Journal of Medical Physics
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   2012| July-September  | Volume 37 | Issue 3  
    Online since August 1, 2012

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An analytic approach to the dosimetry of a new BEBIG 60 Co high-dose-rate brachytherapy source
Subhalaxmi Bhola, T Palani Selvam, Sahoo Sridhar, Ramkrishna S Vishwakarma
July-September 2012, 37(3):129-137
We present a simple analytic tool for calculating the dose rate distribution in water for a new BEBIG high-dose-rate (HDR) 60 Co brachytherapy source. In the analytic tool, we consider the active source as a point located at the geometric center of the 60 Co material. The influence of the activity distribution in the active volume of the source is taken into account separately by use of the line source-based geometric function. The exponential attenuation of primary 60 Co photons by the source materials ( 60 Co and stainless-steel) is included in the model. The model utilizes the point-source-based function, f(r) that represents the combined effect of the exponential attenuation and scattered photons in water. We derived this function by using the published radial dose function for a point 60 Co source in an unbounded water medium of radius 50 cm. The attenuation coefficients for 60 Co and the stainless-steel encapsulation materials are deduced as best-fit parameters that minimize the differen
  4,934 251 -
The influence of the patient size and geometry on cone beam-computed tomography hounsfield unit
Heng Siew Ping, Sivamany Kandaiya
July-September 2012, 37(3):155-158
DOI:10.4103/0971-6203.99239  PMID:22973083
The objective of this work is to study the influence of the patient size and geometry on CBCT Hounsfield Unit and the accuracy of calibration Hounsfield Unit to electron density (HU-ED) using patient specific HU-ED mapping method for dose calculation. Two clinical cases, namely nasopharyngeal carcinoma (NPC) case and prostate case for 4 patients with different size and geometry were enrolled to assess the impact of size and geometry on CBCT Hounsfield Unit. The accuracy of the patient specific HU-ED mapping method was validated by comparing dose distributions based on planning CT and CBCT, dose-volume based indices and the digitally reconstructed radiograph (DRR) by analyzing their line profile plots. Significant differences in Hounsfield unit and line profile plots were found for NPC and prostate cases. The doses computed based on planning CT data sets and CBCT datasets for both clinical cases agree to within 1% for planning target volumes and 3% for organs at risk. The data shows that there are high dependence of HU on patient size and geometry; thus, the use of one CBCT HU-ED calibration curve made of one size and geometry will not be accurate for use with a patient of different size and geometry.
  4,431 183 2
Dosimetric analysis of trigeminal nerve, brain stem doses in CyberKnife radiosurgery of trigeminal neuralgia
H Sudahar, P. G. G. Kurup, V Murali, J Velmurugan
July-September 2012, 37(3):124-128
DOI:10.4103/0971-6203.99225  PMID:22973078
CyberKnife radiosurgery treatment of Trigeminal neuralgia (TN) is performed as a non-invasive image guided procedure. The prescription dose for TN is very high. The brainstem is the adjacent critical organ at risk (OAR) which is prone to receive the very high target dose of TN. The present study is to analyze the dose distribution inside the tiny trigeminal nerve target and also to analyze the dose fall off in the brain stem. Seven TN cases treated between November 2010 and January 2012 were taken for this study retrospectively. The treatment plans were analyzed for target dose conformity, homogeneity and dose coverage. In the brainstem the volume doses D 1% , D 2% were taken for analyzing the higher doses in the brain stem. The dose fall off was analyzed in terms of D 5% and D 10%. The mean value of maximum dose within the trigeminal nerve target was 73.5± 2.1Gy (P=0.0007) and the minimum dose was 50.0±4.1Gy (P=0.1315). The mean conformity index was 2.19 and the probable reason could be the smallest CyberKnife collimator of 5mm used in the treatment plan. The mean D 1% , of the brainstem was 10.5± 2.1Gy (P=0.5316) and the mean value of the maximum point dose within the brainstem was 35.6±3.8Gy. This shows the degree of dose fall off within the brainstem. Though the results of the present study are showing superior sparing of brain stem and reasonable of target coverage, it is necessary to execute the treatment plan with greater accuracy in CyberKnife as the immobilization is noninvasive and frameless.
