Study: Adaptive RT proves easier than expected in correcting IMRT

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Adaptive radiotherapy (ART) for head and neck cancer treatment may solve some of the problems inherent to intensity-modulated radiotherapy (IMRT) and benefit patient with less technical difficulty than previously believed, according to preliminary findings released online Feb. 9 in the International Journal of Radiation Oncology Biology Physics.

While IMRT is the current standard-of-care treatment, it has a major limitation. Since it is based entirely on a CT or MRI scan taken before the treatment begins, and the typical course of radiation treatment for oropharynx cancer lasts six to seven weeks, standard IMRT cannot compensate for common changes that take place in a patient’s body during this time, such as weight loss, shrinkage of tumor or gradual movement of normal tissues. The inability of standard IMRT to keep up with these changes may lead to unanticipated toxicity or a complete miss of the tumor.

The new trial, sponsored by the National Cancer Institute, started patients on standard IMRT and then researchers took CT scans while patients were positioned in the radiation treatment room each day, so they could monitor changes in tumor and normal tissues during the entire course of treatment. Computerized techniques were then used to adapt treatment if there were significant tumor or body changes that could affect quality of treatment.

“This is the first prospective clinical trial of its kind to gauge how ‘refitting’ of IMRT to a patient’s body actually impacts care for a patient who has head and neck cancer,” wrote David Schwartz, MD, vice-chair of radiation medicine at the North Shore-Long Island Jewish (LIJ) Health System, associate professor at the Hofstra North Shore-LIJ School of Medicine, and a senior investigator at The Feinstein Institute for Medical Research.

Twenty-four patients were enrolled in the trial and data for 22 of these patients were analyzed with at least 12 months follow-up. Primary site was base of tongue in 15 patients, tonsil in six patients, and glossopharyngeal sulcus in one patient. Twenty patients (91 percent) had American Joint Committee on Cancer Stage IV disease. Of the patients, 21 (95 percent) received systemic therapy.

All patients required at least one ART replan because of tumor and normal tissue changes; eight patients (36 percent) required a second ART replan. For the patients who required one adaptive replan, parotid salivary glands had shrunk by an average of 16 percent and tumors had shrunk by 5 percent by the time of the replan. For the patients who required a second adaptive replan, parotid glands and tumors had shrunk by 24 percent and 14 percent, respectively. Most ART replans were completed within one day.

With a median follow-up of 31-months, the researchers reported there has been no primary site failure and one nodal relapse, yielding 100 percent local and 95 percent regional disease control at two years.

“What most encouraged us was that ART appears effective with only one or two additional replans,” said Schwartz. “This means that ART does not have to be overly burdensome or expensive to make a difference. This is something that is feasible, and could eventually make a real-world difference in many clinics.”