Characterization of new portal film systems for radiotherapy verification.

Portal images are an important verification tool in radiotherapy. Their use has been limited by their poor image quality, which is due to the inherent lack of contrast at megavoltage energies. Recently CEA and Kodak have introduced new portal film-cassette systems with much improved contrast. We have determined the H-D curves for these systems and found the gamma (gamma) for the CEA system (8.5) to be larger than that for the Kodak EC-L system (6.3). The optimal doses were CEA TLF 1.2 cGy, CEA TVS 15.9 cGy and Kodak EC-L 1.5 cGy. We also obtained phantom images that were evaluated by 11 radiotherapists. They ranked the CEA B High Plus cassette with CEA TVS film the highest, followed by the Kodak EC-L system. Some clinical films of a lateral pelvis are also presented, to demonstrate the improvement in image quality with these new film systems as compared with conventional portal films.     

Portal Verification Using the KODAK ACR 2000 RT Storage Phosphor Plate System and EC® Films

BACKGROUND AND PURPOSE: The suitability of the storage phosphor plate system ACR 2000 RT (Eastman Kodak Corp., Rochester, MN, USA), that is destined for portal verification as well as for portal simulation imaging in radiotherapy, had to be proven by the comparison with a highly sensitive verification film. MATERIAL AND METHODS: The comparison included portal verification images of different regions (head and neck, thorax, abdomen, and pelvis) irradiated with 6- and 15-MV photons and electrons. Each portal verification image was done at the storage screen and the EC film as well, using the EC-L cassettes (both: Eastman Kodak Corp., Rochester, MN, USA) for both systems. The soft-tissue and bony contrast and the brightness were evaluated and compared in a ranking of the two compared images. Different phantoms were irradiated to investigate the high- and low-contrast resolution. To account for quality assurance application, the short-time exposure of the unpacked and irradiated storage screen by green and red room lasers was also investigated. RESULTS: In general, the quality of the processed ACR images was slightly higher than that of the films, mostly due to cases of an insufficient exposure to the film. The storage screen was able to verify electron portals even for low electron energies with only minor photon contamination. The laser lines were sharply and clearly visible on the ACR images. CONCLUSION: The ACR system may replace the film without any noticeable decrease in image quality thereby reducing processing time and saving the costs of films and avoiding incorrect exposures.     

Microradiography: a theoretical basis and practical applications

If low magnification (less than 40x) is required of either thick soft tissue specimens (greater than 20 mm) containing contrast media filled structures or dense tissue, such as bone (greater than 5 mm), a diagnostic, radiographic tube and a 50 kVp setting would prove satisfactory. In this situation Kodak Type R film would provide the required resolution. When the same image enlargement is desired but the soft tissue (greater than 20 mm) does not contain contrast media or the dense tissue is thinner (0.5-5 mm), a specialized radiographic tube is necessary. The unit must be capable of generating a range of 30-40 kVp. Most mammography equipment will produce the necessary kilovoltage if neither a Faxitron nor the resources to build a unit are available. Once again the Kodak Type R or a similar industrial radiographic film would be the film of choice. When high magnification (greater than 40x) is required, indicating thin low density (10-20 mm) or high density (less than 0.5 mm) tissues are being examined, a specialized tube capable of producing 20 kVp is necessary. Kodak High Resolution glass plates or polyester-based film must be used to record the image. Due to grain size visible at high magnifications, both the Kodak Type R radiographic films and the Agfa photographic films proved unsuitable.     

In Vivo Verification of Electron Beam Energy by Patient Exit Dose and Optical Density of Portal Films

BACKGROUND AND PURPOSE: The depth-dose curve of electron beams is mainly determined by their energy. For accelerators with scatter foils, the electron energy can, in principle, be verified by measuring the amount of the contaminating photons. This paper investigates whether exit dose measurements and evaluations of the optical density of portal films can be used to verify the energy of the electron beam in a clinically relevant setting. MATERIAL AND METHODS: During irradiation of the head and neck region of an Alderson-Rando phantom with 6- to 21-MeV electron beams, the exit dose rates behind the phantom and the dose rates at the position of a film cassette were measured. The optical density of films (EC film/EC-L Regular and EC-L Fast cassettes, Eastman Kodak Comp., Rochester, NY, USA) exposed to beams of different energies was evaluated. RESULTS: The exit and the cassette dose rates showed a steep increase with increasing electron energy. Due to its density behavior, the film with both types of cassettes failed to generate images for lower electron energies (6 and 9 MeV) but presented a strong ascent of the optical density-until reaching the saturation-with increasing electron energy. CONCLUSION: Measurements of the exit dose and evaluations of the optical density of portal films can be used to verify and document the energy of electron beams during radiotherapy.     

