PAE planning: Radiation exposure and image quality of CT and CBCT.

PURPOSE: To determine accurate organ doses, effective doses, and image quality of computed tomography (CT) compared with cone beam CT (CBCT) for correct identification of prostatic arteries. METHOD: A dual-energy CT scanner and a flat-panel angiography system were used. Dose measurements (gallbladder (g), intestine (i), bladder (b), prostate (p), testes (t), active bone marrow of pelvis (bmp) and femura (bmf)) were performed using an anthropomorphic phantom with 65 thermoluminescent dosimeters in the pelvis and abdomen region. For the calculation of the contrast-to-noise ratio (CNR) of the pelvic arteries, a patient whose weight and height were almost identical to those of the phantom was selected for each examination type. RESULTS: The effective dose of CT was 2.7 mSv and that of CBCT was 21.8 mSv. Phantom organ doses were lower for CT than for CBCT in all organs except the testes (g: 1.2 mGy vs. 3.3 mGy, i: 5.8 mGy vs. 23.9 mGy, b: 6.9 mGy vs. 19.4 mGy, p: 6.4 mGy vs. 13.2 mGy, t: 4.7 mGy vs. 2.4 mGy, bmp: 5.1 mGy vs. 18.2 mGy, bmf: 3.3 mGy vs. 6.6 mGy). For human pelvic arteries, the CNR of CT was better than that of CBCT, with the exception of one prostate artery that showed stenosis on CT. Evaluation by experienced radiologists also confirmed the better detectability of prostate arteries on CT examination. CONCLUSIONS: In our study preprocedural CT had lower organ doses and better image quality comparedd with CBCT and should be considered for the correct identification of prostatic arteries.

Radiation Exposure and Frequency of Dental, Bitewing and Occlusal Radiographs in Children and Adolescents.

Dental radiographs are valuable diagnostic aids for oral healthcare, but exposure to ionizing radiation carries health risks, especially in children due to their high radio-sensitivity. Valid reference values for intraoral radiographs in children and adolescents are still missing. This study aimed to investigate the radiation dose values and underlying justifications of dental, bitewing and occlusal X-rays in children and adolescents. Data from routinely executed intraoral radiographs between 2002 and 2020 with conventional and digital tube-heads were extracted from the Radiology Information System. The effective exposure was calculated from technical parameters and statistical tests performed. A total number of 4455 intraoral (3128 dental, 903 bitewing and 424 occlusal) radiographs were investigated. For dental and bitewing radiographs, the dose area product (DAP) was 2.57 cGy × cm2 and the effective dose (ED) 0.77 µSv. For occlusal radiographs, the DAP was 7.43 cGy × cm2 and the ED 2.22 µSv. Overall, 70.2% of all intraoral radiographs were dental, 20.3% bitewing and 9.5% occlusal radiographs. The most frequent indication for intraoral radiographs was trauma (28.7%), followed by caries (22.7%) and apical diagnostics (22.7%). Moreover, 59.7% of all intraoral radiographs were taken in boys, especially for trauma (66.5%) and endodontics (67.2%) (p ≤ 0.00). Girls were significantly more frequently X-rayed for caries diagnostics than boys (28.1% vs. 19.1%, p ≤ 0.00). The average ED of 0.77 µSv for intraoral dental and bitewing radiographs in this study was within the range of other reported values. The technical parameters of the X-ray devices were found at the lowest recommended levels to best limit the radiation exposure and to assure acceptable diagnostic efficacy. Intraoral radiographs were performed predominantly for trauma, caries and apical diagnostics-reflecting general recommendations for the use of X-rays in children. For improved quality assurance and radiation protection, further studies are necessary to determine the meaningful dose reference level (DRL) for children.

Frequency of Dental X-ray Diagnostics in Children and Adolescents: What Is the Radiation Exposure?

