Hypofractionated ablative radiotherapy for locally advanced pancreatic cancer

Abstract

The role of radiation in locally advanced unresectable pancreatic cancer (LAPC) is controversial. Randomized trials evaluating standard doses of chemoradiation have not shown a significant benefit from the use of consolidative radiation. Results from non-randomized studies of 3-5-fraction stereotactic body radiotherapy (SBRT) have been similar to standard chemoradiation, but with less toxicity and a shorter treatment time. Doses of SBRT have been reduced to subablative levels for the sake of tolerability. The benefit of both options is unclear. In contrast, ablative doses can be delivered using an SBRT technique in 15-28 fractions. The keys to the delivery of ablative doses are computed tomography (CT) image guidance and respiratory gating. Higher doses have resulted in encouraging long-term survival results. In this review, we present a comprehensive solution to achieving ablative doses for selected patients with pancreatic tumors by using a combination of classical, modern and novel concepts of radiotherapy: fractionation, CT image guidance, respiratory gating, intentional dose heterogeneity, and simultaneous integrated protection.

Keywords: IGRT; SBRT; ablative; locally advanced; pancreatic cancer; respiratory gating.

Fig. 1.

Simultaneous Integrated Boost (SIB) and Simultaneous Integrated Protection (SIP) in the Treatment Planning of Locally Advanced Pancreatic Cancer. This figure illustrates the proximity of gastrointestinal organs to a pancreatic tumor. This patient was treated with a dose of 70 Gy in 28 fractions to the GTV and 98 Gy to the hypoxic center, using feedback-assisted inspiration breath-hold gating and daily diagnostic-quality CT imaging to verify stomach position. GTV = gross tumor volume. S = stomach, J = jejunum, D = duodenum, C = colon, PV = collaterals from an occluded portal vein.

Fig. 2.

Daily CT image guidance allows monitoring of the stomach and small bowel. Daily CT image guidance is an essential component of the safe delivery of ablative doses of radiation to a tumor surrounded by gastrointestional luminal structures. An inspiration breath-hold technique is used to control respiratory motion. The intravenous contrast-enhanced simulation scan on the right is registered with the daily CT scan on the left for verification of luminal organ position. The daily CT can be used for adaptive planning if internal organ position is consistently different from that in the simulation CT.