Scleral Dose Research Articles

Radiobiological Insights of Staged Brachytherapy Using Eye Plaque for Large Uveal Melanoma

I-125 radioactive seeds embedded in an eye plaque is used to deliver the radiation dose of 85Gy to the apex of the tumor. However, it is challenging to treat a lesion in height (>10 mm) because of a high dose (> 500 Gy) to sclera. A staged radiotherapy (SRT) has been implemented successfully in stereotactic radiosurgery when a single dose is risky for a bigger sized lesion. The hypothesis of this work is that the SRT works for eye plaque brachytherapy of uveal melanoma to break the single fraction into two. To apply the concept of SRT, the following questions need to be answered: What are the two fraction doses? What is the time interval between the two fractions? In this work, the two split fraction doses and time interval are calculated using the "incomplete-repair' model. Equation (1) is the linear-quadratic (LQ) model. f(x) is the cell survival curve (SC). Equation (2) and (3) are radiobiological model developed dealing with the split doses by considering the incomplete repair. Ln(f(x)) = -αx - βx2 (1) Ln(fn(x, Ɵ)) = nLn(f(x))-nβx2hn(Ɵ) (2) hn(Ɵ) = (2/n)[ Ɵ/(1- Ɵ)][n-(1- Ɵn)/(1- Ɵ)] (3) Ɵ = exp(-µΔt) (4) x represents the fraction dose, Ɵx is the initial segment of the survival curve, Ɵ determines the rate at which repair proceeds. n is fraction number and µ represent repair constant which equals to ln2/T1/2. T1/2 is the half-life of I-125. For continuous dose vt delivered at dose rate v for time t, with repair constant µ, the LQ model is modified as Ln (f(vt, µ)) = -α(vt) -β(vt)2g(µt) (5) g(µt) = 2[µt-1+exp(-µt)]/(µt)2 (6) Assuming biological effective dose (BED) is the same for the single fraction and split two fractions, SC when n = 1 should be same as when n = 2. Therefore, the equation (7) is derived. Ɵ = [(α/β)x1 - 2(α/β)(x2)2 + (x1)2]/2(x2)2 - 1 (7) x1 is single fraction dose of 85Gy, x2 is the split dose to two fractions. α/β ratio of 10 Gy is used. By fitting the equation (7), the ranges of doses and time intervals were determined. The fraction doses and time interval to get the same BED as single fraction of 85 Gy are determined from 45 Gy to 50 Gy with time interval of 22 days to 76 days for staged brachytherapy eye plaque (SBEP). Our result is matched the treatment protocol for SBEP reported, e.g., 1st fraction dose of 40Gy and 50 Gy of 2nd fraction with 73 days of time interval are used. The max. dose of scleral dose is 328 Gy compared to the single fraction scleral dose of 543Gy. This work could provide guidelines in SBEP in dosage and time interval. The height of tumor matters the most in the SBEP since the taller the tumor, the higher dose to the sclera is. Reference.

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

Brachytherapy with episcleral plaques is the most common primary tumor treatment for uveal melanoma. This study aims to compare the risk of tumor recurrence and metastatic death between two frequently used ruthenium-106 plaque designs: CCB (20.2 mm) and CCA (15.3 mm). Data were obtained from 1387 consecutive patients treated at XXX 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 no minimum scleral dose was used, and accurate plaque positioning was not verified after scleral attachment. Patients treated with CCA plaques had smaller tumors than those treated with CCB plaques (mean diameter 8.6 vs. 10.5 mm, P<0.001). 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. 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<0.001). Multivariate Cox regression analysis revealed a lower risk for tumor recurrence with CCB plaques (HR 0.50). Similarly, patients treated with CCB plaques had a lower risk for uveal melanoma-related mortality (HR 0.77). Adjunct transpupillary thermotherapy did not reduce these risks. Uni- and multivariate time-dependent Cox regressions demonstrated that tumor recurrence was associated with uveal melanoma-related and all-cause mortality. Compared to 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.

