Radiological evaluation of an iodised hydrogel for prostate radiotherapy applications.

PURPOSE: Physical separation of healthy tissue and target volumes in prostate radiotherapy through the insertion of hydrogel can improve patient toxicity rates. An iodised hydrogel may provide anatomical separation of prostate and rectum while being easily visualised through radio-opacity. The aim of this study was to characterise SpaceOAR Vue™ in kilovoltage (kV) images and megavoltage (MV) radiotherapy treatment planning. METHODS: Two cassettes were 3D-printed, one filled with water and the other with SpaceOAR Vue™. Transmission dose through each cassette was measured in slab phantom geometry and compared for 6MV and 10MV photon energies. The SpaceOAR Vue™ slab phantom setup was simulated using computed tomography (CT) and a treatment plan created. The plan was calculated with the hydrogel segmented and material assignment set to water, and the resultant dose compared to corresponding measurement doses. The first 5 patients treated with SpaceOAR Vue™ were assessed with the volume and Hounsfield units (HU) of the hydrogel evaluated in CT and cone beam computed tomography (CBCT) imaging. RESULTS: Transmission through Water and SpaceOAR Vue™ agreed to within 0.5% for both photon energies. Furthermore, the segmentation of SpaceOAR Vue™ and material assignment to water, resulted in a plan dose that agreed to measurement to within 0.5%. Clinically, the SpaceOAR Vue™ volume and HU did not vary over patient treatment course, however was found to display differently on different kV imaging modalities. CONCLUSIONS: SpaceOAR Vue™ was found to be radio-opaque on kV images, but dosimetrically behaved similarly to water in MV treatment beams, making it suitable for clinical use.

Evaluation of the clinical feasibility of cone-beam computed tomography guided online adaption for simulation-free palliative radiotherapy.

Background and purpose: Simulation-free radiotherapy, where diagnostic imaging is used for treatment planning, improves accessibility of radiotherapy for eligible palliative patients. Combining this pathway with online adaptive radiotherapy (oART) may improve accuracy of treatment, expanding the number of eligible patients. This study evaluated the adaptive process duration, plan dose volume histogram (DVH) metrics and geometric accuracy of a commercial cone-beam computed tomography (CBCT)-guided oART system for simulation-free, palliative radiotherapy. Materials and methods: Ten previously treated palliative cases were used to compare system-generated contours against clinician contours in a test environment with Dice Similarity Coefficient (DSC). Twenty simulation-free palliative patients were treated clinically using CBCT-guided oART. Analysis of oART clinical treatment data included; evaluation of the geometric accuracy of system-generated synthetic CT relative to session CBCT anatomy using a Likert scale, comparison of adaptive plan dose distributions to unadapted, using DVH metrics and recording the duration of key steps in the oART workflow. Results: Auto-generated contours achieved a DSC of higher than 0.85, excluding the stomach which was attributed to CBCT image quality issues. Synthetic CT was locally aligned to CBCT anatomy for approximately 80% of fractions, with the remaining suboptimal yet clinically acceptable. Adaptive plans achieved a median CTV V95% of 99.5%, compared to 95.6% for unadapted. The median overall oART process duration was found to be 13.2 mins, with contour editing being the most time-intensive adaptive step. Conclusions: The CBCT-guided oART system utilising a simulation-free planning approach was found to be sufficiently accurate for clinical implementation, this may further streamline and improve care for palliative patients.

Diagnostic Computed Tomography Enabled Planning for Palliative Radiation Therapy: Removing the Need for a Planning Computed Tomography Scan.

