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Physica Medica: PM

Eva Bezak, Rundgham Takam, Eric Yeoh, Loredana G Marcu
BACKGROUND: Out-of-field organs can be affected by secondary radiations originating from high energy linear accelerators, leading to an increased risk of carcinogenesis. The aim of this work was to determine the risk of second primary cancers (SPC) in the organs distal to the prostate during 3D conformal radiotherapy. MATERIALS AND METHODS: Based on previously measured peripheral photon and neutron doses in a Rando phantom using an 18MV photon beam, SPC risks in the out-of-field organs were estimated using the linear-no-threshold and the competitive risk models...
March 13, 2017: Physica Medica: PM
Somayeh Sadat Mehrnia, Bijan Hashemi, Seyed Javad Mowla, Azim Arbabi
Gold nanoparticles (GNPs) have been applied as radiosensitizer in radiotherapy. Limited reports have shown that GNPs may be effective as a dose enhancer agent for electron radiation therapy. Some Monte Carlo Simulation studies have shown that selecting suitable size of GNPs and electron energies are critical for effective dose enhancement. The aim of this study was to assess possible radiosensitization effect of GNPs on cancer cell treated with 4MeV electron beams. Approximately 10nm GNPs were synthesized and characterized by electron microscope and dynamic light scattering...
March 9, 2017: Physica Medica: PM
Josef A Lundman, Adam Johansson, Jörgen Olofsson, Jan Axelsson, Anne Larsson, Tufve Nyholm
PURPOSE: Attenuation correction is a requirement for quantification of the activity distribution in PET. The need to base attenuation correction on MRI instead of CT has arisen with the introduction of integrated PET/MRI systems. The aim was to describe the effect of residual gradient field nonlinearity distortions on PET attenuation correction. METHODS: MRI distortions caused by gradient field nonlinearity were simulated in CT images used for attenuation correction in PET reconstructions...
March 7, 2017: Physica Medica: PM
Juan-Francisco Calvo-Ortega, Marcelino Hermida-López, Sandra Moragues-Femenía, Miquel Pozo-Massó, Joan Casals-Farran
PURPOSE: To evaluate the spatial accuracy of a frameless cone-beam computed tomography (CBCT)-guided cranial radiosurgery (SRS) using an end-to-end (E2E) phantom test methodology. METHODS AND MATERIALS: Five clinical SRS plans were mapped to an acrylic phantom containing a radiochromic film. The resulting phantom-based plans (E2E plans) were delivered four times. The phantom was setup on the treatment table with intentional misalignments, and CBCT-imaging was used to align it prior to E2E plan delivery...
March 3, 2017: Physica Medica: PM
Mohammad Javad Safari, Jeannie Hsiu Ding Wong, Wei Loong Jong, Nathan Thorpe, Dean Cutajar, Anatoly Rosenfeld, Kwan Hoong Ng
PURPOSE: The purpose of this study was to investigate the effects of routine exposure parameters on patient's dose during neuro-interventional radiology procedures. METHODS: We scrutinized the routine radiological exposure parameters during 58 clinical neuro-interventional procedures such as, exposure direction, magnification, frame rate, and distance between image receptor to patient's body and evaluate their effects on patient's dose using an anthropomorphic phantom...
February 27, 2017: Physica Medica: PM
Martin J Menten, Andreas Wetscherek, Martin F Fast
Stereotactic body radiotherapy (SBRT) is rapidly becoming an alternative to surgery for the treatment of early-stage non-small cell lung cancer patients. Lung SBRT is administered in a hypo-fractionated, conformal manner, delivering high doses to the target. To avoid normal-tissue toxicity, it is crucial to limit the exposure of nearby healthy organs-at-risk (OAR). Current image-guided radiotherapy strategies for lung SBRT are mostly based on X-ray imaging modalities. Although still in its infancy, magnetic resonance imaging (MRI) guidance for lung SBRT is not exposure-limited and MRI promises to improve crucial soft-tissue contrast...
February 24, 2017: Physica Medica: PM
Alexandru Dasu, Iuliana Toma-Dasu
The interest in the induction of secondary tumours following radiotherapy has greatly increased as developments in detecting and treating the primary tumours have improved the life expectancy of cancer patients. However, most of the knowledge on the current levels of risk comes from patients treated many decades ago. As developments of irradiation techniques take place at a much faster pace than the progression of the carcinogenesis process, the earlier results could not be easily extrapolated to modern treatments...
