Physica Medica: European Journal of Medical Physics - Articles in Press

Evaluation of an uncollimated printed paper transmission source used under scatter limiting conditions - Corrected Proof

2010-03-08

Abstract: Transmission sources used for image attenuation correction, allowing image quantification, are collimated to reduce scatter. We propose the same effect can be achieved for an uncollimated source by increasing source to patient distance. The aim was to compare planar image performance characteristics and absorbed doses of uncollimated and collimated radioactive printed paper transmission sources.The scatter contribution to the uncollimated 99mTc source data was evaluated for different combinations of detector phantom distance, detector source distance and phantom source distance. Measurements were performed by increasing the Lucite phantom thickness in 1cm steps to 20 cm. Spatial resolution, detection efficiency and entrance absorbed dose rate were measured for the uncollimated and collimated transmission source images.Results derived from the energy spectra, obtained with the uncollimated transmission source indicate that scatter contribution increases with decreasing detector source distance. The scatter component in the uncollimated transmission images (detector source distances≥60cm; phantom source distances≥40cm) was comparable to that obtained with collimated transmission images. Attenuation coefficients obtained compared well (0.168cm−1 vs. 0.171cm−1). The full widths at half maxima differed by less than 0.9mm. The detection efficiency of the uncollimated source was 2.5 times higher than obtained with the collimated source. The entrance absorbed dose obtained from an uncollimated source was 3.75 times larger than that obtained from the collimated source.An uncollimated transmission source (detector source distance≥60cm) results in acceptable image characteristics and presents a low cost, low dose, high efficiency option for transmission imaging.

Physical characterization and comparison of two commercially available micro-MLCs - Corrected Proof

Tarun K. Podder, Greg Bednarz, Yan Yu, James M. Galvin — 2010-03-04

Abstract: In this study, the physical characteristics (penumbra width variation with the source size and shape, interleaf leakage, transmission through the leaves, and the tongue-and-groove effect) of two linear accelerators (BrainLAB's Novalis and Elekta's Synergy-S Beam Modulator) have been investigated. For similar square fields (about 4.5cm×4.5cm) with source-to-surface/skin-distance (SSD) ranging from 90cm to 115cm and measurements taken at the depth of Dmax=1.5cm for 6MV photon beam. The Novalis MLC has penumbra width of 2.4±0.11mm–2.8±0.11mm at the leaf-end and 2.2±0.1mm–2.7±0.1mm on the leaf-side; and those for the Synergy-S MLC are 4.4±0.17mm–5.2±0.2mm and 3.0±0.12mm–3.5±0.12mm. Upon rotating the Synergy-S collimator by 90° (i.e., shifting the leaf movement to the gun–target direction), significant reduction of the leaf-end penumbra width (17%) and increase of leaf-side penumbra width (28%) suggest an elliptical shape of the radiation source spot. Similar rotation of the collimator yielded reduction of the penumbras on both leaf-end (34%) and leaf-side (28%) for Novalis, indicating that the Novalis has a more symmetric source size. For all the field sizes and settings, BrainLAB's Novalis μMLC produce a smaller penumbra for simple square fields compared to the Elekta's Synergy-S. However, this difference became less pronounced for leaf-side penumbra and also for circular fields. The tongue-and-groove effect of the Novalis (23±0.9%) is slightly smaller than that of the Synergy-S (25±1%); while the interleaf leakage and leakage directly through leaves for Synergy-S (1.6±0.07% & 0.9±0.04%) are lower than that of Novalis (2±0.08% & 1.3±0.05%).

