Ruthenium-106 plaque radiotherapy for uveal melanoma: analysis of tumor dimension and location on anatomical and functional results.

BACKGROUND: To report the long-term outcomes of Ru-106 plaque radiotherapy in eyes with uveal melanoma (UM) and to assess the effect of tumor thickness and location on final outcomes. METHODS: Medical records of 234 patients undergoing Ru-106 plaque radiotherapy for UM were reviewed, and the visual outcome, globe preservation, and patient survival were evaluated. The results of 2 groups were compared: 1. between thin (small and medium-sized, thickness < 7 mm, 148 eyes [63.2%]) and thick (thickness ≥ 7 mm, 86 eyes [36.8%]) tumors, and 2. between large (largest basal diameter [LBD] > 12 mm, 109 eyes [46.6%]) and medium/small (LBD ≤ 12 mm, 125 eyes [53.4%]). In addition, a comparison of the juxtapapillary location in 46 eyes (19.7%) versus tumors arising elsewhere and between tumors with and without ciliary involvement in 48 eyes (21.5%) were done. RESULTS: The patients were followed for a median of 54.2 months (range: 6-194.5 months). After adjusting for baseline visual acuity (VA), there was no significant association between final VA and different dimension and tumor location groups. Final globe preservation was 91.9%, and there was no significant difference between different dimension- and ciliary body involvement groups regarding anatomical success rate. The juxtapapillary tumors had lower globe preservation (80.4% vs .94.7%, p = 0.002). The hazard ratio (HR) for enucleation in juxtapapillary tumors was HR = 6.58 (95-CI: 3.84 to 11.21). The overall metastasis rate was 6.8%, with no significant difference in juxtapapillary tumors (4.3% vs.7.4%, p = 0.455). CONCLUSIONS: Ru-106 plaque radiotherapy is an effective treatment for thick and large UM. With this type of treatment, the globe preservation rate is lower in juxtapapillary tumors, but there is no significant difference in the metastasis rate.

A novel analytical method for computing dose from kilovoltage beams used in Image-Guided radiation therapy.

PURPOSE: A modified convolution/superposition algorithm is proposed to compute dose from the kilovoltage beams used in IGRT. The algorithm uses material-specific energy deposition kernels instead of water-energy deposition kernels. METHODS: Monte Carlo simulation was used to model the Elekta XVI unit and determine dose deposition characteristics of its kilovoltage beams. The dosimetric results were compared with ion chamber measurements. The dose from the kilovoltage beams was then computed using convolution/superposition along with material-specific energy deposition kernels and compared with Monte Carlo and measurements. The material-specific energy deposition kernels were previously generated using Monte Carlo. RESULTS: The obtained gamma indices (using 2%/2mm criteria for 95% of points) were lower than 1 in almost all instances which indicates good agreement between simulated and measured depth doses and profiles. The comparisons of the algorithm with measurements in a homogeneous solid water slab phantom, and that with Monte Carlo in a head and neck CT dataset produced acceptable results. The calculated point doses were within 4.2% of measurements in the homogeneous phantom. Gamma analysis of the calculated vs. Monte Carlo simulations in the head and neck phantom resulted in 94% of points passing with a 2%/2mm criteria. CONCLUSIONS: The proposed method offers sufficient accuracy in kilovoltage beams dose calculations and has the potential to supplement the conventional megavoltage convolution/superposition algorithms for dose calculations in low energy range.

Manufacturing and evaluation of a multi-purpose Iranian head and neck anthropomorphic phantom called MIHAN.

A new multi-purpose Iranian head and neck (MIHAN) anthropomorphic phantom was designed and manufactured to be used in diagnostic and therapeutic applications. Geometry of MIHAN phantom was determined based on the average dimensions acquired by CT scans of twenty patients without any medical problems in their head and neck site. Because the phantom was expected to be used with different modalities with a wide range of photon energies, attenuation coefficients of some selected materials were determined using Monte Carlo simulation. Based on analytical and simulation results, acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) were found suitable choices for soft and bony tissues, respectively. They were used in the 3D printer to build the phantom. The suitability of the materials was checked by CT number value comparison between the organs included in the phantom and the corresponding body tissues and also film dosimetry of a typical intensity-modulated radiation therapy (IMRT) plan.. Hounsfield Unit agreement and 95% ± 2% pass rate for the IMRT plan verification proved the suitability of material selection. Also, the film dosimetry showed feasibility of using MIHAN in radiotherapy plan verification workflow. In addition, PLA was introduced as a spongy bone tissue substitute for the first time.

