Download Information Sheet about IMRT and IGRT

Information Sheet about IMRT and IGRT
What is IMRT?
IMRT stands for intensity-modulated radiation therapy (IMRT). This is a technique of high-precision
radiation therapy that uses computer-controlled linear accelerators (known as linacs) to deliver
precise radiation doses that specifically target the tumour. IMRT allows for the radiation dose to shape
precisely to the tumour by ‘modulating’ (varying) the intensity of the radiation beam. As a result high
radiation doses can be focused into the tumour while avoiding the surrounding normal body tissues to
a great extent. Treatment is carefully planned by using computed tomography (CT) or magnetic
resonance (MRI) scans to determine the best beam pattern for radiation therapy delivery. (See
Faculty of Radiation Oncology Position Paper on VMAT.)
The ultimate goal in radiation therapy is to improve the “therapeutic ratio”, which is the balance
between killing the cancer and harming the normal body. IMRT does this by improving cancer
outcomes while keeping the side effects the same or the cancer outcome is maintained and the side
effects are reduced.
What is IGRT?
Technological advances like IMRT demand equally accurate methods of exactly identifying the
position of the target, which we know can change its position within the body from day to day.
Treatment given using sophisticated methods of imaging the target position and systems to track its
movement is referred to as image guided radiation therapy (IGRT). (2013 ASTRO white paper on
IGRT http://www.practicalradonc.org/article/S1879-8500%2813%2900007-6/fulltext)
Improved tumour identification (IGRT) and improved radiation therapy delivery (IMRT) go hand in
hand to improve the therapeutic ratio. The value add of one technology leans on the value add of the
other to improve outcomes and minimise side effects.
How long does IGRT and IMRT add to the treatment delivery?
The initial introduction of these processes in a Department can increase the time it takes to treat a
patient due to both the learning curve and slower hardware and software. However as the procedure
is streamlined and staff become experienced, evidence indicates that some IMRT and IGRT
technologies actually reduce the daily time for each patient. This reduction in total treatment time (515 minutes) can mean improved efficiency, with increased patient throughput in the working day.
How are IMRT and IGRT delivered?
The equipment required for delivery of IMRT is additional to the standard linac setup in most
departments. Additional software for planning IMRT is required. Hardware to test the IMRT delivery as
part of the department’s quality assurance process and additional equipment in delivery of IMRT is
required. An important piece of equipment required is the multi-leaf collimation system, but this is now
generally standard across Australia and New Zealand.
The common forms of IGRT available in Australia/New Zealand are based on CT imaging
technologies. The devices used in these processes are set up in the radiation therapy treatment room
in conjunction with the linac to scan the patient before the radiation therapy is delivered. Specialised
high dose forms of IMRT, e.g. Stereotactic Radiosurgery (SRS) or Stereotactic Body Radiation
Therapy (SBRT), also require special add-on imaging equipment mounted on the floor and roof of the
bunker. IGRT allows the patient’s and tumour’s positions to be aligned in exactly the same position
every day. In doing this it ensures the tumour is targeted accurately every day. The consequence of
not imaging the target is missing the tumour, resulting in ineffective treatment, and an increase in
treatment toxicity as normal tissues around the tumour maybe unnecessarily irradiated. (Faculty of
Radiation Oncology Position Paper on IGRT)
What type of tumours likely benefit for IMRT?
IMRT has been shown to produce improved outcomes compared to three-dimensional conformal
radiation therapy (3DCRT), particularly in patients with concave target volumes. The benefit is mainly
found for body areas that have tissues that are particularly sensitive to the effects of radiation, such
as the brain in head and neck cancer treatment. For some tumour sites there may be little gain to its
use, and patients should discuss with their radiation oncologist as to the value of using IMRT in their
specific situation. Further details are found in the footnote below1.
What type of tumours likely benefit for IGRT?
IGRT is most useful in tumours that have a tendency to move in between treatments or during
treatment (e.g. lung or prostate cancer), to identify changes in tumour size during treatment (e.g. head
and neck cancer or small cell lung cancer) and to track tumours that lie close of sensitive normal
organs (e.g. brainstem or the eyes). (Langen KM, Jones DT. 2001. Organ motion and its
management. International Journal of Radiation Oncology Biology Physics. 50(1): 265-78)
The evidence base for the benefit of IGRT is extensive across many studies. (Faculty of Radiation
Oncology Position Paper on IGRT)
The complexity of the IGRT system and process varies depending on clinical and technical factors.
The effective use of technology such as this relies on the expertise of the radiation oncologist,
radiation therapists and medical physicists working as a multi-disciplinary team.
1
Specific examples:
Around 60 quality studies included three Randomised Controlled Trials (RCTs) in head and neck cancer (205 patients) and
three in breast cancer (664 patients), showed significant improvements with IMRT in each trial. A recent meta-analysis collated
data from 56 trials and showed that IMRT can reduce toxicities when compared to non-IMRT treatments. Reductions in toxicity
lead to improved quality of life and reduced health costs. There have been approximately 70-80 additional non-randomised
studies in head and neck cancer, prostate cancer, breast cancer and other tumour sites. Again they report benefits in acute and
late toxicity, health-related quality of life and tumour control end points. IMRT in the treatment of head and neck cancer reduces
parotid doses, resulting in less saliva dryness and improved quality-of-life. In the dose-escalated treatment of localized prostate
cancer, reduced rates of acute gastrointestinal toxicity have been reported after IMRT treatment.
Prostate Cancer
Dose escalation, improve PSA survival, potential for reduction toxicity from neoadjuvant hormone
treatment, reduced radiation proctitis, reduced radiation cystitis, reduced sexual dysfunction, dominant intra-prostatic lesion
boosts. (Godley et al, 2009; Martin et al, 2009; Cazoulat et al, 2009)
Breast Cancer
IMRT benefits include reduced acute skin reactions, reduced induration and fibrosis, likely improved
cosmesis and pain scores, simultaneous integrated boosts with shorter overall treatment duration.
(Leonard et al, 2009; Donovan et al, 2007; Pignol et al, 2008)
Lung Cancer
Allows for dose escalation and stereotactic high dose techniques. Reduced pneumonitis, reduced rib
fractures, reduced brachial plexus, injury, probably improved curates. (Nelson et al, 2010)