Leopoldo Conte

Comparative study of jaws with multislice computed tomography and cone-beam computed tomography

PurposeThe aim of this study was to compare the dosimetric and diagnostic performance of multislice computed tomography (MSCT) and cone-beam computed tomography (CBCT) in the study of the dental arches.Materials and methodsEffective dose and dose to the main organs of the head and neck were evaluated by means of thermoluminescent dosimeters (TLDs) placed in an Alderson Rando anthropomorphic phantom and using a standard CBCT protocol and an optimised MSCT protocol. Five patients with occlusal plane ranging from 54 cm to 59 cm who needed close follow-up (range 1–3 months) underwent both examinations. Image quality obtained with CBCT and MSCT was evaluated.ResultsEffective dose and dose to the main organs of the head and neck were higher for MSCT than for CBCT. Image quality of CBCT was judged to be equivalent to that of MSCT for visualising teeth and bone but inferior for visualising soft tissues. Beam-hardening artefacts due to dental-care material and implants were weaker at CBCT than at MSCT.ConclusionsWhen panoramic radiography is not sufficient in the study of the teeth and jaw bones, CBCT can provide identical information to MSCT, with a considerable dose reduction. MSCT is, however, indicated when evaluation of soft tissue is required.RiassuntoObiettivoScopo di questo lavoro è confrontare le performances dosimetriche e diagnostiche di tomografia computerizzata multidetettore (TCMD) e tomografia computerizzata a fascio conico (TCFC) nello studio delle arcate dentarie.Materiali e metodiSi è provveduto alla misurazione della dose alle strutture di capo e collo e della dose efficace con dosimetri a termoluminescenza (TLD) posti in un fantoccio antropomorfo Alderson Rando utilizzando un protocollo TCFC ed uno TCMD ottimizzato. Sono stati esaminati 5 pazienti, con circonferenza al piano occlusale entro un range prestabilito (54–59 cm) e che avevano necessità di effettuare controlli ravvicinati nel tempo (range 1-3 mesi), con entrambi i sistemi TC ed è stata valutata la qualità delle immagini ottenute.RisultatiLa dose efficace agli organi è superiore per la TCMD rispetto alla TCFC. La qualità delle immagini della TCFC è stata giudicata sovrapponibile alla TCMD nello studio dei denti e dell’osso, inferiore nella valutazione dei tessuti molli. Artefatti da indurimento del fascio dovuti alla presenza di materiale medicamentoso e protesico incidono negativamente sulla qualità dell’immagine maggiormente nel caso della TCMD rispetto alla TCFC.ConclusioniLo studio delle strutture ossee può essere effettuato, se la radiografia ortopanoramica non è sufficiente, mediante TCFC, che fornisce informazioni sovrapponibili a quelle della TCMD con notevole risparmio di dose; la TCMD è indicata qualora sia necessario valutare anche i tessuti molli.

Optimisation of multislice computed tomography protocols in angio–CT examinations

Purpose.The aim of this paper is to explain a general procedure for the optimisation of multislice computed tomography (MSCT) protocols.Materials and methods.Four angio–CT protocols with a GE LightSpeed Plus 4–slice CT scanner were considered. Effective doses were computed for a sample of patients. First the dose was optimised for arterial–phase scans on a standard patient and adapted to the weight of individual patients with a scaling factor.Results.The mean effective dose for an angio–CT examination ranged from 18.8 mSv to 28.8 mSv, depending on the protocol adopted. Following the optimisation procedure, we drew up a table indicating tube current values for each patient weight. Calculation of the effective dose before and after the optimisation procedure revealed a dose reduction of about 40%.Conclusions.Angio–CT examinations deliver high doses, but these doses can be reduced without affecting image quality.

Hyperfractionated radiotherapy for T2N0 glottic carcinoma: a retrospective analysis at 10 years follow-up in a series of 60 consecutive patients.

