Minimum Dose Level Research Articles

Absorbed dose evaluation of a blood irradiator with alanine, TLD-100 and ionization chamber

Irradiation of blood bags using X-ray irradiators and dosimetry services are required to ensure uniform dose levels in the range 25–50 Gy to prevent Transfusion Associated Graft versus Host Disease (TA-GvHD). An absorbed dose characterization of a Raycell MK2 X-Irradiator was performed using three different dosimetric systems. Results showed a dosimetric accuracy of the ionization chamber together with the Alanine dosimeter. TLDs measurements exhibited a small overestimation by 4% of the absorbed dose. The Dose Uniformity Ratio (DUR), between maximum and minimum dose levels in the canister, was in good agreement with the manufacturer specifications (≤1.5).

Longitudinally Heterogeneous Tumor Dose Optimizes Proton Broadbeam, Interlaced Minibeam, and FLASH Therapy.

Simple SummaryThe aim of any kind of external radiation therapy is to control a tumor with the highest possible probability of the lowest possible side effects. Here, we study further opportunities of reducing the side effects of proton therapy by applying longitudinally heterogeneous dose distributions in the tumor respecting the delivery of a minimum prescribed dose. In our simulations, the longitudinally heterogeneous dose distributions show a reduced dose in the healthy tissue already in the case of proton broadbeam irradiations, but a much higher (calculated) mean cell survival in the case of proton minibeam irradiation. This demonstrates its potential to substantially reduce side effects at a simultaneously higher tumor control probability, opening new opportunities of easier application when striving for high dose-rate applications of proton beams (>~10 Gy/s), in order to additionally profit from the so-called FLASH effects.The prerequisite of any radiation therapy modality (X-ray, electron, proton, and heavy ion) is meant to meet at least a minimum prescribed dose at any location in the tumor for the best tumor control. In addition, there is also an upper dose limit within the tumor according to the International Commission on Radiation Units (ICRU) recommendations in order to spare healthy tissue as well as possible. However, healthy tissue may profit from the lower side effects when waving this upper dose limit and allowing a larger heterogeneous dose deposition in the tumor, but maintaining the prescribed minimum dose level, particularly in proton minibeam therapy. Methods: Three different longitudinally heterogeneous proton irradiation modes and a standard spread-out Bragg peak (SOBP) irradiation mode are simulated for their depth-dose curves under the constraint of maintaining a minimum prescribed dose anywhere in the tumor region. Symmetric dose distributions of two opposing directions are overlaid in a 25 cm-thick water phantom containing a 5 cm-thick tumor region. Interlaced planar minibeam dose distributions are compared to those of a broadbeam using the same longitudinal dose profiles. Results and Conclusion: All longitudinally heterogeneous proton irradiation modes show a dose reduction in the healthy tissue compared to the common SOBP mode in the case of broad proton beams. The proton minibeam cases show eventually a much larger mean cell survival and thus a further reduced equivalent uniform dose (EUD) in the healthy tissue than any broadbeam case. In fact, the irradiation mode using only one proton energy from each side shows better sparing capabilities in the healthy tissue than the common spread-out Bragg peak irradiation mode with the option of a better dose fall-off at the tumor edges and an easier technical realization, particularly in view of proton minibeam irradiation at ultra-high dose rates larger than ~10 Gy/s (so-called FLASH irradiation modes).

An investigation using a validated method based on HS-SPME-GC-MS detection for the determination of 2-dodecylcyclobutanone and 2-tetradecylcyclobutanone in X-ray irradiated dairy products

The headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) technique was used to investigate 2-dodecylcyclobutanone (2-DCB) and 2-tetradecylcyclobutanone (2-TCB) as X-ray induced markers in irradiated dairy products. For the first time, an intensive study on several types of milk and cheeses, was carried out to evaluate both the suitability of this analytical technique for dairy products and how different factors related to these types of food, such as matrix composition, ripening time and technological processes, can affect 2-DCB and 2-TCB extraction. The results demonstrated that these analytes were identified in all types of irradiated samples, even if 2-TCB showed a lower sensibility than 2-DCB. Moreover, for both analytes, increasing irradiation dose over the experimental range of 0.5–5.0 kGy, a linear response was observed in all the matrices studied. The minimum dose level (MDL) and limit of detection (LOD), in irradiated and spiked samples, were 0.5 kGy and 5.0 μg L−1, respectively. Furthermore, linear correlation between 2-DCB and 2-TCB contents was demonstrated. Finally, chemometric analysis highlighted the influence of ripening time and dairy technological processes on extraction capability of the two investigated analytes.

