Radiation Oncology

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Three-dimensional Conformal Therapy 

Introduction

External beam radiation uses high energy photons  to destroy cancer cells within the body.  The photons are in many ways similar to those used in diagnostic x-ray (chest x-ray) or rays from the sun  except they are much higher in energy. The beams are generated by a device called a linear accelerator and deposit radiation dose as they pass through a particular portion of the body. The radiation damages the DNA of cells which ultimately leads to their destruction.  Normal (non cancerous) cells are much better able to repair this type of damage and therefore survive. Like the light from a flash light, radiation dose is delivered only when the machine is on and the patient is not radioactive once the machine is turned off.

What is Conformal Therapy?

One of the most important advances in the delivery of external beam radiation therapy has been the development of three-dimensional conformal therapy.  Traditional conventional radiation therapy is targeted only by the location of  bones seen on plain x-rays which cannot show the actual tumor.  These bony landmarks do not show the unique anatomy of any particular patient. The fields therefore tend to be  large, square shaped  and generic.  This results in more unnecessary radiation to the surrounding tissues.

Conversely, conformal therapy allows for the customization of treatment for each particular individual.  Every person has a unique tumor size, shape, as well as location of  nearby normal organs. Conformal radiation is the process of accurately determining this unique anatomy and tailoring the radiation treatment such that it "conforms" to every patient.  Where conventional therapy would treat all patients with the same big square beams, conformal radiation treats a round tumor by round beams and an elongated  shaped tumor with an elongated shaped beams.  This technology is now applied to nearly all tumor sites.( Breast/Gastrointestinal/Prostate/CNS/Lung/Gyn)

Conformal treatment is a complex process which involves three basic components.  The first is patient  immobilization.  Special body casts are created to improve the reproducibility of the patients position on the machine.  The second step is computed tomography (CT) assisted organ identification.   The precise location and shape of the tumor as well as the surrounding tissues is determined.  The final step involves the use of powerful computer tools to generate the specific beams  which will differentially deliver the radiation to the tumor while sparing the surrounding normal tissues.  Specialized blocks are created to shape the beams which have been generated.  This improvement in technology  means that the radiation beams can be made the smallest size possible to safely treat the cancer while avoiding normal tissues.  The less normal tissue irradiated results in less unwanted side effects.
 

The Treatment Process

Simulation: This is the first step of conformal radiation.  The total time needed for this first day is about 90 minutes.  A custom body mold is made that is customized for each particular area of treatment. By lying in the mold, you will be in the same position on the treatment table every day - up to 67% more accurately than without the cast.  Next is the CT scan in our department. Claustrophobia, a fear of close places, is rarely a problem.  Contrast dye is often used during the CT scan to improve the image of the tumor on the film.  Please tell your doctor or nurse if you are allergic to contrast dye or iodine. Small tattoos the size of a pencil point are then placed  to be used every day for accurate positioning of the treatment beams.  They are permanent but small and in locations that will likely not be publicly visible.
 

3-D Treatment planning:  This process takes place behind the scenes over a 1 week period -you do not need to be present.  The CT scan taken at simulation is examined by the physician who contours the important body organs which are then inputted into the computer.  The physician then directs specially trained physicists and therapists in designing the conformal shape of the radiation beams.  This is the custom tailoring - the radiation beams are designed to mimic the shape of the target with the narrowest margin of normal tissue possible.

Set-up: We check the accuracy of your specific treatment on the actual therapy machine before starting radiation.

Radiation Treatments:  The time course of conformal radiation depends on the disease site being treated but in general ranges from 5 to 7 weeks, Monday through Friday, except for major holidays.  The actual time in the treatment room is 10-15 minutes. Please allow 45-60 minutes total each day for parking, dressing and small delays.  Treatment times are flexible from 7:30 - 5:30 - most requests for a specific time of day can be met.