PHSOR07 Presentation Time: 1:00 PM: Feasibility of Using Dual-Activity Seed Loading When Using Eye Physics Eye Plaques and Plaque Simulator Treatment Planning in Eye Plaque Brachytherapy

<h3>Purpose</h3> Uveal melanoma is a tumor of the eye commonly treated with the application of gold plaques loaded with radioactive I-125 seeds. This study evaluates the dosimetric impact of incorporating dual-activity seed loading in Eye Physics eye plaques under two clinical scenarios that may benefit from this dual-activity approach. <h3>Materials and Methods</h3> Plaque Simulator (Eye Physics, LLC, Los Alamitos, CA) was used to retrospectively re-plan 10 clinical cases for two clinical scenarios: 1) shallow (<5.5 mm) tumors with large base dimensions (16 mm - 19 mm) planned with the largest plaque available from Eye Physics (EP2342 in Fig.1), and 2) tumors very near the optic nerve planned with EP2029N notched plaque (Fig. 1). Five clinical plans were selected for each clinical scenario. The clinical plans chosen were prescribed to at least 2 mm deeper depth than the tumor apex in order to achieve target (base + 2 mm margin) coverage of at least 95%. In the replanning, some of seeds in the plaque were replaced with higher activity seeds. For Scenario 1), EP2342 plaques were planned with the outer ring of sources at twice the activity of the inner sources. For Scenario 2), EP2029N plaques were planned with the 6 seeds closest to the notch at twice the activity of the other sources. Seed loading was kept symmetric for ease of loading, QA, and plaque placement. Plans were based on retinal sketches rather than digitized directly from retinal imaging, so the exact dose to critical structures is an estimate, but the direction and approximate magnitude of the dose change can be analyzed. <h3>Results</h3> In all the cases of large shallow tumors for Scenario 1), the dual-activity plan was able to decrease the prescription depth by 0.8 mm to 1.3 mm. Therefore, doses to all critical structures were consistently lower in dual-activity plans: inner sclera -24.6% ± 1.6%, optic disc -6.5% ± 2.5%, fovea -6.0% ± 3.3% (average ± standard deviation). In 3 out of 5 tumors close to the optic nerve for Scenario 2), the dual-activity plan was able to decrease the prescription depth by 0.5 mm to 0.7 mm. In all 5 of these cases, dose to inner sclera was consistently lower in the re-plans by 20.9%±5.6% and dose to the optic disc and fovea were consistently higher by 19.3%±7% and 21.8%±11.4% respectively. <h3>Conclusions</h3> For large shallow tumors, critical structure dosimetrics were constantly improved due to shallower prescription depth by partially loading with higher activity seeds. The largest dose reduction occurs to the inner sclera since it is close to the plaque, but changes in other critical structures were patient-specific depending the location of the tumor in the eye. It may be beneficial to always plan tumors such as these with dual activities. As this is the largest plaque offered by Eye Physics, this planning approach may allow it to be used for larger tumors while still maintaining reasonable dose to critical structures. For tumors near the optic nerve, the results showed that although scleral dose was decreased, dose to optic disc and fovea were increased. As this difference is due to the location of the tumor relative to the optic nerve and the fovea, it may be beneficial to investigate dual activity plans on a case-by-case basis if scleral dose is a concern for that particular patient.

Dual-source strength seed loading for eye plaque brachytherapy using eye physics eye plaques: A feasibility study.

