System and method for radiation beam measurement normalization

1. A radiotherapy system comprising:

a radiotherapy device operable to direct a radiation beam from a head thereof during operation;

a field detector positioned to be within the radiation beam during operation of the radiotherapy device and operable to generate a beam measurement signal;

a reference detector positioned to be outside of the radiation beam during operation of the radiotherapy device and operable to generate a reference signal; and

at least one computer in signal communication with the field detector and the reference detector and configured with software to normalize the beam measurement signal based on the reference signal and to output a normalized beam measurement.

2. The radiotherapy system of claim 1 , wherein the radiotherapy device is a linear accelerator (LINAC).

3. The radiotherapy system of claim 2 , wherein the normalized beam measurement output is a measurement of a relative intensity of the radiation beam versus position.

4. The radiotherapy system of claim 2 , wherein the reference detector is positioned to measure head scatter from the LINAC.

5. The radiotherapy system of claim 1 , wherein the radiotherapy device includes a movable gantry that carries the head, and the reference detector is carried on the movable gantry so as to move therewith.

6. The radiotherapy system of claim 5 , wherein the head directs the radiation beam away from a first side of the movable gantry and the reference detector is carried on a second side of the movable gantry opposite the first side.

7. The radiotherapy system of claim 1 , further comprising at least one electrometer configured to measure the beam measurement and reference signals and output respective measured beam measurement and reference signals to the at least one computer.

8. The radiotherapy system of claim 7 , wherein the electrometer is connected to the field detector and the reference detector by respective cables.

9. A computer-based method for normalizing a radiation beam measurement, the method comprising using at least one computer configured with software to:

receive a beam measurement signal from a field detector positioned within the radiation beam;

receive a reference signal from a reference detector positioned outside of the radiation beam;

normalize the beam measurement signal based on the reference signal; and

output a normalized beam measurement.

10. The computer-based method of claim 9 , further comprising positioning the reference detector to receive head scatter from a radiotherapy device.

11. The computer-based method of claim 10 , wherein the radiotherapy device is a linear accelerator (LINAC).

12. The computer-based method of claim 11 , wherein positioning the reference detector includes positioning the reference detector on an opposite side of a gantry carrying a radiation beam-emitting head of the LINAC.

13. The computer-based method of claim 11 , wherein the normalized beam measurement is a measurement of a relative intensity of the radiation beam versus position.

14. The computer-based method of claim 10 , further comprising connecting the reference detector to an electrometer with a cable.

15. A system for normalizing a radiation beam measurement, the system comprising at least one computer configured with software to:

receive a beam measurement signal from a field detector positioned within the radiation beam;

receive a reference signal from a reference detector positioned outside of the radiation beam;

normalize the beam measurement signal based on the reference signal; and

output a normalized beam measurement.

16. The system of claim 15 , wherein the normalized beam measurement is a measurement of a relative intensity of the radiation beam versus position.