Generalized EPID calibration for in vivo transit dosimetry - Corrected Proof

2010-03-03

Abstract: Many researchers are studying new in vivo dosimetry methods based on the use of Elelctronic portal imaging devices (EPIDs) that are simple and efficient in their daily use. However the need of time consuming implementation measurements with solid water phantoms for the in vivo dosimetry implementation can discourage someone in their use.In this paper a procedure has been proposed to calibrate aSi EPIDs for in vivo transit dosimetry. The dosimetric equivalence of three aSi Varian EPIDs has been investigated in terms of signal reproducibility and long term stability, signal linearity with MU and dose per pulse and signal dependence on the field dimensions. The signal reproducibility was within ±0.5% (2SD), while the long term signal stability has been maintained well within ±2%. The signal linearity with the monitor units (MU) was within ±2% and within ±0.5% for the EPIDs controlled by the IAS 2, and IAS 3 respectively. In particular it was verified that the correction factor for the signal linearity with the monitor units, klin, is independent of the beam quality, and the dose per pulse absorbed by the EPID.For 6, 10 and 15MV photon beams, a generalized set of correlation functions F(TPR,w,L) and empirical factors f(TPR,d,L) as a function of the Tissue Phantom Ratio (TPR), the phantom thickness, w, the square field side, L, and the distance, d, between the phantom mid-plane and the isocentre were determined to reconstruct the isocenter dose.The tolerance levels of the present in vivo dosimetry method ranged between ±5% and ±6% depending on the tumor body location.In conclusion, the procedure proposed, that use generalized correlation functions, reduces the effort for the in vivo dosimetry method implementation for those photon beams with TPR within ±0.3% as respect those here used.

Experimental analysis of Hb oxy–deoxy transition in single optically stretched red blood cells - Corrected Proof

G. Rusciano — 2010-02-25

Abstract: Raman confocal microscopy, combined with an optical stretcher, is used to study the spatial distribution and the oxidation state of hemoglobin in erythrocytes under stretching condition. In particular, a near infrared laser (λ = 1064 nm) is used to generate multiple time-sharing Optical Tweezers to trap and stretch a single erythrocyte, while a second laser (λ = 532 nm) acts as Raman probe. Our study demonstrates that stretching induces hemoglobin transition to the deoxygenated state. Moreover, by using Principal Component Analysis we prove the reversibility of the hemoglobin transition after application of the optically induced mechanical stress.

Comparison of monitor units calculated by radiotherapy treatment planning system and an independent monitor unit verification software - Corrected Proof

P. Sellakumar, C. Arun, S.S. Sanjay, S.B. Ramesh — 2010-02-22

Abstract: In radiation therapy, the monitor units (MU) needed to deliver a treatment plan are calculated by treatment planning systems (TPS). The essential part of quality assurance is to verify the MU with independent monitor unit calculation to correct any potential errors prior to the start of treatment. In this study, we have compared the MU calculated by TPS and by independent MU verification software. The MU verification software was commissioned and tested for the data integrity to ensure that the correct beam data was considered for MU calculations. The accuracy of the calculations was tested by creating a series of test plans and comparing them with ion chamber measurements. The results show that there is good agreement between the two. The MU difference (MUdiff) between the monitor unit calculations of TPS and independent MU verification system was calculated for 623 fields from 245 patients and was analyzed by treatment site for head & neck, thorax, breast, abdomen and pelvis. The mean MUdiff of −0.838% with a standard deviation of 3.04% was observed for all 623 fields. The site specific standard deviation of MUdiff was as follows: abdomen and pelvis (<1.75%), head & neck (2.5%), thorax (2.32%) and breast (6.01%). The disparities were analyzed and different correction methods were used to reduce the disparity.

Scanning orientation and polarization effects for XRQA radiochromic film - Corrected Proof

Hani Alnawaf, Martin J. Butson, Tsang Cheung, Peter K.N. Yu — 2010-02-12

Abstract: Gafchromic XRQA radiochromic film, is an effective tool for quality assurance and dose assessment in kilovoltage radiotherapy and diagnostic applications. Like other Gafchromic film products, XRQA film exhibits a variation in dose to reflected optical density response with angle of rotation when analysed with a light source that is partially or fully polarised such as a desktop scanner. Although warnings are not given on manufacturers specifications, this can affect dosimetry accuracy and we recommend that it is essential to scan all XRQA films in the same orientation. The effect is not as pronounced as EBT Gafchromic film. The magnitude of this variation has been measured and shown to be up to 16±2% (1SD) using a fully linear polarised light source was seen with a 90° angle rotation. This would be the maximum variation seen on a desktop scanner with a fully polarised light source. For our standard desktop scanner (Epson v700) a mean variation of 2±1% from 0cGy to 20cGy applied dose was measured as compared to 8±2% for EBT Gafchromic. We recommend that to decrease uncertainty in dose measurement, accurate alignment of the calibration films to experimental films be performed on a regular basis. This is especially important if your desktop scanner has a high degree of polarization of its light source.