This study quantifies the dosimetric impact of incorporating two iodine-125 (125I) seed source strengths in Eye Physics eye plaques for treatment of uveal melanoma. Plaque Simulator was used to retrospectively plan 15 clinical cases of three types: (1) Shallow tumors (< 5.5 mm) with large base dimensions (range, 16-19 mm); (2) Tumors near the optic nerve planned with notched plaques; and (3) Very shallow (< 3.0 mm) tumors with moderate base dimensions (range, 13.5-15.5 mm) planned with larger plaques than requested by the ocular oncologist. Circular plaques were planned with outer ring sources twice the source strength of inner sources, and notched plaques with the six seeds closest to the notch at twice the source strength. In cases of type (1), the dual-source strength plan decreased prescription depth, and doses to critical structures were lower: inner sclera -25% ±2%, optic disc -7% ±3%, and fovea -6% ±3%. In four out of five cases of type (2), the dual-source strength plan decreased prescription depth, and dose to inner sclera was lower (-22% ±5%), while dose to optic disc (17% ±7%) and fovea (20% ±12%) increased. In cases of type (3), a smaller dual-source strength plaque was used, and scleral dose was lower (-45% ±3%), whereas dose to optic disc (1% ±14%) and fovea (5% ±5%) increased. Dual-source strength loading as described in this study can be used to cover tumor margins and decrease dose to sclera, and therefore the adjacent retina, but can either decrease or increase radiation dose to optic disc and fovea depending on location and size of the tumor. This technique may allow the use of a smaller plaque, if requested by the ocular oncologist. Clinical determination to use this technique should be performed on an individual basis, and additional QA steps are required. Integrating the use of volumetric imaging may be warranted.

Scleral necrosis after brachytherapy for uveal melanoma: Analysis of risk factors

Radiation-induced scleral necrosis (RISN) is a rare, but a serious complication of brachytherapy for uveal melanoma. We aimed at analysing the incidence, timing and risk factors associated with development of RISN in a large institutional series. All consecutive cases with brachytherapy for uveal melanoma treated by the Departments of Ophthalmology and Radiotherapy at University Hospital Essen between 1999 and 2016 were eligible. Development of RISN during the post-treatment follow-up was recorded. A 1:2 propensity score matched case-control study was performed for the evaluation of the prognostic value of different tumour- and treatment-associated parameters. RISN was documented in 115 (2.9%) of 3960 patients with uveal melanoma included in the final analysis, and occurred at the mean 30.3months (range: 1.26-226 months) after brachytherapy. In the whole cohort, younger age (p= 0.042), plaque type (p= 0.001) and ciliary body involvement (p< 0.0001) were independently associated with the RISN occurrence. In the case-control study, multivariable weighted proportional hazard analysis discovered the association of the following additional tumour- and treatment-associated characteristics with RISN: posterior tumour margin anterior to equatorial region (p= 0.0003), extraocular tumour extension (p= <0.0001), scleral contact dose (p= <0.0001), conjunctival dehiscence after therapy (p= 0.0001), disinsertion of the superior rectus muscle (p= 0.001) and the glaucoma medication (p= 0.014). Our study confirms RISN as a rare complication, which might occur even years later after the brachytherapy for uveal melanoma. Alongside with scleral dose five other tumour and therapy related factors predict the risk of RISN after brachytherapy for uveal melanoma were established.

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.

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.

15 years of 106Ru eye plaque dosimetry at Memorial Sloan-Kettering Cancer Center and Weill Cornell Medical Center using radiochromic film in a Solid Water phantom

Purpose. 106Ru eye plaques are used for treatment of intraocular malignancies, providing a good alternative to enucleation. We perform our own acceptance testing and commissioning of 106Ru eye plaques using radiochromic film as recommended by ISO standard 21439:2009 ‘Clinical dosimetry-beta radiation sources for brachytherapy’. A Solid Water ‘eye’ phantom with several novel features and related tools were developed for accurate radiochromic film dosimetry of eye plaques. Methods. The phantom enables full 3D dosimetric characterization of eye plaques. Films perpendicular to the central axis of the eye plaques are sandwiched between inserts in the phantom. Small holes in the phantom inserts enable marking the films with respect to the eye plaques, assuring exact geometrical co-registration. Special thin unlaminated radiochromic films were utilized, enabling dosimetric measurements virtually at the surface of the eye plaques. Precise film punches were developed in order to cut films with diameters as small as 8.5 mm and make cutouts in films without damaging the cut edges. Results. Full dosimetric characterization of three CCX type and partial characterization of a CIA type 106Ru eye plaques is presented. Replicate film results were reproducible to within 4%–5%. Even 4% non-uniformities in planar dose rates were easily detected. Comparison with Monte Carlo calculations by Hermida-López 2013 Med. Phys. 40 101705-1–101705-13, found good agreement along the central axis, but some lateral differences. Conclusions. Accurate and precise 106Ru eye plaque dosimetry was achieved utilizing radiochromic film in the phantom introduced here. Co-registration of eye plaques and films permits not only precise treatment planning calculations along the central axis of the plaque, but also accounts for dosimetric non-uniformities using 2D or 3D methodologies. Dose measurements on the inner surface of the plaques provide precise assessment of the scleral dose, its homogeneity, and the active area of the plaques for coverage determination.

