Physical considerations on discrepancies in target volume delineation.

BACKGROUND AND PURPOSE: To compare the delineations and interpretations of target volumes by physicians in different radio-oncology centers. MATERIALS AND METHODS: Eleven Swiss radio-oncology centers delineated volumes according to ICRU 50 recommendations for one prostate and one head and neck case. In order to evaluate the consistency of the volume delineations, the following parameters were determined: 1) the target volumes (GTV, CTV and manually expanded PTV) and their extensions in the three main axes and 2) the correlation of the volume delineated by each pair of centers using the ratio of the intersection to the union (called proximity index). RESULTS: The delineated prostate volume was 105+/-55 cm(3) for the CTV and 218+/-44 cm(3) for the PTV. The delineated head and neck volume was 46+/-15 cm(3) for the GTV, 327+/-154 cm(3) for the CTV and 528+/-106 cm(3) for the PTV. The mean proximity index for the prostate case was 0.50+/-0.13 for the CTV and 0.57+/-0.11 for the PTV. The proximity index for the head and neck case was 0.45+/-0.09 for the GTV, 0.42+/-0.13 for the CTV and 0.59+/-0.06 for the PTV. CONCLUSIONS: Large discrepancies between all the delineated target volumes were observed. There was an inverse relationship between the CTV volume and the margin between CTV and PTV, leading to less discrepancies in the PTV than is the CTV delineations. There was more spread in the sagittal and frontal planes due to CT pixel anisotropy, which suggests that radiation oncologists should delineate the target volumes not only in the transverse plane, but also in the sagittal and frontal planes to improve the delineation by allowing a consistency check.

X-ray phase contrast imaging of metallized and non-metallized biological samples.

Imaging of biological samples has been performed with a variety of techniques for example electromagnetic waves, electrons, neutrons, ultrasound and X-rays. Also conventional X-ray imaging represents the basis of medical diagnostic imaging, it remains of limited use in this application because it is based solely on the differential absorption of X-rays by tissues. Coherent and bright photon beams, such as those produced by third-generation synchrotron X-ray sources, provide further information on subtle X-ray phase changes at matter interfaces. This complements conventional X-ray absorption by edge enhancement phenomena. Thus, phase contrast imaging has the potential to improve the detection of structures on images by detecting those structures that are invisible with X-ray absorption imaging. Images of a weakly absorbing nylon fibre were recorded in in-line holography geometry using a high resolution low-noise CCD camera at the ESRF in Grenoble. The method was also applied to improve image contrast for images of biological tissues. This paper presents phase contrast microradiographs of vascular tree casts and images of a housefly. These reveal very fine structures, that remain invisible with conventional absorption contrast only.

The reasons for discrepancies in target volume delineation : a SASRO study on head-and-neck and prostate cancers.

PURPOSE: To understand the reasons for differences in the delineation of target volumes between physicians. MATERIAL AND METHODS: 18 Swiss radiooncology centers were invited to delineate volumes for one prostate and one head-and-neck case. In addition, a questionnaire was sent to evaluate the differences in the volume definition (GTV [gross tumor volume], CTV [clinical target volume], PTV [planning target volume]), the various estimated margins, and the nodes at risk. Coherence between drawn and stated margins by centers was calculated. The questionnaire also included a nonspecific series of questions regarding planning methods in each institution. RESULTS: Fairly large differences in the drawn volumes were seen between the centers in both cases and also in the definition of volumes. Correlation between drawn and stated margins was fair in the prostate case and poor in the head-and-neck case. The questionnaire revealed important differences in the planning methods between centers. CONCLUSION: These large differences could be explained by (1) a variable knowledge/interpretation of ICRU definitions, (2) variable interpretations of the potential microscopic extent, (3) difficulties in GTV identification, (4) differences in the concept, and (5) incoherence between theory (i.e., stated margins) and practice (i.e., drawn margins).

Impact of the introduction of 16-row MDCT on image quality and patient dose: Phantom study and multi-centre survey.

