FDG-PET/CT aids in radiation therapy planning

Mar 4, 2008

For patients with head and neck carcinoma, using FDG-PET/CT for staging and treatment planning shows "clear advantages" because of the precise information it provides on tumor localization and the assessment of nodal and metastatic progress, according to researchers from Wisconsin.

The hybrid imaging modality's prowess leads to "more accurate staging, appropriate changes in radiation therapy planning, and potentially translates into superior outcomes for patients," the researchers said.

The findings come from a study conducted at the Medical College of Wisconsin in Milwaukee to determine FDG-PET/CT's ability to evaluate clinical outcomes for patients receiving FDG-PET/CT-guided definitive radiotherapy, with or without chemotherapy. The study was published in the International Journal of Radiation Oncology, Biology, Physics (March 1, 2008, Vol. 70:3, pp. 678-684).

While CT has been the imaging modality of choice in the past for staging and radiotherapy planning for head and neck cancer, FDG-PET has demonstrated an ability to detect primary tumors, lymph nodes, and distant metastatic disease more accurately than CT.

FDG-PET alone, however, does not always provide adequate information on anatomic structures and the confounding effect of FDG accumulation in certain areas, such as muscles, vocal cords, and salivary glandular tissue. The integration of CT makes both modalities more complete.

"The PET scan has shown more sensitivity and specificity in identifying a tumor and lymph nodes than CT scans," said Dr. Dian Wang, an assistant professor of radiation oncology and a co-author of the study. "So given the excellent accuracy of PET scans, we thought it would be a good idea to combine CT and PET, and utilize that information to better define where the tumor is, so we can provide accurate radiation treatment."

Study parameters

The researchers reviewed 42 patient cases from December 2002 to August 2006. The patients, who had a median age of 55 years, were diagnosed with primary squamous cell carcinoma of the head and neck. All 42 patients received PET/CT imaging for staging and as part of their radiotherapy planning.

Follow-up intervals from the initiation of cancer treatment ranged from seven to 53 months, with a median review of 32 months. After two years, overall survival was 83% and disease-free survival was 71%. After three years, overall survival as 74% and disease-free survival was 67%. Treatment failed for seven of the 42 patients in the study. For those seven cases, the mean time to cancer recurrence was slightly more than nine months.

The study demonstrated "clear advantages of integrated PET/CT imaging in staging and treatment planning for head and neck carcinoma.... The important information it provides improves anatomic tumor localization, and helps assess the extent of nodal and metastatic spread. This leads to more accurate staging, appropriate changes in radiation therapy planning, and potentially translates into superior outcomes for patients," the researchers concluded.

Survival outcomes for the 42 patients in this study are comparable to published survival rates for patients with head and neck cancer, they stated.

Clinical implications

"The selling point to the patient is that we can actually treat the tumor, because the target is much more accurate (with PET) than with CT," Wang added. "Once the patient hears that, the patients want the PET scan."

The group also noted that all 42 patients had abnormal FDG uptake on the treatment planning PET scans, so the maximum standard uptake volume (SUV) of a primary tumor, adenopathy, or both on PET did not correlate with tumor recurrence. Treatment failures had a mean SUV of 12, compared with a mean SUV of 11.7 for all patients.

The fact that the maximum SUV of a primary tumor, adenopathy, or both "was not predictive of risk of disease recurrence may suggest that more metabolically active areas on PET may not warrant dose escalation," the researchers noted.

It was "surprising that we did not see the maximum uptake of FDG associated with clinical outcome like local recurrence and survival," Wang added. "We think that it may be because of the small size of the study, and it is possible that the uptake may not give high volume for the therapy."

More research in this area is warranted, he said.

IMRT benefits

Wang also sees PET/CT as a benefit to intensity-modulated radiotherapy (IMRT) in cancer treatment. Because radiation toxicity remains such a critical issue of radiation therapy planning, IMRT is one technique to target specific tumors with high doses of radiation, while not adversely affecting nearby healthy tissue and organs.

"In our study, we have enhanced [IMRT] technology by improving the target definition," Wang said. "We are using FDG-PET/CT to better define where the tumor is. The toxically radiated volume also has been reduced. When it is combined with advanced IMRT technology, we believe it helps makes the survival profile better than regular IMRT."

By Wayne Forrest
AuntMinnie.com staff writer
March 5, 2008

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