PURPOSE: This study aimed to investigate the feasibility of using diagnostic computed tomography (dCT) for palliative radiation planning, removing the need for a planning computed tomography (pCT) scan. METHODS AND MATERIALS: A sequential 2-stage study was performed. Stage 1 was a retrospective analysis of 150 patients' dCTs and pCTs to review potential barriers to radiation planning, as well as assess the field of view (FOV), patient positioning, couch curvature, and Hounsfield unit (HU) variation, and its dosimetric impact. Stage 2 was a clinical implementation of dCT planning into the clinical care path. Eligible patients were simulated per the standard department protocol in the dCT position. Treatment was planned on the dCT and replicated on the pCT as a backup and comparator. The dCT plan was delivered with cone beam computed tomography (CT) image guidance. After treatment, the delivered plan was recalculated on the modified dCT to compare planned with delivered planning target volume (PTV) dose. RESULTS: Positron emission tomography-CT imaging was the most suited for diagnostic treatment planning. Metastases in the pelvis, abdomen, thoracic, and lumbar spines were the most reproducible. A curved, full-body vac-bag was designed to enable better replication of the posterior body curvature of dCT for treatment. There was minimal variation in mean HU from dCT to pCT scans. Dose difference due to HU variation in the thorax region due to the low-density tissue had the greatest variation. All patients in stage 2 (n = 30) were successfully treated using the dCT plan. Dosimetric evaluations were conducted comparing dCT and modified dCT plans, with the 95% dose coverage change in PTV between -2% to +2.5%. CONCLUSIONS: For palliative patients with bony and soft-tissue metastases, clinically acceptable plans can be produced using dCT. Diagnostic position can be replicated at treatment, eliminating the need for pCT with implications for streamlining and improving care for patients who require palliative radiation therapy.

A novel quality assurance system for eye plaque brachytherapy.

Eye Plaque brachytherapy pre-treatment quality assurance (QA) conducted clinically involves an activity verification of individual seeds via well chamber and does not include a physical measurement of dose-rate of the final assembly. A novel spectroscopic, dose-rate detection system, was evaluated for pre-treatment QA of eye plaque brachytherapy. The system includes a water phantom with sterility management. The system was calibrated using a known-activity I-125 seed, measured at 1 cm in water along the radial axis, compared to TG-43 U1 calculations and verified over a number of distances. A depth dose curve was acquired for a clinical, mixed activity eye plaque and two 'error' plaques. The probe was stepped from a water equivalent source to a detector distance (SDD) of 2.5 to 12 mm along the plaque central axis. The latter measurements aimed to characterise the sensitivity of the system. The calculated and measured single-seed dose-rates agreed to within 0.5 cGy/h from a SDD of 3 mm and above. The clinical plaque showed agreement between measured and treatment planning system (TPS) calculated dose-rates within 2%. Sensitivity testing resulted in a maximum deviation from TPS data of 18%, therefore was able to detect the presence of packing errors. The dose-rate detection system was successfully evaluated for verification of I-125 based eye plaques without compromising sterility, allowing for quick pre-treatment, dose-rate verification of patient-ready plaques. Its agreement with TPS data for the unmodified plaque and its deviation when introducing errors confirms the approach suggested is a viable QA tool.

Semiconductor real-time quality assurance dosimetry in brachytherapy.

With the increase in complexity of brachytherapy treatments, there has been a demand for the development of sophisticated devices for delivery verification. The Centre for Medical Radiation Physics (CMRP), University of Wollongong, has demonstrated the applicability of semiconductor devices to provide cost-effective real-time quality assurance for a wide range of brachytherapy treatment modalities. Semiconductor devices have shown great promise to the future of pretreatment and in vivo quality assurance in a wide range of brachytherapy treatments, from high-dose-rate (HDR) prostate procedures to eye plaque treatments. The aim of this article is to give an insight into several semiconductor-based dosimetry instruments developed by the CMRP. Applications of these instruments are provided for breast and rectal wall in vivo dosimetry in HDR brachytherapy, urethral in vivo dosimetry in prostate low-dose-rate (LDR) brachytherapy, quality assurance of HDR brachytherapy afterloaders, HDR pretreatment plan verification, and real-time verification of LDR and HDR source dwell positions.