Image Guided Radiation Therapy (IGRT)

Radiation is one of the oldest known cancer treatments. Today, two thirds of cancers are treated with Radiation for Local and Regional control of cancer. The challenge facing Radiation therapy has always been to deliver a dose significant to kill the cancer cells without damaging normal healthy tissue. We have progressed from limited view of cancers and lower dose of X-rays, out of fear of causing damage to surrounding normal tissue, to more sophisticated and precise application of technology to target the cancer using 3 –D imaging techniques and dose delivery systems. These improvements were made possible using computer algorithms to guide treatments and new electronic recording system to verify the daily treatment. The ultimate goal of these converging technologies is to allow the physicians to adjust radiation doses based on real time images of the cancer and the surrounding healthy organs.

IMRT- as the name suggests allows the Radiation Oncologists to modulate the intensity of each radiation beam so that each field can have multiple areas of high and low radiation intensity radiation within the same field. This mode of treatment allows limitless possibilities to customize each patient’s treatment based on the tumor characteristics, and limit treatment errors to a greater extent. However, errors may still occur due to patient positioning, Organ motion and breathing. Because most of the planning images were obtained outside the treatment area and surface markings or Tattoos were applied to the skin as reference points, which are always reliable due to the patient variables such as weight gain or loss, Tumor size and position change etc, a greater margin is necessary to compensate.

IGRT- In the last three years, the practice of incorporating sophisticated imaging systems onto the linear accelerators, x-ray arrays and improvement in positioning has added greater accuracy to allow for better targeting of high intensity radiation to the tumor, right prior to the treatment delivery. The combination of C.T, MRI, PET/CT helped in planning and improved the treatment accuracy further by imaging the area of interest in different phases of the respiratory cycle in real time. Electronic portal imaging and Electronic medical records have improved the clinical efficiency and limited treatment errors by providing information that can be viewed and verified by anyone on the care team.

Two types of IGRT are currently in use.

1. Cone Beam CT 

2. Radiographic KV x-rays.

Cone Beam CT- brings the power of CT to the point of delivery, providing up to date volumetric images showing soft tissues, Organs, bony anatomy and alignment in 3-d mode. This 3D functionality of the CT is integrated onto the Linear Accelerator using a secondary, lower energy X-ray source than what is used for treatment delivery. This CT data set is reconstructed through a single gantry motion and displayed before each treatment begins. Because the patient is placed in the treatment position, the differences of tumor location and size between the CT planning images and the current delivery reference images may be determined automatically using advanced registration and positioning software and the treatment couch adjusted automatically before each treatment.

Radiographic Mode Kv imaging works in a similar fashion to cone beam CT, providing high quality, high resolution x-ray images that are 2-dimentional projection images. The same Kv x-ray tubes used in Cone beam CT acquisition may also be operated in an orthogonal plane to the mega voltage beam and associated imager to generate 3D localization and visualization. Soft tissue tumor and overlying bony landmarks can be visualized quickly. Once again computer software may be used to adjust treatment based on these real time x-ray images obtained during the planning stage.

Both of the above methods allow the physicians to compare planning images to images acquired before each treatment and adjust the location and frequency of the multiple beams of IMRT. Another variable however exists-Organ motion during normal breathing. One way is to manually control motion by voluntary breath hold, deep inspiration breathe hold etc. Unfortunately, the effectiveness of these methods are limited by patient compliance especially in patients with COPD.

Gated CT is an electronic method to minimize the effects of breathing during treatment. The systems use multiple CT images through the same axial plane as the tumor in different respiratory motion cycles, acquired during the simulation and are incorporated into the planning phase. The beam delivery is then adjusted so that it is turned on and off at specific intervals based on the stability of the tumor. This way it is possible to immobilize the tumor in one location so that radiation is delivered to this one area while the patient is free to breathe normally. These advances increase the quality of life for patients undergoing head and neck cancer treatments, (reduction of dry mouth) Prostate cancer treatment-avoidance of impotence, incontinence, limits rectal complications etc.

At FRCC and OCCC we are proud to be associated with a team of physicians that provide cutting edge technology to our patients.