Liver Volume Variation Effect on SBRT Planning and Delivery for Upper Abdominal Malignancies

Overview

Standard planning constraints for liver SBRT incorporate strict dose-volume limits for normal liver parenchyma to minimize the risk of radiation-induced liver disease. The presence of diurnal and fasting/fed variations in liver volume therefore carry substantial potential for introducing errors into estimates of dose-volume distribution within normal liver tissue, as well as affecting day-to-day setup fidelity and organ alignment for treatment. This prospective study will examine how diurnal and fast-fed variations in liver volume affect treatment planning for abdominal SBRT.

Stereotactic body radiotherapy (SBRT) is an integral tool in the management of thoracic and upper abdominal malignancies. SBRT delivers ablative radiation doses in a limited number of fractions (thereby reducing interruptions in systemic therapy) with emerging evidence for feasibility and local control benefit. Effective SBRT delivery requires high-precision target localization that accounts for positional variations in both the target and nearby organs at risk (OAR). An absolute requirement for SBRT is accurate target localization and motion management, particularly when treating targets in the chest and abdomen, which are subject to respiratory motion as well as changes in configuration due to deformation of hollow viscera. To ensure adequate targeting, various technical solutions are available, including motion management approaches such as four-dimensional computed tomography (4D-CT), abdominal compression, respiratory gating, and breath hold, as well as daily image-guided radiotherapy (IGRT) techniques such as cone beam computed tomography (CBCT), which facilitate precise daily target verification and minimization of the planning target volumes (PTVs). While the effects of respiratory motion on patient positioning during upper abdominal SBRT are relatively well understood, little is known about the effect of liver volume changes on radiotherapy (RT) dose delivery, despite the potential for morphological variations in the liver to affect patient setup and radiation dose distribution in real time. The liver is a dynamic organ with various functions including glycogen storage, carbohydrate (carb)/lipid/protein metabolism, bile secretion, synthesis of plasma proteins, and metabolism of various substances including steroid hormones and ingested toxins. Liver function is affected by fasting and feeding cycles, with an intrinsic circadian rhythm first observed in animal studies. This trial proposes to affect liver volume to ultimately and positively affect treatment planning for abdominal SBRT.