Abstract
Aim To prospectively evaluate histological significance and predictive
value of changes in apparent diffusion coefficient (ADC) and 18F-FDG
PET/CT parameters in locally advanced rectal cancer (LARC) after neoadjuvant
radiochemotherapy (RCT).
Methods Twenty-one patients with untreated LARC underwent pre-RCT and
post-RCT 18F-FDG PET/CT and diffusion-weighted magnetic resonance
imaging (DW-MRI), followed by surgery. For both datasets, two readers measured
the tumor SUVmax, SUVmean, MTV, TLG, ADCmin, ADCmean, and respective differences
(∆SUVmax, ∆SUVmean, ∆MTV, ∆TLG, ∆ADCmin, ∆ADCmean) for the whole tumor. Tumor
regression grade according to Mandard (TRGm), percentage of residual tumor cells
and fibrosis were estimated by two pathologists in consensus. Relationship
between parameters was assessed on stepwise multivariate regression analysis and
ROC curve analysis to evaluate their performance and predict the treatment
response.
Results Eighteen LARCs were analyzed. SUVmax and SUVmean decreased from
21.3 ± 8.9 to 9.3 ± 5.5 g/mL, (p = 0.0002) and 12.3 ± 5.1 to 5.4 ± 3.1 g/mL,
(p = 0.0002), respectively, after RCT, whereas ADCmin and ADCmean increased from
396 ± 269 to 573 ± 313×10–6 mm2/s (p = 0.014) and
1159 ± 212 to 1355 ± 194×10–6 mm2/s (p = 0.0008),
respectively. TRGm and percentage of residual tumor cells independently
correlated with post-RCT SUVmean (β = 0.73 and β = 0.76, p < 0.001) and
post-RCT SUVmax (β = 0.72 and β = 0.78, p < 0.001), whereas percentage of
fibrosis independently correlated with ∆ADCmean (β = 0.38, p = 0.008). Post-RCT,
SUVmax and SUVmean performed well in predicting TRGm < 3 and residual tumor
cells ≤ 20 %. ΔADCmean predicted fibrosis > 70 % well.
Conclusion Post-RCT SUVmean, SUVmax and ∆ADCmean are complementary
parameters for respectively evaluating residual tumor burden and amount of
fibrosis in LARC. However, only SUV independently correlated with TRGm.
Response of locally advanced rectal cancer (LARC) to
radiochemotherapy: DW-MRI and multiparametric PET/CT in correlation with
histopathology