Children are exposed to ionizing radiation through radiographs during their development for various reasons. At present, there are no officially valid reference values for dental X-rays in children and adolescents for dental X-ray diagnostics. This study retrospectively examined 9680 extraoral dental radiographs in pediatric patients between 2002 and 2020. The aim was to analyze the radiation doses in pediatric patients, which indications were used, and whether there were specific age and gender differences. The evaluation showed that radiation doses were considered low, with dose area products of 2.2 cGy × cm2 for a lateral cephalogram, 14 cGy × cm2 for an orthopantomogram (OPG), and 45 cGy × cm2 for cone beam computer tomography (CBCT). This corresponds to an effective dose of 1.5 µSv for a lateral cephalogram, 7 µSv for an OPG, and 33.8 µSv for CBCT. Of the 9680 images, 78% were orthopantomograms, and only 0.4% were CBCT images. OPG has become more important over the years, as reflected in the indication. Approximately one-third of all extraoral exposures are orthodontic indications. Overall, the indications were similar for both genders. According to the dental indications, boys were X-rayed slightly more frequently than girls (54.5-45.5%). A future publication of dose guide values and corresponding guidelines is of high priority.

Evaluation of the post-processing algorithms SimGrid and S-Enhance for paediatric intensive care patients and neonates.

BACKGROUND: Post-processing software can be used in digital radiography to achieve higher image quality, especially in cases of scattered radiation. SimGrid is a grid-like software based on a Convolutional Neuronal Network that estimates the distribution and degree of scattered radiation in radiographs and thus improves image quality by simulating an anti-scatter grid. S-Enhance is an algorithm programmed to improve contrast visibility of foreign material. OBJECTIVE: The objective of this study was to evaluate the SimGrid and S-Enhance digital radiography post-processing methods for neonatology and paediatric intensive care. MATERIALS AND METHODS: Two hundred and ten radiographs from the neonatal (n = 101, 0 to 6 months of age) and paediatric (n = 109, 6 months to 18 years of age) intensive care units performed in daily clinical routine using a mobile digital radiography system were post-processed with one of the algorithms, anonymized and then evaluated comparatively by two experienced paediatric radiologists. For every radiograph, patient data and exposure data were collected and analysed. RESULTS: Analysis of different radiographs showed that SimGrid significantly improves image quality for patients with a weight above 10 kg (range: 10-30 kg: odds ratio [OR] = 6.683, P < 0.0001), especially regarding the tracheobronchial system, intestinal gas, and bones. Utilizing S-Enhance significantly advances the assessment of foreign material (OR = 136.111, P < 0.0001) and bones (OR = 34.917, P < 0.0001) for children of all ages and weight, whereas overall image quality decreases. CONCLUSION: SimGrid offers a differentiated spectrum in image improvement for children beyond the neonatal period whereas S-Enhance especially improves visibility of foreign material and bones for all patients.

[Radiophysical characteristics of different detectors for use in dosimetry]. / Strahlenphysikalische Einflussgrössen bei der Dosimetrie mit verschiedenen Detektortypen.

The present study investigated the radiophysical influences on the measurement of dosimetry basic data, attributable to field size, photon energy and detector type. A natural diamond detector, two ionisation chambers, different Si-diodes and a EBT-Gafchromic film were studied for this purpose. The characteristics of the detectors were investigated with regard to the measurement of output factors, lateral beam profiles and relative depth-dose curves for narrow and wide photon beams of 15 MV Significant differences in output factors were obtained with different detectors. For narrow fields, the natural diamond detector and the diodes PTW-60012 and SCX_WH-PFD measured output factors close to those of the EBT-Gafchromic film. The output facto rfor large fields was overestimated by the unshielded diode PTW 60012 and the PinPoint-chamber PTW-31006 because of their over-response to scattered photons. The relative depth dose distributions for wide beams at large depths agree well for the diamond, the ionisation chambers and the shielded Diode SCX_ WH-PFD and PTW-60008, while the measured dose was overestimated by an unshielded diode PTW-60012. Considering the influence due to the sensitive materials and the construction of the detectors the manufacturers of dosimeters have specified the application ranges for the various types of detectors.

IMRT with compensators for head-and-neck cancers treatment technique, dosimetric accuracy, and practical experiences.

