Journal of Medical Physics
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   2013| October-December  | Volume 38 | Issue 4  
    Online since November 11, 2013

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Dosimetric comparison between IMRT delivery modes: Step-and-shoot, sliding window, and volumetric modulated arc therapy - for whole pelvis radiation therapy of intermediate-to-high risk prostate adenocarcinoma
Tania De La Fuente Herman, Erich Schnell, Julie Young, Kim Hildebrand, Özer Algan, Elizabeth Syzek, Terence Herman, Salahuddin Ahmad
October-December 2013, 38(4):165-172
DOI:10.4103/0971-6203.121193  PMID:24672150
This study was performed to evaluate dosimetric differences between current intensity modulated radiation therapy (IMRT) delivery modes: Step-and-shoot (SS), sliding window (SW), and volumetric modulated arc therapy (VMAT). Plans for 15 prostate cancer patients with 10 MV photon beams using each IMRT mode were generated. Patients had three planning target volumes (PTVs) including prostate, prostate plus seminal vesicles, and pelvic lymphatics. Dose volume histograms (DVHs) of PTVs and organs at risk (OARs), tumor control probability (TCP) and normal tissue complication probabilities (NTCPs), conformation number, and monitor units (MUs) used were compared. Statistical analysis was performed using the analysis of variance (ANOVA) technique. The TCPs were > 99% with insignificant differences among modalities (P > 0.99). Doses to all critical structures were higher on average with SW method compared to SS, but insignificant. NTCP values were lowest for VMAT in all structures excepting bladder. Normal tissue volumes receiving doses in the 20-30 Gy range were reduced for VMAT compared to SS. Percentage of MUs required for VMAT to deliver a comparable plan to SS and SW was at least 40% less. In conclusion, similar target coverage and normal tissue doses were found by the three compared modes and the dosimetric differences were small.
  4,343 295 -
Impact factor of a scientific journal: Is it a measure of quality of research?
A Shanta, AS Pradhan, SD Sharma
October-December 2013, 38(4):155-157
DOI:10.4103/0971-6203.121191  PMID:24672148
  3,626 661 1
Study of positional dependence of dose to bladder, pelvic wall and rectal points in High-Dose-Rate Brachytherapy in cervical cancer patients
Anil Kumar Talluri, Krishnam Raju Alluri, Deleep Kumar Gudipudi, Shabbir Ahamed, Madhusudhana M Sresty, Aparna Yarrama Reddy
October-December 2013, 38(4):178-184
DOI:10.4103/0971-6203.121195  PMID:24672152
The objective of the study is to examine the variation in doses to, Bladder, pelvic wall and Rectal Points when a patient is simulated in Supine (S Position) and Lithotomy M shaped positions (LM Position), respectively as part of Intracavitary Brachytherapy in Cervical Cancer patients. Patients (n = 19) were simulated and orthogonal images were taken in S Position and LM Positions on a physical simulator. Digital orthogonal X-ray images were transferred to Brachyvision Treatment Planning System via Dicom to generate treatment plans. Radio opaque dye of 7 ml was injected into the Foley bulb for identification and digitization of International Commission on Radiological Units and Measurements (ICRU) Bladder point. Pelvic side wall points were marked in accordance with ICRU 38 recommendations. A Rectal tube containing dummy source marker wire was used to identify Rectal Point. Students't-test was used to analyze the results. Doses in LM Position were lower and statistically significant when compared to S Position for ICRU Bladder Point, pelvic walls and Rectal Point. It was observed that movement of applicator could be the reason for the variations in doses between the two positions. Bladder, pelvic wall and rectal points systematically registered lower doses in LM Position as compared to S Position.
  3,297 162 -
Monte Carlo-based investigation of water-equivalence of solid phantoms at 137 Cs energy
Ramkrushna S Vishwakarma, T Palani Selvam, Sridhar Sahoo, Subhalaxmi Mishra, Ghanshyam Chourasiya
October-December 2013, 38(4):158-164
DOI:10.4103/0971-6203.121192  PMID:24672149
Investigation of solid phantom materials such as solid water, virtual water, plastic water, RW1, polystyrene, and polymethylmethacrylate (PMMA) for their equivalence to liquid water at 137 Cs energy (photon energy of 662 keV) under full scatter conditions is carried out using the EGSnrc Monte Carlo code system. Monte Carlo-based EGSnrc code system was used in the work to calculate distance-dependent phantom scatter corrections. The study also includes separation of primary and scattered dose components. Monte Carlo simulations are carried out using primary particle histories up to 5 Χ 10 9 to attain less than 0.3% statistical uncertainties in the estimation of dose. Water equivalence of various solid phantoms such as solid water, virtual water, RW1, PMMA, polystyrene, and plastic water materials are investigated at 137 Cs energy under full scatter conditions. The investigation reveals that solid water, virtual water, and RW1 phantoms are water equivalent up to 15 cm from the source. Phantom materials such as plastic water, PMMA, and polystyrene phantom materials are water equivalent up to 10 cm. At 15 cm from the source, the phantom scatter corrections are 1.035, 1.050, and 0.949 for the phantoms PMMA, plastic water, and polystyrene, respectively.