Aims and background To report results of hyperfractionated radiotherapy for T2N0 glottic carcinoma at a single institution after extended follow-up. Methods Between 1980 and 1988 at Varese University Hospital, 60 consecutive patients with T2N0 glottic carcinoma received exclusive radiotherapy consisting of 1.5 Gy/fraction twice a day. Treatment gaps during the radiotherapy course were allowed according to individual tolerance. This policy resulted in a wide range of elapsed treatment time: median, 5.7 weeks; range, 3.7-8.9. Median follow-up is 9.8 years. Results As a result of dose/time distribution, 16, 20 and 24 patients received an average weekly dose rate of <10 Gy/week, equal to 10 Gy/week or >10 Gy/week, respectively. Mean total dose for each group was 62.8 Gy, 63.7 Gy and 63.8 Gy, respectively. Five-year local-regional control was 69 ± 6% (95% Cl); ultimate local-regional control, including salvage surgery, was 78 ± 5%. All failures were at the primary site, and no patient developed neck recurrence as first site of failure. The actuarial incidence of grade 2-3 late reactions at 5 years was 42 ± 6%. Most late toxicity events were grade 2: only 2 patients developed grade 3 reactions and none grade 4. None of the several clinical and treatment-related variables showed any statistically significant impact on local-regional control or late toxicity at univariate and multivariate analysis. In particular, 3-year local-regional control rates were 73 ± 11%, 84 ± 8% and 69 ± 10% for an average weekly dose rate of <10 Gy/week, equal to 10 Gy/week and >10 Gy/week, respectively (not significantly different). Conclusions At a very long follow-up, the hyperfractionated regimen tested in the study was shown to be effective and devoid of major complications, provided individual patient acute tolerance is carefully taken into account. Also, time factor did not affect outcome in this series.

Dedicated dental volumetric and total body multislice computed tomography: a comparison of image quality and radiation dose

Aim of this work is to compare the performances of a Xoran Technologies i-CAT Cone Beam CT for dental applications with those of a standard total body multislice CT (Toshiba Aquilion 64 multislice) used for dental examinations. Image quality and doses to patients have been compared for the three main i-CAT protocols, the Toshiba standard protocol and a Toshiba modified protocol. Images of two phantoms have been acquired: a standard CT quality control phantom and an Alderson Rando® anthropomorphic phantom. Image noise, Signal to Noise Ratio (SNR), Contrast to Noise Ratio (CNR) and geometric accuracy have been considered. Clinical image quality was assessed. Effective dose and doses to main head and neck organs were evaluated by means of thermo-luminescent dosimeters (TLD-100) placed in the anthropomorphic phantom. A Quality Index (QI), defined as the ratio of squared CNR to effective dose, has been evaluated. The evaluated effective doses range from 0.06 mSv (i-CAT 10 s protocol) to 2.37 mSv (Toshiba standard protocol). The Toshiba modified protocol (halved tube current, higher pitch value) imparts lower effective dose (0.99 mSv). The conventional CT device provides lower image noise and better SNR, but clinical effectiveness similar to that of dedicated dental CT (comparable CNR and clinical judgment). Consequently, QI values are much higher for this second CT scanner. No geometric distortion has been observed with both devices. As a conclusion, dental volumetric CT supplies adequate image quality to clinical purposes, at doses that are really lower than those imparted by a conventional CT device.

Dosimetric and image quality assessment of different acquisition protocols of a novel 64-slice CT scanner

Dose and image quality assessment in computed tomography (CT) are almost affected by the vast variety of CT scanners (axial CT, spiral CT, low-multislice CT (2-16), high-multislice CT (32-64)) and imaging protocols in use. Very poor information is at the moment available on 64 slices CT scanners. Aim of this work is to assess image quality related to patient dose indexes and to investigate the achievable dose reduction for a commercially available 64 slices CT scanner. CT dose indexes (weighted computed tomography dose index, CTDIw and Dose Length Product, DLP) were measured with a standard CT phantom for the main protocols in use (head, chest, abdomen and pelvis) and compared with the values displayed by the scanner itself. The differences were always below 7%. All the indexes were below the Diagnostic Reference Levels defined by the European Council Directive 97/42. Effective doses were measured for each protocol with thermoluminescent dosimeters inserted in an anthropomorphic Alderson Rando phantom and compared with the same values computed by the ImPACT CT Patient Dosimetry Calculator software code and corrected by a factor taking in account the number of slices (from 16 to 64). The differences were always below 25%. The effective doses range from 1.5 mSv (head) to 21.8 mSv (abdomen). The dose reduction system of the scanner was assessed comparing the effective dose measured for a standard phantom-man (a cylinder phantom, 32 cm in diameter) to the mean dose evaluated on 46 patients. The standard phantom was considered as no dose reduction reference. The dose reduction factor range from 16% to 78% (mean of 46%) for all protocols, from 29% to 78% (mean of 55%) for chest protocol, from 16% to 76% (mean of 42%) for abdomen protocol. The possibility of a further dose reduction was investigated measuring image quality (spatial resolution, contrast and noise) as a function of CTDIw. This curve shows a quite flat trend decreasing the dose approximately to 90% and a sharp fall below that value. A significant decrease in the effective dose to the patient, around 40%, was found; image quality analysis shows a further 10% dose reduction possibility.

