Initial end-to-end testing of the ExacTrac dynamic deep inspiration breath hold workflow using a breath hold breast phantom.

ExacTrac Dynamic (ETD) provides a Deep Inspiration Breath Hold (DIBH) workflow for breast patients. Stereoscopic x-ray imaging combined with optical and thermal mapping allows localisation against simulation imaging, alongside surface guided breath hold monitoring. This work aimed to determine appropriate imaging parameters, the optimal Hounsfield Unit (HU) threshold for patient contour generation and workflow evaluation via end-to-end (E2E) positioning using a custom breast DIBH phantom. After localisation via existing Image Guidance (IG), stereoscopic imaging was performed with a range of parameters to determine best agreement. Similarly, residual errors in prepositioning were minimised using a range of HU threshold contours. E2E positioning was completed for clinical workflows allowing residual isocentre position error measurement and existing IG comparison. Parameters of 60 kV and 25mAs were determined appropriate for patient imaging and HU thresholds between -600 HU and -200 HU enabled adequate prepositioning. The average and standard deviation in residual isocentre position error was 1.0 ± 0.9 mm, 0.4 ± 1.0 mm and 0.1 ± 0.5 mm in the lateral, longitudinal and vertical directions, respectively. Errors measured using existing IG were -0.6 ± 1.1 mm, 0.5 ± 0.7 mm and 0.2 ± 0.4 mm in the lateral, longitudinal and vertical directions, and 0.0 ± 1.0o, 0.5 ± 1.7o and -0.8 ± 1.8o for pitch roll and yaw. The use of bone weighted matching increased residual error, while simulated reduction of DIBH volume maintained isocentre positioning accuracy despite anatomical changes. This initial testing indicated suitability for clinical implementation during DIBH breast treatments.

Investigation of the effects of spinal surgical implants on radiotherapy dosimetry: A study of 3D printed phantoms.

PURPOSE: The use of three-dimensional (3D) printing to develop custom phantoms for dosimetric studies in radiotherapy is increasing. The process allows production of phantoms designed to evaluated specific geometries, patients, or patient groups with a defining feature. The ability to print bone-equivalent phantoms has, however, proved challenging. The purpose of this work was to 3D print a series of three similar spine phantoms containing no surgical implants, implants made of titanium, and implants made of carbon fiber, for future dosimetric and imaging studies. Phantoms were evaluated for (a) tissue and bone equivalence, (b) geometric accuracy compared to design, and (c) similarity to one another. METHODS: Sample blocks of PLA, HIPS, and StoneFil PLA-concrete with different infill densities were printed to evaluate tissue and bone equivalence. The samples were used to develop CT to physical (PD) and effective relative electron density (REDeff ) conversion curves and define the settings for printing the phantoms. CT scans of the printed phantoms were obtained to assess the geometry and densities achieved. Mean distance to agreement (MDA) and DICE coefficient (DSC) values were calculated between contours defining the different materials, obtained from design and like phantom modules. HU values were used to determine PD and REDeff and subsequently evaluate tissue and bone equivalence. RESULTS: Sample objects showed linear relationships between HU and both PD and REDeff for both PLA and StoneFil. The PD and REDeff of the objects calculated using clinical CT conversion curves were not accurate and custom conversion curves were required. PLA printed with 90% infill density was found to have a PD of 1.11 ± 0.03 g.cm-3 and REDeff of 1.04 ± 0.02 and selected for tissue- equivalent phantom elements. StoneFil printed with 100% infill density showed a PD of 1.35 ± 0.03 g.cm-3 and REDeff of 1.24 ± 0.04 and was selected for bone-equivalent elements. Upon evaluation of the final phantoms, the PLA elements displayed PD in the range of 1.10 ± 0.03 g.cm-3 -1.13 ± 0.03 g.cm-3 and REDeff in the range of 1.02 ± 0.03-1.06 ± 0.03. The StoneFil elements showed PD in the range of 1.43 ± 0.04 g.cm-3 -1.46 ± 0.04 g.cm-3 and REDeff in the range of 1.31 ± 0.04-1.33 ± 0.04. The PLA phantom elements were shown to have MDA of ≤1.00 mm and DSC of ≥0.95 compared to design, and ≤0.48 mm and ≥0.91 compared like modules. The StoneFil elements displayed MDA values of ≤0.44 mm and DSC of ≥0.98 compared to design and ≤0.43 mm and ≥0.92 compared like modules. CONCLUSIONS: Phantoms which were radiologically equivalent to tissue and bone were produced with a high level of similarity to design and even higher level of similarity of one another. When used in conjunction with the derived CT to PD or REDeff conversion curves they are suitable for evaluating the effects of spinal surgical implants of varying material of construction.

The impact of smart metal artefact reduction algorithm for use in radiotherapy treatment planning.

The presence of metal artefacts in computed tomography (CT) create issues in radiation oncology. The loss of anatomical information and incorrect Hounsfield unit (HU) values produce inaccuracies in dose calculations, providing suboptimal patient treatment. Metal artefact reduction (MAR) algorithms were developed to combat these problems. This study provides a qualitative and quantitative analysis of the "Smart MAR" software (General Electric Healthcare, Chicago, IL, USA), determining its usefulness in a clinical setting. A detailed analysis was conducted using both patient and phantom data, noting any improvements in HU values and dosimetry with the GE-MAR enabled. This study indicates qualitative improvements in severity of the streak artefacts produced by metals, allowing for easier patient contouring. Furthermore, the GE-MAR managed to recover previously lost anatomical information. Additionally, phantom data showed an improvement in HU value with GE-MAR correction, producing more accurate point dose calculations in the treatment planning system. Overall, the GE-MAR is a useful tool and is suitable for clinical environments.

Scatter and transmission doses from several pediatric X-ray examinations in a nursery.

BACKGROUND: While several studies have investigated the dose from scattered radiation from X-ray procedures in a pediatric nursery, they examined scatter from chest procedures only, or the types of examination were not specified. OBJECTIVE: The aim of this study was to collect scatter and transmission data from several types of X-ray examinations. MATERIALS AND METHODS: Using a "newborn" anthropomorphic phantom and an ion chamber, a series of scatter and transmission dose measurements were performed using typical exposure factors for chest, chest and abdomen, skull, skeletal long bone and spine procedures. The phantom was inside a crib for all exposures. RESULTS: The maximum scatter dose measured at 1 m from the field center was about 0.05 micro Gy per exposure for lateral skulls. Transmission doses for lateral exams were around 0.1 micro Gy per exposure at 1 m from the isocenter. CONCLUSIONS: The study demonstrated that scatter dose to other patients in a neonatal unit is not significant, assuming the distance between adjacent cribs is in the order of 1 m. Transmission doses are also low provided the beam is fully intercepted by the cassette. For an average workload the dose received by imaging technologists would be small.