BACKGROUND AND PURPOSE: With three-dimensional conformal intensity-modulated radiotherapy (3D-c-IMRT) a heterogeneous dose distribution can be achieved in both planning treatment volume and in adjacent normal tissues and organs to be spared. 3D-c-IMRT demands for modified photon fluence profiles which can be accomplished with different techniques. This report deals with the commissioning of metal compensators and the first experiences in clinical use. Dosimetric accuracy, dose coverage and practical experience like treatment delivery time, monitor units and dose outside the treated volume are evaluated. PATIENTS AND METHODS: From January 2002 to April 2004, 24 patients with head-and-neck cancers were treated with 3D-c-IMRT using tin-wax compensators. The dose prescription included a simultaneously integrated boost (SIB). High-dose volume was irradiated with 60-70 Gy (median 66 Gy), low-dose volume with 48-54 Gy (median 52 Gy) administered by a standardized seven- portal coplanar beam arrangement. Dose at one parotid gland was aimed at 26 Gy. The compensators used consisted of tin granules embedded in wax; recalculation was performed with compensators made of the alloy MCP96 as well. RESULTS: In 21 of 24 patients 3D-c-IMRT with tin-wax compensators reduced the median dose to one parotid gland to < 30 Gy. Recalculation with compensators with higher density which allowed higher attenuation revealed better protection of the parotid gland. The treatment delivery time per fraction was between 6 and 12 min (plus time for patient positioning), approximately 300 MU per 2 Gy were applied. The dose outside the treated volume was increased with regard to open fields and comparable with a physical wedge of 15-30 degrees . Quality assurance and treatment of patient were fast and simple. It was shown, that calculated dose distribution corresponded to measured dose distribution with high accuracy. CONCLUSION: The described method offers facilities for a good dose coverage of irregular target volumes with different prescribed doses and a considerable dose reduction in adjacent organs at risk. The dose sparing of organs at risk can be further improved, if a compensator material with higher density is used.

Dosimetric quality assurance for intensity-modulated radiotherapy feasibility study for a filmless approach.

PURPOSE: Test and comparison of various 2-D real-time detectors for dosimetric quality assurance (QA) of intensity-modulated radiotherapy (IMRT) with the vision to replace radiographic films for 2-D dosimetry. MATERIAL AND METHODS: All IMRT treatment plans were created with the Konrad software (Siemens OCS). The final dose calculation was also carried out in Konrad. A Mevatron Primus (Siemens OCS) linear accelerator which provides 6-MV and 15-MV highenergy photon beams was used for the delivery of segmented multileaf-modulated IMRT. Three different 2-D detectors, each based on a different physical (interaction) principle, were tested for the field-related IMRT verification: (1) the MapCheck diode system (Sun Nuclear), (2) the I'mRT QA scintillation detector (Scanditronix/Wellhöfer), and the Seven29 ionization chamber array (PTW). The performance of these detector arrays was evaluated against IMRT dose distributions created and calculated with Konrad and the results obtained were compared with film measurements performed with radiographic films (EDR2, Kodak). Additionally, measurements were performed with point detectors, such as diamond, diodes (PTW) and ionization chambers (PTW, Scanditronics/ Wellhöfer) and radiochromic films (GafChromic film MD55, ISP). RESULTS: The results obtained with all three 2-D detector systems were in good agreement with calculations performed with the treatment-planning system and with the standard dosimetric tools, i.e., films or various point dose detectors. It could be shown that all three systems offer dosimetric characteristics required for performing field-related IMRT QA with relative dose measurements. The accuracy of the 2-D detectors was mostly +/- 3% normalized to dose maximum for a wide dynamic range. The maximum deviations did not exceed +/- 5% even in regions with a steep dose gradient. The main differences between the detector systems were the spatial resolution, the maximal field size, and the ability to perform absolute dosimetric measurements. CONCLUSION: Commercial 2-D detectors have the potential to replace films as an "area detector" for field-related verification of IMRT. The on-line information provided by the respective systems can even improve the efficiency of the QA procedures.

