Monitor units calculation method for proton fields

1. A method for determining a monitor unit that is associated with a process using ions, comprising:

obtaining a depth dose curve;

determining a characteristic parameter based on the depth dose curve;

using the characteristic parameter to determine a first monitor unit factor for a first layer that is associated with a first feature of a range modulator; and

storing the first monitor unit factor in a device having a non-transitory medium;

wherein the act of using the characteristic parameter to determine the first monitor unit factor is performed by a processor.

2. The method of claim 1 , wherein the depth dose curve is obtained by measurement.

3. The method of claim 1 , wherein the depth dose curve is a model.

4. The method of claim 3 , further comprising fitting the model to a measured depth dose curve.

5. The method of claim 1 , further comprising applying a correction factor to the characteristic parameter.

6. The method of claim 5 , wherein the correction factor is based on an entrance dose.

7. The method of claim 5 , wherein the correction factor is a ratio of an entrance dose for a nozzle equivalent thickness associated with a layer, to an entrance dose for a reference nozzle equivalent thickness.

8. The method of claim 5 , wherein the correction factor is based on a fluence at an isocenter.

9. The method of claim 5 , wherein the correction factor is a ratio of a fluence at isocenter for a reference nozzle equivalent thickness, to a fluence at isocenter for a nozzle equivalent thickness associated with a layer.

10. The method of claim 5 , wherein the correction factor is a function of entrance dose, fluence at isocenter, nozzle equivalent thickness associated with a layer, and a reference nozzle equivalent thickness.

11. The method of claim 5 , wherein the correction factor is a correction for a ratio of values of an entrance dose at a monitor position and at an isocenter.

12. The method of claim 1 , further comprising:

obtaining a second monitor unit factor for a second layer that is associated with a second feature of the range modulator; and

combining the first and second monitor unit factors to obtain a monitor unit.

13. The method of claim 12 , wherein the monitor unit is obtained by:

applying a first weighted factor to the first monitor unit factor to obtain a first weighted monitor unit factor;

applying a second weighted factor to the second monitor unit factor to obtain a second weighted monitor unit factor; and

summing the first and second weighted monitor unit factors.

14. The method of claim 1 , wherein the ions comprise protons.

15. A system for determining a monitor unit that is associated with a process using ions, the system comprising a processor, wherein the processor is configured for:

obtaining a depth dose curve;

determining a characteristic parameter based on the depth dose curve; and

using the characteristic parameter to determine a first monitor unit factor for a first layer that is associated with a first feature of a range modulator.

16. The system of claim 15 , wherein the depth dose curve is obtained by measurement.

17. The system of claim 15 , wherein the depth dose curve is a model.

18. The system of claim 17 , wherein the processor is further configured for fitting the model to a measured depth dose curve.

19. The system of claim 15 , wherein the characteristic parameter comprises a normalization factor.

20. The system of claim 19 , wherein the normalization factor is for converting a unit of dose in a model into another unit of dose.

21. The system of claim 15 , further comprising applying a correction factor to the characteristic parameter.

22. The system of claim 21 , wherein the correction factor is based on an entrance dose.

23. The system of claim 21 , wherein the correction factor is a ratio of an entrance dose for a nozzle equivalent thickness associated with a layer, to an entrance dose for a reference nozzle equivalent thickness.

24. The system of claim 21 , wherein the correction factor is based on a fluence at an isocenter.

25. The system of claim 21 , wherein the correction factor is a ratio of a fluence at isocenter for a reference nozzle equivalent thickness, to a fluence at isocenter for a nozzle equivalent thickness associated with a layer.

26. The system of claim 21 , wherein the correction factor is a function of entrance dose, fluence at isocenter, nozzle equivalent thickness associated with a layer, and a reference nozzle equivalent thickness.

27. The system of claim 21 , wherein the correction factor is a correction for a ratio of values of an entrance dose at a monitor position and at an isocenter.

28. The system of claim 15 , wherein the processor is further configured for: further comprising:

obtaining a second monitor unit factor for a second layer that is associated with a second feature of the range modulator; and

combining the first and second monitor unit factors to obtain a monitor unit.

29. The system of claim 28 , wherein the processor is configured to obtain the monitor unit by:

applying a first weighted factor to the first monitor unit factor to obtain a first weighted monitor unit factor;

applying a second weighted factor to the second monitor unit factor to obtain a second weighted monitor unit factor; and

summing the first and second weighted monitor unit factors.

30. The system of claim 15 , wherein the ions comprise protons.

31. A computer product having a set of instructions stored in a non-transitory medium, an execution of which causes a process to be performed, wherein the process is for determining a monitor unit that is associated with a process using ions, the process comprising:

obtaining a depth dose curve;

determining a characteristic parameter based on the depth dose curve; and

using the characteristic parameter to determine a first monitor unit factor for a first layer that is associated with a first feature of a range modulator.

32. The computer product of claim 31 , wherein the process further comprises:

obtaining a second monitor unit factor for a second layer that is associated with a second feature of the range modulator; and

combining the first and second monitor unit factors to obtain a monitor unit.

33. The computer product of claim 32 , the first and second features comprise a first thickness and a second thickness, respectively, of the range modulator.

34. The computer product of claim 31 , wherein the range modulator is for reducing an energy of a beam, and has a step configuration.

35. The method of claim 1 , wherein the range modulator is for reducing an energy of a beam, and has a step configuration.

36. The method of claim 12 , wherein the first and second features comprise a first thickness and a second thickness, respectively, of the range modulator.

37. The system of claim 15 , wherein the range modulator is for reducing an energy of a beam, and has a step configuration.

38. The system of claim 28 , wherein the first and second features comprise a first thickness and a second thickness, respectively, of the range modulator.