  2,597 490 1
Superparamagnetic iron oxide-C595: Potential MR imaging contrast agents for ovarian cancer detection
Daryoush Shahbazi-Gahrouei, Mohammad Abdolahi
October-December 2013, 38(4):198-204
DOI:10.4103/0971-6203.121198  PMID:24672155
Superparamagnetic iron oxide nanoparticles (SPIONs), have played an important role in the promotion of image contrast in magnetic resonance imaging modality. The objective of present study is describing SPIONs conjugated with C595 monoclonal antibody (mAb) against MUC1-expressing ovarian cancer (OVCAR3) cell. Magnetic resonance imaging parameters of the prepared nanoconjugate was investigated in vitro: characterization, cell toxicity, flow cytometry, Prussian blue staining, and cellular uptake as well as biodistribution and magnetic resonance signal intensities under in vivo conditions were also investigated. Magnetic resonance imaging and biodistribution results showed good tumor accumulation and detection, no cytotoxicity, and potential selective as anti-ovarian cancer. In conclusion, based on the findings SPIONs-C595 nanosized-probe is potentially, a selective ovarian molecular imaging tool. Further subsequent in vivo studies and clinical trials are warranted.
  2,691 100 -
Radiation dose estimation of patients undergoing lumbar spine radiography
Prince Kwabena Gyekye, Adu Simon, Emi-Reynolds Geoffrey, Yeboah Johnson, Inkoom Stephen, Cynthia Kaikor Engmann, Wotorchi-Gordon Samuel
October-December 2013, 38(4):185-188
DOI:10.4103/0971-6203.121196  PMID:24672153
Radiation dose to organs of 100 adult patients undergoing lumbar spine (LS) radiography at a University Hospital have been assessed. Free in air kerma measurement using an ionization chamber was used for the patient dosimetry. Organ and effective dose to the patients were estimated using PCXMC (version 1.5) software. The organs that recorded significant dose due to LS radiography were lungs, stomach, liver, adrenals, kidney, pancreas, spleen, galbladder, and the heart. It was observed that the stomach recorded the highest dose (48.2 ± 1.2 μGy) for LS anteroposterior (AP). The spleen also recorded the highest dose (41.2 ± 0.5 μGy) for LS lateral (LAT). The mean entrance surface air kerma (ESAK) of LS LAT (122.2 μGy) was approximately twice that of LS AP (76.3 μGy), but the effective dose for both examinations were approximately the same (LS LAT = 8.6 μSv and LS AP = 10.4 μSv). The overall stochastic health effect of radiation to patients due to LS radiography in the University Hospital is independent of the projection of the examination (AP or LAT).
  2,585 127 -
Evaluation of six scatter correction methods based on spectral analysis in 99m Tc SPECT imaging using SIMIND Monte Carlo simulation
Mahsa Noori Asl, Alireza Sadremomtaz, Ahmad Bitarafan-Rajabi
October-December 2013, 38(4):189-197
DOI:10.4103/0971-6203.121197  PMID:24672154
Compton-scattered photons included within the photopeak pulse-height window result in the degradation of SPECT images both qualitatively and quantitatively. The purpose of this study is to evaluate and compare six scatter correction methods based on setting the energy windows in 99m Tc spectrum. SIMIND Monte Carlo simulation is used to generate the projection images from a cold-sphere hot-background phantom. For evaluation of different scatter correction methods, three assessment criteria including image contrast, signal-to-noise ratio (SNR) and relative noise of the background (RNB) are considered. Except for the dual-photopeak window (DPW) method, the image contrast of the five cold spheres is improved in the range of 2.7-26%. Among methods considered, two methods show a nonuniform correction performance. The RNB for all of the scatter correction methods is ranged from minimum 0.03 for DPW method to maximum 0.0727 for the three energy window (TEW) method using trapezoidal approximation. The TEW method using triangular approximation because of ease of implementation, good improvement of the image contrast and the SNR for the five cold spheres, and the low noise level is proposed as most appropriate correction method.
