Intensity Modulated Radiation Therapy: The cancer treatment of choice

Heralded as the most advanced cancer-fighting technology to date, Intensity Modulated Radiation Therapy (IMRT) is quickly becoming the treatment of choice of cancer victims.

Advances in radiation oncology made over the last 40 years were all designed with a single premise – maximize dose to the tumor and minimize dose to normal tissues. With the introduction of IMRT, the intensity of a radiation beam coming from the Linear Accelerator can be varied into many tiny "beamlets" that effectively pinpoint and destroy cancer cells while minimizing the radiation dose delivered to surrounding healthy tissues.

With IMRT, clinical results indicate prescribed radiation doses to specific tumors can be augmented while maintaining or reducing existing morbidity levels. The reduced dose to normal tissues permits the radiation oncologist greater freedom to explore the clinical effects of target dose escalation with less patient risks.

St. Luke’s Medical Center recently acquired the Smart Beam IMRT from Varian Medical Systems, which is the most complete and the most advanced system among all IMRT products. Varian’s IMRT system supports all IMRT techniques from simple step-and-shoot and electronic compensation techniques to a more advanced sliding window or dynamic IMRT method.

The system has proven to reduce radiation exposure to normal tissues by as much as 30 percent over conventional IMRT treatments that other medical institutions offer. When combined with St. Luke’s Positron Emission Tomography (PET) scanner – the first and only in the country and in Southeast Asia – to provide functional information about the tumor, this evolutionary process will reach even greater heights as it will be able to target tumors at their earliest, sub-clinical stage.

IMRT is accomplished using Helios, an inverse optimization planning system, which is one of the fastest and most precise inverse planning systems available. With the conventional, forward planning method, after the clinicians specify the number of beams and their directions, the dose distribution is calculated and evaluated. Iteractive adjustments of beam parameters may follow to improve the dose distribution. This method can become time-consuming and results in less than optimum results.

With Helios, clinicians are able to specify beam and dose distribution attributes, and the system automatically designs beam profiles with tightly prescribed beam delivery constraints. This results in a faster planning process and exquisitely conformed dose distributions.

Fastest treatment

The Varian Clinac 23EX Linear Accelerator is the ultimate platform for high resolution IMRT with the tightest specifications and the highest dose delivery rate resulting in fastest treatment times. This new Linear Accelerator includes a fully integrated Millennium-120 dynamic multi-leaf collimator (MLC), the industry’s only MLC with 120 leaves, capable of delivering the highest resolution IMRT treatments available.

With the MLC-120, the central portion of the field is defined by two sets of 40 leaves, each projecting 0.5 cm at the center of the target. These 0.5-cm leaf widths are the finest in the industry and are ideal for creating smaller and more conformal radiation.

IMRT is used when increased conformality to irregularly shaped tumors is required and when doses to healthy organs are critical. It may also be used in treatments wherein failure patterns are anticipated. Re-treatment of extra-cranial tumors and tumors of the head and neck can be safely accomplished. Multiple metastatic targets to the brain can be treated to high dose simultaneously with good clinical results.

The use of IMRT for benign intra-cranial tumors such as acoustic neuroma and meningioma may be a viable alternative to radiosurgery. Critical structure-threatening tumors such as optic nerve and olfactory groove meningioma can be controlled and symptoms are reversed. Large extensive tumors of the head and neck can be treated to high doses without compromising the salivary gland functions. In prostate treatments, doses can be increased significantly without increased risks or complications.

In the battle against cancer, St. Luke’s offers an integrated solution, which includes all disciplines of radiation treatment. With the SmartBeam IMRT technology, the world-class hospital definitely has the most advanced arsenal to fight cancer.

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(The author chairs the St. Luke’s Medical Center’s Department of Radiation Oncology.)