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Advanced radiotherapy technology comes to India

N. Vivekanandan

‘RapidArc’ system at the Cancer Institute in Chennai

— Photo: M. Vedhan

FOR BETTER, QUICKER TREATMENT: The RapidArc Linear Accelerator installed at the Cancer Institute, Adyar, in Chennai.

The Cancer Institute (WIA) at Adyar in Chennai will become the first such centre in India to introduce the treatment technique known as RapidArc when Union Minister Anbumani Ramadoss inaugurates it on January 24. The technology, described as revolutionary, was introduced for the first time ever in the U.S. in May 2008. It will change the way radiotherapy is planned and delivered. It is a major advancement from conventional Intensity Modulated Radiotherapy Technology in that it improves dose conformity while significantly shortening treatment times compared to conventional IMRT techniques. While ensuring all the benefits of IMRT, RapidArc delivers treatment within two minutes with precision, enabling physicians to improve the standard of care and treat more patients.

In a typical IMRT procedure, the gantry of the linear accelerator rotates to several ‘fixed’ beam angles. To treat the prostate, usually five to seven specific angled beams are used, each delivering a fraction of the total radiation for that day. Since these fields are limited to certain angles, the ability to avoid or minimise radiation to normal tissue is also limited. In the RapidArc procedure, there are no angles in which the beam stops. The treatment is delivered in one single rotation of the gantry around the body. There is no limitation to where and when the beam will be ‘on’ or ‘off,’ or how fast or slow it is being delivered. So, medical physicists and radiation oncologists will have nearly unlimited choices and degrees of freedom to design sophisticated and highly conformal treatment. This will result in less normal tissue damage in the high-dose treatment fields and fewer side-effects.

Previous approaches to arc IMRT therapy were restrictive, limited as they were by the design of the machine. RapidArc technology delivers precisely sculpted three-dimensional dose distribution with a single 360-degree rotation of the linear accelerator gantry. RapidArc uses Dynamic Multi Leaf Collimator, a variable dose rate, and a variable gantry speed to generate IMRT-quality dose distribution in a single optimised arc. Clinicians can thus deliver a continuously modulated dose to the entire tumour volume while sparing relatively normal or healthy tissue.

With RapidArc, a medical linear accelerator can target radiation beams at a tumour while making one continuous rotation around the patient. Conventional IMRT treatments are slower and more difficult for radiotherapy technologists because they target tumours using a complex sequence of fixed beams from multiple angles.

RapidArc differs from existing techniques such as helical IMRT or intensity-modulated arc therapy as it delivers a dose to the whole volume, rather than slice by slice. A single arc can deliver essentially similar dose distributions compared with IMRT plans. The treatment planning algorithm ensures treatment precision.

RapidArc radiotherapy technology advances the standard of care even in complex treatment plans. For example, in a case of multi-target cancer of the nasopharynx, RapidArc plans were found to be equivalent or better at target coverage, and superior in protecting critical structures including the spinal cord, the brain stem, the eyes, the optic nerve and chiasm, the parotid glands and the brain. RapidArc allows more control to tailor the dosage to suit the size, shape, and location of a tumour. Laboratory studies suggest that faster dose delivery may kill some cancer cells more effectively.

Faster treatment also contributes to precision by reducing the time for motion within anatomical structures. The technique reduces the probability of intrafractional tumour movements caused by the patient moving during treatment. Repositioning can make the treatment even longer.

RapidArc delivers volumetric IMRT in a single arc or multiple arcs of the equipment around the patient and makes it possible to deliver advanced image-guided IMRT two to eight times faster than is possible with conventional IMRT. Radiotherapy studies correlate the ability to spare more healthy tissue with fewer complications and better outcomes. RapidArc delivery produces as little as 400 Monitor Unit per fraction. Fixed-field IMRT treatments of similar quality can generate 1,000 to 2,000 MU.

RapidArc’s single gantry rotation, besides speeding up delivery, may result in less leakage and scattered radiation and a lower overall peripheral dose than in the case of conventional IMRT treatments.

Patient care being at the heart of everything at the Cancer Institute, the decision to invest in this equipment was a straightforward one. The use of this speedier and state-of-the-art technology will enable the institute to treat more patients with less stress and more comfort to them.

Founded as a public voluntary charitable hospital for cancer treatment and research, the institute has grown into a major comprehensive cancer centre with 450 beds and a team of doctors and scientific staff numbering over 150, from being a cottage hospital of 12 beds, 2 nurses and 2 honorary medical officers in 1955. The institute introduced the “supervoltage era” in the treatment of cancer in the country in 1956 with the introduction of the first cobalt therapy unit in Asia and South-East Asia, including Japan and Australia. It was also the first to introduce a Linear Accelerator in the country, in 1976. Today it is the first to introduce RapidArc technology in India.

(Dr. N. Vivekanandan is head of the department of Medical Physics at the Cancer Institute (WIA), Chennai.)

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