February 24, 2017: Physica Medica: PM
Konstantinos Psichis, Nektarios Kalyvas, Ioannis Kandarakis, George Panayiotakis
PURPOSE: An analytical model has been developed for the light propagation in columnar phosphors, based on the optical photon propagation physical and geometrical principles. METHODS: This model accounts for the multiple reflections on the sides of the crystal column, as well as for the infinite forward and backward reflections of the propagated optical photon beams created in the crystal bulk. Additionally it considers the lateral propagated optical photon beams after multiple refractions from the neighbor columns and the optical photon attenuation inside the scintillator...
February 24, 2017: Physica Medica: PM
F Guerreiro, N Burgos, A Dunlop, K Wong, I Petkar, C Nutting, K Harrington, S Bhide, K Newbold, D Dearnaley, N M deSouza, V A Morgan, J McClelland, S Nill, M J Cardoso, S Ourselin, U Oelfke, A C Knopf
BACKGROUND AND PURPOSE: Computed tomography (CT) imaging is the current gold standard for radiotherapy treatment planning (RTP). The establishment of a magnetic resonance imaging (MRI) only RTP workflow requires the generation of a synthetic CT (sCT) for dose calculation. This study evaluates the feasibility of using a multi-atlas sCT synthesis approach (sCTa) for head and neck and prostate patients. MATERIAL AND METHODS: The multi-atlas method was based on pairs of non-rigidly aligned MR and CT images...
February 24, 2017: Physica Medica: PM
Joël Greffier, Fabricio R Pereira, Pierre Viala, Francesco Macri, Jean-Paul Beregi, Ahmed Larbi
This technical note proposes a method to reduce radiation dose for spine interventions under CT guidance without compromising the successful outcome of the procedure. Two consecutive periods of 14months before and after optimization were investigated with 162 and 440 patients, respectively. By optimizing the acquisition parameters (decreased kV and mAs) and appropriately adjusting the reconstruction (kernels, slice thickness, etc) and visualization parameters, image quality was maintained suitable to perform the procedure...
February 23, 2017: Physica Medica: PM
Marco Schwarz, Giovanni Mauro Cattaneo, Livia Marrazzo
The application of high precision hypofractionated regimes (a.k.a. stereotactic body radiotherapy (SBRT)) to the treatment of lung cancer is a 'success story' of radiotherapy. From the technical perspective, lung SBRT is a challenging technique as all aspects of the treatment workflow, from imaging to dose calculation to treatment delivery, should be carefully handled in order to ensure consistency between planned and delivered dose. In this review such technical aspects are presented and discussed, looking at what has been developed over the years...
February 23, 2017: Physica Medica: PM
Francesco Fellin, Roberto Righetto, Giovanni Fava, Diego Trevisan, Dante Amelio, Paolo Farace
PURPOSE: To investigate the range errors made in treatment planning due to the presence of the immobilization devices along the proton beam path. METHODS: The measured water equivalent thickness (WET) of selected devices was measured by a high-energy spot and a multi-layer ionization chamber and compared with that predicted by treatment planning system (TPS). Two treatment couches, two thermoplastic masks (both un-stretched and stretched) and one headrest were selected...
February 22, 2017: Physica Medica: PM
David J Eaton, Justine Tyler, Alex Backshall, David Bernstein, Antony Carver, Anne Gasnier, Julia Henderson, Jonathan Lee, Rushil Patel, Yatman Tsang, Huiqi Yang, Rada Zotova, Emma Wells
PURPOSE: External dosimetry audits give confidence in the safe and accurate delivery of radiotherapy. The RTTQA group have performed an on-site audit programme for trial recruiting centres, who have recently implemented static or rotational IMRT, and those with major changes to planning or delivery systems. METHODS: Measurements of reference beam output were performed by the host centre, and by the auditor using independent equipment. Verification of clinical plans was performed using the ArcCheck helical diode array...
February 21, 2017: Physica Medica: PM
Panagiotis Papadimitroulas
PURPOSE: Monte Carlo (MC) simulations are a well-established method for studying physical processes in medical physics. The purpose of this review is to present GATE dosimetry applications on diagnostic and therapeutic simulated protocols. There is a significant need for accurate quantification of the absorbed dose in several specific applications such as preclinical and pediatric studies. METHODS: GATE is an open-source MC toolkit for simulating imaging, radiotherapy (RT) and dosimetry applications in a user-friendly environment, which is well validated and widely accepted by the scientific community...
