Systems, methods, and devices for radiation beam asymmetry measurements using electronic portal imaging devices
Systems and methods for determining beam asymmetry in a radiation treatment system using electronic portal imaging devices (EPIDs) without implementation of elaborate and complex EPID calibration procedures. The beam asymmetry is determined based on radiation scattered from different points in the radiation beam and measured with the same region of interest ROI of the EPID.
1. A method for determining a radiation beam tilt relative to a collimator axis of rotation of a radiation treatment device, comprising:
emitting a radiation beam from a source positioned at the collimator axis of rotation, the radiation beam passing through an aperture of the collimator positioned around the collimator axis at a first position so as to be received by an electronic portal imaging device positioned at a distance from the source along the collimator axis of rotation;
measuring intensity of the radiation beam received by the electronic portal imaging device;
rotating the collimator around the collimator axis by 180 degrees to a second position and measuring the intensity of the radiation beam that passes through the aperture by the electronic portal imaging device,
comparing the intensity of the radiation beam measured at the first location of the collimator and the intensity of the radiation beam measured at the second location of the collimator,
calculating an asymmetry value from the difference in the measured intensities; and
calculating radiation beam tilt from the asymmetry value.
2. The method of claim 1 , further comprising determining whether the beam tilt is a radial or a transversal tilt relative to the collimator axis of rotation.
3. The method of claim 2 , further comprising initiating a calibrating process to adjust the determined radiation beam tilt.
4. The method of claim 3 , wherein the calibrating process includes one a manual or automatic adjustment.
5. The method of claim 4 , wherein the adjusting includes adjusting one or more of radiation collimating devices, angle and position of steering coils, location of flattening filters, size of a bend magnet shunt current, position and/or symmetry of an ionization chamber, and mechanical elements of the radiation system.
6. The method of claim 5 , wherein the manual adjustment includes adjusting mechanical screws, bolts, or other mechanical pieces of the radiation treatment device.
7. The method of claim 6 , wherein the adjusting is configured to be repeated until the tilt falls within a prescribed range.
8. The method of claim 7 , further comprising displaying completed adjustments and suggested alignments to a user.
9. A non-transitory computer-readable medium including instructions to be executed by a computer processor to determine radiation beam tilt relative to a collimator rotation axis of a radiation treatment device, which when executed by the computer:
sends a signal to a radiation source to emit a radiation beam from a source positioned at the collimator axis of rotation, the radiation beam passing through an aperture of the collimator positioned around the collimator axis at a first position so as to be received by an electronic portal imaging device positioned at a distance from the source along the collimator axis of rotation;
initiates the measuring of intensity of the radiation beam received by the electronic portal imaging device;
controls the rotating of the collimator around the collimator axis by 180 degrees to a second position and initiates measuring of the intensity of the radiation beam that passes through the aperture by the electronic portal imaging device;
initiates comparing the intensity of the radiation beam measured at the first location of the collimator and the intensity of the radiation beam measured at the second location of the collimator;
calculates an asymmetry value from the difference in the measured intensities; and
calculates radiation beam tilt from the asymmetry value.
10. The non-transitory computer-readable medium of claim 9 , further comprising determining whether the beam tilt is a radial or a transversal tilt relative to the collimator axis of rotation.
11. The non-transitory computer-readable medium of claim 10 , further comprising initiating a calibrating process to adjust the determined radiation beam tilt.
12. The non-transitory computer-readable medium of claim 11 , wherein the calibrating process includes one a manual or automatic adjustment, and wherein the adjusting includes adjusting one or more of radiation collimating devices, angle and position of steering coils, location of flattening filters, size of a bend magnet shunt current, position and/or symmetry of an ionization chamber, and mechanical elements of the radiation system.