Reduction of patient dose in medical radiography by utilizing scattered X-rays: Relation between permissible limit of scatter fraction, viewer brightness, and perceptibility of vision - Corrected Proof

Yoshiyuki Asai, Masanobu Uemura, Masao Matsumoto, Hitoshi Kanamori — 2010-02-04

Abstract: This paper proposes a new technique for reducing the patient dose when employing medical radiographs prepared by using screen-film systems. In this technique the patient dose can be reduced by employing scattered X-rays in order to obtain the same film density as that realized without the use of scattered X-rays. The minimum perceptible thickness difference ΔXmin, which can be recognized by liminal vision, was psychophysically calculated by considering the energy spectrum of incident X-ray, sensitivity spectrum of the screen layer, and the perception capability of human vision. From the calculated ΔXmins in various conditions, the permissible upper limit of scatter fraction for obtaining the same ΔXmin for three kinds of luminances, and the fraction of reduction in the primary X-rays were determined.As an example of the results, when the object size required for perception is 1.3 mm, a scatter fraction up to 42% can be permitted at a density D of 1.0 for a luminance of 2548 cd m–2. When we increase the luminance of the viewer from 478 cd m–2 to 2548 cd m–2, the upper limit of the permitted scatter fraction varies from 30% to 42% at a D of 1.0, i.e., the patient dose can be reduced by 17% under the same perceptibility of ΔXmin by utilizing scattered X-rays. This reduction can be successfully achieved by changing the lead content of the grid from 0.45 to 0.38 g cm–2.

Coronary angiography and percutaneous transluminal coronary angioplasty procedures: Evaluation of patients' maximum skin dose using Gafchromic films and a comparison of local levels with reference levels proposed in the literature - Corrected Proof

C. Giordano, L. D'Ercole, R. Gobbi, M. Bocchiola, F. Passerini — 2010-02-01

Abstract: The aim of this study was to evaluate the maximum skin dose (MSD) in patients undergoing interventional cardiology procedures, obtaining local reference levels and comparing these with the reference levels proposed in the literature.The patients' MSD was measured using Gafchromic XR type R films. In order to evaluate reference levels, the number of images acquired, the fluoroscopy times and the KAPTOTAL were recorded for each procedure.For the evaluation of the MSD, 8 coronary angiography (CA) and 16 percutaneous transluminal coronary angioplasty (PTCA) procedures, carried out in the period from May to June 2008, were analyzed.For the CA procedures the MSD values were below 0.5 Gy.For the PTCA procedures, we found a fairly good correlation between fluoroscopy time and MSD (r = 0.80, p = 0.0002) and between MSD and WFP (r = 0.863, p < 0.0001); there was a strong correlation between KAPTOTAL and MSD (r = 0.904, p < 0.0001). Since the correlation between KAPTOTAL and MSD is more striking than that with fluoroscopic time and the WFP, KAP measurements are suitable for online skin dosimetry and may, therefore, be used to avoid radiation-induced skin injuries. A MSD greater than 3 Gy occurred in only one procedure.For calculus of the local reference levels, we extended the data-gathering to 30 procedure CA and to 40 PTCA: we compared local practice with that in other centers using the guidance levels proposed by Balter et al. Our median KAP values were below these proposed guidance levels; our mean KAP values were above these proposed action levels. From a first application of the proposed reference levels, it appears that, according to the recommendations of Balter et al. an investigation into local practice is not necessary.

Influence of Geant4 parameters on dose distribution and computation time for carbon ion therapy simulation - Corrected Proof

Nabil Zahra, Thibault Frisson, Loic Grevillot, Philippe Lautesse, David Sarrut — 2010-01-27

Abstract: The aim of this work was to study the influence of Geant4 parameters on dose distribution and computational time for simulations of carbon ion therapy. The study was done using Geant4 version 9.0. The dose distribution in water for incident monoenergetic carbon ion beams of 300 MeV/u were compared for different values of secondary particle production threshold and different step limits. Variations of depth dose of about 2 mm were observed in some cases, which induced a 30% variation of dose deposit in the Bragg peak region. Other tests were done using Geant4 version 9.2 to verify the results from this study. The two versions provided converging results and led to the same conclusions.

