Analysis for Visual Acuity Prediction After Eye Interventional Radiotherapy.

The aim of this study was to detect clinical factors predictive of loss of visual acuity after treatment in order to develop a predictive model to help identify patients at risk of visual loss. This was a retrospective review of patients who underwent interventional radiotherapy (brachytherapy) with 106Ru plaque for primary uveal melanoma. A predictive nomogram for visual acuity loss at 3 years from treatment was developed. A total of 152 patients were selected for the study. The actuarial probability of conservation of 20/40 vision or better was 0.74 at 1 year, 0.59 at 3 years, and 0.54 at 5 years after treatment. Factors positively correlated with loss of visual acuity included: age at start of treatment (p=0.004) and longitudinal basal diameter (p=0.057), while distance of the posterior margin of the tumor from the foveola was inversely correlated (p=0.0007). We identified risk factors affecting visual function and developed a predictive model and decision support tool (AVATAR nomogram).

Fundus Autofluorescence Change as an Early Indicator of Treatment Effect of Brachytherapy for Choroidal Melanomas

Background: Early confirmation of the effect of brachytherapy for choroidal melanoma showing that tumour coverage is valuable. The irradiated retinal pigment epithelium (RPE) commonly develops atrophy. This study compares the fundus autofluorescence (AF) changes to the development of RPE atrophy following brachytherapy. Methods: Retrospective study of 19 patients treated with ¹⁰⁶Ru and 2 with ¹²⁵I plaques with either a 3- or 6-month follow-up period. Ultra-widefield (UW) composite colour and AF images were obtained with Optomap 200Tx and interpreted as complete, partial, or no RPE changes and complete or partial hyperautofluorescence, hypoautofluorescence, or isoautofluorescence. Results: At the 3-month follow-up, 9 of 13 patients (69%) (95% confidence interval [CI], 0.389–0.896) treated with ¹⁰⁶Ru plaques developed complete homogenous hyperautofluorescence surrounding the tumour, but only 1 of 13 (8%) (95% CI, 0.004–0.379) developed complete RPE atrophy at the same time point. Six patients in the ¹⁰⁶Ru plaque group had their first follow-up with UW imaging at 6 months. Four of them developed homogenous hyperautofluorescence and none developed complete RPE atrophy around the tumour. The 2 patients treated with ¹²⁵I did not demonstrate any clear RPE or AF changes. Conclusion: The effect of ¹⁰⁶Ru plaque treatment on fundus UW imaging is detected as homogenous and well-demarcated hyperautofluorescence before visible RPE atrophy.

PO-1045 Retreatment using Ru-106 or I-125 plaque in uveal melanoma locally recurrent after brachytherapy

PO-1045 Retreatment using Ru-106 or I-125 plaque in uveal melanoma locally recurrent after brachytherapy

95. Pre and Post-Operative Radiation Protection in Ru-106 Opthalmic Brachytherapy

Purpose The use of 106Ru plaque was introduced for choroidal melanomas therapy. The aim of this study is workers and public exposure evaluation, in pre and post-operative phase of the treated patient. In particular attenuation properties of selected shielding materials and exposure levels around patient head and transport/sterilisation safety containers are reported. Methods Exposure was measured around the head of five patients, in multiple positions at various distances from the skin. Dose rates around the transport/sterilisation container were also measured. Attenuation measurements were performed simulating the eye with a 25mm diameter plastic sphere, filled with water and the plaque attached on it. All measurements were performed with a calibrated instrumentations. Selected materials attenuation properties were measured in “narrow” beam mode (IEC 61331-1:2014). A custom code was developed to perform numerical simulation of BS spectrum. Results In Table HVLs and TVLs for selected materials and the average exposure levels (±SD) measured around patients are reported. Five positions around the head, at 10 cm distance from the skin were considered, plus two positions at 1m. Exposure levels around the transport container are nearly constant for any given direction; average values is 1.6 μSv/h/MBq at contact and 0.013 μSv/h/MBq at 1 m. Conclusions Considering typical activity of the implanted plaques, and conservative recovery and assistance times, up to 60 patients may be treated in a year, without exceeding 1mSv/y for post-operative activities. For the same number of patients, even considering a 8 hours/day standing at 1.5 m from the patient bed, the worker received dose is around 0.65 mSv/y. Attenuation properties for selected materials were measured and agree with simulated results. Main contribution to exposure comes from X- γ radiation, BS is almost negligible from radiation protection point of view.

