Purpose This study compared a liquid to solid fiducial markers regarding visibility, artifact characteristics on X-ray imaging and dose perturbation for image-guided proton therapy (IGPT) of abdominal tumors. Additionally, the radio-opaque composition of the liquid fiducial marker was optimized, and the chemical stability after proton beam irradiation was analyzed. Material and methods The fiducial markers inserted into an anthropomorphic abdominal phantom were exposed to X-ray, single-energy computed tomography (SECT), dual-energy CT (DECT) and cone-beam CT (CBCT) to determine contrast-to-noise ratios (CNR) and artifacts. Proton dose perturbation estimations were performed using a Monte Carlo dose algorithm. Chemical stability following proton beam irradiation was assessed with biophysical and optical methods. Results The CNR of the liquid marker with a volume ≥ 100 μl (CNR ≤ 2.69) on 2D X-ray images was superior to the solid markers (CNR ≤ 1.72). The artifact areas (A) and severity in the CT modalities were more pronounced for the solid (e.g., SECT: A ≤ 279.4 mm3) than for the liquid fiducial marker (A ≤ 30.5 mm3). Dose mitigation of ≥ 50% in a proton beam was calculated for solid fiducial markers, while the liquid marker less influenced the dose distribution. Increasing radio-opaque content in the liquid prototypes improved visibility (CNR ≤ 2.97) without significantly increasing artifact volume (SECT: A ≤ 40.5 mm3) or dose perturbation. No degradation of the liquid fiducial marker’s chemical composition was observed. Conclusion The liquid fiducial marker demonstrated comparable visibility and chemical stability with reduced artifact generation and dose perturbation compared to solid markers, indicating superiority for IGPT of abdominal tumors. Optimization of the liquid marker composition may be considered.
PURPOSE Adult Filipinos are highly susceptible to differentiated thyroid carcinoma (DTC), which is managed with thyroidectomy followed by radioactive iodine (RAI) therapy. Currently, there is a lack of iodine-131 S-values for adult Filipinos undergoing RAI therapy post-thyroidectomy, posing internal dose assessment challenges. This study established iodine-131 S-values of post-thyroidectomy adult Filipino mesh-type computational phantoms, enabling organ-level internal dose assessment. METHODS The phantoms were developed by scaling the adult mesh-type reference computational phantoms (MRCPs) based on anthropometric data acquired from the University of the Philippines‒Philippine General Hospital. The thyroid of the scaled phantoms were modified to simulate the effect of thyroidectomy. The S-values of 37 target organs using nine source structures were determined using Particle and Heavy Ion Transport code System. Lastly, the S-values were compared with those of the MRCPs and the Mesh-type Reference Korean Phantoms (MRKPs). Nine phantoms were developed for each sex, representing different sizes of adult Filipinos. RESULTS Deviations were observed between their S-values and those of the adult MRCPs due to phantom scaling and thyroid size reduction. Deviations were also observed upon comparison with the S-values of the MRKPs due to organ-level anatomical differences, which persisted even when compared with adult Filipino phantoms with the closest anatomical measurements to the MRKPs. Additionally, the thyroid-thyroid S-values of the developed phantoms were independent of phantom size, highlighting the effect of thyroidectomy. CONCLUSION The collated S-values are essential in organ-level internal dose assessment, a crucial procedure for Filipinos given their high susceptibility to DTC.
Purpose To assess the feasibility and performance of color K-edge imaging using spectral photon-counting CT (SPCCT) combined with eight high-Z-elements candidates for lung functional imaging. Material and Methods Solutions of gadolinium, holmium, ytterbium, hafnium, tantalum, tungsten, gold, and bismuth, were prepared in 12 tubes from 0 to 2 mg/mL, and inserted into an anthropomorphic lung phantom (QRM GmbH). Scans were performed using lung protocols, on a clinical SPCCT (Philips, Israel), at 120 kVp and 3 radiation exposure levels (50, 75, 150 mAs). Noise and contrast-to-noise ratios (CNR) were measured in all images as well as relative percentage errors (RPE). Linear regressions (slope, intercept) of measured versus prepared concentrations and CNR versus concentration were plotted.. Results On average, mean absolute RPE ranged from 15.9%±8.0% for ytterbium to 34.7%±19.0% for bismuth. Quantification accuracy was excellent for all elements but lower for bismuth. For all elements and exposure levels, mean noise in color K-edge and conventional images was 0.030 ± 0.007 mg/mL and 20.4 ± 2.7 HU, respectively. CNR in color K-edge images increased as the concentrations increased, with an average slope (a) of 43.2 ± 11.8 mL/mg, the highest being for ytterbium (60.1 ± 8.1 mL/mg) and the lowest for bismuth (23.8 ± 5.2 mL/mg). CNR in conventional images also increased as the concentrations increased, with an average slope of 1.7 ± 0.5 mL/mg; the highest was for gadolinium (2.3 ± 0.3 mL/mg) and the lowest for tungsten (1.2 ± 0.1 mL/mg).. Conclusion Color K-edge imaging is feasible with multiple high-Z elements, whilst outperforming the performance of conventional imaging, paving the way for lung SPCCT functional imaging.
