Optimization of temporal phase in multi-phase contrast-enhanced MRI for gross tumor volume determination in pancreatic cancer radiotherapy.

BACKGROUND

Pancreatic cancer is characterized by an insidious onset and rapid progression, and the accurate determination of the gross tumor volume (GTV) constitutes a critical prerequisite for ensuring the efficacy of radiotherapy. Multiphase contrast-enhanced magnetic resonance imaging (CE-MRI) enables the dynamic visualization of tumor hemodynamic perfusion characteristics; however, the tissue discrimination capability varies substantially across different enhancement phases. To date, there is no universal consensus on the optimal imaging phase for GTV determination in pancreatic cancer. This study aimed to quantitatively analyze the differences in imaging and GTV determination of pancreatic cancer using multiphase CE-MRI, thereby providing a basis for selecting the optimal phase for GTV determination.

METHODS

Thirty patients with advanced pancreatic cancer [American Joint Committee on Cancer (AJCC) stage III-IV] who underwent magnetic resonance (MR) simulation were retrospectively enrolled in this study. MR T1-weighted images (T1WI) and contrast-enhanced T1-weighted images (CE-T1WI) were obtained at 15 s, 45 s, 75 s, 150 s, and >20 min after contrast injection. The GTV was determined from these different image sequences and named GTV-T1WI, GTV-15 s, GTV-45 s, GTV-75 s, GTV-150 s, and GTV-20 min. Differences in mean signal intensity (SI), SI contrast, volume, and shape among the different GTVs were compared. Normal pancreatic tissue was defined as a 1 cm3 region of interest of the parenchyma, strictly excluding blood vessels and pancreatic ducts.

RESULTS

The mean SI of the GTV was lower than that of the normal pancreatic tissue at each time phase (P<0.05), ranging from 9.93% to 45.01%. At CE-T1WI-15 s, the SI contrast between GTV and normal pancreatic tissue was the highest at 0.45±0.10, significantly superior to the T1WI (0.34±0.13, P<0.001). The GTV-15 s volume was 21.02±12.43 cm3. Compared with CE-T1WI-15 s, the SI contrast between the GTV and normal pancreatic tissue on T1WI and CE-T1WI-45 s to CE-T1WI-20 min decreased by 22.42-77.43% (P<0.05). Compared with GTV-15 s, the volume of GTV-T1WI and GTV-45 s-GTV-20 min decreased by -14.10-22.75%. Except for GTV-15 s and GTV-45 s, GTV-15 s and GTV-75 s, and GTV-45 s and GTV-75 s, the differences in GTV volumes in the other phases were statistically significant (P<0.05). The shape change trend of GTV at different phases was consistent with the volume compared with that of GTV-15 s. The Dice similarity coefficients (DSCs) of GTV-T1WI, GTV-45 s, GTV-75 s, GTV-150 s, and GTV-20 min were 0.74±0.10, 0.79±0.11, 0.76±0.13, 0.72±0.15, and 0.64±0.13, respectively.

CONCLUSIONS

The CE-T1WI-15 s sequence demonstrated significant improvements in SI contrast and boundary definition. Consequently, it holds significant potential as an optimal sequence for GTV determination in pancreatic cancer radiotherapy, warranting further validation in larger cohorts.