TCP and Dose Response after Brachytherapy for Choroidal Melanoma

Brachytherapy is a commonly used eye-preserving treatment for choroidal melanomas. We hypothesized that the minimum tumor dose is related to risk of tumor recurrence. We studied consecutive patients with primary choroidal melanomas, treated with Ru-106 plaque brachytherapy from 2005 to 2014 at a single institution to an apical dose of 100 Gy. Plans were retrospectively created using 3D image-guided planning software. Pretreatment retinographies were used to contour the tumor; posttreatment retinographies to determine the accurate plaque position. Dose volume histograms were extracted. Patient and tumor characteristics, treatment details, and clinical outcomes were extracted from patient records. All patients were followed regularly until death or study cut-off (Jan 2018). Biologically effective doses (BED) were calculated using source half times, tissue specific factors (α/β=11.5 Gy, T1/2=1.5h), and a well-established model (Gagne et al, Med Phys, 2012) The relationship between tumor dose and risk of recurrence was examined using multivariate Cox regression modelling. Minimum physical dose to the tumor (D99%), transpupillary thermotherapy (TTT), tumor height, largest base dimension, incident eye, and gender were included in the model. Model robustness was assessed by considering alternative dose metrics, BED, and by taking the competing risk of death and TTT during follow-up into account (Aalen-Johansen estimator for cumulative incidence and Fine & Gray’s model for regression analysis). We included 227 patients (108 females, 110 right eyes), with median treatment time of 120h (IQR: 74-191). Median tumor height and largest base dimension were 4 mm (IQR: 3-6) and 11 mm (IQR: 9-13). Median follow-up time was 4.9 years. The estimated 3-year local control was 80% (95% CI: 75-86). The median D99% was 104 Gy (IQR: 63-138); this was the only significant factor associated with recurrence in multivariate modelling (p=0.0007). Hazard ratio (HR) for 10 Gy increase in D99% was 0.90 (95% CI:0.84-0.96). Estimated 3-year local control for D99%=50 Gy and D99%=100 Gy were 70% (95% CI: 58-85) and 81% (95% CI: 73-91), respectively. The median BED99% was 145 Gy (IQR: 73-196); using BED99% in the multivariate model gave no substantial differences in estimates (HR 0.93 (95% CI: 0.90-0.97, p=0.001). Robustness checks with D1-99% and BED1-99% showed D99% and BED99% to be the most significant dose metrics for recurrence. Competing risk analysis showed cumulative incidences at 3 years for recurrence, death, and TTT of 17% (95% CI: 12-22), 14% (95 % CI: 9-18), and TTT 6% (95% CI: 3-9). Accounting for death and TTT, D99% remained the only significant factor for recurrence (p=0.0004), with HR for 10 Gy increase in D99% of 0.90 (95% CI: 0.85-0.95). The minimum dose to the tumor correlated strongly with risk of tumor recurrence, with 100 Gy needed to ensure at least 80% local control at 3-years.

Monte Carlo Simulation of the Treatment of Uveal Melanoma Using Measured Heterogeneous 106Ru Plaques

Background/Aims: Ruthenium plaques are used for the treatment of ocular tumors. The aim of this work is the comparison between simulated absorbed dose distributions tallied in an anthropomorphic phantom, obtained from ideal homogeneous plaques, and real eye plaques in which the actual heterogeneous distribution of ¹⁰⁶Ru was measured. The placement of the plaques with respect to the tumor location was taken into consideration to optimize the effectiveness of the treatment. Methods: The generic CCA and CCB, and the specific CCA1364 and CCB1256 ¹⁰⁶Ru eye plaques were modeled with the Monte Carlo code PENELOPE. To compare the suitability of each treatment for an anterior, equatorial and posterior tumor location, cumulative dose-volume histograms for the tumors and structures at risk were calculated. Results: Eccentric placements of the plaques, taking into account the inhomogeneities of the emitter map, can substantially reduce the dose delivered to structures at risk while maintaining the prescribed dose at the tumor apex. Conclusions: The emitter map distribution of the plaque and the computerized tomography of the patient used in a Monte Carlo simulation allow an accurate determination of the plaque position with respect to the tumor with the potential to reduce the dose to sensitive structures.