February 21, 2017: Physica Medica: PM
Loredana G Marcu
Photons are widely used in radiotherapy and while they are low LET radiation, can still pose a risk in developing second malignant neoplasms (SMN). Due to the physics of photons that allow distribution of energy outside the target volume, out-of-field irradiation is an important component of SMN risk assessment. The epidemiological evidence supporting this risk should be augmented with radiobiological justifications for a better understanding of the underlying processes. There are several factors that impact second cancer risk which can be analysed from a radiobiological perspective: age at irradiation, type of irradiated tissue, irradiated volume, treatment technique, previous irradiation/radiological investigations...
February 21, 2017: Physica Medica: PM
Shabbir Ahamed, Navin Singh, Deleep Gudipudi, Suneetha Mulinti, Anil Talluri, Bhudevi Soubhagya, Madhusudhana Sresty
PURPOSE: To quantify relative merit of MU deprived plans against freely optimized plans in terms of plan quality and report changes induced by progressive resolution optimizer algorithm (PRO3) to the dynamic parameters of RapidArc. MATERIALS AND METHODS: Ten cases of carcinoma hypopharynx were retrospectively planned in three phases without using MU tool. Replicas of these baseline plans were reoptimized using "Intermediate dose" feature and "MU tool" to reduce MUs by 20%, 35%, and 50%...
February 19, 2017: Physica Medica: PM
Takeshi Ohno, Fujio Araki, Ryota Onizuka, Masahiro Hatemura, Toshiaki Shimonobou, Takashi Sakamoto, Shuichiro Okumura, Daichi Ideguchi, Keiichi Honda, Kenji Kawata
This study compared dosimetric properties among four commercial multi-detector CT (MDCT) scanners. The X-ray beam characteristics were obtained from photon intensity attenuation curves of aluminum and off-center ratio (OCR) profiles in air, which were measured with four commercial MDCT scanners. The absorbed dose for MDCT scanners was evaluated with Farmer ionization chamber measurements at the center and four peripheral points in the body- and head-type cylindrical water phantoms. Measured collected charge was converted to absorbed dose using a (60)Co absorbed dose-to-water calibration factor and Monte Carlo (MC)-calculated correction factors...
February 18, 2017: Physica Medica: PM
Yoshitomo Ishihara, Mitsuhiro Nakamura, Yuki Miyabe, Nobutaka Mukumoto, Yukinori Matsuo, Akira Sawada, Masaki Kokubo, Takashi Mizowaki, Masahiro Hiraoka
PURPOSE: To develop a four-dimensional (4D) dose calculation system for real-time tumor tracking (RTTT) irradiation by the Vero4DRT. METHODS: First, a 6-MV photon beam delivered by the Vero4DRT was simulated using EGSnrc. A moving phantom position was directly measured by a laser displacement gauge. The pan and tilt angles, monitor units, and the indexing time indicating the phantom position were also extracted from a log file. Next, phase space data at any angle were created from both the log file and particle data under the dynamic multileaf collimator...
February 16, 2017: Physica Medica: PM
J Sánchez-Jiménez, A López-Montes, L Núñez-Martínez, A Villa-Abaunza, L M Fraile, V Sánchez-Tembleque, J M Udías
(223)Ra-dichloride was approved with the commercial name of Xofigo in 2014 for treatment of metastatic castration-resistant prostate cancer. (223)Ra is obtained by neutron irradiation of (226)Ra yielding (227)Ac, which decays to (227)Th and (223)Fr, both decaying to (223)Ra. Since (223)Ra is predominantly (95.3%) an alpha emitter with a 11.42days long half-life, the radiopharmaceutical, its remnants, the patient, and waste material can be managed and disposed with low radiation protection requirements. (227)Ac is a long-lived (T1/2=21...
February 16, 2017: Physica Medica: PM
Ghada Aldosary, Habib Safigholi, William Song, Jan Seuntjens, Arman Sarfehnia
In this work, the response of Farmer-type ionization chambers fitted with high atomic number (Z) walls is studied, and results of the effects of such walls on polarity and ion recombination correction factors in both continuous and pulsed beams are presented. Measurements were made in a continuous Co-60 beam and a pulsed 6MV linac beam using an Exradin-A12 ionization chamber fitted with the manufacturer's C-552 plastic wall, as well as geometrically identical walls made from aluminum, copper and molybdenum...
February 12, 2017: Physica Medica: PM
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