Computer Code: P70 Credits: 1¼ To receive credit, relinquish attendance voucher at the end of the session.
PRESIDING Peggy J. Fritzsche, MD, San Bernardino, CA President, Radiological Society of North America
ANNOUNCEMENT OF EDUCATION AND infoRAD EXHIBIT AWARDS
INTRODUCTION OF LECTURER Chul S. Ha, MD, Houston, TX Chair of the Subcommittee on Radiation Oncology and Radiobiology, RSNA Scientific Program Committee
ANNUAL ORATION IN RADIATION ONCOLOGY Lester J. Peters, MD, Melbourne, Victoria, Australia
THE INVALUABLE ROLE OF PET IN RADIATION ONCOLOGY
After this lecture, attendees should be able to:
Define the role of FDG PET in selection of patients with nonsmall cell lung cancer and advanced head and neck cancer for definitive (chemo)radiotherapy and in planning of radiotherapy.
Understand the prognostic significance of a complete metabolic response to treatment as opposed to classical anatomic response.
Explain the value of PET in situations where there are equivocal findings at conventional imaging in treatment follow-up.
Discuss the role of PET tracers for tumor hypoxia in predicting the outcome of (chemo)radiotherapy.
Appreciate the potential utility of other novel PET tracers to measure radiobiological parameters of tumors. (Disclosure: This presentation will make reference to certain patients treated with an experimental hypoxic cell cytotoxin, Tirapazamine, manufactured by Sanofi-Synthelabo. Dr Peters has been a consultant to Sanofi-Synthelabo in the design and conduct of a Phase III trial of Tirapazamine.)
Since 1996 my group has conducted a series of prospective studies at the Peter MacCallum Cancer Institute to investigate the role of PET in radiation oncology. This lecture will briefly review our experience in patients referred for definitive (chemo)radiotherapy for non-small cell lung cancer and for local-regionally advanced squamous cell carcinoma of the head and neck. Potential new applications of this technology will then be previewed.
In patients with non-small cell lung cancer, we have shown that FDG PET can exclude patients with distant metastases or a synchronous primary tumor from futile radical therapy, identify patients with resectable disease who should undergo primary surgery, help ensure that all gross disease is contained within a tolerable high-dose radiotherapy volume, and identify patients with residual disease or localized relapse for possible salvage surgery. We have demonstrated a highly significant predictive value for PET staging relative to conventional imaging and have shown that a complete metabolic response at PET is strongly correlated with long-term survival. We have also demonstrated that post-irradiation effects do not impair the ability to evaluate therapeutic response if simple interpretive principles are applied.
In patients with stage III-IV squamous cell carcinoma of the head and neck, FDG PET also has utility in initial staging and treatment planning, but it is particularly valuable in therapeutic monitoring after intensive chemo-radiotherapy. We have shown that a complete metabolic response 12 weeks after therapy allows safe observation of a regressing neck mass, thus avoiding unnecessary or futile surgery. PET also accurately identifies recurrent residual disease in sites with equivocal structural imaging findings in follow-up. PET tracers of tumor hypoxia (FMISO and FAZA) have been studied in the context of clinical trials with the selective hypoxic cell cytotoxin, tirapazamine. Preliminary results indicate that resolution of imageable tumor hypoxia is a prerequisite for local disease control.
The advent of integrated PET/CT scanners and the expanding menu of tracers available can only increase the role of PET in radiation oncology. The concept of treatment planning based on radiobiological parameters rather than simple physical tumor volumes is already gaining credence. Besides hypoxia, tracers such as FLT to measure proliferative cellular activity and FET to evaluate protein synthesis may soon be available. Access to PET imaging should be considered an integral part of modern radiation oncology practice.