Accuracy of real-time MR temperature mapping in the brain: A comparison of fast sequences - Corrected Proof

A. Kickhefel, Jörg Roland, Clifford Weiss, Fritz Schick — 2010-01-25

Abstract: Purpose: To compare magnetic resonance (MR) thermometry based on the proton resonance frequency (PRF) method using a single shot echoplanar imaging (ss EPI) sequence to both of the standard sequences, gradient echo (GRE) and segmented echoplanar imaging (seg EPI) in the in vivo human brain, at 1.5T and 3T.Material and methods: Repetitive MR thermometry was performed on the brain of six volunteers using GRE, seg EPI, and ss EPI sequences on whole-body 1.5T and 3T clinical systems using comparable acquisition parameters. Phase stability and temperature data precision in the human head were determined over 12 min for the three sequences at both field strengths. An ex-vivo swine skeletal muscle model was used to evaluate temperature accuracy of the ss EPI sequence during heating by high intensity focused ultrasound (HIFU).Results: In-vivo examinations of brain revealed an average temperature precision of 0.37 °C/0.39 °C/0.16 °C at 3T for the GRE/seg EPI/ss EPI sequences. At 1.5T, a precision of 0.58 °C/0.63 °C/0.21 °C was achieved. In the ex-vivo swine model, a strong correlation of temperature data derived using ss EPI and GRE sequences was found with a temperature deviation <1 °C.Conclusion: The ss EPI sequence was the fastest and the most precise sequence for MR thermometry, with significantly higher accuracy compared to GRE.

A detection method for streak artifacts and radiological noise in a non-uniform region in a CT image - Corrected Proof

Kuniharu Imai, Mitsuru Ikeda, Yukihiro Enchi, Takanaga Niimi — 2009-12-28

Abstract: By using the CT images obtained by subtracting two CT images acquired under the same conditions and slice locations, we have devised a method for detecting streak artifacts in non-uniform regions and only radiological noise components in CT images. A chest phantom was scanned using 16- and 64-multidetector row helical CT scanners with various mAs values at 120kVp. The upper lung slice image was employed as a target image for evaluating the streak artifacts and radiological noise. One hundred parallel line segments with a length of 80 pixels were placed on the subtracted CT image, and the largest CT value in each CT value profile was employed as a feature variable of the streak artifacts; these feature variables were analyzed with the extreme value theory (Gumbel distribution). To detect only the radiological noise, all CT values contained in the 100 line profile were plotted on normal probability paper and the standard deviation was estimated from the inclination of its fitted line for the CT value plots. The two detection methods devised in this study were able to evaluate the streak artifacts and radiological noise in the CT images with high accuracy.

Dosimetric characterization of an 192Ir brachytherapy source with the Monte Carlo code PENELOPE - Corrected Proof

2009-12-25

Abstract: Monte Carlo calculations are highly spread and settled practice to calculate brachytherapy sources dosimetric parameters. In this study, recommendations of the AAPM TG-43U1 report have been followed to characterize the Varisource VS2000 192Ir high dose rate source, provided by Varian Oncology Systems.In order to obtain dosimetric parameters for this source, Monte Carlo calculations with PENELOPE code have been carried out. TG-43 formalism parameters have been presented, i.e., air kerma strength, dose rate constant, radial dose function and anisotropy function. Besides, a 2D Cartesian coordinates dose rate in water table has been calculated. These quantities are compared to this source reference data, finding results in good agreement with them.The data in the present study complement published data in the next aspects: (i) TG-43U1 recommendations are followed regarding to phantom ambient conditions and to uncertainty analysis, including statistical (type A) and systematic (type B) contributions; (ii) PENELOPE code is benchmarked for this source; (iii) Monte Carlo calculation methodology differs from that usually published in the way to estimate absorbed dose, leaving out the track-length estimator; (iv) the results of the present work comply with the most recent AAPM and ESTRO physics committee recommendations about Monte Carlo techniques, in regards to dose rate uncertainty values and established differences between our results and reference data.The results stated in this paper provide a complete parameter collection, which can be used for dosimetric calculations as well as a means of comparison with other datasets from this source.