Dose-response in choroidal melanoma

PurposeIn choroidal melanoma the radiation threshold dose for local control remains largely unknown. The present study examined a group of patients that received a wide range of minimum tumor dose in order to investigate a dose-response relationship. A literature review is performed to compare our results with available evidence in brachytherapy and charged particle external beam radiotherapy. Materials and methodsA retrospective study was conducted on all choroidal melanomas treated with Strontium-90 (Sr-90) at the University Hospital of Leuven between 1983 and 2012. Local failure was defined as primary endpoint and was estimated according to the competing risk method. ResultsIn 135 patients, the minimum tumor dose (Dmin) ranged from 0 Gy to 287 Gy (median: 27.6 Gy). Multivariable analysis revealed Dmin ≥ 65 Gy (p = 0.04; HR = 0.09) and tumor distant from the optic disc (p < 0.001, HR = 0.09) to be independent variables favoring local control. The scleral dose, the tumor diameter and tumor height did not significantly affect local failure in multivariate analysis. ConclusionThis is the first study to examine a group of patients treated with a Dmin ranging from 0 Gy to >250 Gy. Treatment with a Dmin of 65 Gy is necessary to achieve durable tumor response. The dose-response data provided by our study could be used for the design of future trials examining the ideal dose for the treatment of choroidal melanoma with brachytherapy or charged particle external beam radiotherapy.

Ruthenium brachytherapy for uveal melanoma - single institution experience.

PurposeThe aim of this study was to report on results of uveal melanoma treatment with ruthenium-106 (106Ru) brachytherapy with long-term follow-up, in terms of local tumor control, eye retention rate, radiation retinopathy, and patients’ survival.Material and methodsMedical records of patients treated with ruthenium plaque due to uveal melanoma at the Department of Ophthalmology, Poznan University of Medical Sciences, Poland, between 1994 and 2014 were retrospectively reviewed.ResultsWe identified 126 patients: 53 men, 73 women, mean age 60.04 years (range, 21-89). The largest basal diameter ranged from 4.04 mm to 18.9 mm (median, 10.67 mm), tumor height was 1.9 mm to 7.42 mm (median, 4.8 mm). Median scleral radiation dose was 570 Gy (range, 235-1,500 Gy), median apical dose 100 Gy (range, 60-129 Gy). Median follow-up was 66.5 months (range, 2-261 months). We noted a total of 19 (15%) recurrences. The actuarial rate of recurrence was 9.5% at 3 years, and 13.5% at 5 years postoperatively. Nine (7%) eye globes were lost, median time to enucleation was 5 years. The eye retention rate at 5 years was 92.7% and 81% at 10 years. Forty-three (34%) patients died before the end of the study, 24 (19%) of them due to metastatic disease. Metastatic death was related to: tumor size and TNM stage at presentation (p = 0.002 vs. p = 0.0006, respectively) but not to age, gender, and plaque dosimetry.Conclusions 106Ru brachytherapy is an effective, globe sparing treatment that provides good tumor control and a high rate of survival. However, some ocular complications tend to appear late post-treatment, and therefore long-term follow-up is advised.

Suspected vitreous seeding of uveal melanoma: relevance of diagnostic vitrectomy

AimTo review all cases of suspected vitreous seeding of treated or untreated uveal melanoma at our clinic and to compare clinical, cytological and histological findings with patients’ survival.MethodsRetrospective non-randomised study...

