GAMOS tutorial X-ray Exercises Pedro Arce Dubois CIEMAT http://fismed.ciemat.es/GAMOS

X-ray simulation Exercises Ex. 1: X-ray tube Ex. 2: Writing phase space Ex. 3: Score dose in phantom Ex. 4: Score lateral dose The exercises are sequential Use the commands of the previous exercise (only change what indicated) GAMOS radiotherapy tutorial Pedro Arce

Exercise 1: X-ray tube geometry Tube of inner diameter 60 mm, length 100cm. Wall of 2 mm of pyrex. Filled with vacuum (G4_Galactic material). The tube is placed rotated -90 degrees around the X axis The tube has a window hole of 2.5 cm length and 2.5 cm width, placed at phi 90 degree (so that after rotation it will end at the positive Z side). In the middle of the window hole there is a foil of 125 microns of berilium at Z positive. The centre of the window foil is placed at position (0,0,0) The tube is surrounded by a shield 2 cm thick of lead. In it there is also a hole at the position than the tube GAMOS radiotherapy tutorial Pedro Arce

Exercise 1: X-ray tube geometry The anode is built from an alloy of 90% tungsten and 10 % rhenium. It is a polycone of width 10 mm, radius 20 mm at one side and 5 mm at the other side. The surface has an inclination of 12 degrees. The anode axis coincides with the tube axis and it is placed at 80 mm from the tube wall, with the smaller radius towards the tube center The source of electrons is a cylinder of air of 5 mm radius and 10 microns thick, placed so that its centre is in front of the centre of the anode inclined surface, at mid-distance of radius (=12.5 mm out of centre), and at 50 mm along the tube axis coordinate The primary particles are electrons of 150 keV homogenously distributed in the source cylinder and with initial direction along the Y axis Physics is low energy electromagnetic one GAMOS radiotherapy tutorial Pedro Arce

Exercise 1: study gamma propagation Plot the initial kinetic energy and direction theta angle of all gammas created Plot the kinetic energy and direction theta angle of all gammas when they reach the inner side of the tube (or the window hole inner side) Plot the kinetic energy and direction theta angle of all gammas when they exit the shield Plot the total length that primary electrons travel inside the anode GAMOS radiotherapy tutorial Pedro Arce

Exercise 2a: write phase space Use setup of exercise 1 and write a phase space of the particles that reach a Z plane situated 10 cm below the tube window foil GAMOS radiotherapy tutorial Pedro Arce

Exercise 2b: use bremsstrahlung splitting Same as exercise 2a, but use Z-plane bremsstrahlung splitting Z plane defined at 10 cm from window foil and size 15 X 15 cm Try splitting 100 times and see bias in phase space GAMOS radiotherapy tutorial Pedro Arce

Exercise 3a: score dose in phantom Use the phase space created in exercise 2 Run 1000000 events, reusing phase space file Score dose in phantom voxels Use test_64x64x39.g4dcm Print a report of the dose in each voxel, with errors Make histograms of dose in voxels (PDD, profiles) Write dose in a file, with dose squared, to allow summation of files GAMOS radiotherapy tutorial Pedro Arce

Exercise 3b: place a protection before phantom Repeat exercise 3a, but placing a protection of 2cm of Cerrobend, 10 X 10 cm wide, at the centre of the phantom, touching it Compare dose distributions Plot length of tracks traversing protection GAMOS radiotherapy tutorial Pedro Arce

Exercise 4a: Calculate lateral dose Read phase space from exercise 2 Use point detector scorer to calculate dose in three points At the Z of the window foil at Y = 25.1 cm (1 mm from phantom) At Z 1 meter below the window foil at Y = 25.1 cm At Z 1 meter above the window foil at Y = 25.1 cm GAMOS radiotherapy tutorial Pedro Arce

Exercise 4b: Calculate dispersion in patient Same as exercise 4a, and place patient of exercise 3 Compare equivalent dose in each of the three points GAMOS radiotherapy tutorial Pedro Arce