The purpose was to compare the image quality and patient dose between 4- and 16-row MDCT units and to evaluate the dispersion of the dose delivered for common clinical examinations. Four 4- and 16-row MDCT units were used in the study. Image noise levels from images of a CatPhan phantom were compared for all units using a given CTDI(vol) of 15.0+/-1.0 mGy. Standard acquisition protocols from ten centres, shifted from 4- to 16-row MDCT (plus one additional centre for 16-row MDCT), were compared for cerebral angiography and standard chest and abdomen examinations. In addition, the protocols used with 16-row MDCT units for diagnosis of the unstable shoulder and for cardiac examinations were also compared. The introduction of 16-MSCT units did not reduce the performance of the detectors. Concerning the acquisition protocols, a wide range in practice was observed for standard examinations; DLP varied from 800 to 5,120 mGy x cm, 130 to 860 mGy x cm, 410 to 1,790 mGy x cm and 850 to 2,500 mGy x cm for cerebral angiography, standard chest, standard abdomen and heart examinations, respectively. The introduction of 16-row MDCT did not, on average, increase the patient dose for standard chest and abdominal examinations. However, a significant dose increase has been observed for cerebral angiography. There is a wide dispersion in the doses delivered, especially for cardiac imaging.

Intercomparison of activity measurements for beta-emitters in Swiss nuclear medicine laboratories.

OBJECTIVE: The activity of injected radiopharmaceuticals in nuclear medicine, including beta-emitters used for pain palliation, has to be monitored systematically. The objective of the present work was to evaluate the situation and precision of activity monitoring for beta-emitters in Swiss nuclear medicine laboratories. METHODS: A questionnaire about the monitoring methods used was sent to 50 centers. On the basis of the questionnaire results, an intercomparison of activity measurements with 90Y and 169Er sources was organized. RESULTS: This study showed that most laboratories check beta-emitter activity with a dose calibrator measurement in the original vial provided by the producer or in the injection syringe. They therefore need to have calibration factors for the corresponding measurement geometries. The results of the intercomparison were disappointing overall. Sixteen of 27 90Y measurements and 17 of 22 169Er measurements in the original vial deviated from the reference activity by more than 20%. The situation was similar for the syringe. These discrepancies did not stem from the intrinsic limitation of the measuring method but were mainly attributable to the poor quality of the calibration factors provided by the manufacturers, in addition to lack of follow-up and incorrect background subtraction, particularly for 169Er, by the nuclear medicine laboratories. Manufacturers are being contacted to discuss possible improvements for the situation. CONCLUSION: This study showed that commercial dose calibrators are generally adequate for measurement of the activities of beta-emitters. However, in some cases, the measurement of 90Y can lead to errors reaching +/-50%. For 169Er, with its much lower beta-energy, the situation is even worse; the observed differences can be higher than 1 order of magnitude.

Diagnostic and interventional radiology: a strategy to introduce reference dose level taking into account the national practice.

The purpose of this study is to present a strategy to define the reference dose levels for fluoroscopic, dose-intensive examinations. This work is a part of the project of the Federal Office of Public Health of Switzerland to translate the guidelines of the International Commission on Radiological Protection and the European Union into action. The study will also be used to set reference dose levels on the basis of a national survey. All the fluoroscopic units, involved in the survey, were equipped with a KAP (kerma-area product) meter. All KAP meters were first calibrated to ensure the comparability of the dose measurements. The doses and the dose rates together with subjective image quality measurements were acquired in all the centres. Eight types of examination were chosen by a panel of radiologists, and each of the five centres involved agreed to monitor 20 patients per examination type. A wide variation in the dose and the image quality in fixed geometry was observed. For example, the skin dose rate for abdominal examinations varied in the range of 12-42 mGy min(-1) for comparable image quality. Average KAP values of 67, 178, 106, 102, 473, 205, 307 and 316 Gy cm2 were recorded for barium meal, abdominal angiography, cerebral angiography, barium enema, hepatic embolisation, biliary drainage, cerebral embolisation and femoral stenting, respectively. The values obtained in this limited study are generally higher than the ones available in the literature and strategies to optimise these studies have to be discussed. A strict control concerning the denomination of the examination type involved in such a study is mandatory to obtain reliable data. This can only be done through a close collaboration between physicians, radiographers and medical physicists.

Objective assessment of image quality in conventional and digital mammography taking into account dynamic range.

The goal of this work is to develop a method to objectively compare the performance of a digital and a screen-film mammography system in terms of image quality. The method takes into account the dynamic range of the image detector, the detection of high and low contrast structures, the visualisation of the images and the observer response. A test object, designed to represent a compressed breast, was constructed from various tissue equivalent materials ranging from purely adipose to purely glandular composition. Different areas within the test object permitted the evaluation of low and high contrast detection, spatial resolution and image noise. All the images (digital and conventional) were captured using a CCD camera to include the visualisation process in the image quality assessment. A mathematical model observer (non-prewhitening matched filter), that calculates the detectability of high and low contrast structures using spatial resolution, noise and contrast, was used to compare the two technologies. Our results show that for a given patient dose, the detection of high and low contrast structures is significantly better for the digital system than for the conventional screen-film system studied. The method of using a test object with a large tissue composition range combined with a camera to compare conventional and digital imaging modalities can be applied to other radiological imaging techniques. In particular it could be used to optimise the process of radiographic reading of soft copy images.

