Positron Emission Tomography after Three-Dimensional Conformal Radiation

William Levin, MD
University of Pennsylvania Cancer Center
Last Modified: November 6, 2001

Presenter: K.E. Rosenzweig
Presenter's Affiliation: Memorial Sloan-Kettering Cancer Center, New York
Type of Session: Scientific

Frequently, clinicians have difficulty interpreting CT scans and MRI's done on patients with cancer, particularly after surgery or radiation therapy. Positron emission tomography (PET) is an imaging technique that measures glucose metabolism in cells. There is evidence that tumor cells have increased uptake and metabolism of these sugar molecules, as compared to non-malignant cells. Fluorodeoxyglucose (FDG)is the radioactive tracer used in this technique. Standard uptake values (SUV) measure the intensity of tracer identified on the PET study. It is generally accepted that a higher SUV is more likey to represent malignancy as opposed to scaring or inflammation.

Materials and Methods

  • In this study, PET was used to evaluate response after treatment of NSCLC (non-small cell lung cancer) with three-dimensional conformal radiation therapy (3D-CRT).
  • This was a review of 50 patients, the majority of which had stage III disease.
  • Median radiation dose was 70 Gy.
  • Median age was 68.
  • The majority of patients also received chemotherapy.
  • Median time to first post-treatment PET scan was 4 months.
  • Local failure was determined by clinical assessment, pathology and computed tomography.
  • SUV's were calculated for the primary tumor in all patients.


  • Median follw-up was 9 months.
  • Patients with a post-treatment SUV of less than or equal to 3.5 and greater than 3.5 had subsequent local failure rates of 17% and 77%, respectively. This was a highly significant difference.
  • Patients who had a subsequent local failure had an increse in the SUV.
  • In fact, all patients with SUV >3.5 failed.
  • Patients with SUV <3.5 had longer survival than those >3.5.

    Author's Conclusions

  • A decrease in post-treatment SUV to <=3.5 on PET scan after 3D-CRT is highly predictive for subsequent local control.
  • This suggests that PET scans can be used to assess treatment response after RT.

    Clinical/Scientific Implications

  • The ability of PET to distinguish between cancer and non-malignant entities continues to be evaluated.
  • Further studies should be done to compare pretreatment PET scans with post-treatment scans in patients with lung cancer.
  • Additionally, administration of the PET scan and interpretation of results must be done by a dedicated, experienced team.
  • The role of PET scans in the diagnosis, treatment planning, and follow-up of patients with lung cancer will continue to evolve as more studies on this important technology are reported.

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