Roberto Ropolo

Computed tomography dose measurements with radiochromic films and a flatbed scanner

Gafchromic XR-QA films were developed for patient dosimetry in diagnostic radiology. A possible application of these films is the measurement of doses in computed tomography. In this study a method to evaluate the CTDI using Gafchromic XR-QA film and a flatbed scanner was developed and tested. Film samples were cut to dimensions of 6 x 170 mm2 in order to have an integration area similar to that of a pencil ionization chamber, with the possibility of changing the integration length. Prior to exposing these films to a computed tomography beam, the angular dependence of the film dose response was investigated by exposing film strips to a static x-ray beam at different angles in the range 0 degrees-180 degrees. A difference of 49% was found between the response with the axis beam parallel to the film surface (90 degrees) and with the axis beam perpendicular (0 degrees and 180 degrees). Integrating over a 360 degrees exposure like the one in computed tomography, a difference of less than 2% was estimated, which is comparable with the measurement error obtainable with XR-QA film. A calibration with a CT beam in the scout mode was performed and film strips were then exposed to single axial scans and to helical scans both in air and in phantoms. Two different types of flatbed scanners were used to read the film samples, a Microtek ScanMaker 9800XL scanner and an Epson Expression 10000 XL scanner, and the accuracy of the results were compared. For beam collimations above 10 mm differences between CTDI measured by film and CTDI measured by ionization chamber below 9% were found for the Epson scanner, with an average estimated error at 1 sigma level of 5%. For the Microtek scanner and for the same film samples, differences below 11% with an average error at 1 sigma level of 8% were founded. The 1 sigma uncertainty of the measured CTDI was provided by the method for each measurement, and it was shown that about the 95% of the differences between the CTDI measurements with radiochromic films and with the ionization chamber were below the estimated 2 sigma uncertainty, for both scanners. After an accurate calibration procedure and the consideration of the uncertainty associated with the measurement, Gafchromic XR-QA films can be used to evaluate the CTDI.

Patient and operator exposure during percutaneous vertebroplasty

PurposeThe purpose of this study was to compare exposure of patient and operator to ionising radiation during percutaneous vertebroplasty performed under combined computed tomography (CT) and fluoroscopic guidance or fluoroscopic guidance alone.Materials and methodsWith the collaboration of our physics department, we measured exposure on ten patients undergoing vertebroplasty with combined CT and fluoroscopic guidance and on ten undergoing vertebroplasty with fluoroscopic guidance alone.ResultsMean operator dose was approximately 0.8 microSv during vertebroplasty done with combined CT and fluoroscopic guidance and 5.8 microSv in procedures with fluoroscopic guidance alone. Mean patient dose was approximately 6 mSv for combined guidance and 8 mSv for fluoroscopic guidance, a difference that was not found to be statistically significant.ConclusionsAlthough combined CT and fluoroscopic guidance is normally preferred for difficult areas such as the cervical and upper thoracic vertebrae, to ensure operator radiation protection, the technique should also be considered for areas normally treated under fluoroscopic guidance alone. However, a larger patient series is needed to correctly evaluate the real contribution of low-dose CT to patient exposure.RiassuntoObiettivoScopo del lavoro è confrontare la dose a cui sono esposti paziente e operatore in corso di vertebroplastica percutanea sotto guida combinata TC e radioscopica e sotto esclusiva guida radioscopica.Materiali e metodiIn collaborazione con la fisica sanitaria abbiamo eseguito misurazioni su 10 pazienti sottoposti a vertebroplastica con guida combinata e su 10 pazienti sottoposti a vertebroplastica con guida esclusivamente radioscopica.RisultatiIn base a questo studio si osserva come la dose all’operatore sia in media circa 0,8 microSv in corso di vertebroplastica eseguita con guida combinata TC e radioscopica, mentre si attesti attorno a 5,8 microSv se eseguita con guida esclusivamente radioscopica; per quanto riguarda i pazienti la dose è di circa 6 mSv per la guida combinata e circa 8 mSv nel caso di guida esclusivamente radioscopica; tale differenza non risulta statisticamente significativa.ConclusioniSe la guida combinata TC e radioscopica risulta preferibile per sedi complesse come il trattamento a livello del rachide cervicale e dorsale “alto” essa è da prendersi in considerazione qualora si privilegi la protezionistica dell’operatore anche per quei metameri vertebrali solitamente trattati con esclusiva guida radioscopica, tuttavia serve una più ampia casistica per poter valutare il reale contributo della TC a basso dosaggio nell’esposizione del paziente.

