Medical Physics Unit

Firenze, Italy

Medical Physics Unit

Firenze, Italy
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Fiandra C.,University of Turin | Fusella M.,University of Turin | Giglioli F.R.,Medical Physics Unit | Filippi A.R.,University of Turin | And 2 more authors.
Medical Physics | Year: 2013

Purpose: Patient-specific quality assurance in volumetric modulated arc therapy (VMAT) brain stereotactic radiosurgery raises specific issues on dosimetric procedures, mainly represented by the small radiation fields associated with the lack of lateral electronic equilibrium, the need of small detectors and the high dose delivered (up to 30 Gy). Gafchromic™ EBT2 and EBT3 films may be considered the dosimeter of choice, and the authors here provide some additional data about uniformity correction for this new generation of radiochromic films. Methods: A new analysis method using blue channel for marker dye correction was proposed for uniformity correction both for EBT2 and EBT3 films. Symmetry, flatness, and field-width of a reference field were analyzed to provide an evaluation in a high-spatial resolution of the film uniformity for EBT3. Absolute doses were compared with thermoluminescent dosimeters (TLD) as baseline. VMAT plans with multiple noncoplanar arcs were generated with a treatment planning system on a selected pool of eleven patients with cranial lesions and then recalculated on a water-equivalent plastic phantom by Monte Carlo algorithm for patient-specific QA. 2D quantitative dose comparison parameters were calculated, for the computed and measured dose distributions, and tested for statistically significant differences. Results: Sensitometric curves showed a different behavior above dose of 5 Gy for EBT2 and EBT3 films; with the use of inhouse marker-dye correction method, the authors obtained values of 2.5% for flatness, 1.5% of symmetry, and a field width of 4.8 cm for a 5 × 5 cm2 reference field. Compared with TLD and selecting a 5% dose tolerance, the percentage of points with ICRU index below 1 was 100% for EBT2 and 83% for EBT3. Patients analysis revealed statistically significant differences (p < 0.05) between EBT2 and EBT3 in the percentage of points with gamma values <1 (p = 0.009 and p = 0.016); the percent difference as well as the mean difference between calculated and measured isodoses (20% and 80%) were found not to be significant (p = 0.074, p = 0.185, and p = 0.57). Conclusions: Excellent performances in terms of dose homogeneity were obtained using a new blue channel method for marker-dye correction on both EBT2 and EBT3 Gafchromic™ films. In comparison with TLD, the passing rates for the EBT2 film were higher than for EBT3; a good agreement with estimated data by Monte Carlo algorithm was found for both films, with some statistically significant differences again in favor of EBT2. These results suggest that the use of Gafchromic™ EBT2 and EBT3 films is appropriate for dose verification measurements in VMAT stereotactic radiosurgery; taking into account the uncertainty associated with Gafchromic film dosimetry, the use of adequate action levels is strongly advised, in particular, for EBT3. © 2013 American Association of Physicists in Medicine.

News Article | November 22, 2016

University of Adelaide medical physics honours student Mark Brooke has become the University’s 15th John Monash Scholar. Announced at the Sydney Opera House last night by NSW Premier Mike Baird, Mark is the only South Australian to receive one of the prestigious scholarships. He will use his scholarship to pursue his research interest in proton therapy – a more targeted radiation therapy suitable for treating cancer in children. “I'm very proud to be named a John Monash Scholar,” says Mark. “The foundation provides outstanding support, not only during the course of study but throughout one's entire career. I look forward to making a real difference in Australia's future through improving the quality of radiation therapy. “Proton therapy is much more targeted than conventional X-ray therapy, making it vital for tackling paediatric cancers and tumours located near critical structures such as the brain stem or spinal cord. Australia really must implement proton therapy treatment if we wish to provide top quality care for cancer sufferers. Switzerland has become a world leader in both research and implementation of proton therapy, and I am committed to seeing Australia follow this same path.” During a summer research project and in his honours year, Mark developed two new algorithms for proton therapy. Next September, with the help of the John Monash Scholarship sponsored by the Ian Potter Foundation, Mark plans to start a Master of Science in Biomedical Engineering at ETH Zurich, Switzerland. The John Monash Scholarships are awarded to outstanding Australians with leadership potential and support up to three years of postgraduate study at prestigious universities around the world. “Mark is an outstanding young academic, and our national panel were enormously impressed with him,” says Dr Peter Binks, Interim CEO with the General Sir John Monash Foundation. “His field of proton therapy for cancer is a very important one, with great implications for both Adelaide and Australia.” As a child, Mark had an aversion to hospitals. As a haemophiliac, he regularly visited hospitals three-four times a week. While he’s been able to live a largely unrestricted lifestyle, he was hospitalised for several days with serious bleeding in his lungs while studying for his final high school exams. Mark overcame this set back to still achieve a perfect score ATAR (99.95) and become Dux of his school, Immanuel College. “It took all my mental strength to complete my studies, but I found solace in the science, realising that illness is something that can be understood and treated,” he says. “I no longer fear hospitals; instead I want to help others similarly overcome their illnesses.” At the University of Adelaide, Mark has won a variety of awards including a 2014 Prime Minister’s Australia Asia Outgoing Undergraduate Award – enabling him to undertake an internship in the Medical Physics Unit of the Queen Mary Hospital in Hong Kong – and achieved a Grade Point Average of 6.818/7 in his Honours Degree of Bachelor of Science in High Performance Computational Physics. He has been an active volunteer, including as a mentor in the University’s Peer Mentoring Program and in the Peer Assisted Study Sessions. He also volunteers as a children’s tennis coach. Having to avoid contact sports, Mark embraced tennis and has competed at a high level.