A New Verification Film System for Routine Quality Control of Radiation Fields: Kodak EC-L

BACKGROUND: The use of modern irradiation techniques requires better verification films for determining set-up deviations and patient movements during the course of radiation treatment. This is an investigation of the image quality and time requirement of a new verification film system compared to a conventional portal film system. MATERIAL AND METHODS: For conventional verifications we used Agfa Curix HT 1000 films which were compared to the new Kodak EC-L film system. 344 Agfa Curix HT 1000 and 381 Kodak EC-L portal films of different tumor sites (prostate, rectum, head and neck) were visually judged on a light box by 2 experienced physicians. Subjective judgement of image quality, masking of films and time requirement were checked. RESULTS: In this investigation 68% of 175 Kodak EC-L ap/pa-films were judged "good", only 18% were classified "moderate" or "poor" 14%, but only 22% of 173 conventional ap/pa verification films (Agfa Curix HT 1000) were judged to be "good". CONCLUSIONS: The image quality, detail perception and time required for film inspection of the new Kodak EC-L film system was significantly improved when compared with standard portal films. They could be read more accurately and the detection of set-up deviation was facilitated.     

A clinical comparison of different film systems for radiotherapy portal imaging.

Portal films are an important tool for verification of the shaping and positioning of external radiation fields to the target volume in radiotherapy. One limitation of port films is their inherent lack of contrast, which is due to the low attenuation of the exposing megavoltage radiation by the tissues being imaged. Recently, Kodak introduced a new portal film-cassette system, Kodak EC-L, with much improved contrast compared with conventional film. The aim of this study was to determine if the enhanced contrast of the Kodak EC-L system actually provides better clinical results. To simulate clinical use, port films were taken using an anthropomorphic phantom that was artificially shifted and/or rotated by a predetermined distance. Identical images were taken using a conventional port film system (AGFA-Gevaert Curix MR4 in lead-lined cassette) and the Kodak EC-L system. Twelve different operators (6 physicists and 6 radiation therapists) were asked to diagnose the problem from a total of 20 port films (10 per treatment site), allowing for direct comparison of the 2 types of films. While the diagnosis of the field displacement improved using the Kodak film, it did not speed-up the decision-making process. It was also found that experienced operators were more accurate at evaluating the films. The results indicate that, for the situations studied (head and neck, pelvis), the Kodak system exhibits better contrast and leads to improved decision making.     

Filmless Evaluation of the Mechanical Accuracy of the Isocenter in Stereotactic Radiotherapy

BACKGROUND AND PURPOSE: The Winston-Lutz test verifies the mechanical accuracy of the isocenter in stereotactic radiotherapy. A lead ball inside a small beam is exposed to film applying different combinations of the gantry angle and the table angle. The increasing replacement of films by digital images requires alternative imaging methods. The suitability of two different electronic portal imaging systems and of a system based on digital luminescence radiography was investigated. MATERIAL AND METHODS: The imaging systems included the portal imaging devices BEAMVIEW PLUS and OPTIVUE1000 (both Siemens Medical Solutions, Erlangen, Germany) and the luminescence system KODAK ACR 2000 RT (Eastman Kodak Comp., Rochester, NY, USA). 6-MV photons from the linear accelerators PRIMUS and ONCOR (both Siemens Medical Solutions) were applied. First, only the small beam covering the lead ball was exposed. Second, an additional bigger open beam part in a certain distance to the small beam was applied. RESULTS: For all three investigated imaging systems, which are using preprocessing imaging software, only for the beam arrangement with additional open beam parts, the lead ball could be detected inside the small beam. Only for the application of a dosimetric software tool to the luminescence system, the metal ball inside the small beam became visible without an additional open beam part. CONCLUSION: Applying the proposed beam arrangements, the Winston-Lutz test can be done by digital and filmless imaging systems, thereby saving time as well.     