Stochastic modelling of the role of cisplatin in altered fractionation schedules for head and neck cancer - Corrected Proof

Loredana Marcu, Eva Bezak — 2009-12-25

Abstract: Advanced head and neck cancers are one of the most challenging cancers facing the oncologists due to their aggressiveness attributable to the high hypoxic content and the tumour's ability to repopulate during radiotherapy. Alterations of radiotherapy fractionation schedules are possible ways to improve tumour control. Clinical trials have shown that both hyperfractionated radiotherapy (multiple fractions a day, over the same treatment time), and accelerated radiotherapy (higher doses per fraction, six days a week, over 5 weeks or less) are more effective than conventional radiotherapy in the management of head and neck cancer. However, the treatment choice between hyperfractionated and accelerated radiotherapy is still debated, due to very similar results obtained regarding tumour control. Furthermore, while radiotherapy alone has an impact on the short-term prognosis of advanced head and neck cancer, the long-term benefits have been moderate. Cisplatin is a chemotherapeutic agent which combined with conventional radiotherapy has shown to improve patient survival. The present paper employs a Monte Carlo modelling approach in assessing the effect of combined cisplatin-altered fractionation schedule on tumour response. The growth of a head and neck carcinoma has been modelled using probabilistic functions sampled by computer generated random number sequences, maintaining the biological constitution of a tumour. The tumour growth model has been built to simulate the in vivo processes taking place before and after radiotherapy/chemotherapy. The model has shown that adding cisplatin to radiotherapy improves tumour control in both hyperfractionated and accelerated radiotherapy.

Viewing boxes: A survey in diagnostic radiology departments of Moroccan hospitals - Corrected Proof

F. Bentayeb, K. Nfaoiu, O. Basraoui, A.C.P. Azevedo — 2009-12-25

Abstract: This work consists on a survey of the performance of viewing boxes installed in diagnostic radiology departments and included several aspects: checking the illuminance of the diagnostic rooms where the viewing boxes are located as well as the viewing boxes luminance levels and homogeneity. Seven hospitals took part in the survey, being three in the city of Casablanca and four in Rabat. A total of 136 viewing boxes and 18 diagnostic rooms have been checked. It was found that one diagnostic room works under normal conditions and that 80% of the viewing boxes present luminance levels below the international recommendations and the homogeneity is inadequate in 85%. Some simple and cheap initiatives can be performed in these departments to increase luminance and improve homogeneity levels such as cleaning and bulbs replacement.

Calculating and controlling the error of discrete representations of Pareto surfaces in convex multi-criteria optimization - Corrected Proof

David Craft — 2009-12-21

Abstract: A discrete set of points and their convex combinations can serve as a sparse representation of the Pareto surface in multiple objective convex optimization. We develop a method to evaluate the quality of such a representation, and show by example that in multiple objective radiotherapy planning, the number of Pareto optimal solutions needed to represent Pareto surfaces of up to five dimensions grows at most linearly with the number of objectives. The method described is also applicable to the representation of convex sets.

Using the “STEP Test” to evaluate processing speed in Moroccan hospitals - Corrected Proof

K. Nfaoiu, F. Bentayeb, O. Basraoui, A.C.P. Azevedo — 2009-12-07

Abstract: The STEP Test is a simple method that can be used to quickly evaluate processing speed of automatic processors. It allows the identification of large deviations (>20%) in the processor-chemicals-film system. STEP means Sensitometric Test for the Evaluation of Processing. The performance of the processors taking part in the survey are calculated and compared to a standard processor where the film is processed under ideal conditions, according to manufacturer's recommendations. For each processor, in the dark room, a film is exposed to a sensitometer light, processed and the sensitometric curve is obtained. This survey was performed in 8 Moroccan hospitals in the cities of Casablanca and Rabat and included 11 processors. It was concluded that 50% of the processors present processing problems and are functioning under inadequate conditions since they present deviations larger than 20%.