Schwarz M.,Trento Hospital | Schwarz M.,National Institute of Nuclear Physics, Italy | Molinelli S.,Medical Physics Unit
Physica Medica | Year: 2016

The treatment of prostate cancer with either protons or carbon ions is not a novelty, and several thousands of patients were treated with hadrontherapy in the past decades. The standard treatment approach consisted in two lateral opposed fields for both protons and carbon ions, mostly delivered with scattered beams and using conventional fractionation and hypofractionation for protons and carbon ions, respectively. Similar (RBE-weighted and BED) doses to photon therapy (XRT) have been delivered, with comparable results in terms of both local control and toxicity. The advancements in dose deposition and image guidance of the early '00s that improved the quality of XRT treatments and then allowed for hypofractionation, are being matched with some delay by hadrontherapy in these very years. Pencil beam scanning is now the norm in proton therapy, and volumetric image guidance is being developed in all new hadrontherapy facilities. There is therefore the possibility of truly taking advantage of superior dose distributions of hadrons and safely apply it to innovative treatment protocols, such as an intraprostatic boost and the treatment of larger volume for advanced stage disease. This full integration between the best of technology and new clinical approaches is probably necessary in order to obtain clinical results that are truly superior to the current state of the art of XRT. © 2016 Associazione Italiana di Fisica Medica.

Mattioli F.,Neuropsychology Unit | Ambrosi C.,University of Brescia | Mascaro L.,Medical Physics Unit | Scarpazza C.,Neuropsychology Unit | And 5 more authors.
Stroke | Year: 2014

Background and Purpose - Early poststroke aphasia rehabilitation effects and their functional MRI (fMRI) correlates were investigated in a pilot, controlled longitudinal study. Methods - Twelve patients with mild/moderate aphasia (8 Broca, 3 anomic, and 1 Wernicke) were randomly assigned to daily language rehabilitation for 2 weeks (starting 2.2 [mean] days poststroke) or no rehabilitation. The Aachen Aphasia Test and fMRI recorded during an auditory comprehension task were performed at 3 time intervals: mean 2.2 (T1), 16.2 (T2), and 190 (T3) days poststroke. Results - Groups did not differ in terms of age, education, aphasia severity, lesions volume, baseline fMRI activations, and in task performance during fMRI across examinations. Rehabilitated patients significantly improved in naming and written language tasks (P<0.05) compared with no rehabilitation group both at T2 and T3. Functional activity at T1 was reduced in language-related cortical areas (right and left inferior frontal gyrus and middle temporal gyrus, right inferior parietal lobule and superior temporal gyrus) in patients compared with controls. T2 and T3 follow-ups revealed a cortical activation increase, with significantly greater activation in the left hemisphere areas in rehabilitated patients at T2 and T3, and a time×treatment effect at T2 in the left inferior Broca area after rehabilitation. Left inferior frontal gyrus activation at T2 significantly correlated with naming improvement. Conclusions - Early poststroke aphasia treatment is useful, has durable effects, and may lead to early enhanced recruitment of brain areas, particularly the left inferior frontal gyrus, which persists in the chronic phase. © 2013 American Heart Association, Inc.