Portal imaging

Portal imaging is the acquisition of images with a radiotherapy beam. Imaging theory suggests that the quality of portal images could be much higher if the efficiency of the imaging media in detecting radiation could be improved. Introduction of new media (films and electronic portal imaging devices) has confirmed this by markedly increasing the quality of portal images. Images from these devices can then be used to verify a patient's treatment. Geometric verification requires the portal image to be registered with a reference image. Dosimetric verification requires the portal imager to be calibrated for dose. This review gives a brief overview of the current areas of interest in portal imaging: imaging theory; imaging media, film and electronic portal imaging devices; image registration; and dosimetry using these devices.     

A comparison of mammography screen-film combinations.

A comparison study was performed to evaluate the image quality and radiation dose of six mammographic screen-film combinations: a Min-R screen with OM-1, SO-155, and SO-177 films (Eastman Kodak); a Min-R medium screen (Eastman Kodak) with OM-1 film; an HR Mammo medium screen (Fuji Medical Systems USA) with OM-1 film; and a Min-R fast screen with T-Mat M II film (Eastman Kodak). SO-177 films were processed with an extended cycle. Exposures of an acrylic test object with embedded masses, fibers, and specks and of a preserved breast specimen were made, for two paired image comparison tests in which the visibility of diagnostic features, contrast, and noise were judged. In most areas of image quality evaluated, a Min-R screen with OM-1, SO-155, and SO-177 films was superior. These three screen-film combinations had similar imaging characteristics, even though OM-1 film requires a higher radiation exposure. Images produced with a Min-R fast screen and T-Mat M II film were significantly lower in quality.     

A digital fluoroscopic imaging system for verification during external beam radiotherapy

A digital fluoroscopic (DF) imaging system has been constructed to obtain portal images for verification during external beam radiotherapy. The imaging device consists of a fluorescent screen viewed by a highly sensitive video camera through a mirror. The video signal is digitized and processed by an image processor which is linked on-line with a host microcomputer. The image quality of the DF system was compared with that of film for portal images of the Burger phantom and the Alderson anthropomorphic phantom using 10 MV X-rays. Contrast resolution of the DF image integrated for 8.5 sec. was superior to the film resolution, while spatial resolution was slightly inferior. The DF image of the Alderson phantom processed by the adaptive histogram equalization was better in showing anatomical landmarks than the film portal image. The DF image integrated for 1 sec. which is used for movie mode can show patient movement during treatment.     

The Electronic Portal Imaging System Siemens Beamview Plus® Versus the Conventional Verification Films CEA-TVS® and DuPont CQL-7®A Critical Appraisal of Visual Image Quality

AIM: The aim of this study was the validation of the visual image quality of electronic portal imaging devices (EPID) and conventional verification films from the point of view of the end-viewers of portal films, the radiotherapists. MATERIAL AND METHODS: The verification image was represented in two different forms, viz. an electronic portal image employing Siemens Beamview Plus (on a computer monitor) and two different portal films using the conventional verification films CEA-TVS and DuPont CQL-7 (on a negatoscope). A total of 270 image sets (simulation film and portal image) were evaluated by each radiotherapist, evaluation extending to 90 sets of each type of verification film. Each set was evaluated by three specialists in radiotherapy examining subjective visual image quality whereby the following aspects served as evaluation criteria: contrast, artifacts, determination of actual radiation field edge position, anatomical structures and main structural feature for the determination of treatment field position. In addition, the anatomical structures employed for visual feature correlation between reference and portal films were classified according to their importance. RESULTS: In general the electronic portal image was rated significantly "visible" or better. Only the evaluation of artifacts showed an appreciable disadvantage for electronic portal imaging caused by physical artifacts due to radiographic technique and data processing aspects peculiar to the Siemens Beamview Plus 1.1. and also caused by different image processing tools reducing physical artifacts and enhancing the visibility of anatomical structures and likewise of anatomical artifacts (e.g. intestinal gas). By calculating the Spearman correlation coefficient to detect a possible relationship between the different criteria of subjective visual image quality, the research demonstrated that artifacts when limited to a tolerable proportion had no significant impact on the other criteria. CONCLUSIONS: As data of EPIDS are digital, images can be postprocessed and enhanced in a wide variety of ways. Using this tool the electronic portal imaging device provides images that, in terms of visual image quality, are at least comparable to the two evaluated types of radiographic films and also have the added advantage that such images are stored and can be transferred electronically being presupposition for digital patient documentation.     

