Intratreatment FDG-PET During Radiation Therapy for Gynecologic and Gastrointestinal Cancers

Overview

This study expands on protocol (NCT01908504"PET adaptive RT") designed to evaluate the utility of adaptive PET-CT planning for radiation therapy (RT). Radiation therapy is used in many malignant diseases as a curative treatment modality. However, critical normal tissue is often in close approximation to disease, and portions of such tissue must receive high doses of radiation for appropriate treatment. Positron Emission Tomography (PET) adapted radiation therapy, as defined in the current protocol, may allow for a means of determining the eventual response to therapy, at a time point when adaptation of treatment plan may be possible to improve outcomes. This protocol will build upon the findings the previous protocol (NCT01908504 "PET adaptive RT") that evaluated the utility of intra-treatment PET imaging in multiple types of cancers. The current focus will be more specific to certain types of gastrointestinal and gynecologic cancers treated with RT, identified from the prior study to warrant further research.

Intra-treatment PETs have only recently been studied in small pilot series. In rectal cancer, a prospective trial from MSKCC demonstrated that a PET-CT obtained in the second week of neoadjuvant chemoradiotherapy was able to discriminate sub-optimal responders with a sensitivity of 94% and an accuracy of 78%, though the most useful metric was a novel "visual response score" based on interpreting radiologists scoring rather than more established objective data available from PET, like SUV. A study from China in non-small cell lung cancer found that decreases in SUV and MTV on intra-treatment PET-CTs after 40Gy of chemoradiation therapy were significantly greater in patients responding to treatment by post-treatment RECIST criteria. For head and neck cancers, a Belgian study found that intra-treatment SUVmax at 47Gy was associated with significant differences in overall survival. Therefore, there is emerging evidence that an intra-treatment PET may also be of significant prognostic utility, at an early enough time point to potentially alter treatment accordingly. All participants will be required to complete two research PET scans in addition to standard of care planning CT's for radiation therapy. For all subjects with cancer of the cervix and vulva an intra-treatment PET-CT will be obtained and used to develop a volume adaptive treatment plan for the remainder of the course. Subjects with esophageal and anal canal cancer will have an adapted plan if the treating radiation oncologist determines an adapted plan is clinically relevant.