A GPU Simulation Tool for Training and Optimisation in 2D Digital X-Ray Imaging

Conventional radiology is performed by means of digital detectors, with various types of technology and different performance in terms of efficiency and image quality. Following the arrival of a new digital detector in a radiology department, all the staff involved should adapt the procedure parameters to the properties of the detector, in order to achieve an optimal result in terms of correct diagnostic information and minimum radiation risks for the patient. The aim of this study was to develop and validate a software capable of simulating a digital X-ray imaging system, using graphics processing unit computing. All radiological image components were implemented in this application: an X-ray tube with primary beam, a virtual patient, noise, scatter radiation, a grid and a digital detector. Three different digital detectors (two digital radiography and a computed radiography systems) were implemented. In order to validate the software, we carried out a quantitative comparison of geometrical and anthropomorphic phantom simulated images with those acquired. In terms of average pixel values, the maximum differences were below 15%, while the noise values were in agreement with a maximum difference of 20%. The relative trends of contrast to noise ratio versus beam energy and intensity were well simulated. Total calculation times were below 3 seconds for clinical images with pixel size of actual dimensions less than 0.2 mm. The application proved to be efficient and realistic. Short calculation times and the accuracy of the results obtained make this software a useful tool for training operators and dose optimisation studies.

Interventional procedures for biliary drainage with bilioplasty in paediatric patients: dosimetric aspects

Purpose . This study was undertaken to evaluate patient dose in paediatric liver transplant recipients treated by percutaneous biliary drainage and bilioplasty proceduresMaterials and methods . Effective dose rates and entrance skin-dose (ESD) rates per minute of fluoroscopy were measured by using a plexiglas phantom (thickness 10 cm) simulating the patient and by varying the exposure parameters (type of pulsed fluoroscopy, image intensifier diameter, presence of diaphragms) to identify the technique delivering the lowest patient dose. In vivo measurements were performed during three interventional proceduresResults . The effective dose rate proved to be lowest for a particular type of pulsed fluoroscopy, with maximum magnification and with field-limiting diaphragms. The in vivo measurements showed a maximum ESD value of around 50 mGy (the threshold for transient erythema is 2,000 mGy, ICRP 60). The effective dose values were in the range of 0.9–1.5 mSvConclusions . We established exposure parameters providing the desired image quality with the lowest dose for the equipment used and for a specific type of interventional procedure. The measured ESD values allow us to exclude the risk of deterministic effects on the skin. The effective dose values and considerations regarding the likelihood of radiation-induced cancer led to the conclusion that the radiological risk for the patient is largely justified by the benefits of these kinds of procedureRiassuntoObiettivo . Valutazione della dose al paziente per procedure di drenaggio biliare e bilioplastica percutanea in pazienti pediatrici trapiantati di fegatoMateriali e metodi . Sono stati misurati i ratei di dose efficace e di dose superficiale in ingresso (ESD) per minuto di scopia, simulando la presenza del paziente con fantoccio in plexiglass di 10 cm di spessore e variando i parametri di esposizione (tipo di scopia pulsata, diametro IB, presenza di diaframmi) al fine di individuare le modalità che consentono di minimizzare la dose. Nel corso di tre procedure sono state effettuate misure in vivoRisultati . I valori di rateo di dose efficace sono risultati minimi per un particolare tipo di scopia pulsata, per il massimo ingrandimento e in presenza di diaframmatura. I risultati delle misure in vivo mostrano un valore massimo di ESD di circa 50 mGy (valore soglia per eritema temporaneo 2000 mGy, ICRP 60). I valori di dose efficace sono compresi tra 0,9 e 1,5 mSvConclusioni . Sono stati stabiliti i parametri di esposizione che consentono di ottenere la qualità di immagine desiderata con la minima dose, per l’apparecchiatura utilizzata e per questa tipologia di procedure. I valori di ESD misurati permettono di escludere il rischio di insorgenza di danni deterministici alla cute. I valori di dose efficace e le considerazioni conseguenti relative alla probabilità di induzione di tumori letali consentono di affermare che i benefici associati a questo tipo di procedure giustificano ampiamente l’esposizione del paziente al rischio radiologico associato