Generation of material-specific energy deposition kernels for kilovoltage x-ray dose calculations.

PURPOSE: Dose calculation of kilovoltage x rays used in Image-Guided Radiotherapy has been investigated in recent years using various methods. Among these methods are model-based ones that suffer from inaccuracies in high-density materials and at interfaces when used in the kilovoltage energy range. The main reason for this is the use of water energy deposition kernels and simplifications employed such as density scaling in heterogeneous media. The purpose of this study was to produce and characterize material-specific energy deposition kernels, which could be used for dose calculations in this energy range. These kernels will also have utility in dose calculations in superficial radiation therapy and orthovoltage beams utilized in small animal irradiators. METHODS: Water energy deposition kernels with various resolutions; and high-resolution, material-specific energy deposition kernels were generated in the energy range of 10-150 kVp, using the EGSnrc Monte Carlo toolkit. The generated energy deposition kernels were further characterized by calculating the effective depth of penetration, the effective radial distance, and the effective lateral distance. A simple benchmarking of the kernels against Monte Caro calculations has also been performed. RESULTS: There was good agreement with previously reported water kernels, as well as between kernels with different resolution. The evaluation of effective depth of penetration, and radial and laterals distances, defines the relationship between energy, material density, and the shape of the material-specific kernels. The shape of these kernels becomes more forwardly scattered as the energy and material density are increased. The comparison of the dose calculated using the kernels with Monte Carlo provides acceptable results. CONCLUSIONS: Water and material-specific energy deposition kernels in the kilovoltage energy range have been generated, characterized, and compared to previous work. These kernels will have utility in dose calculations in this energy range once algorithms capable of employing them are fully developed.

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

PURPOSE: 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. METHODS: 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. RESULTS: 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 ± 13.11 years. The mean follow-up time was 47.56 ± 36.87 months. 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 ± 1.10 mm, respectively. The mean tumor thickness decreased to 2.60 ± 0.63 mm, 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. CONCLUSION: Our study showed that Ru-106 plaque radiotherapy is an effective and safe method of treatment in VPTs.

RUTHENIUM-106 BRACHYTHERAPY IN THE TREATMENT OF CIRCUMSCRIBED CHOROIDAL HEMANGIOMA.

PURPOSE: To examine the efficacy and safety of Ruthenium-106 plaque radiotherapy in the treatment of circumscribed choroidal hemangioma. METHODS: Twenty-one eyes of 21 patients diagnosed with symptomatic circumscribed choroidal hemangioma who underwent Ruthenium-106 plaque radiotherapy were included in the study. Clinical response, ancillary tests finding improvement, and major side effects were evaluated. RESULTS: From the initial to the 1-year follow-up visits, vision improved in 12 eyes (57%), was stable in 7 eyes (33%), and became worse in 2 eyes (10%). Based on fluorescein angiography and optical coherence tomography, subretinal fluid and cystoid macular edema resolved in all patients. Changes in logarithm of minimum angle of resolution visual acuity (P = 0.038); tumor thickness (P = 0.0001) and largest diameter (P = 0.007) on ultrasonography; and subfoveal thickness on optical coherence tomography (P < 0.0001), were statistically significant between the initial and the 1-year follow-up visits. Side effects as observed during the follow-up period included: radiation-related retinopathy in 5 (24%) eyes, radiation-related papillopathy in 1 eye (5%), and subretinal fibrosis in 2 eyes (10%). Subretinal fibrosis was the only permanent radiation-related side effect. CONCLUSION: Ruthenium-106 plaque radiotherapy is an effective and safe method of treatment for symptomatic circumscribed choroidal hemangiomas. The incidence of permanent visual loss is low with prompt treatment of complications.

Ruthenium-106 brachytherapy for thick uveal melanoma: reappraisal of apex and base dose radiation and dose rate.