Characterization of tissue-specific pre-log Bayesian CT reconstruction by texture-dose relationship.

Tissue textures have been recognized as biomarkers for various clinical tasks. In computed tomography (CT) image reconstruction, it is important but challenging to preserve the texture when lowering x-ray exposure from full- toward low-/ultra-low dose level. Therefore, this paper aims to explore the texture-dose relationship within one tissue-specific pre-log Bayesian CT reconstruction algorithm. To enhance the texture in ultra-low dose CT (ULdCT) reconstruction, this paper presents a Bayesian type algorithm. A shifted Poisson model is adapted to describe the statistical properties of pre-log data, and a tissue-specific Markov random field prior (MRFt) is used to incorporate tissue texture from previous full-dose CT, thus called SP-MRFt algorithm. Utilizing the SP-MRFt algorithm, we investigated tissue texture degradation as a function of x-ray dose levels from full dose (100mAs/120kVp) to ultralow dose (1mAs/120kVp) by using quantitative texture-based evaluation metrics. Experimental results show the SP-MRFt algorithm outperforms conventional filtered back projection (FBP) and post-log domain penalized weighted least square MRFt (PWLS-MRFt) in terms of noise suppression and texture preservation. Comparable results are also obtained with shifted Poisson model with 7×7 Huber MRF weights (SP-Huber7). The investigation on texture-dose relationship shows that the quantified texture measures drop monotonically as dose level decreases, and interestingly a turning point is observed on the texture-dose response curve. This important observation implies that there exists a minimum dose level, at which a given CT scanner (hardware configuration and image reconstruction software) can achieve without compromising clinical tasks. Moreover, the experiment results show that the variance of electronic noise has higher impact than the mean to the texture-dose relationship.

Validation of an alternative method for the identification of 2‐dodecylcyclebutanone (2‐DCB) of irradiated meats by solid‐phase microextraction (SPME) gas chromatography–mass spectrometry (GC‐MS)

SummaryA rapid and simple procedure to detect irradiated food containing fat is proposed. This method is based on HS‐SPME coupled with GC‐MS to determine the presence of a radiolytic product in irradiated meats: 2‐dodecylcyclobutanone (2‐DCB) and is proposed as an alternative to EN 1785:2003, which is a long and complex procedure. The qualitative confirmation method is validated on different type of meats: chicken, turkey, duck, beef, pork on both nonirradiated and irradiated samples at different dose levels (0.05, 0.12, 0.5, 1.0 and 3.0 kGy) with a biological X‐ray irradiator. The validation parameters investigated are selectivity, minimum dose level (MDL), limit of detection (LOD), sensitivity and specificity. The MDL and LOD values were 0.5 kGy and 5.0 ng mL−1, respectively, for all matrices. No false positives or false negatives occurred, and 100% of samples were correctly identified. The results show that HS‐SPME GC‐MS is suitable for routine analysis.

Benchmark profile and inferences for joint-exposure quantal data in quantitative risk assessment

In risk assessment, it is often desired to make inferences on the minimum dose levels (benchmark doses or BMDs) at which a specific benchmark risk (BMR) is attained. The estimation and inferences of BMDs are well understood in the case of an adverse response to a single-exposure agent. However, the theory of finding BMDs and making inferences on the BMDs is much less developed for cases where the adverse effect of two hazardous agents is studied simultaneously. Deutsch and Piegorsch [2012. Benchmark dose profiles for joint-action quantal data in quantitative risk assessment. Biometrics 68(4):1313–22] proposed a benchmark modeling paradigm in dual exposure setting—adapted from the single-exposure setting—and developed a strategy for conducting full benchmark analysis with joint-action quantal data, and they further extended the proposed benchmark paradigm to continuous response outcomes [Deutsch, R. C., and W. W. Piegorsch. 2013. Benchmark dose profiles for joint-action continuous data in quantitative risk assessment. Biometrical Journal 55(5):741–54]. In their 2012 article, Deutsch and Piegorsch worked exclusively with the complementary log link for modeling the risk with quantal data. The focus of the current paper is on the logit link; particularly, we consider an Abbott-adjusted [A method of computing the effectiveness of an insecticide. Journal of Economic Entomology 18(2):265–7] log-logistic model for the analysis of quantal data with nonzero background response. We discuss the estimation of the benchmark profile (BMP)—a collection of benchmark points which induce the prespecified BMR—and propose different methods for building benchmark inferences in studies involving two hazardous agents. We perform Monte Carlo simulation studies to evaluate the characteristics of the confidence limits. An example is given to illustrate the use of the proposed methods.