SU‐E‐T‐15: A Comparison of COMS and EP917 Eye Plaque Applicators Using Different Radionuclides

Purpose:To investigate the effect of plaque design and radionuclides on eye plaque dosimetry.Methods:The Monte Carlo N‐particle Code version 6 (MCNP6) was used for radiation transport simulations. The 14 mm and 16 mm diameter COMS plaques and the model EP917 plaque were simulated using brachytherapy seeds containing I‐125, Pd‐103, and Cs‐131 radionuclides. The origin was placed at the scleral inner surface. The central axis (CAX) doses of both COMS plaques at −1 mm, 0 mm, 1 mm, 2 mm, 5 mm, 10 mm, 15 mm, 20 mm, and 22.6 mm were compared to the model EP917 plaque. Dose volume histograms (DVHs) were also created for both COMS plaques for the tumor and outer sclera then compared to results for the model EP917 plaque.Results:For all radionuclides, the EP917 plaque delivered higher dose (max 343%) compared to the COMS plaques, except for the 14 mm COMS plaque with Cs‐131 at 1 mm and 2 mm depths from outer sclera surface. This could be due to source design. For all radionuclides, the 14 mm COMS plaque delivered higher doses compared to the 16 mm COMS plaque for the depths up to 5 mm. Dose differences were not significant beyond depths of 10 mm due to ocular lateral scatter for the different plaque designs. Tumor DVHs for the 16 mm COMS plaque with Cs‐131 provided better dose homogeneity and conformity compared to other COMS plaques with I‐125 and Pd‐103. Using Pd‐103, DVHs for the 16 mm COMS plaque delivered less dose to outer sclera compared to other plaques.Conclusion:This study identified improved tumor homogeneity upon considering radionuclides and plaque designs, and found that scleral dose with the model EP917 plaque was higher than for the 16 mm COMS plaque for all the radionuclides studied.

Independent dosimetric assessment of the model EP917 episcleral brachytherapy plaque.

To investigate the influence of slot design on dose distributions and dose-volume histograms (DVHs) for the model EP917 plaque for episcleral brachytherapy. Dimensions and orientations of the slots were measured for three model EP917 plaques and compared to data in the Plaque Simulator (PS) treatment planning software (version 5.7.6). These independently determined coordinates were incorporated into the MCNP Monte Carlo simulation environment to obtain dose from the plaques in a water environment and in a clinical environment with ocular structures. A tumor volume was simulated as 5 mm in apical height and 11 mm in basal diameter. Variations in plaque mass density and composition; slot length, width, and depth; seed positioning; and Ag-marker rod positioning were simulated to examine their influence on plaque central axis (CAX) and planar dose distributions, and DVHs. Seed shifts in a single slot toward the eye and shifts of the(125)I-coated Ag rod within the capsule had the greatest impact on CAX dose distribution. A shift of 0.0994 mm toward the eye increased dose by 14%, 9%, 4.3%, and 2.7% at 1, 2, 5, and 10 mm, respectively, from the inner sclera. When examining the fully-modeled plaque in the ocular geometry, the largest dose variations were caused by shifting the Ag rods toward the sclera and shifting the seeds away from the globe when the slots were made 0.51 mm deeper, causing +34.3% and -69.4% dose changes to the outer sclera, respectively. At points along the CAX, dose from the full plaque geometry using the measured slot design was 2.4%±1.1% higher than the manufacturer-provided slot design and 2.2%±2.3% higher than the homogeneous calculation of PS treatment planning results. The ratio of D10 values for the measured slot design to the D10 values for the manufacturer-provided slot design was higher by 9%, 10%, and 19% for the tumor, inner sclera, and outer sclera, respectively. In comparison to the measured slot design, a theoretical plaque having narrower and deeper slots delivered 30%, 37%, and 62% lower D10 doses to the tumor, inner sclera, and outer sclera, respectively. While the measured positions of the slots on the model EP917 plaque were in close agreement (<0.7 mm) with the PS values, small differences in the slot shape caused substantial differences in dose distributions and DVH metrics. Increasing slot depth by 0.1 mm decreased outer scleral dose by 20%, yet shifting the Ag rods in the seeds toward the globe by 0.1 mm increased outer scleral dose by 35%. The clinical medical physicist is advised to measure these types of plaques upon acceptance testing before clinical use to inspect slot shape and position for comparison with data used for treatment planning purposes.