[Improvement of the accuracy of the Laplace transform method for the determination of radiotherapy spectra of clinical linear accelerators]. / Erhöhung der Genauigkeit der Laplace-Transformations-methode zur Bestimmung des Bremsstrahlungsspektrums klinischer Linearbeschleuniger.

The present study focused on the reconstruction of the bremsstrahlung spectrum of a clinical linear accelerator from the measured transmission curve, with the aim of improving the accuracy of this method. The essence of the method was the analytic inverse Laplace transform of a parameter function fitted to the measured transmission curve. We tested known fitting functions, however they resulted in considerable fitting inaccuracy, leading to inaccuracies of the bremsstrahlung spectrum. In order to minimise the fitting errors, we employed a linear combination of n equations with 2n-1 parameters. The fitting errors are now considerably smaller. The measurement of the transmission function requires that the energy-dependent detector response is taken into account. We analysed the underlying physical context and developed a function that corrects for the energy-dependent detector response. The factors of this function were experimentally determined or calculated from tabulated values.

VERIDOS: a new tool for quality assurance for intensity modulated radiotherapy.

BACKGROUND: The use of intensity modulated radiation fields needs an extended quality assurance concept. This consists of a linac related part and a case related part. Case related means the verification of an individual treatment plan, optimized on a CT data set of an individual patient and prepared for the treatment of this patient. This part of the quality assurance work is usually time consuming, delivers only partially quantitative results and is uncomfortable without additional help. It will be shown in this paper how the software VERIDOS will improve the optimization of the case related part of the quality assurance work. MATERIAL AND METHODS: The main function of the software is the quantitative comparison of the calculated dose distribution from the treatment planning software with the measured dose distribution of an irradiated phantom. Several additional functions will be explained. Two self-developed phantoms made of RW3 (solid water) and GAFCHROMIC films or Kodak EDR2 films for the measurement of the dose distributions were used. VERIDOS was tested with the treatment planning systems Helay-TMS and Brainscan. RESULTS: VERIDOS is a suitable tool for the import of calculated dose matrices from the treatment planning systems Helax-TMS and Brainscan and of measured dose matrices exported from the dosimetry software Mephysto (PTW). The import from other treatment planning systems and scanning software applications for film dosimetry is generally possible. In such case the import function has to be adapted to the special header of the import matrix. All other functions of this software tool like normalization (automatically, manually), working with corrections (ground substraction, factors), overlay/comparison of dose distributions, difference matrix, cutting function (profiles) and export functions work reliable. CONCLUSIONS: VERIDOS improves the optimization of the case related part of the quality assurance work for intensity modulated radiation therapy (IMRT). The diverse functions of the software offer the radiation physicist a wide base to verify the IMRT plan independent from the mode of its delivery (compensator technology or MLC technology).

[Intensity modulated radiotherapy (IMRT) with compensators]. / Intensitätsmodulierte Strahlentherapie (IMRT) mit Kompensatoren.

The irradiation with intensity-modulated fields is possible with static as well as dynamic methods. In our university hospital, the intensity-modulated radiotherapy (IMRT) with compensators was prepared and used for the first time for patient irradiation in July 2001. The compensators consist of a mixture of tin granulate and wax, which is filled in a milled negative mould. The treatment planning is performed with Helax-TMS (MDS Nordion). An additional software is used for editing the modulation matrix ("Modifix"). Before irradiation of the first patient, extensive measurements have been carried out in terms of quality assurance of treatment planning and production of compensators. The results of the verification measurements have shown that IMRT with compensators possesses high spatial and dosimetric exactness. The calculated dose distributions are applied correctly. The accuracy of the calculated monitor units is normally better than 3%; in small volumes, further dosimetric inaccuracies between calculated and measured dose distributions are mostly less than 3%. Therefore, the compensators contribute to the achievement of high-level IMRT even when apparatuses without MLC are used. This paper describes the use of the IMRT with compensators, presents the limits of this technology, and discusses the first practical experiences.