Experimental determination of the effective point of measurement of cylindrical ionization chambers for high-energy photon and electron beams - Corrected Proof

Yanxiao Huang, Christian Willomitzer, Golam Abu Zakaria, Guenther H. Hartmann — 2009-11-18

Abstract: Measurements of depth-dose curves in water phantom using a cylindrical ionization chamber require that its effective point of measurement is located at the measuring depth. Recommendations for the position of the effective point of measurement with respect to the central axis valid for high-energy electron and photon beams are given in dosimetry protocols. According to these protocols, the use of a constant shift Peff is currently recommended. However, this is still based on a very limited set of experimental results. It is therefore expected that an improved knowledge of the exact position of the effective point of measurement will further improve the accuracy of dosimetry. Recent publications have revealed that the position of the effective point of measurement is indeed varying with beam energy, field size and also with chamber geometry. The aim of this study is to investigate whether the shift of Peff can be taken to be constant and independent from the beam energy. An experimental determination of the effective point of measurement is presented based on a comparison between cylindrical chambers and a plane-parallel chamber using conventional dosimetry equipment. For electron beams, the determination is based on the comparison of halfvalue depth R50 between the cylindrical chamber of interest and a well guarded plane-parallel Roos chamber. For photon beams, the depth of dose maximum, dmax, the depth of 80% dose, d80, and the dose parameter PDD(10) were used. It was again found that the effective point of measurement for both, electron and photon beams Dosimetry, depends on the beam energy. The deviation from a constant value remains very small for photons, whereas significant deviations were found for electrons. It is therefore concluded that use of a single upstream shift value from the centre of the cylindrical chamber as recommended in current dosimetry protocols is adequate for photons, however inadequate for accurate electron beam dosimetry.

A dosimetric analysis comparing electron beam with the MammoSite brachytherapy applicator for intact breast boost - Corrected Proof

A.P. Shah, J.B. Strauss, M.C. Kirk, S.S. Chen, A. Dickler — 2009-10-16

Abstract: Introduction: Electron beam radiation is the modality most often used to deliver an operative bed boost to breast cancer patients after completing whole breast radiation. However, electrons can potentially provide inadequate coverage. The MammoSite breast brachytherapy applicator may provide dosimetric advantages in the delivery of an operative bed boost and its role in this setting is not yet defined.Materials and methods: The study population consisted of 15 patients with early stage breast cancer treated with partial breast irradiation (PBI) using the MammoSite device. For each patient, a theoretical boost plan using electrons and a second theoretical boost plan using the MammoSite applicator were created. To assess the adequacy of each boost plan, the PTV V90, PTV V95, and PTV V100 were calculated. To assess dose to normal tissues, the ipsilateral breast V50, ipsilateral lung V30, and heart V20 were calculated.Results: The mean PTV V100 for the MammoSite boost was 95.5%, compared to 77.4% for the electron boost (p<0.001). The mean PTV V95 was 97.8%, compared to 93.3% for the electron boost (p=0.02). The mean PTV V90, mean breast V50, mean lung V30, and mean heart V20 were not statistically different for MammoSite compared to electrons.Conclusions: A tumor bed boost using the MammoSite breast brachytherapy applicator provides superior target coverage and delivers similar doses to the ipsilateral breast and lung compared to a boost delivered with electrons. More investigation into the role of balloon brachytherapy in the delivery of a breast boost is warranted.

A comprehensive SWOT audit of the role of the biomedical physicist in the education of healthcare professionals in Europe - Corrected Proof

2009-10-05

Abstract: Although biomedical physicists provide educational services to the healthcare professions in the majority of universities in Europe, their precise role with respect to the education of the healthcare professions has not been studied systematically. To address this issue we are conducting a research project to produce a strategic development model for the role using the well-established SWOT (Strengths, Weaknesses, Opportunities, Threats) methodology. SWOT based strategic planning is a two-step process: one first carries out a SWOT position audit and then uses the identified SWOT themes to construct the strategic development model. This paper reports the results of a SWOT audit for the role of the biomedical physicist in the education of the healthcare professions in Europe. Internal Strengths and Weaknesses of the role were identified through a qualitative survey of biomedical physics departments and biomedical physics curricula delivered to healthcare professionals across Europe. External environmental Opportunities and Threats were identified through a systematic survey of the healthcare, healthcare professional education and higher education literature and categorized under standard PEST (Political, Economic, Social-Psychological, Technological-Scientific) categories. The paper includes an appendix of terminology. Defined terms are marked with an asterisk in the text.

