Sequential PET/CT with [18F]-FDG Predicts Pathological Tumor Response to Preoperative Short Course Radiotherapy with Delayed Surgery in Patients with Locally Advanced Rectal Cancer Using Logistic Regression Analysis.

Biagio Pecori,Alfredo Budillon,Maria Mormile,Secondo Lastoria,Francesco Bianco,Giampaolo De Palma,Antonio Avallone,Paolo Muto,Daniela Rega,Antonella Petrillo,Marco Celentani,Fabiana Tatangelo,Paolo Delrio,Luigi Aloj,Corradina Caracò

doi:10.1371/journal.pone.0169462

Abstract

Previous studies indicate that FDG PET/CT may predict pathological response in patients undergoing neoadjuvant chemo-radiotherapy for locally advanced rectal cancer (LARC). Aim of the current study is evaluate if pathological response can be similarly predicted in LARC patients after short course radiation therapy alone. Methods: Thirty-three patients with cT2-3, N0-2, M0 rectal adenocarcinoma treated with hypo fractionated short course neoadjuvant RT (5x5 Gy) with delayed surgery (SCRTDS) were prospectively studied. All patients underwent 3 PET/CT studies at baseline, 10 days from RT end (early), and 53 days from RT end (delayed). Maximal standardized uptake value (SUVmax), mean standardized uptake value (SUVmean) and total lesion glycolysis (TLG) of the primary tumor were measured and recorded at each PET/CT study. We use logistic regression analysis to aggregate different measures of metabolic response to predict the pathological response in the course of SCRTDS. Results: We provide straightforward formulas to classify response and estimate the probability of being a major responder (TRG1-2) or a complete responder (TRG1) for each individual. The formulas are based on the level of TLG at the early PET and on the overall proportional reduction of TLG between baseline and delayed PET studies. Conclusions: This study demonstrates that in the course of SCRTDS it is possible to estimate the probabilities of pathological tumor responses on the basis of PET/CT with FDG. Our formulas make it possible to assess the risks associated to LARC borne by a patient in the course of SCRTDS. These risk assessments can be balanced against other health risks associated with further treatments and can therefore be used to make informed therapy adjustments during SCRTDS.

Highlights

In patients with locally advanced rectal cancer (LARC), SCRTDS is known to be a valuable therapeutic option
Formulas make it possible to assess the risks associated to LARC borne by a patient in the course of SCRTDS
When we consider the possibility of aggregating different measures of metabolic behavior at different times with a logistic regression model, we find that the best specification is based on the level of total lesion glycolysis (TLG) at the early PET and on the overall proportional reduction of TLG from the baseline to the delayed PET

Summary

Introduction

In patients with LARC, SCRTDS is known to be a valuable therapeutic option. As compared to traditional neoadjuvant radiochemotherapy (NRC), SCRTDS leads to similar results in terms of the rate of R0 resection and satisfactory results in terms of downstaging and pathological response [1,2,3]. Not all patients benefit from neoadjuvant treatments and using new imaging modalities to make individual assessments of response to therapy could be of great clinical value to adjust subsequent strategies for each individual patient. Such strategies range from a tailored surgical approach, to administering an adjuvant regimen, or even to a wait and see policy without surgery for patients with high surgical risks [10, 11]. Conventional imaging modalities such as computed tomography (CT), magnetic resonance imaging (MRI), and endorectal ultrasound (EUS), successfully used for the initial staging of rectal cancer, perform poorly after neoadjuvant therapies, given that they are unable to accurately distinguish desmoplastic reactions or fibrosis from still viable tumors [12,13,14]

Objectives

Methods

Results

Discussion

Conclusion