Radiotherapy apparatus

1. A radiotherapy apparatus for providing radiation treatment to a patient, comprising:

a source of therapeutic radiation;

a first detector configured to detect the therapeutic radiation and generate a first detector output;

a support configured to support the patient between the source and the first detector;

a second detector assembly configured to derive an internal image of the patient on the support and to generate a second detector output; and

a control apparatus configured to:

receive the first and second detector outputs;

reconstruct, from detector output information of only the first detector output, a volume image representing a radiation dose delivered to the patient by the source; and

display the volume image against a background of an image derived from the second detector assembly.

2. The radiotherapy apparatus according to claim 1 , wherein the source emits x-radiation at an energy of at least 1 MeV.

3. The radiotherapy apparatus according to claim 1 , wherein the source comprises a linear accelerator.

4. The radiotherapy apparatus according to claim 1 , wherein the first detector is a flat-panel scintillation detector.

5. The radiotherapy apparatus according to claim 1 , wherein the volume image is a difference image showing a difference between a delivered dose derived from the first detector, and a previously-determined planned dose.

6. The radiotherapy apparatus according to claim 1 , wherein the second detector assembly comprises a source of diagnostic radiation of lower energy than the therapeutic radiation, and a second detector for the diagnostic radiation.

7. The radiotherapy apparatus according to claim 6 in which the source of diagnostic radiation and the second detector are combined into a single unit.

8. The radiotherapy apparatus according to claim 1 , wherein the second detector assembly comprises a magnetic-resonance imaging apparatus.

9. The radiotherapy apparatus according to claim 1 , wherein the second detector assembly comprises an ultrasound apparatus.

10. The radiotherapy apparatus according to claim 1 , wherein the image derived from the second detector assembly is a two-dimensional radiograph.

11. The radiotherapy apparatus according to claim 10 , wherein the two-dimensional radiograph was obtained at a different time than that of the image derived from the first detector.

12. The radiotherapy apparatus according to claim 11 , wherein the two-dimensional radiograph and the image are taken along substantially co-linear directions.

13. The radiotherapy apparatus according to claim 1 , wherein the image derived from the second detector assembly is a section taken from a volume image created using the output of the second detector assembly.

14. The radiotherapy apparatus of claim 1 , wherein the image derived from the second detector assembly is a section taken from one of a plurality of volume images created using the output of the second detector assembly, each depicting the patient at a different phase of a breathing cycle.

15. The radiotherapy apparatus according to claim 14 , wherein the control apparatus is configured to select the volume image based on analysis of the image derived from the first detector.

16. The radiotherapy apparatus according to claim 1 , wherein the image derived from the first detector is a two-dimensional radiograph.

17. A radiotherapy apparatus for providing radiation treatment to a patient, comprising:

a first imaging system configured to direct therapeutic radiation toward the patient and to detect the therapeutic radiation after passing through the patient using only a first detector positioned downstream of the patient in a path of the therapeutic radiation;

a second imaging system configured to;

direct diagnostic radiation at lower energy than the therapeutic radiation toward the patient; and

capture, using a second detector, an internal image of the patient after the diagnostic radiation passes through the patient; and

a control apparatus configured to:

reconstruct, using the detector output of only the first imaging system, a volume image representing a radiation dose delivered to the patient; and

display the volume image against a background of an image derived from the second imaging system.

18. The radiotherapy apparatus according to claim 17 , wherein the therapeutic radiation has an energy of at least 1 MeV.

19. The radiotherapy apparatus according to claim 17 , wherein the control apparatus is configured to reconstruct the volume image using a computed tomography back projection technique.

20. A radiotherapy method for providing radiation therapy to a patient, comprising:

receiving a first output from a first imaging system configured to direct therapeutic radiation toward the patient and to detect, using a first detector positioned downstream of the patient in a path of the therapeutic radiation, the therapeutic radiation after passing through the patient;

reconstructing, based on a detector output of only the first output, a volume image representing a radiation dose delivered to the patient;

receiving a second output from a second imaging system configured to:

direct diagnostic radiation at lower energy than the therapeutic radiation toward the patient; and

detect the diagnostic radiation after passing through the patient; and

displaying the volume image against a background of an image derived from the second output.

21. The radiotherapy method of claim 20 , wherein the image derived from the second output is a section taken from one of a plurality of volume images created using data corresponding to the detected diagnostic radiation.