Fetal dose reduction in head and neck radiotherapy of a pregnant woman.

BACKGROUND AND PURPOSE: A pregnant woman was referred for post-operative radiotherapy of a malignant schwannoma in the head and neck region. A best-treatment plan was devised in order to minimize the fetal dose. MATERIAL AND METHODS: The fetal dose resulting from radiological examinations was determined according to international protocols, that resulting from radiotherapy was calculated according to Recommendation 36 of the American Association of Physicists in Medicine (AAPM) Task Group. Pre-treatment dosimetry was performed with an anthropomorphic phantom. Several alternative treatment plans were evaluated. The use of a multileaf collimator (MLC) and a virtual wedge (VW) was compared to cerrobend blocks (CB) and physical wedge (PW). In-vivo dosimetry was performed using a vaginal probe containing thermoluminescent dosimeters (TLD). RESULTS: The total fetal dose resulting from diagnostic and radiotherapy procedures was estimated to be 36 mGy. The technique based on MLC and VW was elected for patient treatment. Measurements for this configuration resulted in afetal dose reduction of 82%. The shielding of the patient's abdomen further reduced the fetal dose by 42%. CONCLUSION: The use of VW and MLC for the treatment of a pregnant woman is highly recommended. Each case should be individually studied with pre-treatment and in-vivo dosimetry.

Use of and irradiation from plain lumbar spine radiography in Switzerland.

PRINCIPLES: Plain lumbar spine radiographic examination (LSRE) is frequently used in medical practice and delivers a high dose of ionising radiation. The objectives of the study were to determine the annual frequency of LSRE in Switzerland and its distribution according to practitioners' and patients' characteristics, as well as the related population dose of ionising radiation. METHODS: Data were extrapolated from a nationwide questionnaire survey on radiation exposure resulting from medical imaging in 1998, involving physicians and other healthcare providers performing radiological examinations in Switzerland. RESULTS: An estimated number of 273,000 LSRE are performed annually in Switzerland (39 LSRE per 1000 inhabitants per year). The collective dose to the population due to LSRE was 1130 Sv (0.16 mSv per person per year). 50-60% of these procedures were performed to confirm or rule out a diagnosis, the majority (85%) in the context of an illness. CONCLUSIONS: LSRE is the third most frequent radiographic procedure performed and delivers the highest population dose of ionising radiation of any radiodiagnostic procedure. Efforts to reduce the frequency and the radiation dose of this procedure must be kept up, technically by optimising the equipment and radioprotection measures, and clinically by implementing evidence-based approaches to appropriate indications for this imaging technique.

Monte Carlo calculation of the sensitivity of a commercial dose calibrator to gamma and beta radiation.

The detection process used in a commercial dose calibrator was modeled using the GEANT 3 Monte Carlo code. Dose calibrator efficiency for gamma and beta emitters, and the response to monoenergetic photons and electrons was calculated. The model shows that beta emitters below 2.5 MeV deposit energy indirectly in the detector through bremsstrahlung produced in the chamber wall or in the source itself. Higher energy beta emitters (E > 2.5 MeV) deposit energy directly in the chamber sensitive volume, and dose calibrator sensitivity increases abruptly for these radionuclides. The Monte Carlo calculations were compared with gamma and beta emitter measurements. The calculations show that the variation in dose calibrator efficiency with measuring conditions (source volume, container diameter, container wall thickness and material, position of the source within the calibrator) is relatively small and can be considered insignificant for routine measurement applications. However, dose calibrator efficiency depends strongly on the inner-wall thickness of the detector.

Management of patient dose and image noise in routine pediatric CT abdominal examinations.

The aim was to propose a strategy for finding reasonable compromises between image noise and dose as a function of patient weight. Weighted CT dose index (CTDI(w)) was measured on a multidetector-row CT unit using CTDI test objects of 16, 24 and 32 cm in diameter at 80, 100, 120 and 140 kV. These test objects were then scanned in helical mode using a wide range of tube currents and voltages with a reconstructed slice thickness of 5 mm. For each set of acquisition parameter image noise was measured and the Rose model observer was used to test two strategies for proposing a reasonable compromise between dose and low-contrast detection performance: (1) the use of a unique noise level for all test object diameters, and (2) the use of a unique dose efficacy level defined as the noise reduction per unit dose. Published data were used to define four weight classes and an acquisition protocol was proposed for each class. The protocols have been applied in clinical routine for more than one year. CTDI(vol) values of 6.7, 9.4, 15.9 and 24.5 mGy were proposed for the following weight classes: 2.5-5, 5-15, 15-30 and 30-50 kg with image noise levels in the range of 10-15 HU. The proposed method allows patient dose and image noise to be controlled in such a way that dose reduction does not impair the detection of low-contrast lesions. The proposed values correspond to high- quality images and can be reduced if only high-contrast organs are assessed.

