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Penumbral Dose Characteristics of Physical and Virtual Wedge Profiles

International Journal of Medical Physics, Clinical Engineering and Radiation Oncology 2017年第2期6卷 216-224页

作者： Salman Farrukh Nasir Ilyas Muhammad Naveed Abdul Haseeb Muhammad Bilal Dr najamuddin Javed Iqbal Atomic Energy Medical Centre JPMC Karachi Pakistan Institute of Space and Planetary Astrophysics University of Karachi Karachi Pakistan

Purpose: Both physical and virtual wedges are used in radiotherapy to get uniform and desired dose distribution in clinical setting. All linear accelerators of different venders have computer controlled dynamic wedges called virtual wedge filters. Penumbra is one of the important photon beam characteristics needed to be understood in radiation therapy at the time of commissioning of Treatment Planning system (TPS) as well as applying various treatment planning algorithms in clinical applications. In this study we measured the dose profiles of open field, physical wedges (PW) and virtual wedges (VW) for energies (6 MV & 15 MV), various field sizes (10 × 10, 15 × 15 & 20 × 20 cm2), depths (dmax, 10 cm, 20 cm) and wedge angles (15°, 30°, 45° and 60°). From beam profile we calculated the penumbral width for open and wedged fields. The study was carried out on Siemens ONCOR IMRT Plus linear accelerator. The obtained penumbral width of PW and VW of all wedge angles was subtracted from the penumbral width of open field. The deviations in penumbral width were compared and statistically analyzed as a function of energy, depth, field size and wedge angles. Material and Method: The penumbral width was measured using IBA CC13 ion chamber in IBA Blue phantom (a 3D water phantom). The source to surface distance (SSD) during our study was kept 100cm and measurement was taken for 10 × 10, 15 × 15, 20 × 20 cm2 field sizes and for 15°, 30°, 45°, 60° wedges. These measurements were taken for both 6 MV and 15 MV photon energies. Virtual wedge profiles were acquired using LDA-99 linear detector array (IBA, Germany). The deviations in penumbral width for both PW and VW were calculated by subtracting the penumbral width from open field penumbral width in gun direction (in-plane) and deviation in VW penumbral width, and were obtained by subtracting the open field penumbral width in left-right direction (cross-plane) direction. The measured deviations were plotted for both PW and VW. Statis

关键词： Physical Wedge Virtual Wedge Penumbra and Deviations

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Characterizing Potential Fishing Zone of Skipjack Tuna during the Southeast Monsoon in the Bone Bay-Flores Sea Using Remotely Sensed Oceanographic Data

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International Journal of Geosciences 2013年第1期4卷 259-266页

作者： Mukti Zainuddin Alfa Nelwan Siti Aisjah Farhum najamuddin Muhammad A. Ibnu Hajar Muhammad Kurnia Sudirman Faculty of Marine Science and Fisheries Hasanuddin University Makassar Indonesia

Potential fishing zones for skipjack tuna in the Bone Bay-Flores Sea were investigated from satellite-based oceanography and catch data, using a linear model (generalized linear model) constructed from generalized additive models and geographic information systems. Monthly mean remotely sensed sea surface temperature and surface chlorophyll-a concentration during the southeast monsoon (April-August) were used for the year 2012. The best generalized additive model was selected to assess the effect of marine environment variables (sea surface temperature and chlorophyll-a concentration) on skipjack tuna abundance (catch per unit effort). Then, the appropriate linear model was constructed from the functional relationship of the generalized additive model for generating a robust predictive model. Model selection process for the generalized additive model was based on significance of model terms, decrease in residual deviance, and increase in cumulative variance explained, whereas the model selection for the linear model was based on decrease in residual deviance, reduction in Akaike’s Information Criterion, increasing cumulative variance explained and significance of model terms. The best model was selected to predict skipjack tuna abundance and their spatial distribution patterns over entire study area. A simple linear model was used to verify the predicted values. Results indicated that the distribution pattern of potential fishing zones for skipjack during the southeast monsoon were well characterized by sea surface temperatures ranging from 28.5℃ to 30.5 ℃ and chlorophyll-a ranging from 0.10 to 0.20 mg·m-3. Predicted highest catch per unit efforts were significantly consistent with the fishing data (P 2 = 0.8), suggesting that the oceanographic indicators may correspond well with the potential feeding ground for skipjack tuna. This good feeding opportunity for skipjack was driven the dynamics of upwelling operating within study area which are capable of creating a h

关键词： Skipjack Tuna Satellite Data Generalized Additive Model Linear Model Upwelling Potential Fishing Zones Bone Bay and Flores Sea Southeast Monsoon

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