3D Conformal Radiation Therapy
The development, implementation, and use of 3D treatment planning and delivery techniques have been major research interests at academic hospitals for more than twenty years. Two advances that led to the interest in 3D radiotherapy were the development of CT scanners in the 1970s and affordable, high-speed computers in the 1980s.
3D anatomy
CT scanners are important since they can be used to obtain a detailed 3D description of a patient's internal anatomy. The 3D information is used to create elaborate 3D models of the tumor volume and any organs to be protected during irradiation. The Department of Radiation and Cellular Oncology at The University of Chicago owns and operates its own high-speed, spiral CT scanner. Roughly 80% of our patients are scanned in the department for the purpose of 3D conformal radiotherapy treatment planning.
In the first movie, you can see a series of CT images of a patient treated for head and neck cancer. The movie starts at the level of the shoulders and proceeds through the neck and into the head and eyes. In the second movie, you see a model of the patient built from the CT scan. The model includes a tumor volume, spinal cord, eyes and optic nerves.
3D treatment planning
The goal of 3D conformal radiotherapy treatment planning is to shape the spatial distribution of the prescribed radiation dose so that it matches the shape of the 3D target volume (cancerous cells) as closely as possible, while at the same time, minimizing dose to surrounding normal anatomy (healthy cells). At The University of Chicago, we use the PlanUNC (or PLUNC) system for 3D treatment planning. PLUNC was developed at the University of North Carolina. Important features of the system include a beam's-eye-view display, the ability to create digitally-reconstructed radiographs, fully 3D dose calculations, and plan comparison tools, such as dose-volume histograms.
Beam's-eye-view display
A beam's-eye-view display (BEV) is a computer-generated image that presents a patient's anatomy as it would appear to a viewer located at the radiation source and looking toward the isocenter (link to high-precision RT). Like the radiation beam, BEV images are fully divergent. Dosimetrists use BEV images as an aid to decide which beam orientations yield the best view of the target volume without irradiating too much normal anatomy. They also use BEV images to design shielding blocks to protect normal anatomy from unnecessary irradiation.
Digitally-reconstructed radiographs
A digitally-reconstructed radiograph (DRR) is similar to a BEV, except a DRR is a computer-generated image that shows how bony anatomy would appear to a viewer located at the radiation source and looking toward the isocenter. We use DRR's to verify that the treatment plan is being delivered with high precision (link to high-precision RT).
3D dose calculations
After the BEV display is used to aim several radiation beams at a patient's tumor, PLUNC is used to calculate the resulting distribution of radiation dose in the patient. The calculations are fully 3D since they use 3D descriptions of the radiation beams and 3D models of the patient's anatomy. Dosimetrists and radiation oncologists use the results to evaluate whether the treatment plan delivers adequate dose to the tumor, without subjecting healthy organs to an unnecessary radiation hazard.
Dose volume histograms
In most cases, dosimetrists design several different treatment plans for each patient. Dose volume histograms are used as an aid to decide which treatment plan is best suited for an individual patient. In its most basic form, the histograms reveal what fraction of a given organ is irradiated to a given dose of radiation. For example, lung tissue is destroyed by a radiation dose of 22 Gy. To preserve normal lung function, we use the histograms to ensure that no more than 50% of a patient's total lung volume is irradiated to a dose of 22 Gy or higher.
Using PLUNC, we design sophisticated 3D treatment plans that are uniquely tailored to each patient's specific needs. In addition, our group of medical physicists and computer programming experts are working continually to add new features to the system. The goal is to ensure that our patients receive the highest quality care available.
Our providers apply all their experience and training, the latest research results, and the most advanced technologies to offer you the best cancer diagnosis and treatment available today.