Optimisation in stereotactic radiosurgery of AVMs: I. Mathematical considerations.

One forward-planning method and five inverse-planning methods for optimisation of treatment in radiation therapy were compared in the particular case of radiosurgery with micro-multi-leaves collimator (MMLC) and arc therapy. The "manual" method, two matrix methods (singular value decomposition and non-negative least square fit), two gradient methods (quasi-Newton and conjugate gradient algorithms) and the "simulated annealing" stochastic method were investigated. The performance of these methods was assessed in terms of the speed of convergence to an optimum, the ability to account for the organs at risk, and probability of targeted success. The study employed an adapted version of the GRATIS treatment planning system. A group of 22 patients previously treated by arc therapy for arteriovenous malformations (AVMs) were studied to evaluate the performance of the various optimisation methods for MMLC and arc therapy. The conjugate gradient method proved to be the most appropriate for most cases.

Optimisation in stereotactic radiosurgery of AVMs: II. Comparison of arc and MMLC therapy.

Two stereotactic surgery methods, arc and micro-multileave collimator (MMLC) therapy, were compared in the particular case of arteriovenous malformations (AVMs) treatment. Different methods of the treatment optimisation were used. The comparison covered a group of 22 patients suffering from peripheral and central AVMs of different sizes who underwent initially arc therapy. Several parameters were evaluated to compare the two methods: 2D and 3D isodose representations, dose-volume histograms (DVHs) and probability of success. The 3D isodoses were compared for the 22 patients showing a better conformity for the MMLC (three cases are presented). The DVHs of the AVM were also in favour of MMLC. In terms of probability of success, the results showed that are therapy was superior only in the case of small spherical lesions. MMLC therapy proved to be superior to arc therapy in all cases but central spherical small volume AVMs.

A new test phantom with different breast tissue compositions for image quality assessment in conventional and digital mammography.

Our objective is to describe a new test phantom that permits the objective assessment of image quality in conventional and digital mammography for different types of breast tissue. A test phantom, designed to represent a compressed breast, was made from tissue equivalent materials. Three separate regions, with different breast tissue compositions, are used to evaluate low and high contrast resolution, spatial resolution and image noise. The phantom was imaged over a range of kV using a Contour 2000 (Bennett) mammography unit with a Kodak MinR 2190-MinR L screen-film combination and a Senograph 2000D (General Electric) digital mammography unit. Objective image quality assessments for different breast tissue compositions were performed using the phantom for conventional and digital mammography. For a similar mean glandular dose (MGD), the digital system gives a significantly higher contrast-to-noise ratio (CNR) than the screen-film system for 100% glandular tissue. In conclusion, in mammography, a range of exposure conditions is used for imaging because of the different breast tissue compositions encountered clinically. Ideally, the patient dose-image quality relationship should be optimized over the range of exposure conditions. The test phantom presented in this work permits image quality parameters to be evaluated objectively for three different types of breast tissue. Thus, it is a useful tool for optimizing the patient dose-image quality relationship.

Determination of the efficiency of commercially available dose calibrators for beta-emitters.

OBJECTIVES: The goals of this investigation are to determine whether commercially available dose calibrators can be used to measure the activity of beta-emitting radionuclides used in pain palliation and to establish whether manufacturer-supplied calibration factors are appropriate for this purpose. METHODS: Six types of commercially available dose calibrators were studied. Dose calibrator response was controlled for 5 gamma-emitters used for calibration or typically encountered in routine use. For the 4 most commonly used beta-emitters ((32)P, (90)Sr, (90)Y, and (169)Er) dose calibrator efficiency was determined in the syringe geometry used for clinical applications. Efficiency of the calibrators was also measured for (153)Sm and (186)Re, 2 beta-emitters with significant gamma-contributions. Source activities were traceable to national standards. RESULTS: All calibrators measured gamma-emitters with a precision of +/-10%, in compliance with Swiss regulatory requirements. For beta-emitters, dose calibrator intrinsic efficiency depends strongly on the maximal energy of the beta-spectrum and is notably low for (169)Er. Manufacturer-supplied calibration factors give accurate results for beta-emitters with maximal beta-energy in the middle-energy range (1 MeV) but are not appropriate for use with low-energy ((169)Er) or high-energy ((90)Y) beta-emitters. beta-emitters with significant gamma-contributions behave like gamma-emitters. CONCLUSION: Commercially available dose calibrators have an intrinsic efficiency that is sufficient for the measurement of beta-emitters, including beta-emitters with a low maximum beta-energy. Manufacturer-supplied calibration factors are reliable for gamma-emitters and beta-emitters in the middle-energy range. For low- and high-energy beta-emitters, the use of manufacturer-supplied calibration factors introduces significant measurement inaccuracy.