Personalized Models for Injected Activity Levels in SPECT Myocardial Perfusion Imaging.

We propose a patient-specific ("personalized") approach for tailoring the injected activities to individual patients in order to achieve dose reduction in SPECT-myocardial perfusion imaging (MPI). First, we develop a strategy to determine the minimum dose levels required for each patient in a large set of clinical acquisitions (857 subjects) such that the reconstructed images are sufficiently similar to that obtained at conventional clinical dose. We then apply machine learning models to predict the required dose levels on an individual basis based on a set of patient attributes which include body measurements and various clinical variables. We demonstrate the personalized dose models for two commonly used reconstruction methods in clinical SPECT-MPI: 1) conventional filtered backprojection (FBP) with post-filtering and 2) ordered-subsets expectation-maximization (OS-EM) with corrections for attenuation, scatter and resolution, and evaluate their performance in perfusion-defect detection by using the clinical Quantitative Perfusion SPECT software package. The results indicate that the achieved dose reduction can vary greatly among individuals from their conventional clinical dose and that the personalized dose models can achieve further reduction on average compared with a global (non-patient specific) dose reduction approach. In particular, the average personalized dose level can be reduced to 58% and 54% of the full clinical dose, respectively, for FBP and OS-EM reconstruction, while without deteriorating the accuracy in perfusion-defect detection. Furthermore, with the average personalized dose further reduced to only 16% of full dose, OS-EM can still achieve a detection accuracy level comparable to that of FBP with full dose.

Multi-scenario based robust intensity-modulated proton therapy (IMPT) plans can account for set-up errors more effectively in terms of normal tissue sparing than planning target volume (PTV) based intensity-modulated photon plans in the head and neck region

BackgroundIn a previous report, we compared the conformity of robust intensity-modulated proton therapy (IMPT) plans with that of helical tomotherapy plans for re-irradiations of head and neck carcinomas using a fixed set-up error of 2 mm. Here, we varied the maximum set-up errors between 0 and 5 mm and compared the robust IMPT-plans with planning target volume (PTV) based intensity-modulated photon therapy (IMRT).FindingsSeven patients were treated with a PTV-based tomotherapy plan. Set-up margins of 0, 2, and 5 mm were subtracted from the PTV to generate target volumes (TV) TV0mm, TV2mm, and TV5mm, for which robust IMPT-plans were created assuming range uncertainties of ±3.5% and using worst case optimization assuming set-up errors of 0, 2, and 5 mm, respectively. Robust optimization makes use of the feature that set-up errors in beam direction alone do not affect the distal and proximal margin for that beam. With increasing set-up errors, the body volumes that were exposed to a selected minimum dose level between 20% and 95% of the prescribed dose decreased. In IMPT-plans with 0 mm set-up error, the exposed body volumes were on average 6.2% ± 0.9% larger than for IMPT-plans with 2 mm set-up error, independent of the considered dose level (p < 0.0001, F-test). In IMPT-plans accounting for 5 mm set-up error, the exposed body volumes were by 11.9% ± 0.8% smaller than for IMPT-plans with 2 mm set-up error at a fixed minimum dose (p < 0.0001, F-test). This set-up error dependence of the normal tissue exposure around the TV in robust IMPT-plans corresponding to the same IMRT-plan led to a decrease in the mean dose to the temporal lobes and the cerebellum, and in the D2% of the brain stem or spinal cord with increasing set-up errors considered during robust IMPT-planning. ConclusionsFor recurrent head and neck cancer, robust IMPT-plan optimization led to a decrease in normal tissue exposure with increasing set-up error for target volumes corresponding to the same PTV.

Successful antiscalant field trial — Optimization at higher pH and seawater temperature — Larnaca Desalination Plant

A desalination plant has been operating for a number of years at elevated pH both at the first and second reverse osmosis stages at feed seawater temperature up to 30°C. The main reason for operating at higher pH was to enhance the boron rejection capability of existing membranes and thus omit the operation of the second stage whenever lower seawater temperatures allow to do so and subsequently produce more water with less energy. However, a higher pH in conjunction with high seawater temperatures creates conditions for membrane scaling. Therefore an appropriate cost effective antiscalant has to be used at minimum dose level. This paper describes field trials of selecting and applying an appropriate antiscalant and the dosing optimisation process in function of feed seawater temperature and pH.