Singh M.,University of Delhi | Sahare P.D.,University of Delhi | Kumar P.,Medical Physics Unit
Radiation Measurements | Year: 2013

A new highly sensitive, low-Z (Zeff ≈ 10.8) TLD phosphor, Eu3+ doped NaLi2PO4, was successfully synthesized via solid state diffusion method. The formation of the single phase compound was confirmed by Powder X-Ray diffraction (PXRD) analysis. Variation of the doping level has shown that the impurity (Eu3+) concentration for maximum TL sensitivity is 0.5 mol%. Heat treatments given to achieve the high TL sensitivity of this phosphor also showed that it needs to be annealed at 973 K for 1 h. Incorporation of the impurity in the Eu+3 states was confirmed by the PL emission peaks. The TL glow curve consists of a prominent dosimetry peak at around 458 K besides small shoulders on both sides at around 400 and 500 K. The dose response of the phosphor was found to be sub-linear up to 10 Gy of the dose and later it becomes linear till it start saturating beyond 1 kGy. The TL sensitivity of the newly developed NaLi2PO 4:Eu3+ phosphor to γ radiation from 137Cs (in the linear dose range) was compared to some standard commercially available phosphors, such as, TLD-100, TLD-400, TLD-700H and TLD-900. It was found to be much more sensitive than these phosphors except TLD-700H, which is ∼2 times more sensitive. Easy method of synthesis, simple glow curve structure, high sensitivity, low fading, wide range of doses and very good reusability make the phosphor a suitable candidate for the TL dosimetry. © 2013 Elsevier Ltd. All rights reserved.

Sahare P.D.,University of Delhi | Singh M.,University of Delhi | Kumar P.,Medical Physics Unit
Journal of Radioanalytical and Nuclear Chemistry | Year: 2014

Ce3+-doped NaLi2PO4 orthophosphate (with different impurity concentrations, i.e., 0.01–0.3 mol%) was prepared by a solid state reaction method. Formation of the material was confirmed using powder X-ray diffraction analysis. TL intensity was found to be the highest for the material having impurity concentration 0.2 mol% after annealing it at around 600 K for 1 h and subsequently quenching to room temperature. A typical glow curve consists of three peaks at around 454, 493 and 570 K (dosimetry peak). Good sensitivity (~8 times more than that of TLD-100), low fading (~15 % in 2 months), low-Z material (Zeff ≈ 10.8), very wide dose response (i.e., 0.1 Gy–1.0 kGy of γ rays) make the material a ‘good’ thermoluminescent dosimeter (TLD) phosphor suitable for personnel, medical and environmental dosimetry of high-energy radiation using TL. It could also be used during cancer therapy and sterilization of food where high doses are needed to be monitored. © 2014, Akadémiai Kiadó, Budapest, Hungary.

Sahare P.D.,University of Delhi | Singh M.,University of Delhi | Kumar P.,Medical Physics Unit
Radiation Measurements | Year: 2015

Nanocrystalline samples of Mn-doped CaF2 were synthesized by chemical coprecipitation method. The impurity concentration was varied in the range of 0.5-4.0 mol%. The structure of the synthesized material was confirmed using powder XRD analysis. TEM images of the nanoparticles show their size occurring mostly in the range of 35-40 nm, with clusters of some impurity phases formed on annealing of the material at higher temperatures. Detailed studies on TL showed that the structures of glow curves depend on Mn concentrations and annealing temperatures. Optimization of the concentration and annealing temperature showed that the sample (doped with 3.0 mol% and annealed at 673 K) has almost a single dosimetric glow peak appearing at around 492 K. EPR and PL spectra were further studied to understand the reasons for changes in the glow curve structures. All detailed studies on TL, PL and EPR showed that the changes in glow curve structures are caused not only by the stress connected with the difference in ionic radii of host Ca2+ and the guest impurity Mn3+/Mn2+, but are also governed by other reasons, like diffusion of atmospheric oxygen and formation of impurity aggregates, such as, MnO2, Mn3O4, etc. This is true not only for nanocrystalline CaF2:Mn but could also be so for the bulk CaF2:Mn (TLD-400) and would thus help in understanding complex glow curve structure, high fading and the loss of reusability on annealing beyond 673 K. © 2015 Published by Elsevier Ltd © 2015 Published by Elsevier Ltd.