Possibility of limiting the un-justified irradiation in 131I therapy of Graves' disease: A thyroid mass-reduction based method for the optimum activity calculation - Corrected Proof

Antonio C. Traino, Mariano Grosso, Giuliano Mariani — 2009-10-05

Abstract: Objective: In Graves' disease therapy, the amount of 131I is usually decided following two different modalities: the administration of a fixed activity or of an activity individually calculated based on a fixed value of target absorbed dose. Although the effectiveness of each of these approaches is good (about 80% of patients cured), the ALARA principle must be applied avoiding the un-justified radioactivity to the patient himself, the people living/working near him and the environment. In this paper a new approach to the 131I therapy in Graves' disease, based on the optimum value of the final thyroid mass, is presented.Design: 97 Graves' disease patients (29 males) were randomly assigned into three groups (GR1, GR2, GR3). In two of them (GR1, GR3) the radioiodine administering activity was calculated based on two fixed thyroid absorbed dose values (100Gy for GR1; 400Gy for GR3), in GR2 it was calculated based on the desired final optimum thyroid mass value mf=0.24m0/U0Results: The rate of cured patients are 48% (GR1), 97% (GR2) (z-test, p<0.001) and 97% (GR3). The average activity administered to GR2 (393±157MBq) is lower than that administrered to GR3 patients (524±201MBq) (p=0.007, two-tails unpaired t-test); the thyroid absorbed dose in GR2 (262±78Gy) is lower than in GR3 patients (407±23Gy) (p<0.001, two-tails unpaired t-test).Conclusion: Our results demonstrate that the thyroid-mass based approach optimizes the treatment avoiding an un-justified excess or a not-effective too low activity without time and resources consuming.

Registration of on-board X-ray images with 4DCT: A proposed method of phase and setup verification for gated radiotherapy - Corrected Proof

2009-10-05

Abstract: Current gated radiation therapy starts with simulation 4DCT images of a patient with lung cancer. We propose a method to confirm the phase of 4DCT for planning and setup position at the time of treatment. An intensity-based rigid algorithm was developed in this work to register an orthogonal set of on-board projection X-ray images with each phase of the 4DCT. Multiple DRRs for one of ten 4DCT phases are first generated and the correlation coefficient (CC) between the projection X-ray image and each DRR is computed. The maximum value of CC for the phase is found via a simulated annealing optimization process. The whole process repeats for all ten phases. The 4DCT phase that has the highest CC is identified as the breathing phase of the X-ray. The phase verification process is validated by a moving phantom study. Thus, the method may be used to independently confirm the correspondence between the gating phase at the times of 4DCT simulation and radiotherapy delivery. When the intended X-ray phase and actual gating phase are consistent, the registration of the DRRs and the projection images may also yield the values of patient shifts for treatment setup. This method could serve as the 4D analog of the conventional setup film as it provides both verification of the specific phase at the time of treatment and isocenter positioning shifts for treatment delivery.

Noninvasive prediction of vertebral body compressive strength using nonlinear finite element method and an image based technique - Corrected Proof

Ahad Zeinali, Bijan Hashemi, Shahram Akhlaghpoor — 2009-09-25

Abstract: Noninvasive prediction of vertebral body strength under compressive loading condition is a valuable tool for the assessment of clinical fractures. This paper presents an effective specimen-specific approach for noninvasive prediction of human vertebral strength using a nonlinear finite element (FE) model and an image based parameter based on the quantitative computed tomography (QCT). Nine thoracolumbar vertebrae excised from three cadavers with an average age of 42 years old were used as the samples. The samples were scanned using the QCT. Then, a segmentation technique was performed on each QCT sectional image. The segmented images were then converted into three-dimensional FE models for linear and nonlinear analyses. A new material model was implemented in our nonlinear model being more compatible with real mechanical behavior of trabecular bone. A new image based MOS (Mechanic of Solids) parameter named minimum sectional strength ((σuA)min) was used for the ultimate compressive strength prediction. Subsequently, the samples were destructively tested under uniaxial compression and their experimental ultimate compressive strengths were obtained. Results indicated that our new implemented FE model can predict ultimate compressive strength of human vertebra with a correlation coefficient (R2=0.94) better than usual linear and nonlinear FE models (R2=0.83 and 0.85 respectively). The image based parameter introduced in this study ((σuA)min) was also correlated well with the experimental results (R2=0.86). Although nonlinear FE method with new implemented material model predicts compressive strength better than the (σuA)min, this parameter is clinically more feasible due to its simplicity and lower computational costs. This can make future applications of the (σuA)min more justified for human vertebral body compressive strength prediction.