P216] Dosimetric study of several beta-emitting ophthalmic plaques with different plaque materials, by Monte Carlo simulation

Purpose Dosimetric investigation of brachytherapy eye plaques (based on CCB, COB and CIB models) for different coated radionuclides and different plaque materials for the treatment of uveal melanoma. Methods An eye model (including cornea, lens, optic nerve and tumor) and a plaque (with 0.1 mm window, 0.2 mm radionuclide coated foil and 0.7 mm backing), were simulated in a spherical water phantom, using Geant4.10.4. Dose-depth profiles were plotted for Ru-106, Sr-90, Ho-166, Re-188 and Pr-142 plaques. The dose deposited in the tumor and behind the plaque’s backing was calculated for the silver, gold and stainless steel plaques. For validation, dosimetry of CCB, COB and CIB plaques were performed using radiochromic EBT3 film and Plaque Simulator software, and the obtained dose rates were compared with Geant4.10.4 and the manufacturer’s (BEBIG) results. Results The ratio of dose at a point behind the silver backing to the reference point (2 mm depth) was 1.56%, 0.13%, 0.28%, 0.39% and 0.18% for Ru-106, Sr-90, Ho-166, Re-188 and Pr-142 CCB model plaques, respectively. The dose rate at the reference point was 66.4%, 50.7%, 34.8%, 41.87% and 47.1% of the dose rate at a depth of 0.5 mm for the mentioned plaques, respectively. With the same activity, Ho-166 plaque delivered the highest dose to the scleral, while Ru-106 plaque delivered the lowest. The dose per decay at the tumor apex (5 mm depth) was 3.59e−11 Gy, 5.27e−12 Gy, 7.96e−13 Gy, 2.24e−12 Gy and 3.36e-12 Gy for the mentioned plaques, respectively. The deposited dose in the tumor decreased by 50% for gold Ru-106 plaques and increased by 20% for stainless steel ones. Conclusions From the perspective of dose distribution, Ru-106 plaques can be replaced by Sr-90 or Pr-142 plaques for the tumor apex up to 3 mm. The dose fall-off for Ho-166 and Re-188 plaques are more severe, which limits their use only for superficial lesions. Gold plaques show more attenuation and can be made thinner. They may be used in COB and CIB models, due to their vicinity of optic nerve and iris, respectively. For tumor apex up to 5 mm only Ru-106 delivered the sufficient dose.

Retina dose as a predictor for visual acuity loss in 106Ru eye plaque brachytherapy of uveal melanomas

Background and purposeTo evaluate the retina dose as a risk factor associated with loss of visual acuity (VA) in 106Ru plaque brachytherapy. Material/methods45 patients receiving 106Ru plaques brachytherapy (median follow-up 29.5 months) were included in this study. An in-house developed treatment planning system with Monte Carlo based dose calculation was used to perform treatment planning and dose calculation. Risk factors associated with loss of VA were evaluated using the Cox proportional hazards models, Kaplan–Meier estimates and Pearson correlation coefficients. ResultsA significant correlation was found between VA loss and mean (r = 0.49, p = 0.001) and near maximum (r = 0.47, p = 0.001) retina dose D2% and tumor basal diameter (r = 0.50, p < 0.001). The Kaplan–Meier and Cox proportional hazards model yielded a significantly higher risk for VA loss (>0.3Snellen) for patients receiving a maximum dose of >500 Gy (p = 0.002). A Cox multivariate analysis including the macula dose (p = 0.237) and basal diameter (p = 0.791) showed that a high maximum retinal dose is the best risk factor (p = 0.013) for VA loss. ConclusionThe study showed that retina dose (D2% and Dmean) is a suitable predictor for VA loss.