Radiation dose evaluations during radiological contrast studies in patients with morbid obesity

PurposeThe purpose of this study was to evaluate the radiation dose to patients during radiological contrast studies performed after vertical banded gastroplasty (VBG) or Roux-en-Y gastric bypass (RYGBP) surgery in patients with morbid obesity.Materials and methodsDose evaluations were performed on a sample of 39 patients (32 women and 7 men) with a mean weight of 117 kg (range 68–175 kg) and a mean body mass index (BMI) of 43.7 (range 22.2–54.9). Between the second and seventh postoperative day, patients underwent radiological follow-up after oral administration of approximately 70 ml of water-soluble iodinated contrast material (Gastrografin) and images acquired in anteroposterior, right and left oblique projections with the patient upright and then supine. Exposure conditions, dose-area product (DAP) and entrance skin dose (ESD) were recorded for each procedure. On the basis of these data, the effective dose (ED) was calculated using simulation software based on the Monte Carlo method for determining the absorbed dose to organs. To assess the optimal exposure conditions and the dose contributions of fluoroscopy and radiography, the effective dose rates were also evaluated using Plexiglas phantoms of different thickness to simulate different patient sizes.ResultsThe phantom measurements showed a fourfold dose increase when passing from normal-sized patients to obese patients. Mean DAP value obtained from in-vivo measurements was 70 Gy cm2 (range 17–147 Gy cm2), and mean effective dose was 21 mSv (range 5–45 mSv).ConclusionsWhen performing radiological contrast studies in patients with morbid obesity, every possible precaution should be taken to minimise patient dose. Special care should be taken to evaluate justification of the radiological procedure.RiassuntoObiettivoScopo del lavoro è stato quello di valutare la dose al paziente nel corso di esami contrastografici eseguiti in pazienti affetti da obesità patologica sottoposti ad interventi chirurgici di gastroplastica o bypass gastrico.Materiali e metodiLe valutazioni sono state effettuate per 39 esami, su di un campione di pazienti costituito da 32 donne e 7 uomini, con peso medio di 117 kg (intervallo 68–175 kg) e con indice di massa corporeo medio di 43,7 (intervallo 22,2–54,9). I pazienti operati nell’arco di tempo della durata dello studio sono stati sottoposti a controllo radiologico post-operatorio tra la II e la VII giornata mediante somministrazione per os di circa 70 ml di MdC iodato idrosolubile (Gastrografin) e acquisizione di radiogrammi eseguiti dapprima in ortostatismo in proiezione AP, obliqua destra e sinistra e successivamente a paziente supino. Per l’intera durata di ciascuna procedura sono state registrate le condizioni di esposizione e i valori di prodotto dose per area (DAP) e di dose di ingresso al paziente (ESD). Sulla base dei dati rilevati è stato effettuato un calcolo della dose efficace (ED) al paziente utilizzando un programma di calcolo basato sul metodo Monte Carlo per la stima della dose assorbita agli organi. Al fine di valutare le condizioni ottimali di esposizione e i contributi alla dose totale legati alla scopia e alla grafia, sono state inoltre effettuate misure di dose con fantocci di plexiglass di diversi spessori per simulare i pazienti di diversa corporatura.RisultatiLe misurazioni su fantoccio hanno dimostrato che il passaggio da spessori analoghi a quelli dei pazienti normotipo a quelli dei pazienti oggetto dello studio può comportare un aumento di dose di un fattore quattro. Il valore medio di prodotto dose per area ottenuto nelle misurazioni in vivo è stato di 70 Gy cm2 (intervallo 17–147 Gy cm2), mentre il valore medio di dose efficace è stato di 21 mSv (intervallo 5–45 mSv).ConclusioniNell’esecuzione di esami contrastografici in pazienti obesi occorre adottare tutte le precauzioni possibili per ridurre al minimo la dose al paziente. Particolare attenzione deve essere posta alla giustificazione dell’esame.