Chiropractor's use of radiography in Switzerland.

OBJECTIVE: In this article, we investigate the use of diagnostic radiology by chiropractors in Switzerland, with the aim of determining their contribution to the annual radiation collective dose. METHODS: We approached 138 chiropractors possessing radiologic equipment and asked them to provide, among other information, the frequency of radiographic examinations. The dose associated with each type of radiographic examination was established separately. The collective dose was determined by convolution of frequency and dosimetric information. RESULTS: The number of chiropractic radiographic examinations performed in Switzerland in 1998 was 60,000, mainly spinal and pelvic examinations. The associated annual collective dose was found to be 144 Sv (an annual effective dose of 20 microSv per capita). The chiropractic contribution to the total dose due to conventional radiography in Switzerland is about 6%. CONCLUSIONS: Considering the number of chiropractors in Switzerland (less than 200), their contribution to the collective dose is relatively high. This is due to the high effective dose associated with the main types of examinations performed (eg, lumbar spine). It is therefore necessary to develop and apply guidelines for the use of this type of radiographic examination, as well as quality control programs, in order to optimize the radiographic technique and hence reduce the doses.

Influence of scatter reduction method and monochromatic beams on image quality and dose in mammography.

In mammography, the image contrast and dose delivered to the patient are determined by the x-ray spectrum and the scatter to primary ratio S/P. Thus the quality of the mammographic procedure is highly dependent on the choice of anode and filter material and on the method used to reduce the amount of scattered radiation reaching the detector. Synchrotron radiation is a useful tool to study the effect of beam energy on the optimization of the mammographic process because it delivers a high flux of monochromatic photons. Moreover, because the beam is naturally flat collimated in one direction, a slot can be used instead of a grid for scatter reduction. We have measured the ratio S/P and the transmission factors for grids and slots for monoenergetic synchrotron radiation. In this way the effect of beam energy and scatter rejection method were separated, and their respective importance for image quality and dose analyzed. Our results show that conventional mammographic spectra are not far from optimum and that the use of a slot instead of a grid has an important effect on the optimization of the mammographic process. We propose a simple numerical model to quantify this effect.

Detection of low-contrast objects: experimental comparison of single- and multi-detector row CT with a phantom.

PURPOSE: To compare single-detector row computed tomography (CT) and multi-detector row CT by using an experimental phantom containing a contrast-detail modulus for detection of low-contrast structures to optimize acquisition protocols. MATERIALS AND METHODS: The parameters milliampere seconds, reconstructed section thickness, and elementary collimation for multi-detector CT were varied for two pitches with single- and multi-detector CT. For objective assessment of image quality, contrast-to-noise ratio (CNR) was calculated for an 8-HU low-contrast 15-mm-diameter object. Subjective assessment of image quality was performed by means of visual detection of low-contrast objects of various sizes by four independent observers. For each acquisition protocol, the effective doses required to obtain the CNR thresholds allowing 100% detection of 5-, 7-, and 9-mm-diameter objects were compared at single- and multi-detector CT at comparable section sensitivity profile with analysis of variance. RESULTS: Significant correlation was found between CNR measurements and subjective object detection (r = 0.95, P <.05). CNRs of 1.0, 0.8, and 0.6 were required to detect 100% of the 5-, 7-, and 9-mm-diameter objects, respectively. For reconstructed section thickness of 5-10 mm, comparable x-ray doses were required with single- and multi-detector CT to detect objects. For reconstructed sections thinner than 5 mm, single- and multi-detector CT allowed detection of only the 7- and 9-mm-thick objects, but a higher x-ray dose was required for multi- than for single-detector CT (P <.05). CONCLUSION: Multi-detector CT is less effective than single-detector CT in detection of small low-contrast objects if sections thinner than 5 mm are used. Results for single- and multi-detector CT were similar for sections 5 mm or thicker.