Optic disc dose reduction in ocular brachytherapy using 125 I notched COMS plaques: A simulation study based on current clinical practice.

PURPOSE: Although notched Collaborative Ocular Melanoma Study (COMS) plaques have been widely used, optic disc dose reduction by notched COMS plaques has not been discussed in the literature. Therefore, this study investigated optic disc dose reduction in ocular brachytherapy using 125 I notched COMS plaques in comparison with optic disc dose for 125 I standard COMS plaques. METHODS: For this simulation study, an in-house brachytherapy dose calculation program was developed using MATLAB software by incorporating the American Association of Physicists in Medicine Task Group-43 Update (AAPM TG-43U1) dosimetry formalism with a line source approximation in a homogeneous water medium and COMS seed coordinates in the AAPM TG 129. Using this program, optic disc doses for standard COMS plaques (from 12 to 22 mm in diameter in 2 mm increments) and notched COMS plaques with one seed removed (Case #1, from 12 to 22 mm) and with two seeds removed (Case #2, from 14 to 22 mm) were calculated as a function of tumor margin-to-optic disc distance (DT) for various tumor basal dimensions (BDs) for prescription depths from 1 to 10 mm in 1 mm intervals. A dose of 85 Gy for an irradiation time of 168 h was prescribed to each prescription depth. Then absolute and relative optic disc dose reduction by notched COMS plaques (Cases #1 and #2) was calculated for all prescription depths. RESULTS: Optic disc dose reduction by notched COMS plaques (Cases #1 and #2) had five unique trends related to maximum optic disc dose reduction and corresponding optimal DT for each BD in each plaque. It increased with increasing prescription depth. CONCLUSIONS: The results presented in this study would enable the clinician to choose an adequate plaque type among standard and notched 125 I COMS plaques and a prescription depth to minimize optic disc dose.

A practical approach to estimating optic disc dose and macula dose without treatment planning in ocular brachytherapy using 125I COMS plaques.

BACKGROUND: It has been reported that proximity of the tumor to the optic disc and macula, and radiation dose to the critical structures are substantial risk factors for vision loss following plaque brachytherapy. However, there is little dosimetry data published on this. In this study, therefore, the relationship between distance from tumor margin and radiation dose to the optic disc and macula in ocular brachytherapy using 125I Collaborative Ocular Melanoma Study (COMS) plaques was comprehensively investigated. From the information, this study aimed to allow for estimation of optic disc dose and macula dose without treatment planning. METHODS: An in-house brachytherapy dose calculation program utilizing the American Association of Physicists in Medicine Task Group-43 U1 formalism with a line source approximation in a homogenous water phantom was developed and validated against three commercial treatment planning systems (TPS). Then optic disc dose and macula dose were calculated as a function of distance from tumor margin for various tumor basal dimensions for seven COMS plaques (from 10 mm to 22 mm in 2 mm increments) loaded with commercially available 125I seeds models (IAI-125A, 2301 and I25.S16). A prescribed dose of 85 Gy for an irradiation time of 168 h was normalized to a central-axis depth of 5 mm. Dose conversion factors for each seed model were obtained by taking ratios of total reference air kerma per seed at various prescription depths (from 1 mm to 10 mm in 1 mm intervals) to that at 5 mm. RESULTS: The in-house program demonstrated relatively similar accuracy to commercial TPS. Optic disc dose and macula dose decreased as distance from tumor margin and tumor basal dimension increased. Dose conversion factors increased with increasing prescription depth. There existed dose variations (<8%) among three 125I seed models. Optic disc dose and macula dose for each COMS plaque and for each seed model are presented in a figure format. Dose conversion factors for each seed model are presented in a tabular format. CONCLUSIONS: The data provided in this study would enable clinicians in any clinic using 125I COMS plaques to estimate optic disc dose and macula dose without dose calculations.

Dosimetric verification and commissioning for a small animal image-guided irradiator.

In recent years, small animal image-guided irradiators have been widely utilized in preclinical studies involving rodent models. However, the dosimetry commissioning of such equipment involving kilovoltage small-field dosimetry has not received as much interest as the megavoltage small-field dosimetry used clinically. To date, a paucity of measured kilovoltage beam data, especially for field sizes less than 3 mm, can be found in the literature. For improvement of rodent treatments in the future, this work aims to provide comprehensive and accurate beam data for the small animal radiation research platform (SARRP, Xstrahl) using EBT3 Gafchromic films and Monte Carlo calculation, with submillimeter resolution and accuracy. This work includes three primary tasks: (1) establish an optimized film measurement protocol for small field dosimetry of kilovoltage photon beam. (2) Acquire dosimetric data including (a) depth dose curves from the surface to 6 cm depth (b) beam profiles, (c) penumbra, (d) cone factors and (e) 2D dose distribution. These tasks were undertaken for a 220 kVp photon beam with five different small field widths and 33 cm source to surface distance (0.5 mm and 1 mm circular fields, 3 × 3 mm2, 5 × 5 mm2, 10 × 10 mm2 square fields). Beam data was measured with EBT3 films. (3) Provide comparative dosimetry for film measurements, Monte Carlo calculations, and the dose calculations performed with the SARRP treatment planning system, Muriplan. For the majority of parameters, film measurement agreed with Monte Carlo simulation within 1%. There were, however, discrepancies between measured beam data and Muriplan treatment planning data. Specifically, for PDD, Muriplan underestimates the dose for field sizes of 0.5 mm and 1 mm. For beam profiles comparisons, the calculation from Muriplan predicts a smaller lateral distance between the 50% isodose lines compared to film measurement. There is a difference of 0.18, 0.72, 0.6 mm between Muriplan and film for field sizes of 3, 5, 10 mm, respectively. This work demonstrates that accurate and precise kilovoltage small-field dosimetry can be conducted using EBT3 Gafchromic film with an optimized protocol. In addition, discrepancies between measured beam data and Muriplan were identified.

Antipsychotic combination using low-dose antipsychotics is as efficacious and safe as, but cheaper, than optimal-dose monotherapy in the treatment of schizophrenia: a randomized, double-blind study.

The use of antipsychotic combination has been increasing during the last decade. This study aimed to compare the efficacy and safety of low-dose amisulpride plus low-dose sulpiride with full-dose amisulpride in the treatment of acute schizophrenia. In this 6-week, double-blind, fixed-dose study, patients were randomized to antipsychotic combination (400 mg/day amisulpride plus 800 mg/day sulpiride, N=46) or monotherapy (800 mg/day amisulpride, N=46) groups. Efficacy measurements included the Positive and Negative Syndrome Scale (PANSS) and subscales, and other scales. Safety and quality of life were also assessed. Response was defined as a 30% reduction in the PANSS total score. Both groups were similar in terms of the following: (a) clinical characteristics at baseline, (b) response rates, and (c) score changes in all psychopathology measures, quality of life, and all side-effect scales after 6 weeks of treatment. There were also no significant between-group differences in changes in other safety measurement. However, the combination strategy did reduce treatment costs. The current study suggests that an antipsychotic combination of low-dose antipsychotics is as efficacious and safe as, but cheaper than, optimal-dose monotherapy in the treatment of schizophrenia.