The use of low dose x‐ray scanners for passenger screening at public transportation terminals should require documentation of the “informed consent” of passengers

The use of low dose x‐ray scanners for passenger screening at public transportation terminals should require documentation of the “informed consent” of passengers

High-dose inhaled steroid therapy for asthma

Only a small minority of patients with asthma have symptoms severe enough to require high-dose inhaled steroid therapy. Because they need more aggressive treatment, this group is disproportionately represented in tertiary care referral centers. Therapeutic effects are dose dependent, and the daily dose of steroid required to normalize pulmonary function far exceeds that for symptom relief. Studies show that, if titrated to minimum dose levels of each the combination of inhaled and oral steroids provides a better balance between antiasthmatic and systemic glucocorticoid activity compared with oral steroid alone. Also, rapidly metabolized inhaled steroids such as budesonide may be associated with a lower risk for the osteoporotic complications seen with long-term oral steroid use. However, high doses of inhaled steroids may lead to adrenocortical suppression and hence estrogen deficiency in postmenopausal women. Morning dosing may mitigate this effect. Oropharyngeal thrush may be prevented by lowering the dose frequency or using a spacer. During prolonged inhaled steroid therapy, patient compliance has proved an important determinant of outcome.

The evaluation of high-speed screen/film combinations in cephalometric radiography

Cephalometric radiographs of a tissue equivalent plastic encased dry skull, each made with eight different screen/film combinations, were compared for usefulness in making orthodontic analyses. The eight screen/film combinations chosen ranged in relative speed from 80 to 600. Only one grid cassette was used, and it was a Par speed screen/film combination. Ten orthodontists identified 13 selected anatomic landmarks and rated the adequacy of their radiographic images. The density of each cephalometric radiograph was analyzed for each anatomic landmark. The results showed a difference in density readings for the various landmarks visualized. The optical density preferences of the 13 anatomic landmarks ranged between 0.87 and 2.09. The study leads to the conclusion that cephalometric radiographs can be taken with screen/film combinations that provide maximum useful information with a minimum dose level to the patient.

Effect of intratesticular administration of gonadotropins on testicular and plasma androgen concentration in the lizard, Uromastix hardwicki

An acute effect of intratesticular injections of varying doses of ovine FSH (NIH-FSH-S12), ovine LH (NIH-LH-S20), and a lizard hypophyseal extract was observed on testicular and plasma androgen concentrations in Uromastix hardwicki. FSH and LH were used in a dose range of 0.25–4.00 ng and the hypophyseal extract was administered at concentrations representing 10–160 μg of fresh pituitary tissue obtained from adult male Uromastix. The test material was injected directly into one testis while the contralateral testis was likewise treated with an equal volume of saline. The control lizards received intratesticular injections of saline on both sides. Testicular and plasma androgen concentrations were measured 3 hr following the injections, using a specific RIA for testosterone. A significant increase in androgen concentration both in the testis and the plasma was obtained with 0.25 ng of FSH and 4.00 ng of LH. Both FSH and LH induced a significant rise in plasma androgen at 1.00 ng, but the increase was markedly greater in the FSH treated lizards. The homologous hypophyseal extract was shown to be active at the minimum dose level used (10 μg). The testosterone content of the uninjected testis in treated lizards was not significantly different from that of the control lizards. It is concluded that the intratesticular route of administration can be used as a sensitive and rapid method for studying in vivo responsiveness of the testis to mammalian and nonmammalian gonadotropins.

Continued studies on the adjuvancy effect of natural and synthetic double-stranded RNA preparations with inactivated Newcastle disease vaccines in fowls

The adjuvant effect of the natural ds-RNA, BRL 5907, with inactivated Newcastle disease vaccines was confirmed using different oil-based formulations and could be given either as single injections or separately at adjacent sites. A minimum dose level of 0-04 mg BRL 5907 per bird was required for a significant enhancement of antibody levels following vaccination. While the synthetic ds-RNA Poly IC gave a similar response to that observed with BRL 5907, no significant effects could be detected with two other natural ds-RNA materials.