Calculation of tumour and normal tissue biological effective dose in 90Y liver radioembolization with different dosimetric methods

PURPOSE Radioembolization with 90Y microspheres is an effective treatment for unresectable liver tumours. Two types of microspheres are available: resin (SIR-Spheres®) and glass (Theraspheres®). The aim of this study is to compare biological effective dose (BED) values obtained with three different dosimetric methods. METHODS 29 HCC patients were included in this study: 15 were treated with resin(mean injected activity 1.5GBq, range 0.8-2.7GBq) and 14 with glass microspheres (2.6GBq, range 1.3-4.1GBq). Average doses to tumours and normal liver tissues were calculated with AAPM, multi-compartmental MIRD and Voxel-based methods and consequently the BED values were obtained. Planar images were used for the AAPM method: 99mTc-MAA SPECT-CT attenuation and scatter corrected images (resin) and 99m Tc-MAA SPECT attenuation corrected (glass) were employed for the other two methods. RESULTS Regardless of type of microspheres, both for tumours and normal liver tissues, no significant statistical differences were found between MIRD and Voxel for both doses and BED values. Conversely AAPM gave discordant results with respect to the other two methods (Mann-Whitney p-values⩽0.01). For resin spheres the calculated tumour-to-normal tissue ratios on planar images were on average 14 times greater than those obtained on SPECT-CT images, while they were 4 times greater on glass. A linear correlation was observed between MIRD and Voxel BEDs. CONCLUSIONS The AAPM method appears to be less precise for absorbed dose and BED estimation, while MIRD and voxel based dosimetry are more confident each other.

Evaluation of a commercial automatic treatment planning system for liver stereotactic body radiation therapy treatments

PURPOSE Automated treatment planning is a new frontier in radiotherapy. The Auto-Planning module of the Pinnacle3 treatment planning system (TPS) was evaluated for liver stereotactic body radiation therapy treatments. METHODS Ten cases were included in the study. Six plans were generated for each case by four medical physics experts. The first two planned with Pinnacle TPS, both with manual module (MP) and Auto-Planning one (AP). The other two physicists generated two plans with Monaco TPS (VM). Treatment plan comparisons were then carried on the various dosimetric parameters of target and organs at risk, monitor units, number of segments, plan complexity metrics and human resource planning time. The user dependency of Auto-Planning was also tested and the plans were evaluated by a trained physician. RESULTS Statistically significant differences (Anova test) were observed for spinal cord doses, plan average beam irregularity, number of segments, monitor units and human planning time. The Fisher-Hayter test applied to these parameters showed significant statistical differences between AP e MP for spinal cord doses and human planning time; between MP and VM for monitor units, number of segments and plan irregularity; for all those between AP and VM. The two plans created by different planners with AP were similar to each other. CONCLUSIONS The plans created with Auto-Planning were comparable to the manually generated plans. The time saved in planning enables the planner to commit more resources to more complex cases. The independence of the planner enables to standardize plan quality.

Automated quality control in Computed Radiography

Purpose.The purpose of this paper is to describe the automation of quality control procedures on photostimulable imaging plates by means of an image-processing tool providing automatic reading of the images and automatic calculation of the quality parameters monitored.Materials and methods.Quality-control procedures were performed according to the main available guidelines. The quality assurance programme was applied to several Kodak and Philips devices in four radiological departments. The automatic imageprocessing tool was developed using public domain software (Java-based ImageJ software) and contains both reading and computation procedures.Results.The quality checks and algorithms described were successfully applied, proving useful for identification of defective plates and for implementation of the quality assurance programme. The use of automation allowed significant savings in the time required for quality checks.Conclusions.Completely automated image reading allows substantial economic and human resources savings, as it eliminates much of the transfer, reproduction, processing and filing procedures.