Accuracy of alignment in breast irradiation: a retrospective analysis of clinical practice

The objective of the study was to determine the accuracy of patient positioning in radiotherapy for breast cancer. Portal images were obtained using a fast electronic megavoltage radiotherapy imaging system in 30 cases of breast cancer. Quantitative analysis of 530 megavolt portal images and comparison with 30 digitized simulation films were performed. Five linear measurements were taken for each simulation and verification film. Central lung distance (CLD) is the distance from the dorsomedial beam edge to the inner thoracic wall in the central plane of the beam. Cranial lung distance (CrLD) is the distance from the dorsomedial beam edge to the inner thoracic wall in the plane of the beam at 4 cm from the central plane. Central beam edge to skin distance (CBESD) is the distance from the skin to the ventrolateral beam edge in the central plane of the beam. The central irradiated width (CIW) is defined as the distance from the dorsomedial beam edge to the skin. The craniocaudal distance (CCD) is defined as the distance from a particular landmark to the caudal field border. Concerning patient position in the field, mean standard deviations of the difference between simulation and treatment images were 3.9 mm for the CLD, 3.2 mm at +4 cm, 3.6 mm for the CIW, 3.3 mm for the CBESD, 3.8 mm for the CCD. In 90% of all set-up for treatment, errors were less than 1 cm. The variation of the CLD was the largest set-up error. This parameter is clinically the most significant. Future treatment delivery should be improved by introducing patient positioning devices such as thermoplastic shells. The electronic portal imaging device (EPID) appears to be an adequate tool to study the accuracy of treatment set-ups like this.     

Evaluation of radiographs developed by a new ultrarapid film processing system

The image quality of radiographs developed by a new ultrarapid processor was evaluated to determine if faster processing causes degradation in the image. The processor used was the Konica Super-Rapid SRX-501 model. Two films designed for this processor (Konica MGH-SR and MGL-SR) were processed in 45 sec and were compared with standard rapid processing in 90 sec of corresponding conventional films (Kodak TMG and OC). Rare-earth screens (Kodak Lanex Regular and Lanex Medium) used with the new and conventional films interleaved during angiographic studies or for phantom images were assessed for image quality. The basic imaging properties of the screen-film systems were examined by measuring (1) Hurter and Driffield curves, (2) modulation transfer functions by using the slit method, and (3) noise Wiener spectra. Subjective clinical assessment showed that the images obtained with ultrarapid processing were acceptable, with increased contrast and graininess. Hurter and Driffield curve measurements confirmed higher gradients. Modulation transfer function measurements were the same as for the conventional films. Noise Wiener spectrum measurements showed a 10% increase in noise for MGH-SR vs TMG film and a 30% increase for MGL-SR vs OC film. We conclude that acceptable image quality can be obtained using ultrarapid processing, with processing time approximately 60% that of conventional rapid processing. Potential applications include all areas in which rapid availability of the radiograph for interpretation is important. Although the processor studied was the first of its kind available, our evaluation indicates that the technology is available for a new class of ultrarapid processors.     

Analysis of film response to electron beams using a laser scanner system developed in the laboratory.

An optical scanner system, which incorporates a He-Ne laser, photodiode detectors, and a platform for placing film, was built in the laboratory. The laser system operates at the green wavelength of 543.5 nm and functions as a scanning densitometer for measurement of optical changes in a film resulting from irradiation .The central axis electron depth dose of selected electron energies 10,12 and 14 MeV were analysed using Kodak X-Omat and Kodak Extended Dose Range (EDR2) films. The Kodak X-Omat film is routinely used for high-energy electron dose distributions in radiation therapy. The electron depth-dose measured with X-Omat film was found to agree well with standard depth-dose curves in water, obtained using an ion chamber. Conversely, the recently introduced Kodak EDR2 showed an energy dependence for electron beams, the percentage depth-dose curve shifting towards the surface for 12 and 14 MeV electron beams compared to that in water.     