Berta L.,Medical Physics Unit | Mascaro L.,Medical Physics Unit | Feroldi P.,Medical Physics Unit | Maroldi R.,University of Brescia
Physica Medica | Year: 2014

This work aims to construct a method to objectively evaluate CT image quality when new clinical protocol performances must be compared with a standard reference. We compare iterative reconstruction in the image space with filtered back projection reconstruction and accurately quantify the dose reduction.The comparison strategy accounts for both physical and clinical image qualities that are evaluated using a standard metric. The quasi-ideal observer metric is also explored to verify its reportedly high correlation with perceived image quality.Water or spatial resolution phantom images are used to characterise the physical image quality using the classic metrics in the Fourier domain by calculating the modulation transfer functions and noise power spectra (NPS).The clinical-image quality is evaluated with a 4-alternative forced-choice test. The human observers are asked to detect a positive image that contains a simulated lesion in a background image. Then, the same positive images are characterised with the quasi-ideal observer metric, which calculates the non-prewhitening matched filter signal-to-noise ratio (SNRNPWMF).Iterative reconstruction strongly reduces the image noise, but the NPS are slightly shifted to lower frequencies, which gives the images a coarse graininess. Compared with the reference FBP protocol for abdomen exams, the highest dose reduction is 40% if the standard metric is used and 30% if the SNRNPWMF metric is used. The detectability test results achieve a better correlation with SNRNPWMF than with the standard metric.The identified Fourier metric is a useful descriptor of human quality perception and can be used for future protocol optimisation. © 2013 Associazione Italiana di Fisica Medica.

Bahl S.,Medical Physics Unit | Lochab S.P.,Inter University Accelerator Center | Kumar P.,Medical Physics Unit
Radiation Physics and Chemistry | Year: 2016

With the advent of newer techniques for dose reduction coupled with the development of more sensitive detectors, the radiation doses in radiological medical investigation are decreasing. Nevertheless, keeping the tenet in mind that all radiation doses could entail risk, there is a need to develop more sensitive dosimeters capable of measuring low doses. This paper gives the account of the development of a new and sensitive phosphor CaSO4:Dy,Mn and its characterization. The standard production procedure based on the recrystallization method was used to prepare CaSO4:Dy,Mn. The Thermoluminescence (TL) studies were carried out by exposing it with gamma radiation (Cs-137) from 10μGy to 100Gy. The theoretical studies to determine the number of peaks and kinetic parameters related to the TL glow peaks in CaSO4:Dy,Mn was performed using the Computerized Glow Curve Deconvolution (CGCD) method. Experiments were performed to determine optimum concentration of the dopants Dysprosium (Dy) and Mangnese (Mn) in the host CaSO4 so that maximum sensitivity of the phosphor may be achieved. The optimum dopant concentration turned out to be 0.1mol%. As there were two dopants Dy and Mn their relative ratio were varied in steps of 0.025 keeping the concentration of total dopant (Dy and Mn) 0.1mol% always. The maximum TL intensity was seen in the CaSO4:Dy(0.025),Mn(0.075) combination. The TL sensitivity of this phosphor was found to be about 2 and 1.8 times higher than that of popular phosphor CaSO4:Dy and LiF:Mg,Cu,P (TLD-700H) respectively. This new phosphor CaSO4:Dy,Mn showed fading of 11% which is similar to that of the standard phosphor CaSO4:Dy. The paper concludes that the new, highly sensitive TL phosphor CaSO4:Dy,Mn has shown higher sensitivity and hence the potential to replace commonly used CaSO4:Dy. © 2015 Elsevier Ltd.

El Naqa I.,Medical Physics Unit | Pater P.,Medical Physics Unit | Seuntjens J.,Medical Physics Unit
Physics in Medicine and Biology | Year: 2012

Radiobiological models are essential components of modern radiotherapy. They are increasingly applied to optimize and evaluate the quality of different treatment planning modalities. They are frequently used in designing new radiotherapy clinical trials by estimating the expected therapeutic ratio of new protocols. In radiobiology, the therapeutic ratio is estimated from the expected gain in tumour control probability (TCP) to the risk of normal tissue complication probability (NTCP). However, estimates of TCP/NTCP are currently based on the deterministic and simplistic linear-quadratic formalism with limited prediction power when applied prospectively. Given the complex and stochastic nature of the physical, chemical and biological interactions associated with spatial and temporal radiation induced effects in living tissues, it is conjectured that methods based on Monte Carlo (MC) analysis may provide better estimates of TCP/NTCP for radiotherapy treatment planning and trial design. Indeed, over the past few decades, methods based on MC have demonstrated superior performance for accurate simulation of radiation transport, tumour growth and particle track structures; however, successful application of modelling radiobiological response and outcomes in radiotherapy is still hampered with several challenges. In this review, we provide an overview of some of the main techniques used in radiobiological modelling for radiotherapy, with focus on the MC role as a promising computational vehicle. We highlight the current challenges, issues and future potentials of the MC approach towards a comprehensive systems-based framework in radiobiological modelling for radiotherapy. © 2012 Institute of Physics and Engineering in Medicine.

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