PURPOSE: To evaluate the outcomes of ruthenium-106 ((106)Ru) brachytherapy in terms of radiation parameters in patients with thick uveal melanomas. MATERIAL AND METHODS: Medical records of 51 patients with thick (thickness ≥ 7 mm and < 11 mm) uveal melanoma treated with (106)Ru brachytherapy during a ten-year period were reviewed. Radiation parameters, tumor regression, best corrected visual acuity (BCVA), and treatment-related complications were assessed. RESULTS: Fifty one eyes of 51 consecutive patients including 25 men and 26 women with a mean age of 50.5 ± 15.2 years were enrolled. Patients were followed for 36.1 ± 26.5 months (mean ± SD). Mean radiation dose to tumor apex and to sclera were 71 (± 19.2) Gy and 1269 (± 168.2) Gy. Radiation dose rates to tumor apex and to sclera were 0.37 (± 0.14) Gy/h and 6.44 (± 1.50) Gy/h. Globe preservation was achieved in 82.4%. Preoperative mean tumor thickness of 8.1 (± 0.9) mm decreased to 4.5 (± 1.6) mm, 3.4 (± 1.4) mm, and 3.0 (± 1.46) mm at 12, 24, and 48 months after brachytherapy (p = 0.03). Four eyes that did not show regression after 6 months of brachytherapy were enucleated. Secondary enucleation was performed in 5 eyes because of tumor recurrence or neovascular glaucoma. Tumor recurrence was evident in 6 (11.8%) patients. Mean Log MAR (magnification requirement) visual acuity declined from 0.75 (± 0.63) to 0.94 (± 0.5) (p = 0.04). Best corrected visual acuity of 20/200 or worse was recorded in 37% of the patients at the time of diagnosis and 61.7% of the patients at last exam (p = 0.04). Non-proliferative and proliferative radiation-induced retinopathy was observed in 20 and 7 eyes. CONCLUSIONS: Thick uveal melanomas are amenable to (106)Ru brachytherapy with less than recommended apex radiation dose and dose rates.

Corneal Patch Graft: A New Approach for Scleral Necrosis Secondary to Plaque Radiotherapy.

PURPOSE: To evaluate the anatomical outcomes of corneal patch grafts in patients with progressive scleral necrosis secondary to plaque radiotherapy used for uveal malignant melanoma management. METHODS: In this case series, 4 patients with progressive scleral necrosis after Ru-106 plaque radiotherapy underwent corneal patch grafts with the anterior corneal button from Descemet stripping automated endothelial keratoplasty donor tissue to strengthen the sclera and to improve appearance of the eye. RESULTS: Ciliary body involvement was evident in all cases. All 4 patients had received radiation doses of 400 Gy or more to the tumor base. The mean time interval between plaque radiotherapy and scleral necrosis was 24.5 ± 7.5 months (range, 18-34 months). Successful results were achieved in all patients with tectonic graft. No patients experienced graft thinning, rejection, infection, or tumor recurrence in a mean follow-up of 28.5 ± 7.9 months (range, 20-39 months). CONCLUSIONS: Corneal patch graft by anterior corneal button from Descemet stripping automated endothelial keratoplasty donor tissue results in successful restoration of globe integrity and satisfactory cosmetic appearance in patients with scleral necrosis secondary to plaque radiotherapy.

Monte Carlo derivation of AAPM TG-43 dosimetric parameters for GZP6 Co-60 HDR sources.

Cobalt 60 source is generally available on high dose rate (HDR) afterloading equipment especially for treatment of gynecological lesions. The GZP6 remote afterloader (Nuclear Power Institute of China) utilizes (60)Co sources for treatment of intracavitary and intraluminal malignancies. In this study, the AAPM TG-43 dosimetric parameters of three sources in GZP6 system have been studied using MCNP4C Monte Carlo (MC) code; and the results are compared with other available (60)Co HDR sources. The presented parameters consist of air kerma strength, dose rate constant, radial dose function and anisotropy function. They show less than 1% uncertainty. The TG-43 based dosimetry data can be used not only to validate the dedicated treatment planning software (TPS), but also to introduce new complementary software to enhance the system performance in gynecological treatments.