CIRS Anthropomorphic Phantom Research Articles

Dose comparative study between two different 3D mobile intra-operative systems

3D imaging devices, when coupled to an image guided surgery system, allow for a more precise surgical approach than classical C-arms. Nevertheless, the exposure to radiation of both patient and staff remains a concern and therefore the choice of imaging device plays an important role. Two 3D imaging systems, an imaging mobile device with an O-ring geometry and an imaging mobile device with a C-arm geometry, have been compared in terms of absorbed doses to organs as well as ambient dose equivalent. Absorbed organ doses were evaluated for thoracic and pelvic examinations using TLDs placed within a CIRS anthropomorphic phantom representing an adult woman. Equivalent ambient dose measurements were performed at various positions in the room around the X-ray system using a calibrated dose rate meter. Results suggest that the O-ring system exposes both patient and staff to higher levels of radiation than the C-arm system. Indeed, organ absorbed doses were found to be 3.5 and 1.7 higher for the O-ring system than for the C-arm system for the same thoracic and pelvic explorations respectively. Concerning the ambient dose equivalent, it was found that for a single 3D image acquisition at a radial distance of one meter from the isocentre, measurements for the O-ring system were approximately 30% larger than the C-arm system.

Dosimetry assessment of patient-specific 3D printable materials for HDR surface brachytherapy

Purpose3D printable material water equivalence was investigated within the range of Iridium-192 source energies. The aim is to compare the dose calculated by our treatment planning system (TPS) with the dose measured in the presence of printed materials. The purpose of this investigation is to assess the feasibility of using 3D materials for brachytherapy surface applicators. Methods and materialsCheetah was examined both in a water tank and with the CIRS anthropomorphic phantom. Calibrated Gafchromic EBT3-V3 film was used and the measurements compared with TG-43 calculations on Oncentra®Brachy. A 3D-printed slab 5 mm thick was created to position the source and two films were irradiated at 5 mm and 15 mm of distance. A curved mould with 7 trajectories was created and coupled with CIRS phantom. A set of CT images of phantom and mould was acquired and imported on TPS, where a target was defined and a dose plan was created. Plan was delivered with two films positioned between two different slabs of phantom, at reciprocal distance of 2 cm, orientated perpendicularly to the source axis. ResultsAll PDDs show a maximum difference of 4.7% (average 2.2%). At 5 mm and at 15 mm, the gamma pass rate is 100% with tolerance 2%/1 mm DTA. Results of films placed intra-slabs show a high pass rate (>99%) with tolerances of 2% dose and 1 mm DTA. Conclusion3D material investigated is water equivalent at Ir-192 energies and agreed with Oncentra®Brachy dose calculations which suggest that it is a suitable material for superficial brachytherapy.

Characterization of a novel liquid fiducial marker for multimodal image guidance in stereotactic body radiotherapy of prostate cancer.

Liquid fiducial markers have shown to be a promising alternative to solid gold markers in terms of imaging artifact reduction, patient comfort, and compatibility with different imaging modalities. This study aims to investigate the performance of the novel BioXmark® liquid marker for state-of-the-art multimodal imaging used in prostate cancer (PCa) radiotherapy, encompassing kV CT/CBCT, multiparametric MRI, and kV x-ray imaging. In addition, automatic detection of the liquid markers in x-ray imaging for prostate motion monitoring during treatment was investigated. A total of eight BioXmark® liquid markers with varying volumes (range 5-300 μL) were casted on a square grid into a gelatin phantom insert. A cylindrical gold marker (QLRAD, length = 7 mm, Ø = 1 mm) was inserted for reference. Liquid marker visibility and streaking artifacts in CT/CBCT imaging were evaluated by placing the gelatin phantom into a CIRS anthropomorphic phantom. Relevant MRI characteristics such as the T2 and T1 relaxation times, the ADC value, and the relative proton density (ρH) were quantified by placing the gelatin phantom insert next to a T1MES mapping phantom and a water-filled syringe for reference. Ex vivo multiparametric MRI images were acquired by placing the gelatin phantom next to a resected prostate specimen. Anterior-posterior x-ray projection images were obtained by placing the gelatin phantom insert on top of an anthropomorphic pelvic phantom with internal pelvic bony structures and were acquired for five positions relative to the bony anatomy and 24 clinically relevant x-ray exposure settings. To quantify individual automatic marker detection, single markers were artificially isolated in the x-ray images using postprocessing. Markers of all sizes were clearly visible on CT and CBCT images with only the largest marker volumes (100-300 μL) displaying artifacts similar in size to the gold fiducial marker. Artifact size increased with increasing liquid marker volume. Liquid markers displayed good contrast in ex vivo T1-weighted and ρH-weighted images. The markers were not visible in the ex vivo T2-weighted image. The liquid markers induced a chemical shift artifact in the obtained ADC-map. Automated detection in x-ray imaging was feasible with high detection success (four of five positions) for marker volumes in the range of 25-200 μL. None of the liquid markers were detected successfully when superimposed on a bony edge, independent of their size. This study is the first to show the compatibility of BioXmark® liquid markers with multimodal image-guided radiotherapy for PCa. Compared to a solid gold marker, they had favorable results in both visibility and induced imaging artifacts. Liquid marker visibility in MRI imaging of the prostate does not solely depend on the low ρH value (not visible on T2-weighted image) but is also influenced by its relaxation times. Automated marker detection in x-ray images was feasible but better adapted marker detection algorithms are necessary for marker localization in the presence of bony edges. Hence, the liquid marker provides a minimally invasive (fine needles) and highly applicable alternative to current solid gold markers for multimodal image-guided prostate radiotherapy treatments.

WE‐E‐M100F‐04: Commissioning and Validation of a Beam Model for Calculating Megavoltage CT Dose From Imaging with a Helical Tomotherapy Unit

Purpose: To commission and validate an MVCT beam model that allows for the calculation of dose received by patients due to megavoltage imaging on a helical tomotherapy unit (Tomotherapy, Inc., Madison, WI). Method and Materials: Percent depth dose and profile data were collected in order to commission a new MVCT beam model. The fluence output for the beam model was adjusted to match the measured dose in phantom. The model was then verified through a series of absorbed dose measurements in three phantoms (20‐cm cylindrical phantom, CIRS anthropomorphic phantom, and 30‐cm “cheese” phantom). The multiple scan average dose was recorded for all three phantoms with various changes to CT collimator pitch and ion chamber location (central versus peripheral points). Results: The delivered doses and the computed doses were on average within 1.5% for all three phantoms, when the ion chamber was centrally located; and within 3.5%, when the chamber was located on the peripheral edge of the phantoms. The measured dose in the anthropomorphic phantom was 2.3 cGy with a pitch of 1.0 (4 mm couch movement per gantry rotation), 1.4 cGy with a pitch 2.0, and 0.90 cGy with a pitch of 3.0, these matched within 1% to the calculated dose. The computed versus measured dose was also within 1% when calculating dose in different tissue densities (lung and bone). Conclusion: This study has shown that with the development of a new MVCT beam model, dose delivered from MVCT imaging can be calculated. Validation measurements, in phantom, have verified that the computed dose can be reported to within 1.5% of the measured dose. The rationale for implementing this MVCT beam model is to provide a future method for calculating patient‐specific MVCT dose. Conflict of Interest: Co‐authors are either funded by a research grant or employed by TomoTherapy, Inc.