At the Centre Hospitalier Universitaire Vaudois (CHUV) in Lausanne, Switzerland, Velocity is helping physicians overcome the limitations of planning software and adaptively plan complex head and neck cancer treatments.
The patient lost so much weight midway through his six weeks of radiation treatment for head and neck cancer that his immobilization mask no longer fit correctly. It began to slip, making proper patient positioning and accurate delivery of the planned dose difficult, if not impossible, even with image guidance. Contouring the intricate structures of the head and neck all over again could be challenging and time consuming. Instead, adapting the treatment plan to the changes in the patient's anatomy as well as to shrinkage in the tumor volume was made easier and faster by Velocity software.
“In the year before acquiring Velocity, we
replanned two treatments. In the first
month with Velocity, we were able to
do four adaptive plans."
Esat Mahmut Özsahin, MD, PhD, CHUV
The value of deformable registration
Clinicians in the radiation oncology department at CHUV started using Velocity because they needed contouring software that was both capable of deformable registration of images and available cost-effectively on more computers.
Deformable registration is important for at least two reasons, says Esat Mahmut Özsahin, MD, PhD, deputy chairman of CHUV's department of radiation oncology. First, it allows doctors to use diagnostic PET images more accurately. Second, by deformably registering and fusing preoperative and postoperative CT images, doctors can be more precise in planning postoperative irradiation, especially in the neck region. "Deformable fusion gives you the exact situation of the initial tumor, where you are going to give a postoperative radiation boost," says Özsahin.
Making adaptive planning feasible in more cases
Deformable image registration is also necessary for adaptive planning in situations where patients undergo significant changes before their course of radiation treatment is completed. "Usually, we finish the treatment as originally planned unless a critical structure such as the spinal cord is involved," says Özsahin. When that happens, the treatment planning process starts from the beginning with a new planning CT and contouring of the same structures again. "With TomoTherapy, we can look dosimetrically and estimate very roughly if we need to do adaptive planning, but without Velocity we would need to manually recontour all the volumes," explains Özsahin. Velocity addresses that problem. It streamlines the process by allowing doctors to propagate contours from the original planningCT to the new one.
Approximately three to four percent of the head and neck patients treated at CHUV experience changes significant enough to warrant adaptive planning. For example, in one of these patients, a large tumor of the oral cavity grew and infiltrated the skin in the two weeks between the planning CT and the start of treatment, requiring an adapted plan. "In the year before acquiring Velocity, we replanned two treatments. In the first month with Velocity, we were able to do four adaptive plans," says Özsahin. "Velocity not only saves time, but you are doing correct treatment. Even if the changes are small, you have the facility with Velocity to adapt to them."
Dose summation -- a Velocity bonus
CHUV chose Velocity specifically for deformable registration. Dose summation came as a bonus for patients who, after being treated with radiation, developed new cancers years later. One of Özsahin's patients is a typical example. Treated for esophageal cancer five years ago, he presented with a pulmonary lesion close to the previously irradiated volume. "With Velocity, we were able to deform the previous planning CT, with all the dosimetry, to the new planning CT," says Özsahin. "We summed the doses and used that information to find the best the best angle to irradiate the new volume while avoiding the previously irradiated volume."
When planning TomoTherapy treatments, CHUV radiation oncologists frequently encounter a limitation that Velocity eliminates. "TomoTherapy planning software doesn't allow us to join dosimetries from two plans. This limitation requires a single plan, including any boosts you may want to give," explains Özsahin. However, if doctors want to wait a few weeks to plan the boost so they can take into account tumor shrinkage or patient weight loss, they can do that using Velocity. "For anal canal cancer, for example, we are delivering 36 Gy with TomoTherapy. Then, we deliver a boost of up to 59.4 Gy using a linear accelerator. We do separate TomoTherapy and linac plans and use Velocity to fuse them so we have the accurate total dosimetry for the patient." This is very new, he adds, and only possible with Velocity.