ASTRO Patient Summary: The Influence of Intrafraction Movement on Margins for Prostate Radiotherapy
When a patient is set up for radiation treatment, the physician applies pinpoint skin marks called "tattoos" to guide the x-ray beams each day and to assure that the correct area is being targeted. It is normal for there to be some movement of the radiation target within the body. In this study, the researchers looked at the movement of the prostate from day to day. In order to assure that the prostate tissue is radiated every day, there is a small amount of tissue surrounding the prostate that is included in the radiation field, the so-called "margin". This way, even if the prostate moves a bit, it would still be in the field. Unfortunately, treating this margin means radiating normal tissue. This study used the Calypso® 4D Localization System, which utilizes electromagnetic tracking with implanted markers. Instead of the tattoos, the patients had 3 tracking devices implanted in the borders of the prostate. These devices, in conjunction with an electromagnetic system, were used to position the patient for treatment each day. The system also monitored position during treatment, allowing for pausing of the treatment and repositioning if necessary. The researchers found that the system allowed them to have a much smaller field of radiation around the prostate because they were able to correct for any movement. This allowed them to spare more healthy tissue than with the tattoo method. This technology is early in development and further study is needed, but results are promising.