IMRT/VMAT
What is IMRT?
Intensity-modulated radiation therapy (IMRT) is an advanced method of precision radiation therapy that uses a computer-controlled linear accelerator to deliver precise doses of radiation to malignant tumours or specific areas within the tumour.
How does it work?
IMRT modulates (or controls) the intensity of a radiation beam in multiple small volumes to better match the radiation dose to the three-dimensional (3-D) shape of the tumour, allowing for precise adjustment.
Each radiotherapy beam is divided into many smaller beams that can vary in intensity of radiation. This allows different doses of radiation to be delivered through the tumour. This means that the tumour receives a very high dose, while nearby normal healthy cells receive a much lower dose.
A combination of multiple intensity-modulated fields, typically coming from different beam directions, produces a tailored radiation dose that maximizes tumour dose while minimizing dose to adjacent normal tissue.
What are the benefits for the patient?
It safely delivers a higher effective dose of radiation to the tumour with fewer side effects than traditional radiotherapy techniques.
NOTE : The complexity of IMRT results in a slightly longer treatment duration compared to conventional radiotherapy, and requires additional planning and safety checks before a patient begins treatment.
What is VMAT?
Volumetric Modulated Arc Therapy (VMAT) is a new radiotherapy technique that delivers a continuous dose of radiation while the treatment machine is rotating. This technique precisely tailors the radiation dose to the tumour while minimizing the dose to surrounding organs.
How does it work?
In this method the treatment is performed in her single or multiple arc rotations of the linac gantry. During this rotation, the multi-leaf collimator (MLC) is dynamically moved, and at the same time the dose rate is varied by changing the rotation speed of the gantry. In the VMAT, to achieve a highly conformal dose distribution by increasing the degrees of freedom, dose rate changes in one arc are achieved by a jumble of gantry velocities combined with dynamic MLC, all specified by a number of control points for rotation.
The VMAT can produce a similar or better dose distribution compared to IMRT while achieving shorter treatment times and halving the number of monitor units.
What are the benefits for the patient?
Prolonging treatment time has several undesirable consequences.
– Patients have to spend a lot of time on the radiation couch, which can lead to patient distress.
– Longer treatment times may increase the time it takes quality assurance physicians to review the dose distribution before administering to the patient.
– In particularly demanding radiotherapy, such as stereotactic radiotherapy, which delivers large doses of radiation in fractionated doses, it often takes him 30-45 minutes to complete radiotherapy with IMRT.
VMAT can alleviate these shortcomings of his IMRT