IMRT - Intensity-modulated radiation therapy

Overview of IMRT - Intensity-modulated radiation therapy in India

IMRT (Intensity Modulated Radiation Therapy) is an advanced type of radiation therapy, which uses high-energy rays such as X-Rays, protons and more to kill cancer cells. IMRT is a very specific way to deliver radiation to match the exact type of cancer and allow the beams of radiation to rotate in any direction, adjusting the intensity of the radiation.

IMRT can be used to treat both cancerous (malignant) tumors as well as non-cancerous (benign) tumors, anywhere in the body where there are cancers or tumors.

The main purpose of IMRT is not only to provide the most accurate dose of radiation to the cancerous tumours targeted, but also to minimise the radiation dose delivered to surrounding normal tissue and reduce the risk of damage to surrounding normal tissue.

What Is Intensity-Modulated Radiation Therapy?

IMRT (intensity-modulated radiation therapy) is the type of external radiation therapy that uses beams of radiation to target and kill the cancerous tumor and spare healthy tissue from receiving high doses of radiation. IMRT is a good option for treating tumors located next to sensitive organs.

IMRT is just like all other forms of external beam radiation therapy compared to traditional radiation therapy (to kill cancer cells, utilising very intense and well-controlled beams of radiation). Linacs or linear accelerators are utilised to produce the rays of X-ray or gamma radiation that are directed at the tumour when using IMRT.

When intensity modulation is used with beam therapy (to direct higher versus lower doses to specific volumes of tissue), the total volume of healthy tissue that can sustain damage from the radiation will be decreased, and therefore reduce the side effects you may experience from treatment. Since your body will not actually touch the LINAC during treatment and you will not feel any pain, in most cases, until after, other people will begin to develop side effects from having received ionising radiation. 

The amount of RT you will experience will depend on the type of tissue being treated; for example, an ear canal would only feel very little fatigue compared to, for example, a pelvis or abdomen.

Types of IMRT - Intensity-modulated radiation therapy:

Volumetric Arc Therapy

Volumetric Arc Therapy is also called VMAT and Rapid Arc and uses a rotating treatment machine to deliver arc-shaped radiation treatments at varying intensity levels while the machine rotates around the patient. Distributing radiation this way provides higher levels of accuracy and provides a quicker completion time of the treatment with less overall radiation dose than traditional IMRT. Most of the time, treatments will take 10 to 15 minutes, depending on how complicated the treatment is based on the scan.

TomoTherapy

TomoTherapy is a way to receive treatment using a radiation couch that is moved with a doughnut-shaped machine, where the radiation source slowly spirals around you to distribute radiation to you. TomoTherapy is also called helical tomotherapy or helical IMRT.

Procedure:

The process of Intensity Modulated Radiation Therapy usually takes place in multiple stages:  

Simulation and Treatment Planning: 

CT Simulation: Before the start of treatment therapy, there is a CT simulation that is done on the patient. At this time, the patient's tumour and surrounding area will be visualised via a CT scan to be able to establish and design the best way to deliver radiation therapy. To help to keep the patient as still as possible, devices may be used for immobilisation (e.g., mould or mask).  

Treatment Planning: Treatment planning will be a cooperative effort between the radiation oncologist and the medical physicist using computerised planning software. The radiation oncologist will draw the tumor on the imaging (CT) data, and the computer program will determine what angles and what intensities the radiation beams to be used for the radiation treatment should be provided in relation to the tumor. This step is very important to guarantee that the radiation is going to be optimally directed to the tumor while sparing as much healthy tissue as possible.

Treatment Delivery:

Patient Positioning: Patients go through the same immobilisation method as they did during simulation when they come for treatment to ensure they are in the same position.

Radiation Beam Delivery: A linear accelerator rotates around the patient's body and delivers various radiation beams through a predetermined treatment map while modulating the intensity and direction of each beam according to that map.

Monitoring: Most Intensity Modulated Radiation Therapy delivery systems use imaging technology such as Cone Beam CT (CBCT) to verify that the patient has been positioned correctly for treatment at the beginning of each chemotherapy. Quality Assurance ensures that all treatment is undertaken in accordance with the intended plan and significantly reduces the margin of error.

Treatment Sessions: 

Fractionation: Treatments are generally delivered across several sessions (called fractions). Sessions are scheduled daily over multiple weeks to optimise the balance between control of the tumor and healing of the tissue. 

Session Duration: Each session typically lasts 15 to 30 minutes long, while the beam-on time will only be seconds to minutes long. 

Because Intensity Modulated Radiation Treatment uses very precise techniques, each treatment plan is specifically tailored to each individual. Personalising treatment is particularly important for patients with tumours that are located very close to sensitive structures such as the head and neck, prostate and some brain tumours.