Implications of using high contrast mammography X-ray film-screen combinations

The objective of this study was to determine the implications of using Fuji AD-M and Kodak min-R 2000, two high contrast X-ray film types developed for mammography. Evaluation of the Fuji AD-M film was divided into two parts. The first part was a contralateral comparison between mammograms using Fuji AD-M and Fuji UM-MA HC film-screen combinations. Fuji AD-M contrast was about 25% higher than that of Fuji UM-MA HC. The effect of increased contrast on image quality was investigated by visually grading the quality of information in different parts of each mammogram. Fuji AD-M film was generally judged to be better for overall diagnosis. However, 2.3% of mammograms produced using Fuji AD-M film were not acceptable and might have led to a technical recall of the patient. In the second part of this study, sets of mammograms from women attending mobile screening units were reviewed. One unit used Fuji AD-M film and the other used Kodak min-R 2000 film. Both samples of mammograms were digitized and analysed. The average film gradients between an optical density (OD) of 0.25 and 2.00 above base plus fog were 4.38 for Fuji AD-M film and 3.77 for Kodak min-R 2000 film. The main breast regions of the mammograms were judged to be satisfactorily displayed when breast tissues were above ODs of approximately 0.6 for Fuji AD-M film and 0.8 for Kodak min-R 2000 film.     

Sensitometric evaluation of a new F-speed dental radiographic film

OBJECTIVE: To compare a new experimental Kodak (Eastman Kodak, Rochester, NY, USA) F-speed dental X-ray film with Ektaspeed Plus and Ultra-speed. METHODS: The three types of film were exposed and processed under standardized conditions. Values of base plus fog, speed, and film contrast were derived. Resolution was compared by a line-pair plate. RESULTS: Under these experimental conditions, the speed of the new film was just into the F-speed range, and a little over twice as fast as Ultra-speed. The Ektaspeed Plus emulsion was somewhat slower than previously recorded when it was first introduced, but around the centre of the E-speed range. Ektaspeed Plus and the new F-speed film had almost identical film contrasts, the F-speed film having slightly greater contrast in the higher density range. Ultra-speed contrast was marginally greater in the lower density range, but was overtaken by both of the other emulsions at higher densities. All three emulsions had low values of base plus fog. Both E- and F-speed films resolved 10 line-pairs per millimetre well, though both emulsions were inferior to Ultra-speed. CONCLUSIONS: The new F-speed film, since marketed as Insight, provides a further saving in radiation exposure, with no evident deterioration in film contrast or resolution.     

Sensitometric comparison of speed group E and F dental radiographic films.

OBJECTIVE: To evaluate the sensitometric characteristics of Insight, (Eastman Kodak, Rochester, NY, USA) a new F-speed film, in fresh and depleted processing solutions and compare them with Ektaspeed Plus. METHODS: Two sets each of Insight (IP) and Ektaspeed Plus (EP) films were exposed to radiation levels ranging from 10.7 to 685.2 microGy. One set of films was processed in fresh chemicals while the other set was processed in solutions that had been used for 5 days to process over 500 radiographs. Unexposed films of both types were processed in both solutions to determine base-plus-fog density. Speed and contrast were measured according to ISO definitions and at other levels of density. RESULTS: IP was in speed group F as measured at optical density 1 above base-plus-fog when processed under both conditions. It was 25% faster than EP when both were processed in new solutions and 35% faster in the old solutions, permitting a 20-24% reduction in exposure time. The speeds of both film types decreased when processed in used solutions, but the decrease was smaller for IP than for EP. Speeds at other density levels were greater for IP than EP. Contrast as defined by ISO, and over other density ranges, was similar for both films. CONCLUSIONS: Insight is an F-speed film with a speed at least 25% greater than Ektaspeed Plus. IP is more resistant than Ektaspeed Plus to decreases in speed when processed in used chemicals. Contrast of IP and EP is comparable over several density ranges.     