Outcome Analysis of Visual Acuity and Side Effect after Ruthenium-106 Plaque Brachytherapy for Medium-sized Choroidal Melanoma.

PURPOSE:The purpose of this study is to report on treatment outcomes for medium-sized choroidal melanoma treated with Ruthenium-106 (Ru-106) plaque brachytherapy.METHODS:A retrospective case series of 28 patients received Ru-106 brachytherapy treatment for choroidal melanoma. The prescribed tumor dose was 85 Gy to a depth of 5 mm.RESULTS:Median follow-up was 31.2 months. At 12 and 24-month postirradiation, the best corrected visual acuity ≥20/70 (LogMar ≥−0.54) was 53.8% and 64.2%, respectively. Median time to tumor regression was estimated to be 10 months (95% CI = 9–18 months), with 100% of response rate by 32 months. Radiation-induced side effects were limited, and there were no postradiation enucleations.CONCLUSIONS:The majority of patients maintained good visual acuity, with no enucleations and minimal side effects. In this cohort, the Ru-106 plaque brachytherapy proved to be an efficacious and safe treatment option for patients with medium-sized choroidal melanomas with a maximal tumor height of 5 mm.

Advanced Treatment Planning for Ophthalmic Plaque Brachytherapy of Uveal Melanomas

Brachytherapy (BT) treatments for uveal melanomas using ophthalmic plaques (i.e. 125I COMS and 106Ru eye plaques) achieves excellent clinical results with high tumor control and low toxicity rates. However, in comparison to state of the art external beam therapy and other BT techniques treatment planning of ophthalmologic plaque BT is underdeveloped regarding volumetric dose assessments, automated dose optimization routines and post-implantation quality assurance. The aim of this study was to (i) present a versatile and advanced treatment planning system (TPS) for ophthalmic plaque BT for both 125I COMS and 106Ru plaques and (ii) to demonstrate its potential in improving treatment planning. The TPS enables automated optimization of treatment plans based on Monte Carlo (MC) dose calculation and dose-volume histograms (DVH) as well as handling of multimodal image sets. In a first step, a resizable 3D eye model including all relevant critical structures was established, which enables to define both the tumor location and exact geometry by echography and funduscopy. Patient specific eye model adaptation can be achieved via post-implantation MR scans. An applicator library and respective dose look-up tables were generated by MC methods (MCNP6, Los Alamos, USA) that allow to generate DVHs for the target and all organs-at-risk (OAR). The current library of different plaques includes a 125I COMS plaque (Amersham Health model 6711) as well as several 106Ru plaques. The plaque geometry and 125I seeds were modeled according to AAPM TG 129 recommendations. The novel TPS allows calculating of full 3D dose distributions and DVH based on a cubic grid of 200 μm. The obtained results for the 125I COMS plaque and the values provided by AAPM TG 129 report were in good agreement. A maximum dose difference of 3 % up to a depth of 8 mm and 6 % up to a depth of 10 mm were obtained. Individualized modeling of the 3D eye based on fused funduscopic and post-implantation MR images allows to adjust treatment times and provide more accurate geometric definitions of the tumor and plaque location to improve the accuracy of the obtained DVHs. The implemented optimization routines can be used to define the optimal plaque size and safe eccentric plaque positions with respect to the tumor center to allow significant reductions of OAR doses. So far dose constrains for OARs (e.g. retinal doses of more than 500 Gy as a factor associated with visual acuity loss) were obtained from retrospective studies for treatment plan optimization. An advanced 3D TPS was developed and validated for plaque BT of uveal melanomas, which was designed to overcome the limitations of traditional treatment planning methods. The new TPS allows for a better and individualized treatment by including more image information and automated optimization into the planning process. The plaque library is currently updated to include more plaque types.

