3D Dosimetry Based on LiMgPO4 OSL Silicone Foils: Facilitating the Verification of Eye-Ball Cancer Proton Radiotherapy

Abstract

A direct verification of the three-dimensional (3D) proton clinical treatment plan prepared for tumor in the eyeball, using the Eclipse Ocular Proton Planning system (by Varian Medical Systems), has been presented. To achieve this, a prototype of the innovative two-dimensional (2D) circular silicone foils, made of a polymer with the embedded optically stimulated luminescence (OSL) material in powder form (LiMgPO4), and a self-developed optical imaging system, consisting of an illuminating light source and a high-sensitive CCD camera has been applied. A specially designed lifelike eyeball phantom has been used, constructed from 40 flat sheet LMP-based silicone foils stacked and placed together behind a spherical phantom made by polystyrene, all to reflect the curvature of the real eyeball. Two-dimensional OSL signals were captured and further analyzed from each single silicone foil after irradiation using a dedicated patient collimator and a 58.8 MeV modulated proton beam. The reconstructed 3D proton depth dose distribution matches very well with the clinical treatment plan, allowing for the consideration of the new OSL system for further 3D dosimetry applications within the proton radiotherapy area.

A Multi-Point Optical Fibre Sensor for Proton Therapy

“…This is comparable to 2021 field size results seen for the Hyperscint TM multipoint system, which saw up to 32% discrepancy between scintillator results and the treatment planning system's calculation in the penumbral region for MeV photons [14]. The results are superior to those observed in a 3D multilayer OSL foil eye study performed by Sadel et al in 2021, though the 3D nature of the 2021 study significantly increased its complexity [27].…”

“…A reuseable array where the sensing material is not subject to radiation damage and is (relatively) easily replaced at low cost, such as small volumes of plastic optical fibre scintillators with long extensions leading to electronics outside of the irradiation chamber, would provide a cost-effective and long-lasting solution. Further, unlike the long processing time and one-time use of radiochromic film and the potential fading of signal over time and limited number of repeated readouts in optically stimulated luminescence (OSL) materials [27][28][29], after calibration, the analysis of scintillation signals obtained over an irradiation can be carried out in under 1 min using purpose-written Python code; there is no signal loss over time since the signal is digital and recorded in real time. These sensors can also be used repeatedly and, depending on the scintillator material used, experience little to no loss in signal at radiotherapeutic doses and dose rates [30].…”

Optically stimulated luminescence in state-of-the-art LYSO:Ce scintillators enables high spatial resolution 3D dose imaging

“…The spatial distribution of the energy deposited in the scintillator is reflected by the OSL-photons, which can be extracted using appropriate optical excitation and an imaging setup. As previously suggested 11 – 14 , this makes OSL an excellent photon emission candidate to develop a passive and reusable novel 3D dosimeter. Three-dimensional dosimetry is continuously being developed as an appropriate tool for validation and quantification of complex treatment plans in modern radiotherapy (RT).…”

Developing a 3D-printing-based method to create anthropomorphic dosimeters for radiotherapy-delivery verification

“…In future work, the 3D liver dosimeters will be used in proton spot scanning to investigate a protocol-specific plan during deformation in an anthropomorphic motion phantom [20]. Furthermore, replacing the radiochromic component with an optical stimulated luminescence component to make the dosimeters reusable is being investigated [21,22] which would likely increase clinical applicability.…”