Search

Background: Ocular melanoma is a rare kind of eye malignancy that threatens the patient's eyesight. Radiotherapy and surgical removal are the most commonly used therapeutic modalities, and nanomedicine has lately entered this field. Brachytherapy using Ruthenium‐106 (106Ru) ophthalmic plaques has been used for decades to treat ocular melanoma, with the applicator placed on the patient's eyes until the prescribed dose reaches the tumor apex. Purpose: To investigate the efficiency of hydrogen nanobubbles (H2‐NBs) employment during intraocular melanoma brachytherapy using a 106Ru electron emitter plaque. Methods: The Monte Carlo (MC) simulation and experimental investigation using a 3D‐designed phantom and thermoluminescence dosimetry (TLD) were employed. Various concentrations of H2‐NBs with a diameter of 100 nm were simulated inside tumor tissue. The results were presented as deposited energy and dose enhancement factor (DEF). An equivalent Resin phantom of the human eyeball was made using AutoCAD and 3D‐Printer technologies. The glass‐bead TLDs dosimeter were employed and placed inside the phantom. Results: Using a 1% concentration of H2‐NBs, a DEF of 93% and 98% were achieved at the tumor apex of 10 mm from the experimental setup and MC simulation, respectively. For simulated concentrations of 0.1%, 0.3%, 0.5%, 1%, and 4% H2‐NBs, a maximum dose enhancement of 154%, 174%, 188%, 200%, and 300% were achieved, respectively, and a dose reduction was seen at about 3 mm from the plaque surface. Conclusion: H2‐NBs can be used as an absorbed dose enhancer in 106Ru eye brachytherapy because of their unique physical characteristics. Reducing plaque implantation time on the patient's eye, reducing sclera absorbed dose, and decreasing the risk of patients' healthy organs irradiation are reported as some of the potential benefits of using H2‐NBs. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to evaluate the feasibility of defining an in vivo dosimetry (IVD) protocol as a patient‐specific quality assurance (PSQA) using the bead thermoluminescent dosimeters (TLDs) for point and 3D IVD during brachytherapy (BT) of gynecological (GYN) cancer using 60Co high‐dose‐rate (HDR) source. Methods: The 3D in vivo absorbed dose verification within the rectum and bladder as organs‐at‐risk was performed by bead TLDs for 30 GYN cancer patients. For rectal wall dosimetry, 80 TLDs were placed in axial arrangements around a rectal tube covered with a layer of gel. Ten beads were placed inside the Foley catheter to get the bladder‐absorbed dose. Beads TLDs were localized and defined as control points in the treatment planning system (TPS) using CT images of the patients. Patients were planned and treated using the routine BT protocol. The experimentally obtained absorbed dose map of the rectal wall and the point dose of the bladder were compared to the TPSs predicted absorbed dose at these control points. Results: Relative difference between TPS and TLDs results were −8.3% ± 19.5% and −7.2% ± 14.6% (1SD) for rectum‐ and bladder‐absorbed dose, respectively. Gamma analysis was used to compare the calculated with the measured absorbed dose maps. Mean gamma passing rates of 84.1%, 90.8%, and 92.5% using the criteria of 3%/2 mm, 3%/3 mm, and 4%/2 mm were obtained, respectively. Eventually, a "considering level" of at least 85% as pass rate with 4%/2‐mm criteria was recommended. Conclusions: A 3D IVD protocol employing bead TLDs was presented to measure absorbed doses delivered to the rectum and bladder during GYN HDR‐BT as a reliable PSQA method. 3D rectal absorbed dose measurements were performed. Differences between experimentally measured and planned absorbed dose maps were presented in the form of a gamma index, which may be used as a warning for corrective action. [ABSTRACT FROM AUTHOR]

Introduction In order to treat uveal Melanoma, first, radioactive seeds are laid on a silicone- made substance which is called Silastic after that they are inserted in the plaque, and finally, this plaque containing silicone-made substance is stitched to the sclera surface. The dose gradient within the tumor and healthy tissues can be varied due to changing the Silastic thickness between sclera surface and radioactive seeds. In turn, this leads to difference in the amount of absorbed dose of tumor and healthy tissues. Present study is to investigate the optimum Silastic thickness in uveal Melanoma brachytherapy. Materials and Methods To measure changes of depth dose of the plaque in a sphere with a radius of 12 mm, MCNP4C code was applied. Exact specifications of a 20-mm Collaborative Ocular Melanoma Study (COMS) plaque, Silastic and three I-125 seed sources, 6711 model were integrated in simulation. Dose calculations were performed using F6 tally in spheres with a radius of 0.2 mm. Results By measuring the changes of dose rate of plaque in distances of 0.2 to 18 mm from the sclera surface and having the prescribed dose for the absolute treatment of eye melanoma, final absorbed doses by tumor and healthy tissues for each different Silastic thicknesses of 0, 0.5, 1, 1.5, and 2 were calculated. Conclusion Considering the results and sclera tolerance, it was concluded that the thickness of Silastic must not exceed 0.5 mm, because increasing the Silastic thickness from this area, increases absorbed dose by healthy tissues and also the treatment time. [ABSTRACT FROM AUTHOR]

To investigate the 106Ru dose distribution in an intraocular pseudotumor by micro silica glass beads thermo-luminescence dosimeters (TLD). Dosimetry was conducted using Monte Carlo (MC) simulation as well as an experimental setup by employing an in-house eye equivalent phantom. A BEBIG CCA model of 106Ru plaque was used. Bead TLDs were modeled using MCNPX code, choosing water and plexiglass as phantom mediums along with CCA plaque. The deposited energy and electron energy spectra were calculated using *f8 and f4 tallies, respectively. A dedicated eye-equivalent phantom was designed and fabricated by 3D-printing techniques to place glass beads. Absorbed dose at the central axis of the CCA plaque by beads TLDs was compared to manufacturer-reported data and simulation results. Maximum, minimum, and mean relative differences of 23%, 7%, and 15% with the manufacturer and 14%, 0%, and 1.6% with the simulation were obtained, respectively. Replacing glass bead material with water resulted in an average relative difference of 33.9% in absorbed energy per mass unit, corresponding to 21% and 44.8% at the first (0.5 mm depth) and last dosimetry points (9.5 mm depth), respectively. It has also been shown that glass beads can shadow each other, leading to a dose reduction of 15%. A specific eye equivalent phantom with a pseudotumor was constructed, and silica glass beads were used for dosimetry. The results of the experiment and the MC simulation are in good accord. In the case of 106Ru ophthalmic brachytherapy plaque dosimetry, replacing glass beads material with water led to a mean difference of about 34% as well as shadowing effects. This emphasizes how crucial it is to employ a reliable correction factor in clinical applications. • Creating an eye equivalent phantom capable of introducing different materials as tumour foundation. • Using TLD glass beads as a dosimeter in ocular plaque dosimetry. • Monte Carlo analysis of glass beads' material as a dosimeter. • Glass beads vs. water show 33.95% dose difference in CCA plaque dosimetry, highlighting correction factor importance. [ABSTRACT FROM AUTHOR]