Dose Distributions and Treatment Margins in Ocular Brachytherapy with 106Ru Eye Plaques

Brachytherapy with ¹⁰⁶Ru eye plaques is the most common treatment modality for small to medium-sized uveal melanomas in Europe. So far, no standardized or widely accepted dose prescription protocol for the irradiation of intraocular tumors with ¹⁰⁶Ru eye plaques has been defined. For ¹²⁵I plaques, the minimum dose required for tumor control should be at least 85 Gy. Concerning ¹⁰⁶Ru plaques, the dose prescriptions at the University Hospital of Essen foresees minimum doses of 700 Gy to the tumor base and 130 Gy to the tumor apex. These dose prescriptions are expected to ensure sufficient treatment margins. We apply these dose prescriptions to different eye plaque types and tumor sizes and discuss the resulting treatment margins. These investigations are based on Monte Carlo simulations of dose distributions of 3 different eye plaque types. The treatment margin in apical direction has an expansion of at least 0.8 mm for all investigated eye plaques. For symmetrically formed eye plaques, the treatment margin at the base of the tumor goes beyond the visible edge of the plaque. This study focuses on the shape of 85-Gy isodose lines and on treatment margins for different eye plaque types and tumor sizes and shall help exchange knowledge for ocular brachytherapy.

Use of Ruthenium-106 Brachytherapy for Iris Melanoma: The Scottish Experience

PurposeTo analyse long-term outcomes of ruthenium-106 (106Ru) plaque brachytherapy for the treatment of iris melanoma.MethodsWe retrospectively reviewed medical records of 19 consecutive patients with pure iris melanoma treated with 106Ru...

PV-0185: Retina dose as risk factor for worse visual outcome in 106Ru plaque brachytherapy of uveal melanoma

PV-0185: Retina dose as risk factor for worse visual outcome in 106Ru plaque brachytherapy of uveal melanoma

Monte Carlo Estimation of Absorbed Dose Distributions Obtained from Heterogeneous 106Ru Eye Plaques

Background: The distribution of the emitter substance in ¹⁰⁶Ru eye plaques is usually assumed to be homogeneous for treatment planning purposes. However, this distribution is never homogeneous, and it widely differs from plaque to plaque due to manufacturing factors. Methods: By Monte Carlo simulation of radiation transport, we study the absorbed dose distribution obtained from the specific CCA1364 and CCB1256 ¹⁰⁶Ru plaques, whose actual emitter distributions were measured. The idealized, homogeneous CCA and CCB plaques are also simulated. Results: The largest discrepancy in depth dose distribution observed between the heterogeneous and the homogeneous plaques was 7.9 and 23.7% for the CCA and CCB plaques, respectively. In terms of isodose lines, the line referring to 100% of the reference dose penetrates 0.2 and 1.8 mm deeper in the case of heterogeneous CCA and CCB plaques, respectively, with respect to the homogeneous counterpart. Conclusions: The observed differences in absorbed dose distributions obtained from heterogeneous and homogeneous plaques are clinically irrelevant if the plaques are used with a lateral safety margin of at least 2 mm. However, these differences may be relevant if the plaques are used in eccentric positioning.

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

Background and purposeTo analyze treatment plan robustness and plan optimization strategies of 106Ru eye plaque brachytherapy using a novel software tool. Materials and methodsA treatment planning software was developed that allows to calculate dose–volume metrics. Plaque misplacements were simulated and evaluated with respect to the effect on tumor coverage and dose changes in critical structures. Two treatment plan optimization approaches were analyzed: (a) reducing plaque size and (b) shifting the plaque away from organs-at-risk (OAR). ResultsMaximum tumor sizes were identified which can be covered by the prescribed dose for different robustness levels (0–2mm). For an apex height of 5mm a 1mm uncertainty yielded changes in D2% to the lens of up to ±13Gy in anterior and ±20Gy to the optic nerve in posterior tumors. By reducing the plaque size Dmean and D2% to lens, optic nerve and macula were decreased by >60% for most simulated cases. Similarly, by shifting the plaque away from the lens dose reductions of 15%/mm in anterior and even 30%/mm in central tumors were achieved. ConclusionCritical structures in the treatment of uveal melanomas with 106Ru plaques can benefit from the proposed, computational treatment plan optimization.

OC-0151: Radiation induced toxicity and tumour control in pts treated for uveal melanoma with ru-106 plaques

OC-0151: Radiation induced toxicity and tumour control in pts treated for uveal melanoma with ru-106 plaques