Effect of Change in Orientation of Enhanced Dynamic Wedges on Radiotherapy Treatment Dose

Transcription

1 International Journal of Advancements in Research & Technology, Volume 2, Issue 5, May Effect of Change in Orientation of Enhanced Dynamic Wedges on Radiotherapy Treatment Dose Saeed Ahmad Buzdar 1, M. Afzal Khan 1, Aalia Nazir 1, M. A. Gadhi 2, Altaf H. Nizamani 3, Hussain Saleem 4 1 Department of Physics, The Islamia University of Bahawalpur, Pakistan 2 Department of Medical Physics, Bahawalpur Institute of Nuclear Medicine & Oncology (BINO), Bahawalpur, Pakistan 3 Department of Physics, University of Sind Jamshoro, Hyderabad, Pakistan 4 Department of Computer Science, University of Karachi, Karachi, Pakistan saeed.buzdar@iub.edu.pk, afzalrao@hotmail.com, alia.nazir@iub.edu.pk, asghargadhi@gmail.com, altaf_nizamani@yahoo.com, hussainsaleem@uok.edu.pk (Corresponding Author) ABSTRACT W distribution by compensating dose inhomogeneity [1],[2],[3],[4],[5],[6]. To improve the dose distribution, concept of Static wedge has been extended to Dynamic wedge [7] which is capable to make any wedge angle, by the movement of one pair of independent jaws [8],[9],[10],[11] and resulting in reduced attenuation and beam hardening effects [12],[13]. Enhanced Dynamic Wedges (EDW) offer many advantages over conventional hard wedges for linear accelerator treatments. Along with these advantages the responsibility to deliver the correct dose is increased so that this complex technology is utilized to improve the treatment outcome. This involves determining the enhanced dynamic wedge factors for various field sizes and depths for use in the hand calculation of monitor units (MUs). The precise illustration of dynamic wedges in the treatment planning computer necessarily also be confirmed. This is required so that the final isodose distributions are correct and the MUs calculated by the treatment planning computer match with those determined by hand calculation [14],[15]. Different approaches have been followed in order to address the quality assurance of EDW [16],[17],[18]. Modern radiotherapy practice motivates the development of more modern and sophisticated approaches to assure quality for our clinical radiotherapy treatment methods [19],[20]. This work is an attempt to enhance the reliability of EDW commissioning by analyzing the dose calculation in two different wedge orientations. Enhanced Dynamic Wedges are used in radiotherapy treatment to modify the dose distribution in target volume so that a desired dose distribution is achieved. The technique being highly advanced and computer controlled, requires enhanced degree of quality assurance. The investigation aimed to verify the constancy of treatment dose, when the orientation of the enhanced dynamic wedge (EDW) is reversed. It has been noted that there is a slight change in the monitor units with the reversal of EDW orientation. The calculated dose for two opposite orientations of EDW has been compared for 6 and 10 MV photon beams, by two different calculation systems (Pencil Beam & Collapsed Cone) to assure the quality of EDW technique as well as to increase its reliability. The difference in the calculated dose for Y1-IN and Y2-OUT orientation, for three different field sizes and all seven wedge angels, is very small and hence not enough to change the wedge factor significantly. Keywords : Radiotherapy, Wedge Factor, Enhanced Dynamic Wedges, Radiotherapy, Quality Assurance 1 INTRODUCTION 2 MATERIALS & METHODS EDGED fields are often used in radiation therapy This investigation has been done for two photon energies 6 treatment by high-energy beams to modify the isodose and 10 MV of Varian Linear Accelerators, for all seven Enhanced Dynamic wedges (EDWs) 100, 150, 200, 250, 300, 450, 600. The objective was to calculate the monitor units at normalization depth of 5 cm, for 95 cm SSD. (100 Monitor Units were desired to be delivered at that depth). Treatment dose has been calculated for three symmetric field sizes 4x4, 10x10 and 20x20 so that the effect will be noted on all three kinds of the field sizes (the small, medium and large field). This practice has been repeated for all seven Enhanced Dynamic Wedges, and for both photon energies. Oncentra MasterPlan treatment planning system has been used for the dose calculation. Oncentra Master Plan treatment planning system contains two calculation algorithms Pencil Beam and Collapsed Cone Convolution. This diversity has been utilized to ensure the reliability of the calculations. 3. OBSERVATIONS AND DISCUSSION The treatment dose for two photon energies, for three field sizes has been calculated and presented in tables and figures below. These results are a comparison of two reverse orientations of same EDW, for same field size and photon energy. Further a comparison of two calculation algorithms is also presented. It helps to verify the difference in dose for two wedge orientations. It can be seen that both pencil beam and collapsed cone calculation algorithms are indicating almost similar variation in dose when the EDW orientation is reversed from Y1 IN to Y2 OUT.