Proper orthogonal decomposition analysis of spatio-temporal behavior of renal scintigraphies - Corrected Proof

P. Veltri, A. Vecchio, V. Carbone — 2009-08-20

Abstract: We present a preliminary application of proper orthogonal decomposition (POD) to data sets coming from spatial and temporal evolution of renal scintigraphy. Renal functionalities or pathologies are hardly recognized from the raw scintigraphic images and their identifications could depend on the subjective point of view of the operator. The proposed technique is able to distinguish independent events starting from a more complex phenomenon. The spatio-temporal fields, representing the radiation emitted by the radiopharmaceutical technetium-99m with mercaptoacetiltriglicin (MAG3) within the kidney, have been analyzed for six randomly selected patients. In particular our study was performed on four patients affected by renal pathologies while two scintigraphies refer to healthy patients. First of all POD represents an efficient filtering procedure to cut off noise from the raw images by only selecting the few most energetic modes. When healthy kidneys are analyzed, POD is able to separate the main processes taking place in the organ. When applied to pathological samples, POD underlines the regions of the organ interested by the troubles allowing to analyze them independently. This analysis can be complementary to the identification made by hand by the operator.

Can DCEMRI assess the effect of green tea on the angiogenic properties of rodent prostate tumors? - Corrected Proof

2009-08-03

Abstract: The purpose of this research was to test whether dynamic contrast enhanced MRI could assess the effect of green tea on the angiogenic properties of transplanted rodent tumors. Copenhagen rats bearing AT6.1 prostate tumors inoculated in the hind limbs were randomly assigned to cages in which they were allowed to only drink either plain water (control group) or water containing green tea extract (treated group). Assignments were made after a baseline MRI experiment (week 0) was performed on each rat at 4.7T. All the rats were subsequently imaged at day 7 (week 1) and day 14 (week 2) to follow tumor growth and vascular development. The two-compartment pharmacokinetic model was used to analyze the dynamic contrast Gd-DTPA enhanced MRI data on a pixel-by-pixel basis over the tumor area to obtain the volume transfer constant (Ktrans) and extravascular extracellular space (ve). An identity Chi-squared test showed that the distributions of averaged histograms (n=6) of Ktrans and ve were significantly different from week 0 to both weeks 1 and 2 (p<0.001) in both the control and the treated rats due to increasing areas of tumor necrosis. However, the tumor growth rate was statistically indistinguishable between control and treated rats. There was no significant difference in the distributions of Ktrans and ve between control and treated rats. The results showed that no effects of green tea on tumor micro-vasculature were measurable by dynamic Gd-DTPA enhanced MRI.

Hot and cold contrasts in high-resolution Tc-99m planar scintigraphy: A survey of fifty-two camera heads using the PICKER thyroid phantom - Corrected Proof

Alain Seret — 2009-07-16

Abstract: This study was aimed at comparing the sensitivity and hot and cold contrasts obtained when imaging the PICKER thyroid phantom using gamma cameras fitted with either their ultra-high or high-resolution low-energy parallel hole collimator.Seventeen camera models from Elscint, General Electric, Siemens and Sopha Medical Vision were involved in the study for a total of 30 cameras and 52 camera heads. A single operator conducted the study in order to minimize the impact of human factors. The phantom contained about 74MBq 99mTc and was imaged at 10cm from the collimator face with the energy window that are recommended by the camera manufacturer. A total of 1 million counts were accumulated.Hot and cold contrasts were in mean of about 0.05 higher when using an ultra-high-resolution than when using a high-resolution low-energy collimator. This higher contrast was obtained at the expense of a mean reduction in sensitivity of 30%. In particular, Elscint cameras demonstrated a 30% lower sensitivity whatever the collimator type. The Sopha Medical Vision DST and DSX cameras and the General Electric Magicam camera offered the lowest contrasts among the cameras with a high-resolution collimator. Although this was accompanied by a higher than the mean sensitivity for the DST and DSX, the Magicam demonstrated sensitivity roughly identical to the mean of all the cameras with a high-resolution collimator.