Prospective assessment of primary rectal cancer response to preoperative radiation and chemotherapy using 18-fluorodeoxyglucose positron emission tomography

PURPOSE: The purpose of this prospective study a-as to determine the abilit y of fluorine-18 fluorodeoxyglucose positron emission tomography to assess extent of pathologically confirmed rectal cancer response to preoperative r adiation and 5-fluorouracil-based chemotherapy. METHODS: Patients with prim ary rectal cancer deemed eligible for preoperative radiation and 5-fluorour acil-based chemotherapy because of a clinically bulky or tethered tumor or endorectal ultrasound evidence of T3 and/or N1 were prospectively enrolled. Positron emission tomography and CT scans were obtained before preoperativ e radiation and 5-fluorouracil-based chemotherapy (5,040 cGy to the pelvis and 2 cycles of bolus 5-fluorouracil with leucovorin) and repeated four to fire weeks after completion of radiation and 5-fluorouracil-based chemother apy. In addition to routine pathologic staging, detailed assessment of rect al cancer response to preoperative radiation and 5-fluorouracil-based chemo therapy was performed independently by two pathologists. Positron emission tomography parameters studied included conventional measures such as standa rdized uptake value (average and maximum), positron emission tomography-der ived tumor volume (size), and two novel parameters: visual response score a nd change in total lesion glycolysis. RESULTS: Of 21 patients enrolled, pro spective data (pretreatment and posttreatment positron emission tomography, and complete pathologic assessment) were available an 15 patients. All 15 demonstrated pathologic response to preoperative radiation and 5-fluorourac il-based chemotherapy. This was confirmed in 100 percent of the cases by po sitron emission tomography compared with 78 percent (7/9) by CT, In additio n, one positron emission tomography parameter (visual response score) accur ately estimated the extent of pathologic response in 60 percent (9/15) of c ases compared with 22 percent (2/9) of cases with CT. CONCLUSIONS: This pil ot study demonstrates that fluorine-18 fluorodeoxyglucose positron emission tomography imaging adds incremental information to the preoperative assess ment of patients with rectal cancer. However, further studies in a larger s eries of patients are needed to verify these findings and to determine the value of fluorine-18 fluorodeoxyglucose positron emission tomography in a p reoperative strategy aimed at identifying patients suitable for sphincter-p reserving rectal cancer surgery.