HEALTHWATCH
New tool to fight cancer
DR. TEJINDER KATARIA
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Image Guided Radiotherapy brings hope to millions of cancer patients.
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Many benefits: IGRT is expected to improve cure rates for cancer.
That cancer is fast becoming one of the largest killers worldwide is well known. While the distribution of cancer cases among sexes worldwide is fairly even, the age distribution is quite different in developed and developing countries. There are sig
nificantly more cases in children and adolescents in developing countries, while a greater part of the elderly population is afflicted by cancer in the developed countries.
That’s the bad news. The good news is that recent advances in use of imaging techniques like CT-scan, MRI, and PET scans and now Image Guided Radiotherapy (IGRT) have aided in the treatment and, more importantly, the protection of healthy organs by identifying more accurately the exact area affected by cancer.
Traditional treatment
Typically, the treatment of cancer can be done by surgery (surgically removing the affected tissues), radiotherapy (use of ionising radiation to kill malignant cells) and/or chemotherapy (medication-based treatment where a combination of medicines is given). Each modality is used alone or in combination with other treatment approaches.
It is estimated that at least 50 per cent of the patients undergo radiotherapy. Earlier, conventional radiotherapy would locate the approximate location of the tumour and involve giving radiation to the surrounding healthy cells as well. This would damage the healthy cells, tissues and organs. The delivery of radiation therapy often also had to rely on assumptions about target locations based on data, which could be a week or more old at the time of treatment.
The introduction of Intensity Modulated Radiation Therapy (IMRT) further enhanced the capacity of focusing radiation to cancer bearing areas. However, even this technology had a drawback. Tumours may move, both during a treatment session and from one treatment session to another, as a result of normal internal organ action (digestion, elimination, and breathing). As a result of this unplanned position/ movement, the tumour may not receive the full amount of radiation and normal tissues may receive more radiation than they can tolerate.
To overcome this very challenge, IGRT was introduced in 2003. Here, the tumour-bearing area, mapped by the radiation oncologist, is imaged and a reconstruction of the anatomy by virtual CT-scan is carried out in the treatment machine. The images can be acquired using either treatment X-rays (megavoltage imaging) or diagnostic X-rays (Kilovoltage imaging) also known as Cone Beam CT-scanning; the advantage of the latter is a lesser dose of x-ray radiation being received by the patient.
Image guided radiotherapy or IGRT is best suited for sites where internal organ motion is expected, for example: cancer of lung, breast and liver (breathing motion), stomach and prostate (filling), brain (neck movement). The use of image guidance will not only improve the focus and precise delivery of radiation, but is also expected to improve the cure rates for cancers where the dose delivery is limited with conventional methods of radiotherapy due to proximity of affected tissues to critical organs like eyes, brain, heart, lungs and spinal cord.
New technique
Today, IGRT has become a harbinger of hope for cancer patients across the globe. Not only has this technique significantly improved survival rates, it has also resulted in reducing the side-effects of radiation like difficulty in swallowing food and pneumonia for patients with cancers in the chest. Another advantage is that, as the cancers shrink with treatment, it will be possible for physicians to implement Adaptive Radiotherapy using IGRT. Adaptive Radiotherapy is a new concept in radiotherapy where individual patient data is collected for the first few fractions of treatment and is then used to individualise treatment for the remaining fractions and treatment is re-planned based upon the tumour shrinkage.
As compared to conventional radiotherapy, by increasing the daily dose of radiation with image guidance, smaller normal tissue coverage can be given, thus reducing the overall treatment time. This increases the compliance for treatment completion and reduces the overall visits to the hospital, thereby resulting in greater patient comfort.
The writer is a Consultant in Radiation Oncology based in Gurgaon.
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