Evaluation of ceramic marker for the treatment of ocular melanoma with proton therapy

Abstract

BioMarc Secure TM , a fiducial marker with ceramic core (zirconium oxide) and carbon coating, was evaluated for use in the localization and alignment of ocular melanoma targets using proton pencil beam scanning (PBS). Measurements and Monte Carlo (MC) simulations were performed to estimate the dose attenuation behind the marker. Imaging tests were performed to evaluate the visibility of marker for x-ray based alignment. An anthropomorphic phantom with implanted fiducial marker was scanned to obtain two-dimensional kilo-voltage (kV) x-ray and threedimensional computed tomographic (CT) images. For dose shadow measurements, an in-house phantom was constructed using solid water, Styrofoam and EBT3 gafchromic film. Dose attenuation behind the marker was measured at multiple depths and for three cardinal orientations: parallel, perpendicular, and transverse. The measurements were performed at the proton pencil beam gantry at the Seattle Cancer Care Alliance Proton Therapy center. A beam model for pencil beam gantry was created in the validated MC simulation toolkit GATE (GEANT4 Applications for Tomographic Emission). MC simulations were set up to mimic the measurement geometry and dose attenuation behind the marker was studied for a single layer PBS beam. Additional simulations were performed in water using the clinical relevant spread out Bragg peak (SOBP) beam. Qualitative analysis of the planar kV images showed excellent visibility of marker. Reconstruction artifacts in the form of light and dark streaks were present on the CT images. The film and MC simulations showed significant dose attenuation behind the marker that worsened when marker was placed close to the distal edge. Dose shadows of up to 45% and range loss of up to 1.1 mm were seen behind the marker. The transverse marker orientation in the clinical SOBP beam showed dose reduction of up to 61% and range pull-back of 2.4 mm. The dose attenuation was found to be a function of marker orientation and location within the SOBP. The analysis showed that small volumes behind the marker can see severe under-dosing. This effect should be taken into account during the planning of treatment. Comparing the results of this study to published results for tantalum marker, the BioMarc Secure marker was found to be inferior due to its greater dose attenuation and extended dose shadow on larger underlying volume. Furthermore, its bigger physical size may mean more discomfort to patient.

Treatment of ocular tumors through a novel applicator on a conventional proton pencil beam scanning beamline

“…Proton therapy is widely used for the treatment of ocular (including intra-ocular) tumors 1 – 3 with excellent control rates 4 – 6 . Although access to proton therapy has increased greatly with the opening of many of clinical proton therapy centers globally, this has not translated to increased access to proton-based ocular treatments.…”

Carbon Fiducial Markers for Tumor Localization in Stereotactic Irradiation of Uveal Melanoma

“…Habermehl et al [21] reported less radiation dose perturbation with fiducials due to zirconium's lower atomic number compared with tantalum. In contrast, Saini et al [22] noted that fiducials have a greater radiation dose attenuation than that of tantalum rings and cause greater discomfort for patients because of the larger size.…”

“…More specifically, when the markers are positioned between the tumor and radiation source, a marker shadow reduces the therapeutic effect of the irradiation. Reports have compared radiation attenuation from either fiducials or tantalum rings with use of phantom models, with varying results [18][19][20][21][22]. Studies of tantalum rings with proton beam therapy show a dose attenuation shadow that ranged from 22 to 82%, depending on marker depth and beam orientation [19].…”

Proton therapy range verification method via delayed γ-ray spectroscopy of a molybdenum tumour marker

“…The dimensions of the HTM would be similar to those of solid fiducial markers used in PT treatment planning of ocular (Newhauser et al 2007), liver (Ohta et al 2015) and prostate cancers (Huang et al 2011, Giebeler et al 2009, which are already clinically employed and are already being studied in the context of in-vivo proton RV (Cho et al 2016). The effect of artifacts on planning CT images and dose shadowing from beam perturbations, which can lead to changes to the planned dose, are already being investigated for various fiducial markers (Huang et al 2011, Cheung et al 2010, Giebeler et al 2009, Newhauser et al 2007, Habermehl et al 2013, Saini et al 2017, and will need to be carefully evaluated for each HTM. The toxicity and biological half life of the HTM in the human body will also need to be characterized.…”