2 International Journal of Advancements in Research & Technology, Volume 2, Issue 5, May TABLE 1: MONITOR UNITS FOR ALL EDW ANGLES, FOR TWO WEDGE ORIENTATION, CALCULATED FROM PENCIL BEAM AND COLLAPSED CONE ALGORITHM. ENERGY OF BEAM 6 MV PHOTON AND THREE FIELD SIZES 4 X 4, 10 X 10 AND 20 X 20 6 MV Photon Field Size (cm 2 ) EDW angle (deg) Pencil Beam Collapsed Cone Y1 IN Y2 OUT % DEV Y1 IN Y2 OUT % DEV x x x

3 International Journal of Advancements in Research & Technology, Volume 2, Issue 5, May TABLE 2: MONITOR UNITS FOR ALL EDW ANGLES, FOR TWO WEDGE ORIENTATION, CALCULATED FROM PENCIL BEAM AND COLLAPSED CONE ALGORITHM. ENERGY OF BEAM 10 MV PHOTON AND THREE FIELD SIZES 4 X 4, 10 X 10 AND 20 X MV Photon Field Size (cm 2 ) EDW angle (deg) Pencil Beam Collapsed Cone Y1 IN Y2 OUT % DEV Y1 IN Y2 OUT % DEV x x x

4 International Journal of Advancements in Research & Technology, Volume 2, Issue 5, May Percentage Deviation 0.05% 0.03% 0.03% 0.01% 0.01% -0.01% Fig-1: between the doses for two EDW Orientations, for 10 MV Photon and 4x4 cm 2 Field Size % -0.30% -0.40% -0.50% -0.60% -0.70% -0.80% Fig-4: Y1 IN & Y2 OUT Percent deviation in MUs, for 6 MV Photon and 4x4 cm 2 Field Size Fig-2: Y1 IN & Y2 OUT Percent deviation in MUs, for 10 MV Photon and 10x10 cm 2 Field Size Fig-5: Y1 IN & Y2 OUT Percent deviation in MUs, for 6 MV Photon and 10x10 cm 2 Field Size 0.16% Fig-3: Y1 IN & Y2 OUT Percent deviation in MUs, for 10 MV Photon and 20x20 cm 2 Field Size 0.16% Fig-6: Y1 IN & Y2 OUT Percent deviation in MUs, for 6 MV Photon and 20x20 cm 2 Field Size

