Consequences of additional use of contrast-enhanced 18F-FDG PET/CT in target volume delineation and dose distribution for pancreatic cancer

Objective:

To compare the differences between contrast-enhanced (CE) fluorine-18 fludeoxyglucose (¹⁸F-FDG) positron emission tomography (PET)/CT and CECT in target volume delineation and radiotherapy (RT) dose distribution, and to evaluate the sparing of organs at risk (OARs) in the treatment plan of locally advanced pancreatic cancer (LAPC).

Methods:

21 consecutive patients with LAPC with histologically or cytologically confirmed adenocarcinoma underwent both non-CECT and ¹⁸F-FDG scans; 11 of whom also underwent CECT scans. Intensity-modulated RT plans (prescribed dose, 54 Gy) were constructed to cover the corresponding gross tumour volume (GTV). The differences among GTV_CT, GTV_PET, GTV_PET-CT and OARs in these different image sets as well as the uniformity of target dose were analysed.

Results:

The mean non-CE GTV_CT, GTV_PET and GTV_PET-CT were 76.9 ± 47.8, 47.0 ± 40.2 and 44.5 ± 34.7 cm³ (mean ± standard deviation), respectively. The non-CE GTV_PET-CT was significantly smaller than the non-CE GTV_CT (p < 0.001). The CE GTV_PET-CT was significantly smaller than the CE GTV_CT (p = 0.033). For both the non-CE GTV_CT and the CE GTV_CT, the intestine V₄₀ (the percentage of the intestine volume irradiated by 40 Gy), intestine V₅₀, intestine D_max (the mean maximum dose), cord D_max, left kidney V₃₀, right kidney V₃₀, left kidney D_mean (the mean dose), right kidney D_mean and liver V₃₀ were 5.90%, 2.52%, 5500 cGy, 2194 cGy, 3.40%, 0.68%, 747 cGy, 550 cGy and 5.37%, respectively. There are significant differences between the non-CE CT and the non-CE PET-CT in intestine D_max (p = 0.023) and right kidney D_mean (p = 0.029).

Conclusion:

Co-registration of ¹⁸F-FDG PET with CECT may improve the accuracy of GTV delineation in LAPC and might reduce the adverse effect of irradiation.

Advances in knowledge:

Individual adaptation of RT based on functional CE ¹⁸F-FDG PET/CT imaging is possible and highly promising in LAPC.Pancreatic cancer (PC) is the fourth most common cause of cancer death in the USA with 5-year overall survival (OS) rates of <5%.¹ PC is a notoriously insidious disease, and about 70% of patients newly diagnosed with this malignancy are not amenable to curative surgery.² Concurrent chemoradiotherapy is the main treatment for locally advanced or recurrent PC, and radiotherapy (RT) plays a key role for local control. There are still many unresolved issues related to the delineation of the gross tumour volume (GTV) in locally advanced PC (LAPC), such as the difficulty in distinguishing the vasculature from tumour parenchyma, defining the tumour boundary on contrast-enhanced CT (CECT) in the absence of functional positron emission tomography (PET) imaging, and the presence of adjoining organs at risk (OARs), such as the small intestine, spinal cord, kidney and liver. The delineation of the GTV based on PET-CT fusion images could improve RT planning by reducing the target volume and the exposure volumes of the respective OARs and safely escalating the target radiation dose. Conventional enhanced CT scanning could not identify the extent of local tumour and lymph node invasion from peripheral structures precisely,³ which may result in inaccurate target delineation.Our study aimed to explore the value of the CE fluorine-18 fludeoxyglucose (¹⁸F-FDG) PET-CT fusion images for target volume delineation, dose distribution in OARs and the uniformity of target dose compared with the results of CT scan-based plans in LAPC.