Dosimetry techniques for radiotherapy

1. A radiotherapy apparatus comprising:

a source of therapeutic radiation for delivering a dose to a patient;

a detector for detecting the therapeutic radiation after attenuation by the patient; and

a control unit having a processor configured to execute computer-executable instructions that, when executed by the processor, cause the control unit to be configured to:

receive a sequence of dose delivery instructions;

receive patient data describing a patient geometry;

cause the apparatus to perform the dose delivery instructions a first time and receive first information from the detector, the first information comprising a first delivered radiation fluence;

perform a first computational analysis, based on the received first information and the patient data, to determine a first dose distribution;

subsequent to completion of the first computational analysis, cause the apparatus to perform the dose delivery instructions a second time; and

during the second performance of the dose delivery instructions:

receive second information from the detector including a second delivered radiation fluence;

perform a second computational analysis based on the received second information and the patient data to determine a second dose distribution;

compare the second dose distribution to the first dose distribution; and

provide an alert signal based on the comparison.

2. The radiotherapy apparatus according to claim 1 , wherein the processor is configured to execute the instructions to thereby:

provide the alert signal when the comparison between the second dose distribution and the first dose distribution exceeds a predetermined threshold.

3. The radiotherapy apparatus according to claim 1 , wherein the detector is a portal image detector.

4. The radiotherapy apparatus according to claim 1 , wherein the processor is configured to execute the instructions to thereby:

perform the dose delivery instructions at a first time during a first calendar day; and

perform the dose delivery instructions at a second time during a later calendar day.

5. The radiotherapy apparatus according to claim 1 , wherein:

the source includes sensors to measure radiation output of the source, and

the first delivered radiation fluence and second delivered radiation fluence are determined by computing a difference between an output beam measured by the sensors and an attenuated beam measured by the detector.

6. The radiotherapy apparatus according to claim 1 , wherein the patient data includes data defining an external surface of the patient.

7. The radiotherapy apparatus according to claim 6 , wherein at least one of the first computational analysis or the second computational analysis includes back-projection of stored radiation fluence information through a body made of a standard material comprising water and having a shape corresponding to the external surface of the patient to determine at least one of the first dose distribution or the second dose distribution.

8. The radiotherapy apparatus according to claim 1 , wherein the patient data includes data defining at least one of tissue types or tissue densities within the patient.

9. The radiotherapy apparatus according to claim 8 , wherein at least one of the first computational analysis or the second computational analysis includes back-projection of stored radiation fluence information through the data defining tissue types to determine at least one of the first dose distribution or the second dose distribution.

10. The radiotherapy apparatus according to claim 1 , wherein the patient data is derived from one of a CT scan or an MRI scan of the patient.

11. The radiotherapy apparatus according to claim 1 , wherein the sequence of dose delivery instructions includes steps and the processor is configured to execute the instructions to thereby:

perform the first computational analysis based on the received first information resulting from a subset of the steps within the sequence of dose delivery instructions, and

perform the second computational analysis during the second performance of the dose delivery instructions and after a corresponding subset of the steps within the sequence of dose delivery instructions.

12. The radiotherapy apparatus according to claim 11 , wherein the processor is configured to execute the instructions to perform multiple pairs of computational analyses after different subsets of the steps within the sequence of dose delivery instructions.

13. A computer-implemented method for delivering a dose of therapeutic radiation from a source to a patient, the method performed by a processor and comprising:

receiving a sequence of dose delivery instructions;

receiving patient data describing a patient geometry;

performing the dose delivery instructions a first time;

receiving first information from the detector, the first information comprising a first delivered radiation fluence;

performing a first computational analysis, based on the received first information and the patient data, to determine a first dose distribution;

performing the dose delivery instructions a second time after the first computational analysis is complete;

receiving second information from a detector, the second information comprising a second delivered radiation fluence;

performing a second computational analysis based on the received second information and the patient data to determine a second dose distribution;

comparing the second dose distribution to the first dose distribution; and

providing an alert signal based on the comparison.

14. The computer-implemented method according to claim 13 , further comprising:

providing the alert signal when the comparison between the second dose distribution and the first dose distribution exceeds a predetermined threshold.

15. The computer-implemented method according to claim 13 , wherein the first performance of the dose delivery instructions takes place on a first calendar day and the second performance of the dose delivery instructions takes place on a later calendar day.

16. The computer-implemented method according to claim 13 , wherein:

the source includes sensors to measure radiation output of the source, and

the first delivered radiation fluence and second delivered radiation fluence are determined by computing a difference between an output beam measured by the sensors and an attenuated beam measured by the detector.

17. The computer-implemented method according to claim 13 , wherein the sequence of dose delivery instructions includes steps and the method further comprises:

performing the first computational analysis based on the received first information resulting from a subset of the steps within the sequence of dose delivery instructions; and

performing the second computational analysis during the second performance of the dose delivery instructions and after a corresponding subset of the steps within the sequence of dose delivery instructions.

18. The computer-implemented method according to claim 13 , further comprising:

performing multiple pairs of computational analyses after different subsets of the steps within the sequence of dose delivery instructions.

19. A radiotherapy apparatus for delivering a dose of therapeutic radiation to a patient, comprising a control unit having a processor configured to execute computer-executable instructions that, when executed by the processor, cause the control unit to be configured to:

receive a sequence of dose delivery instructions;

receive patient data including a patient geometry;

cause the apparatus to perform the dose delivery instructions a first time;

receive first information, including a first delivered radiation fluence, from a detector;

perform a first computational analysis based on the received first information and the patient data to determine a first dose distribution;

cause the apparatus to perform the dose delivery instructions a second time;

receive second information, including a second delivered radiation fluence, from the detector;

perform a second computational analysis based on the received second information and the patient data to determine a second dose distribution;

compare the second dose distribution to the first dose distribution; and

provide an alert signal based on the comparison.