Randomized, crossover trial: comparing the effects of standardized egg-white meal and Vital® on global gastric emptying parameters and intragastric meal distribution in healthy Asian participants

BACKGROUND AND AIM

Measurements of gastric emptying and accommodation for alternative test-meal protocol during gastric emptying scintigraphy (GES), such as high-calorie nutrient drinks, are not fully established. We aimed to compare the effects of standardized egg-white meal (EWM) versus high-calorie nutrient drink (Vital®; Abbott Laboratories) on global GES parameters and intragastric meal distribution at immediate scan (IMD0h).

METHODS

Of 84 screened participants, 60 asymptomatic healthy Asian population (38 females; 24.0 ± 1.5 years; 23.8 ± 2.6 kg/m2) were recruited in this 2 × 2 (AB/BA) crossover trial. Participants were randomized to a 4-h GES with 99mTc-radiolabeled EWM (~255.8 kcal), followed by a 200 mL Vital® (300 kcal), or vice versa, separated by a 2-week washout period. Global meal retention (GMR), power-exponential model emptying parameters (half-emptying [T1/2], lag phases [Tlag2%, Tlag5%, Tlag10%]), and IMD0h were determined and compared.

RESULTS

GMRs for both test meals were within the international standard references for solid GES. Compared to EWM, Vital® exhibited significantly lower GMRs (faster emptying) from 0.5 to 3 h (all P < 0.001) but comparable at 4 h (P = 0.153). Similar observations were found for the model-based T1/2 and the different Tlag thresholds (all P < 0.001). Furthermore, IMD0h was found to be lower with Vital®, indicating lower gastric accommodation (faster antral filling) immediately post-ingestion (P < 0.001). Both test meals showed significant moderate-to-strong positive associations at the late-phase GE (GMR 2-4 h, T1/2) (all P < 0.05).

CONCLUSIONS

Overall, Vital® is an acceptable alternative test meal to the EWM for GES; however, exercise caution when interpreting early-phase GE. The normative values for global GES parameters and IMD0h are also established.

Evaluation of volumetric modulated arc therapy (VMAT) - based total body irradiation (TBI) in pediatric patients

Background

The dosimetric characterization of volumetric modulated arc therapy (VMAT)-based total-body irradiation (TBI) in pediatric patients is evaluated.

Materials and methods

Twenty-two patients between the ages of 2 and 12 years were enrolled for VMAT-based TBI from 2018 to 2020. Three isocenters were irradiated over three overlapping arcs. While prescribing 90% of the TBI dose to the planning treatment volume (PTV), two fractions (2 Gy each) were delivered each day; hence 12 Gy was delivered in six fractions. During treatment optimization, the mean lung and kidney doses were set not to exceed 7 Gy and 7.5 Gy, respectively. The maximum lens dose was also set to less than 4 Gy. Patient quality assurance was carried out by comparing treatment planning system doses to the 3-dimensional measured doses by the ArcCHECK^® detector. The electronic portal imaging device (EPID) gamma indices were also obtained.

Results

The average mean lung dose was 7.75 ± 0.18 Gy, mean kidney dose 7.63 ± 0.26 Gy, maximum lens dose 4.41 ± 0.39 Gy, and the mean PTV dose 12.69 ± 0.16 Gy. The average PTV heterogeneity index was 1.15 ± 0.03. Average differences in mean kidney dose, mean lung dose, and mean target dose were 2.79% ± 0.88, 0.84% ± 0.45 and 0.93% ± 0.47, respectively; when comparing planned and ArcCHECK^® measured doses. Only grade 1-2 radiation toxicities were recorded, based on CTCAE v5.0 scoring criteria.

Conclusions

VMAT-TBI was characterized with good PTV coverage, homogeneous dose distribution, planned and measured dose agreement, and low toxicity.

