Radiotherapy Computer Planning
Radiotherapy planning is the process that occurs in between your planning CT scan date and your radiotherapy treatment start date. You do not need to be present for this, as it is all done on computers with the information the therapy radiographers obtained when you had your planning CT scan. We have decided to include a little information on this process, because it may help you understand why there is a delay between your CT scan date and your radiotherapy treatment start date. You really do not need to know any of this so don't spend too much time on this page unless you're interested!!
After you have had your radiotherapy planning CT scan, the 3D data is sent to the planning department. Your clinical oncologist will then outline the area (volume) they wish to treat and also outline areas they wish to avoid with the radiation.
It is then the therapy radiographers’ or physicists’ job to produce a method (radiotherapy plan) to treat the area the clinical oncologist wants, whilst avoiding the areas s/he wishes to avoid. The finished plan has iso-dose curves to show which areas are receiving what dose (amount) of radiation. They are very similar to the contour lines on maps to show how high a mountain is, or isobars on traditional weather maps to show the low and high pressure systems.
On this image:
- The area the clinical oncologist wishes to treat is outlined in red dotted marks .
- The other lines represent the dose of radiation the patient will receive .
- The yellow line represents 100% of the dose and the dark green line represents 98% of the dose.
- The right kidney (outlined in purple on the left of the image) receives no dose.
Please remember you do not need to know any of this information. We have only included it for those that are interested!
To enable the clinical oncologist to accurately outline the area they wish to treat, they might use a combination of the data from the radiotherapy CT planning scan and an MRI scan. This is often the case with brain tumours and is called MRI fusion. In this image the clinical oncologist is using both MRI (inner circle) and CT data to outline the tumours in this patient's brain. With some brain tumours the clinical oncologist wants to treat the area where the tumour was located before it was taken out (de-bulked) by the surgeon. MRI Fusion allows the pre-operative MRI scan to be overlaid with the post-operative CT planning scan.
Intensity-Modulated Radiation Therapy (IMRT) planning allows the clinical oncologist to shape how the radiation dose will be in the patient. If you look at the top image, on this page, again you can see they have outlined the spinal cord. (maroon line). The computer planners have made an excellent plan to avoid treating the spinal cord, but have had to come very close to it. In the IMRT plan (image to the right), they have managed to curve the radiation dose perfectly around the spinal cord and even avoid treating the patient's vertebra (Purple line). As we said in the IMRT section, IMRT is not suitable for all radiotherapy treatments or patients, but as you can clearly see, when it is suitable a superior plan can be created for the patient.
Reviewed: March 2015