WE-A-17A-12: The Influence of Eye Plaque Design On Dose Distributions and Dose- Volume Histograms

Purpose: To investigate the effect of slot design of the model EP917 plaque on dose distributions and dose-volume histograms (DVHs). Methods: The dimensions and orientation of the slots in EP917 plaques were measured. In the MCNP5 radiation simulation geometry, dose distributions on orthogonal planes and DVHs for a tumor and sclera were generated for comparisons. 27 slot designs and 13 plaques were evaluated and compared with the published literature and the Plaque Simulator clinical treatment planning system. Results: The dosimetric effect of the gold backing composition and mass density was < 3%. Slot depth, width, and length changed the central axis (CAX) dose distributions by < 1% per 0.1 mm in design variation. Seed shifts in the slot towards the eye and shifts of the {sup 125} I-coated Ag rod within the capsule had the greatest impact on CAX dose distribution, increasing by 14%, 9%, 4%, and 2.5% at 1, 2, 5, and 10 mm, respectively, from the inner sclera. Along the CAX, dose from the full plaque geometry using the measured slot design was 3.4% ± 2.3% higher than the manufacturer-provided geometry. D{sub 10} for the simulated tumor, inner sclera, and outer sclera for the measured plaque was alsomore » higher, but 9%, 10%, and 20%, respectively. In comparison to the measured plaque design, a theoretical plaque having narrow and deep slots delivered 30%, 37%, and 62% lower D{sub 10} doses to the tumor, inner sclera, and outer sclera, respectively. CAX doses at −1, 0, 1, and 2 mm were also lower by a factor of 2.6, 1.4, 1.23, and 1.13, respectively. Conclusion: The study identified substantial sensitivity of the EP917 plaque dose distributions to slot design. However, it did not identify substantial dosimetric variations based on radionuclide choice ({sup 125}I, {sup 103}Pd, or {sup 131}Cs). COMS plaques provided lower scleral doses with similar tumor dose coverage.« less

Three-dimensional MRT/CT Treatment Planning for 106Ru Eye Plaques Commissioned Using Radiochromic Film in a Solid Water Phantom

Three-dimensional MRT/CT Treatment Planning for 106Ru Eye Plaques Commissioned Using Radiochromic Film in a Solid Water Phantom

SU-E-T-13: Comparison of Dose Rates with and without Gold Backing of USC #9 Radioactive Eye Plaque Using MCNP5.

To show the effect of gold backing on dose rates for the USC #9 radioactive eye plaque. An I125 source (IsoAid model IAI-125A) and gold backing was modeled using MCNP5 Monte Carlo code. A single iodine seed was simulated with and without gold backing. Dose rates were calculated in two orthogonal planes. Dose calculation points were structured in two orthogonal planes that bisect the center of the source. A 2×2 cm matrix of spherical points of radius 0.2 mm was created in a water phantom of 10 cm radius. 0.2 billion particle histories were tracked. Dose differences with and without the gold backing were analyzed using Matlab. The gold backing produced a 3% increase in the dose rate near the source surface (<1mm) relative to that without the backing. This was presumably caused by fluorescent photons from the gold. At distances between 1 and 2 cm, the gold backing reduced the dose rate by up to 12%, which we attribute to a lack of scatter resulting from the attenuation from the gold. Dose differences were most pronounced in the radial direction near the source center but off axis. The dose decreased by 25%, 65% and 81% at 1, 2, and 3 mm off axis at a distance of 1 mm from the source surface. These effects were less pronounced in the perpendicular dimension near the source tip, where maximum dose decreases of 2% were noted. I 125 sources embedded directly into gold troughs display dose differences of 2 - 90%, relative to doses without the gold backing. This is relevant for certain types of plaques used in treatment of ocular melanoma. Large dose reductions can be observed and may have implications for scleral dose reduction.