Development and characterization of an LED-based detector for dosimetry in diagnostic radiology

Light-emitting diodes (LEDs) could be a potential dosimetry candidate because they are radiation hard, spectrally selective, direct band gap, and low-cost devices. Thus, an LED-based detector prototype was designed and characterized for dosimetry. A 20 × 20 cm2 array of surface mount device LED chips was sandwiched in photovoltaic mode between two intensifying screens to form a dosimetric system. The system was enclosed in a light-tight air cavity using black vinyl tape. The screens converted diagnostic X-ray beams into fluorescent blue light. LEDs, applied in detector mode, converted the fluorescent light into radiation-induced currents. A digital multimeter converted the analog currents into digital voltage signals. Prototype characterization was executed using (a) IEC 61267's RQR 7 (90 kVp) and RQR 8 (100 kVp) beam qualities, and (b) low (25 mAs) and high (80 mAs) beam quantities. A standard dosimeter probe was simultaneously exposed with the prototype to measure the prototype's absorbed dose. In all exposures, the X-ray beams were perpendicularly incident on both the dosimeter and prototype, at a fixed source to detector distance-60 cm. The LED array prototype's minimum detectable dose was 0.139 mGy, and the maximum dose implemented herein was ~ 13 mGy. The prototype was 99.18 % and 98.64 % linearly sensitive to absorbed dose and tube current-time product (mAs), respectively. The system was ± 4.69 % energy, ± 6.8 % dose, and ± 7.7 % dose rate dependent. Two prototype data sets were 89.93 % repeatable. We fabricated an ultrathin (5 mm), lightweight (130 g), and a relatively low-cost LED-based dosimetric prototype. The prototype executed a simple, efficient, and accurate real-time dosimetric mechanism. It could thus be an alternative to the current passive dosimetric systems.

Application of Bpw34 photodiode and cold white LED as diagnostic X-ray detectors: A comparative analysis

This study compares the real-time dosimetric performance of a bpw34 photodiode (PD) and cold white light-emitting diodes (LEDs) based on diagnostic X-ray-induced signals. Signals were extracted when both the transducers were under identical exposure settings, including source-to-detector distance (SDD), tube voltage (kVp), and current-time product (mAs). The transducers were in a photovoltaic configuration, and black vinyl tape was applied on transducer active areas as a form of optical shielding. X-ray beam spectra and energies were simulated using Matlab-based Spektr functions. Transducer performance analysis was based on signal linearity to mAs and air kerma, and sensitivity dependence on absorbed dose, energy, and dose rate. Bpw34 PD and cold white LED output signals were 84.8% and 85.5% precise, respectively. PD signals were 94.7% linear to mAs, whereas LED signals were 91.9%. PD and LED signal linearity to dose coefficients were 0.9397 and 0.9128, respectively. Both transducers exhibited similar dose and energy dependence. However, cold white LEDs were 0.73% less dose rate dependent than the bpw34 PD. Cold white LEDs demonstrated potential in detecting diagnostic X-rays because their performance was similar to that of the bpw34 PD. Moreover, the cold white LED array's dosimetric response was independent of the heel effect. Although cold white LED signals were lower than bpw34 PD signals, they were quantifiable and electronically amplifiable.

A Review: Photonic Devices Used for Dosimetry in Medical Radiation

Numerous instruments such as ionization chambers, hand-held and pocket dosimeters of various types, film badges, thermoluminescent dosimeters (TLDs) and optically stimulated luminescence dosimeters (OSLDs) are used to measure and monitor radiation in medical applications. Of recent, photonic devices have also been adopted. This article evaluates recent research and advancements in the applications of photonic devices in medical radiation detection primarily focusing on four types; photodiodes – including light-emitting diodes (LEDs), phototransistors—including metal oxide semiconductor field effect transistors (MOSFETs), photovoltaic sensors/solar cells, and charge coupled devices/charge metal oxide semiconductors (CCD/CMOS) cameras. A comprehensive analysis of the operating principles and recent technologies of these devices is performed. Further, critical evaluation and comparison of their benefits and limitations as dosimeters is done based on the available studies. Common factors barring photonic devices from being used as radiation detectors are also discussed; with suggestions on possible solutions to overcome these barriers. Finally, the potentials of these devices and the challenges of realizing their applications as quintessential dosimeters are highlighted for future research and improvements.