An empirical calibration method for an a-Si portal imaging device: applications in pretreatment verification of IMRT

PurposeA new calibration method for an amorphoussilicon (a-Si) electronic portal imaging device (EPID) used for dose measurements in pretreatment verification (field-related) of intensity-modulated radiation therapy (IMRT) with sliding-window technique. The method is independent of data contained in the multileaf collimator (MLC) leaf-motion files and of any calculations made by the treatment planning system (TPS).Materials and methodsSensitivity of the EPID is dependent on radiation energy. For fluence-modulated fields, different dose/reading calibration factors are associated with each pixel of the image acquired by calculating equivalent areas representing the exact ratio between primary and scatter components. The dose measured in the detector plane was compared with that calculated with TPS by using gamma-analysis. Each calibration factor was compared with that calculated by considering the individual contributions of primary and secondary radiation obtained using the convolution method with analytical kernel for homogeneous media.ResultsIn 837/854 (98%) of the clinical fields analysed, the proportion of irradiated area in which the gamma-index was <1.0 exceeded 95%. The overall average gamma-index was 0.39. There was good agreement between the dose/reading calibration factors obtained with the empirical algorithm and with the convolution method.ConclusionsThe proposed calibration method is suitable for routine clinical pretreatment verification in IMRT.RiassuntoObiettivoIl lavoro è finalizzato all’implementazione di un nuovo metodo di calibrazione di un dispositivo portale al silicio amorfo (EPID) impiegato per misure di dose nelle verifiche pre-trattamento (field-related) con tecnica di radioterapia ad intensità modulata (IMRT) sliding window. Il metodo risulta indipendente dai dati contenuti nel file di movimentazione del collimatore multilamellare (MLC) e dai calcoli del sistema di pianificazione del trattamento (TPS).Materiali e metodiLa sensibilità dell’EPID dipende dall’energia della radiazione. Per campi a fluenza modulata si associano ai pixel dell’immagine diversi fattori di calibrazione dose/lettura calcolando delle aree equivalenti rappresentative del rapporto puntuale tra le componenti primaria e diffusa. La dose misurata al piano del rivelatore viene confrontata, mediante analisi gamma, con quella calcolata con TPS. Ciascun fattore di calibrazione viene confrontato con quello calcolato considerando separatamente i contributi di radiazione primaria e secondaria ottenuti con metodo di convoluzione di un kernel analitico per mezzi omogenei.RisultatiPer 837/854 campi clinici analizzati (98%), la percentuale di area irradiata in cui l’indice gamma risulta inferiore a 1,0 è superiore al 95%. L’indice gamma medio complessivo è 0,39. L’accordo tra i fattori di calibrazione dose/lettura ottenuti rispettivamente con metodo empirico e metodo di convoluzione è buono.ConclusioniIl procedimento di calibrazione proposto risulta adeguato allo scopo e può essere impiegato di routine.

3D imaging of radioactivity in man measured with a whole body counter

In the Medical Physics Department of the University of Insubria, Varese, Italy, a whole body counter is in use, for clinical and radioprotection measurements. It consists of a scanning bed, four opposite (anterior-posterior and laterallateral) NaI(Tl) detectors and a shielding based on the shadow-shield principle. By moving the bed on which the patient lies in the supine position, the longitudinal profiles of the counts measured by each probe along the patient axis are obtained. Making the assumption that radioactivity is distributed in N voxel sources located in N selected positions in the patient, this distribution is calculated by solving an over-determined system of linear equations. The solution can be calculated using different methods. An iterative method and a regularization technique are presented. The algorithm proposed allows the evaluation of the distribution of the radioactivity in 3D in voxels with dimensions ranging from 15 to 20 mm, depending on the size of the patient. The 3D distribution of the radioactivity and the knowledge of the time of the intake allow the assessment of the effective dose.

A new method for the quantitative analysis of gated SPECT polar scintigraphic maps

We have developed a software, which allows to do non conventional percent quantitative analysis on scintigraphic polar map obtained from conventional processing of gated-SPECT acquisitions. Polar maps are 8 bit images of perfusion, motion, ejection fraction (EF) and thickening, of the heart. The software is written in Matlab, analyses the whole polar map and four ROIs corresponding to the theoretical LAD, LCX, RCA territories (perfused by these arteries) and extra-ROIs region. An intensity segmentation is performed. The area corresponding to pixels lower and higher than a varying cut-off are calculated on the whole image and for each ROI. The software calculates an intensity-area histogram, which is the analogous of the Dose-Volume Histogram used in radiation therapy: in this case, the histogram has the meaning of a Perfusion- or a Motion-Volume histogram. Then, the software applies the Lyman-Wolbarst algorithm, to calculate the area equivalent histogram reduction (e.g. the perfused area in the hypothesis that all pixels are perfused at 100%.). The makes a direct comparison between two different polar maps by choice. The comparison between the numerical quantification of motion and perfusion maps, allows the physicians to get a clinical evaluation of the stunned myocardium.