Radiation therapy is used predominately to treat cancer and usually in some combination with chemo and/or surgery. The two major ways of delivering radiation are through external beam (ie. with a linear accelerator) or brachytherapy (implanting tiny radioactive seeds directly to the site of the tumor). In our clinic, we have four linear accelerators (linac for short).
|this is one of the linacs we have- radiation shoots out of the yellow circle source|
|first image: PET scan, second: CT scan, third: PET-CT fusion- Bright area indicates location of disease source|
The physicist and/or MD will contour (basically color in 3-D) the major organs in the treatment area.
|organ contours source|
At this time, the physicist takes over and does the bulk of our work: treatment planning. The idea is to use our treatment planning software to experiment with different radiation beam angles, energies, and techniques to design a plan that delivers the maximum amount of dose to the tumor while limiting the dose to all of the healthy tissues.
|one of my treatment plans for a brain cancer case|
|six beams to treat the prostate at center source|
Once the treatment plan meets the goals (or gets as close as possible), we present the plan to the radiation oncologist for approval. Finally, the plans are exported to the linac consoles so that the radiation therapists can treat the patients.
|plan for treating a lung cancer|
Patients are generally treated once a day for several days (traditionally ranging from 10 to 44 treatments). The idea behind this is to allow the normal tissue some time to recover between each treatment. Normal tissue recovers more quickly from radiation and will partially heal itself between treatments while the cancerous tissues do not experience this same recovery.
The rotation I just completed was IMRT/Rapid Arc. These are two special techniques used to allow us to better spare dose to normal tissue. A conventional treatment can treat with any size box or rectangle. The IMRT technique makes use of the set of 120 "leaves" inside the linac. These leaves are 5 mm wide lead blocks that each move independently (and very quickly) across the radiation field while the beam is on to selectively block out and treat desired areas.
|this is a snapshot of the treatment- blue lines indicate the leaf position at this point in time, yellow box jagged outline indicates the starting and ending position of the leaves|
|two 180-degree rapid arc fields|
|ellie's opinion of this post|