Image quality and breast dose of 24 screen-film combinations for mammography

In this study the effect of different mammographic screen-film combinations on image quality and breast dose, and the correlation between the various image quality parameters, breast dose and the sensitometric parameters of a film were investigated. Three Agfa (MR5-II, HDR, HT), two Kodak (Min-R M, Min-R 2000), one Fuji (AD-M), one Konica (CM-H) and one Ferrania (HM plus) single emulsion mammographic films were combined with three intensifying screens (Agfa HDS, Kodak Min-R 2190 and Fuji AD-MA). The film characteristics were determined by sensitometry, while the image quality and the dose to the breast of the resulting 24 screen-film combinations were assessed using a mammography quality control phantom. For each combination, three images of the phantom were acquired with optical density within three different ranges. Two observers assessed the quality of the 72 phantom images obtained, while the breast dose was calculated from the exposure data required for each image. Large differences among screen-film combinations in terms of image quality and breast dose were identified however, that, could not be correlated with the film's sensitometric characteristics. All films presented the best resolution when combined with the HDS screen at the expense of speed, and the largest speed when combined with the AD-MA screen, without degradation of the overall image quality. However, an ideal screen-film combination presenting the best image quality with the least dose was not identified. It is also worth mentioning that the best performance for a film was not necessarily obtained when this was combined with the screen provided by the same manufacturer. The results of this study clearly demonstrate that comparison of films based on their sensitometric characteristics are of limited value for clinical practice, as their performance is strongly affected by the screens with which they are combined.     

Performance characteristics and quality assurance aspects of kilovoltage cone-beam CT on medical linear accelerator.

A medical linear accelerator equipped with optical position tracking, ultrasound imaging, portal imaging, and radiographic imaging systems was installed at University of Pittsburgh Cancer Institute for the purpose of performing image-guided radiation therapy (IGRT) and image-guided radiosurgery (IGRS) in October 2005. We report the performance characteristics and quality assurance aspects of the kilovoltage cone-beam computed tomography (kV-CBCT) technique. This radiographic imaging system consists of a kilovoltage source and a large-area flat panel amorphous silicon detector mounted on the gantry of the medical linear accelerator via controlled arms. The performance characteristics and quality assurance aspects of this kV-CBCT technique involves alignment of the kilovoltage imaging system to the isocenter of the medical linear accelerator and assessment of (a) image contrast, (b) spatial accuracy of the images, (c) image uniformity, and (d) computed tomography (CT)-to-electron density conversion relationship were investigated. Using the image-guided tools, the alignment of the radiographic imaging system was assessed to be within a millimeter. The low-contrast resolution was found to be a 6-mm diameter hole at 1% contrast level and high-contrast resolution at 9 line pairs per centimeter. The spatial accuracy (50 mm +/- 1%), slice thickness (2.5 mm and 5.0 mm +/- 5%), and image uniformity (+/- 20 HU) were found to be within the manufacturer's specifications. The CT-to-electron density relationship was also determined. By using well-designed procedures and phantom, the number of parameter checks for quality assurance of the IGRT system can be carried out in a relatively short time.     

Effects of processing conditions on mammographic image quality

RATIONALE AND OBJECTIVES: Any given mammographic film will exhibit changes in sensitometric response and image resolution as processing variables are altered. Developer type, immersion time, and temperature have been shown to affect the contrast of the mammographic image and thus lesion visibility. The authors evaluated the effect of altering processing variables, including film type, developer type, and immersion time, on the visibility of masses, fibrils, and speaks in a standard mammographic phantom. MATERIALS AND METHODS: Images of a phantom obtained with two screen types (Kodak Min-R and Fuji) and five film types (Kodak Min-R M, Min-R E, Min-R H; Fuji UM-MA HC, and DuPont Microvision-C) were processed with five different developer chemicals (Autex SE, DuPont HSD, Kodak RP, Picker 3-7-90, and White Mountain) at four different immersion times (24, 30, 36, and 46 seconds). Processor chemical activity was monitored with sensitometric strips, and developer temperatures were continuously measured. The film images were reviewed by two board-certified radiologists and two physicists with expertise in mammography quality control and were scored based on the visibility of calcifications, masses, and fibrils. RESULTS: Although the differences in the absolute scores were not large, the Kodak Min-R M and Fuji films exhibited the highest scores, and images developed in White Mountain and Autex chemicals exhibited the highest scores. CONCLUSION: For any film, several processing chemicals may be used to produce images of similar quality. Extended processing may no longer be necessary.