| Magnetic resonance imaging (MRI) is traditionally used | | | | of active breathing control device. An active breathing |
| in the diagnostic and staging parts of a patient's | | | | device allows imaging in only one specific part of the |
| treatment pathway. More recently however, it has also | | | | patient's breathing cycle. The benefit of this is that it |
| been used to help determine the planning target | | | | allows for the scan to be constructed with the tumour |
| volume (PTV). In many CNS patients their diagnostic | | | | in one position, and therefore hopefully not as effected |
| MRI scan is fused with their radiotherapy planning CT | | | | by organ motion. The same active breathing device is |
| scan. (REF) The oncologist is then able to outline the | | | | then used each day while the patient is having their |
| Tumour mass on the MRI as a GTV, which can then | | | | radiotherapy treatment, so the tumour is localised while |
| be superimposed on the planning CT scan, to check | | | | the treatment machine is delivering dose. This |
| the area for treatment and the margins to be used. | | | | technique does require much cooperation from the |
| This fusion of images, is advantages for two reasons. | | | | patient, and would only be suitable for patients whose |
| Firstly the MRI image shows far greater resolution in | | | | thoracic tumours were not too severe to have caused |
| soft tissue, than the CT, and secondly because the CT | | | | severely laboured, or erratic breathing patterns. |
| scan is carried out post surgery following de-bulking, | | | | Another type of tumour tracking device uses |
| whilst the MRI is carried out prior to any clinical | | | | reference points that are actually attached to the |
| intervention. Therefore the oncologist is in effect, able | | | | patient's skin surface. These reference points are then |
| to treat where the gross tumour was actually initially | | | | tracked while the patient is being CT scanned to |
| located. | | | | determine at which point in their breathing cycle they |
| Functional MRI (fMRI) is a relatively new technology, | | | | were at any given point during the scan. When the |
| which is used with the aim to try to determine | | | | data from the CT scan is then being consolidated, this |
| precisely which part of the brain is handling which | | | | additional motion information is added allowing the |
| critical functions. This is called brain mapping and is | | | | actual specific motion of any tumour to be linked to |
| used primarily during surgery before the patient comes | | | | each patient's own specific breathing cycle. |
| for any radiotherapy. The use of fMRI has been | | | | The 3rd 4DCT method effectively builds a margin |
| extended more recently, as it has now also been used | | | | around the GTV as it continually moves within the |
| as tool, in order to monitor the growth and function of | | | | body. This technique aims to determine the true extent |
| any remaining brain tumour following treatment. | | | | of each patient's actual tumour motion, so a |
| Functional computerised tomography (4DCT) is a | | | | personalised plan can be produced which gives a |
| normal CT scanner with software incorporated, or | | | | treatment dose to the GTV, even though it is moving |
| hardware adaptations, which allow it to look at organ | | | | throughout the treatment. The main problem with this |
| motion in relation to bony anatomy. These fall into | | | | technique is a large volume normally needs to be |
| three main categories; 1 Breath Hold, 2 Gating and 3 | | | | treated, if the tumour motion is of significance and is |
| Tracking the movements of the tumour. | | | | therefore not generally useful when using radical |
| Another method, which can also be used to monitor | | | | radiotherapy treatment techniques. |
| and control organ motion linked to breathing, is a type | | | | |