Treating Soft Tissue Carcinoma with Stereotactic Body Radiotherapy

(Palo Alto, CA, USA). A 72-year-old man with Merkel cell carcinoma was treated for a soft tissue tumor in his thigh, which had developed close to where a similar tumor had been treated with conventional radiotherapy six months earlier.

"In this case, it was important that we avoid exposing the previously-treated area to any additional radiation,” said Todd Scarbrough, M.D., radiation oncologist and director of the MIMA Cancer Center. "Using RapidArc, we completed each of his treatment sessions in just five minutes, including imaging and treatment. In the past, using conventional IMRT, this type of treatment would have required 30 minutes per session to complete.”

RapidArc makes it possible to quickly deliver an advanced image-guided, intensity-modulated radiation therapy (IMRT) treatment with one 360° rotation of the treatment machine around the patient. In this case, however, the physicians designed a treatment that was delivered with just half a rotation around the patient. "The tumor was near the surface of his thigh, so a full arc would have exposed too much of his normal leg to the treatment beam,” Dr. Scarbrough said.

Dr. Scarbrough's team planned the RapidArc treatment using Varian's Eclipse treatment planning software, which allowed them to visualize how the dose would be distributed within the patient's leg. "The RapidArc plan gave us a dose distribution that was superior to what we could have achieved with traditional IMRT,” Dr. Scarbrough said. "Eclipse made it easy to create a plan that would avoid the previously-irradiated tissues. We just superimposed the dose distribution from his earlier treatments onto the new CT [computed tomography] scans, created a structure out of that area, and instructed the software to avoid it as if it were a critical organ. It was very easy to do.”

Stereotactic body radiotherapy involves delivering higher-than-usual doses of radiation to a tumor over a shorter-than-usual timeframe. It requires great accuracy and precision, both in terms of targeting and in terms of beam-shaping, to minimize the exposure of surrounding tissues. MIMA's RapidArc protocol achieves the necessary level of precision. Three-dimensional (3D) X-ray images of the targeted area are used to fine-tune patient positioning prior to each treatment. Then, as the treatment machine rotates around the patient, the treatment beam is continually shaped and reshaped to match the dimensions of the tumor.

"Any time you have a spherical lesion that is deep within the body, and you want to deliver a high dose, RapidArc is going to be the ideal way to treat,” Dr. Scarbrough said. "Our plan is to use RapidArc any time the treatment plan gives us a dose distribution that is equal to or better than what we can get with standard IMRT, because RapidArc is so much faster. And that's much better for our patients.” Dr. Scarbrough's team is now working on RapidArc treatment plans for a prostate and a lung cancer case scheduled to begin treatment later this month.

Melbourne Internal Medical Associates offers patients medical care throughout Brevard County, FL, USA. The MIMA Cancer Center's department of radiation oncology treats 80-90 patients per day, and has been offering image-guided radiotherapy (IGRT) using technology from Varian Medical Systems since April 2005.

Varian Medical Systems is a world-leading manufacturer of medical devices and software for treating cancer and other medical conditions with radiotherapy, radiosurgery, proton therapy, and brachytherapy. The company supplies informatics software for managing comprehensive cancer clinics, radiotherapy centers, and medical oncology practices.

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