Expression of 12 cytokines in aqueous humour of uveal melanoma before and after combined Ruthenium‐106 brachytherapy and transpupillary thermotherapy

To determine the aqueous humour levels of 12 cytokines in eyes with uveal melanoma and whether their expression changes after combined Ru-106 brachytherapy and transpupillary thermotherapy (TTT). Aqueous humour samples were collected from 20 patients with previously untreated uveal melanoma undergoing combined Ru-106 brachytherapy and TTT, both at the time of plaque placement and removal. Using multiplex biochip array technology, 12 different cytokines were measured, including interleukin (IL)-1α, IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, vascular endothelial growth factor (VEGF), tumour necrosis factor (TNF)-α, interferon (IFN)-γ, epidermal growth factor (EGF) and monocyte chemoattractant protein (MCP)-1. Aqueous humour from 20 patients undergoing cataract surgery was used as control. IL-6, IL-8, IFN-γ and MCP-1 were highly expressed in uveal melanoma, whereas IL-2, IL-10 and TNF- α were low in expression. There was a positive correlation between tumour height and IL-8 level (p = 0.020). Vascular endothelial growth factor tends to be highly expressed in melanoma-containing eyes (p = 0.056). Levels of IL-6, IL-8 and IL-1β increased after the mean 117 ± 38 hrs of brachytherapy and adjunctive TTT with a tumour apex dose of 61 ± 28 Gy and a scleral contact dose of 786 ± 226 Gy. Increase in levels of IL-6 (p = 0.003) and IL-8 (p = 0.046) positively correlated with scleral contact dose. Cytokines such as IL-6, IL-8, IFN-γ and MCP-1 may be implicated in the progression of uveal melanoma. Ocular irradiation from a Ru-106 plaque promoted an increase in the levels of IL-6, IL-8 and IL-1β, modulation of which could be useful in managing radiation-related side effects.

WE‐A‐BRB‐01: Accurate Dosimetric Characterization of a Fully Loaded 20 Mm COMS I‐125 Eye Plaque Using Specially Designed GAFCHROMICTM Film

Purpose: The majority of eye plaques used in the U.S. are of Collaborative Ocular Melanoma Study (COMS) design with I‐125 brachytherapy seeds. Treatment planning is usually done using the TG‐43 formalism, not accounting for the gold alloy backing and Silastic insert, which significantly reduce the dose, as calculated by BrachyDose Monte Carlo (MC) (www.physics.carleton.ca/clrp/eye_plaque/). Dosimetric characterization of a fully loaded 20 mm COMS plaque using radiochromic film is reported. Methods: A 20 mm COMS eye plaque was uniformly loaded with 24 6711 I‐125 seeds at 6.75 U/seed. Measurements were performed using specially designed single layer GAFCHROMIC EBT1 film sandwiched perpendicular to the plaqueˈs central axis at depths 0 – 19 mm between inserts of a Solid Water “eye” phantom located at the center of a 30×30×30 cm3 full scatter Solid Water phantom. The films were calibrated using a 6711 I‐125 seed in Solid Water, applying the TG‐43 formalism. Results: Dose distributions in planes perpendicular to the central axis of the plaque are radially isotropic and uniform. Measured depth dose on central axis as well as off‐axis profiles, agree well with the results of MC. At 3 mm from the inner sclera, the measured dose rate is 12.5% lower than TG‐43 dose rate in homogenous water, similar to 11.9% for MC. The thin flexible film enabled measurements of the dose at the surface of the plaque. Results on duplicate films agree within 5.5%. Conclusions: GAFCHROMIC film in a Solid Water phantom is a convenient, accurate, and reproducible dosimeter for I‐125 eye plaque dosimetry. Dose measurements on the inner surface of the plaque enable precise assessment of the scleral dose and its homogeneity, and of the active area of the plaque for coverage determination. This work validates the MC simulations about the dose reduction effect by the plaqueˈs backing and insert.In‐Kind support of materials provided by Oncura, Inc., Arlington Heights, IL and by International Specialty Products, Inc., Wayne, NJ