5 International Journal of Advancements in Research & Technology, Volume 2, Issue 5, May Table-1 and Table-2 present the data sets obtained for the monitor units (MUs) calculated, when dose was normalized on a depth of 5 cm, with 95 cm SSD (100 MUs on this depth). These tables contain the information for change in the dose for two different orientation of EDW, for field sizes 4x4, 10x10 and 20x20, for each photon energy 6 and 10 MV. Additionally, all the exploration has been done for both the calculation systems integrated with Oncentra MasterPlan Treatment Planning System; the Pencil Beam and Collapsed Cone Convolution. This similar kind of deviation between doses for two opposite orientation, confirmed by both the calculation algorithms, indicates reliability of the results. The percentage deviation between monitor units calculated for two opposite orientations have been plotted against wedge angles, for three field sizes and both photon energies, are represented below in Fig-1 to Fig-6. The dotted curve is deviation obtained by Pencil Beam algorithm while solid line representing the calculations made through Collapsed Cone Convolution algorithm. The percentage deviation between two doses, for two opposite orientations of EDW, for three different field sizes, is graphically represented in figure 1 to figure 6. Percent Deviation seems to increase with increasing wedge angle. The maximum percentage difference is for 6 MV calculated by Pencil beam, and for Collapsed Cone calculations. While this difference is remarkably small for 10 MV, the maximum deviation is 0.10 % for Pencil beam calculations, and 0.12 % for Collapsed Cone. The overall results are within 1 % deviation. This constancy enhances the reliability of the EDW to be used for modification of the dose distribution. The change in the dose, due to change in the wedge orientation, needs to be further investigated. Lots of experiments have been done to study the role, effectiveness and procedures of Enhance Dynamic wedges, but this thing need to be explored too. Even this change is not too big to effect the treatment planning, but it needs to be optimized to ensure that this is not some inaccuracy of the dose calculation system. 4 CONCLUSION The effect on treatment dose due to change in the orientation of EDW (from Y1 IN to Y2 OUT) has been analyzed and it is found that there is a slight change in the dose by reversing the wedge orientation but this is not enough to change the wedge factors significantly. The constancy in the monitor unit calculation is verified to assure the quality of Enhanced Dynamic Wedges. REFERENCES [1] M. 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6 International Journal of Advancements in Research & Technology, Volume 2, Issue 5, May Saeed Ahmad Buzdar is presently an Assistant Professor in the Department of Physics, The Islamia University of Bahawalpur. He has completed his Ph.D in Medical Physics from the Islamia University Bahawalpur, Pakistan. Recently he is a Post Doc Fellow at University College London, U.K. He is also associated with Medical Physics Research Group at the Islamia University Bahawalpur, Pakistan. His areas of interests are Medical Physics, Physics of Radiation Therapy, Physics of Medical Imaging, Computational Physics, and Radiation Dosimetry. Muhammad Afzal Khan is Professor at Department of Physics, The Islamia University Bahawalpur, Pakistan. He got associated there since He started research in collaboration with Department of Medical Physics at Ninewells Hospital & Medical School, University of Dundee, UK in 1995 and had conducted research in MR Imaging with hospital service work in diagnostic radiology and radiotherapy of cancer. He was awarded Ph.D in On his return, he took up various academic assignments and continued his research in Medical Physics. He has worked closely with Bahawalpur Institute of Nuclear Medicine and Oncology (BINO-Cancer Hospital of Pakistan Atomic Energy Commission) and Quaid-e-Azam Medical College, Bhawalpur to complete more than twenty research projects. Hussain Saleem is Assistant Professor and Ph.D. Research Scholar at Department of Computer Science, University of Karachi, Pakistan. He received B.S. in Electronics Engineering from Sir Syed University of Engineering & Technology, Karachi in 1997 and has done Masters in Computer Science from University of Karachi in He also received Diploma in Statistics from University of Karachi in He bears vast experience of more than 16 years of University Teaching, Administration and Research in various dimensions of Computer Science. Hussain is the Senior Instructor and has been associated with the Physics Labs at Aga Khan Ex. Students Association Karachi since He served as Bio-Medical Engineer at Aga Khan University in , where he practiced to handle Radiology and MRI equipments. Hussain is the Author of several International Journal publications. His field of interest is Software Science, System Automation, Hardware Design & Engineering, Data Analysis, and Simulation & Modeling. He is senior member of Pakistan Engineering Council (PEC). Aalia Nazir has completed Ph.D. in Medical Physics from The Islamia University, Bahawalpur, Pakistan in During her studies she had conducted research at University of Dundee Scotland UK. Her areas of interests are Medical Physics, Physics of Radiation Therapy, Physics of Medical Imaging, Computational Physics, Radiation, Dosimetry, Radiology, Magnetic Resonance Imaging (MRI), Gel Dosimetry and use of Nanotechnology for the treatment of cancer. Muhammad Asghar Gadhi is a Medical Physicist at the Department of Medical Physics, Bahawalpur Institute of Nuclear Medicine & Oncology (BINO), Bahawalpur, Pakistan. He received M.Phil. in Medical Physics in 2007 from The Islamia University of Bahawalpur, Pakistan. His areas of interests are Medical Physics, Physics of Radiation Therapy, Physics of Medical Imaging, Computational Physics, and Radiation Dosimetry. Altaf Hussain Nizamani is working as Assistant Professor at the Institute of Physics, University of Sindh, Jamshoro, Pakistan. He received Ph.D degree in Ion-Trapping and Quantum computation technology from the University of Sussex, Brighton, UK in His areas of interests are Scalable Ion trap chips for the quantum computing and information technology, ultra high vacuum system designing, FPGA and Real-time LabVIEW programming, LASER cooling & trapping and computational Physics.