  2,418 129 -
Estimation of absorbed dose in clinical radiotherapy linear accelerator beams: Effect of ion chamber calibration and long-term stability
Ramamoorthy Ravichandran, Johnson Pichy Binukumar, Cheriyathmanjiyil Antony Davis
October-December 2013, 38(4):205-209
DOI:10.4103/0971-6203.121199  PMID:24672156
The measured dose in water at reference point in phantom is a primary parameter for planning the treatment monitor units (MU); both in conventional and intensity modulated/image guided treatments. Traceability of dose accuracy therefore still depends mainly on the calibration factor of the ion chamber/dosimeter provided by the accredited Secondary Standard Dosimetry Laboratories (SSDLs), under International Atomic Energy Agency (IAEA) network of laboratories. The data related to N d,water calibrations, thermoluminescent dosimetry (TLD) postal dose validation, inter-comparison of different dosimeter/electrometers, and validity of N d,water calibrations obtained from different calibration laboratories were analyzed to find out the extent of accuracy achievable. N d,w factors in Gray/Coulomb calibrated at IBA, GmBH, Germany showed a mean variation of about 0.2% increase per year in three Farmer chambers, in three subsequent calibrations. Another ion chamber calibrated in different accredited laboratory (PTW, Germany) showed consistent N d,w for 9 years period. The Strontium-90 beta check source response indicated long-term stability of the ion chambers within 1% for three chambers. Results of IAEA postal TL "dose intercomparison" for three photon beams, 6 MV (two) and 15 MV (one), agreed well within our reported doses, with mean deviation of 0.03% (SD 0.87%) (n = 9). All the chamber/electrometer calibrated by a single SSDL realized absorbed doses in water within 0.13% standard deviations. However, about 1-2% differences in absorbed dose estimates observed when dosimeters calibrated from different calibration laboratories are compared in solid phantoms. Our data therefore imply that the dosimetry level maintained for clinical use of linear accelerator photon beams are within recommended levels of accuracy, and uncertainties are within reported values.
  1,822 118 -
A study on comparison of Gafchromic EBT2 film response under single and cumulative exposure conditions
K Ganapathy, P.G.G. Kurup, V Murali, M Muthukumaran, J Velmurugan
October-December 2013, 38(4):173-177
DOI:10.4103/0971-6203.121194  PMID:24672151
Gafchromic films are used as dosimeter for in vivo and in phantom dose measurements. The dose response of Gafchromic EBT2 film under single and repeated exposure conditions is compared in this study to analyze the usability of Gafchromic EBT2 films in cumulative dose measurements. The post-irradiation change in response of the film is studied for up to 4 days after irradiation. The effect of repeated exposure to scanner light on the response of the film is also studied. To check usability of Gafchromic EBT2 films in cumulative dose measurements, three EBT2 films were exposed to a daily fraction dose of 100 cGy, 150 cGy and 200 cGy, respectively, for 4 days. The dose response of the films exposed to cumulative irradiation was compared with the dose measured from films exposed to the same dose but in a single exposure. It is observed that the post-irradiation darkening of the film does not saturate and continue to take place even 4 days after irradiation. The dose measured from the EBT2 films after 4 days from irradiation was around 2% higher than the dose measured from the same films at 24 hours post-irradiation. It was also observed that the repeated exposure to scanner light does not produce any significant change in the film response. The dose response of films exposed to cumulative irradiation agrees with the dose response of films exposed to the same dose in a single irradiation with less than 3% difference. Gafchromic EBT2 films can be used to measure the cumulative dose delivered over multiple fractions, when the delivered dose is uniform across the film.
  1,792 146 -
Total body irradiation (TBI): Preliminary experience on clinical implementation
Ramamoorthy Ravichandran, Johnson Pichy Binukumar, Cheriyathmanjiyial Antony Davis, Zakia Al Rahbi, Rajan Balakrishnan, Zahid Al Mandhari
October-December 2013, 38(4):210-211
DOI:10.4103/0971-6203.121200  PMID:24672157
  1,500 117 -
News and Events
Tharmarnadar Ganesh
October-December 2013, 38(4):212-215
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