Monte Carlo dosimetry for and eye plaque brachytherapy with various seed models

PurposeDose distributions are calculated for various models of and seeds in the standardized plaques of the Collaborative Ocular Melanoma Study (COMS). The sensitivity to seed model of dose distributions and dose distributions relative to TG‐43 are investigated.MethodsMonte Carlo simulations are carried out with the EGSnrc user‐code BrachyDose. Brachytherapy seeds and eye plaques are fully modeled. Simulations of one seed in the central slot of a 20 mm Modulay (gold alloy) plaque backing with and without the Silastic (silicone polymer) insert and of a 16 mm fully loaded Modulay/Silastic plaque are performed. Dose distributions are compared to those calculated under TG‐43 assumptions, i.e., ignoring the effects of the plaque backing and insert and interseed attenuation. Three‐dimensional dose distributions for different and seed models are compared via depth‐dose curves, isodose contours, and tabulation of doses at points of interest in the eye. Results are compared to those of our recent BrachyDose study for COMS plaques containing model 6711 or 200 seeds [R. M. Thomson et al., Med. Phys. 35, 5530–5543 (2008)].ResultsAlong the central axis of a plaque containing one seed, variations of less than 1% are seen in the effect of the Modulay backing alone for different seed models; for the Modulay/Silastic combination, variations are 2%. For a 16 mm plaque fully loaded with seeds, dose decreases relative to TG‐43 doses are 11%–12% (19%–20%) and 14%–15% (20%) at distances of 0.5 and 1 cm from the inner sclera along the plaque's central axis, respectively. For the same prescription dose, doses at points of interest vary by up to 8% with seed model. Doses to critical normal structures are lower for all seed models than for with the possible exception of the sclera adjacent to the plaque; scleral doses vary with seed model and are not always higher for than for .ConclusionsDose decreases relative to doses calculated under TG‐43 assumptions vary slightly with seed model (for each radionuclide). Dose distributions are sensitive to seed model; however, variations are generally no larger than the magnitudes of other systematic uncertainties in eye plaque therapy.

MO‐FF‐A2‐05: A Novel Stereotactic Radiosurgical Device for the Treatment of Age‐Related Macular Degeneration (AMD)

Purpose: Age‐related Macular Degeneration (AMD) is the leading cause of blindness in people over 65 in the U.S. It is caused by a proliferation of capillaries in the retina and can result in profound and rapid loss of central vision. As a neovascular disease, it has been shown to be susceptible to radiotherapy. Recently, a 100kVp tabletop stereotactic radiosurgical (SRS) device has been developed to deliver highly‐collimated beams of X‐rays to the fovea to treat AMD. This study is an evaluation of that system. Method and Materials: The device delivers a three‐port, 16Gy single fraction dose to the macula. Using a suction‐enabled contact lens assembly (“the I‐Guide”) to stabilize the eye, three 4mm diameter beams of 100kVp x‐rays are delivered to the fovea, directed by a positioning robot. The beams enter the eye through the sclera and avoid the radio‐sensitive lens. The I‐Guide includes reflective fiducials that are monitored by cameras, and the real‐time position of the beam on the retina is calculated from the fiducial positions. Because of uniformity across adult eye populations, a class‐solution treatment plan was implemented using a single parameter (eye length). Software manages treatment time and automatic gating of beam in case of excessive eye motion. A clinical trial is underway. Results: 100kVp proves an optimal energy for ophthalmic radiotherapy. A therapeutic dose to the retina can be delivered with negligible impact to the brain and the scleral entry dose is well‐tolerated. The scatter from the narrow beam is minimal to sensitive structures in the eye. Submillimeter targeting precision was demonstrated in the lab and in the clinic. Submillimeter motion‐management was also demonstrated. Conclusion: The eye‐specific SRS device shows great promise for providing a precise and non‐invasive method of treating AMD.Research sponsored by Oraya Therapeutics.