  4,356 244 2
Commissioning and initial acceptance tests for a commercial convolution dose calculation algorithm for radiotherapy treatment planning in comparison with Monte Carlo simulation and measurement
Farhad Moradi, Seyed Rabi Mahdavi, Ahmad Mostaar, Mohsen Motamedi
July-September 2012, 37(3):145-150
DOI:10.4103/0971-6203.99237  PMID:22973081
In this study the commissioning of a dose calculation algorithm in a currently used treatment planning system was performed and the calculation accuracy of two available methods in the treatment planning system i.e., collapsed cone convolution (CCC) and equivalent tissue air ratio (ETAR) was verified in tissue heterogeneities. For this purpose an inhomogeneous phantom (IMRT thorax phantom) was used and dose curves obtained by the TPS (treatment planning system) were compared with experimental measurements and Monte Carlo (MCNP code) simulation. Dose measurements were performed by using EDR2 radiographic films within the phantom. Dose difference (DD) between experimental results and two calculation methods was obtained. Results indicate maximum difference of 12% in the lung and 3% in the bone tissue of the phantom between two methods and the CCC algorithm shows more accurate depth dose curves in tissue heterogeneities. Simulation results show the accurate dose estimation by MCNP4C in soft tissue region of the phantom and also better results than ETAR method in bone and lung tissues.
  3,609 167 2
Pocket-size solid-state iPOD and flash drives for gigabyte storage, display and transfer of digital medical images: Technology Update
Sankaran Ananthanarayanan
July-September 2012, 37(3):159-162
DOI:10.4103/0971-6203.99240  PMID:22973084
  3,563 143 1
Use of ubiquitous materials for the estimation of accidental exposures
AS Pradhan, JL Kim, JI Lee
July-September 2012, 37(3):121-123
DOI:10.4103/0971-6203.99223  PMID:22973077
  3,156 172 4
Discrepancies in determining electron energy for lumpectomy boost treatment
Aime M Gloi, Robert Buchanan
July-September 2012, 37(3):138-144
DOI:10.4103/0971-6203.99234  PMID:22973080
The aim of this study was to compare lumpectomy cavity depth measurements obtained through ultrasound (U/S) and retrospective computed tomography (CT). Twenty-five patients with stage T1-2 invasive breast cancer formed the cohort of this study. Their U/S and CT measurements were converted into electron energy and compared. The mean U/S depth was 3.6 ± 1.3 cm, while the mean CT depth was 4.9 ± 1.9 cm; the listed error ranges are one standard deviation. Electron energies for treatment ranged from 6 MeV to 12 MeV based on the U/S determination. There was no significant correlation between cavity depths measured by U/S and CT (R 2 = 0.459, P < 0.002). Furthermore, only 20% of CT-based electron energy determinations matched the corresponding U/S determinations. This ratio increased to 40% when taking into account an upper limit based on the depth of organs at risk below the cavity. The study shows that there is a significant discrepancy between cavity depths determined by U/S and CT. It also supports the concept that post-lumpectomy radiotherapy boosts should be tailored according to the needs and comfort of individual practices and institutions.
  3,084 132 -
Computed organ doses to an Indian reference adult during brachytherapy treatment of esophagus, breast, and neck cancers
Biju Keshavkumar
July-September 2012, 37(3):151-154
DOI:10.4103/0971-6203.99238  PMID:22973082
This study aims to generate the normalized mean organ dose factors (mGy min -1 GBq -1 ) to healthy organs during brachytherapy treatment of esophagus, breast, and neck cancers specific to the patient population in India. This study is in continuation to the earlier published studies on the estimation of organ doses during uterus brachytherapy treatments. The results are obtained by Monte Carlo simulation of radiation transport through MIRD type anthropomorphic mathematical phantom representing reference Indian adult with 192 Ir and 60 Co high dose rate sources in the esophagus, breast, and neck of the phantom. The result of this study is compared with a published computational study using voxel-based phantom model. The variation in the organ dose of this study to the published values is within 50%.
  2,997 163 -
Medical Radiological Physics
AR Reddy
July-September 2012, 37(3):163-165
  2,513 165 -
Dosimetry of Internal Emitters in Nuclear Medicine and Radiation Protection
AR Sundararajan
July-September 2012, 37(3):166-167
  1,957 155 -
News and Events
Tharmarnadar Ganesh
July-September 2012, 37(3):168-169
  1,366 78 -
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