Computed Tomography-Guided Online Adaptive Stereotactic Body Radiation Therapy for Liver Tumors: A Retrospective Study.

Abstract

We present a computed tomography-guided online adaptive radiation therapy (CT-ART) experience in liver stereotactic body radiation therapy (SBRT). A retrospective registry study evaluated patients with hepatocellular carcinoma or liver metastasis treated with CT-ART. Physicians were offered 2 plans, the original plan transposed onto the cone beam CT with adapted contours and a new plan generated with updated contours. Treatment distance from planning target volume (PTV) to nearest organ at risk (OAR) was determined by calculating the distance from PTV to nearest OAR on cone beam CT for simulation and each fraction. Thirteen patients received SBRT 45 to 60 Gy (median, 50 Gy) in 5 fractions. Median PTV was 98.6 cc. Of 65 fractions, 77% (50) were adapted. Distance from PTV to nearest OAR over the course of treatment varied for 10 of 13 patients (range, 0-1.1 cm). Three patients without change in PTV-OAR distance all had PTV-OAR overlap at simulation. Despite having no PTV-OAR overlap at time of simulation, during treatment, 3 patients developed an overlap between PTV and nearest OAR. PTV V100% ≥ 95% criteria were met in 92% of adapted and 64% of scheduled plans (P = .042) and among fractions with PTV and OAR overlap, 87% of adapted and 33% of scheduled plans met PTV V100% goal (P = .045). For fractions with PTV-OAR overlap, maximum dose (Dmax) to nearest OAR was lower with adapted plan (P = .026). Adapted plans had lower mean stomach Dmax (P = .012) and lower mean duodenum Dmax (P = .05). We demonstrate the distance between PTV and nearest OAR varies throughout a course of CT-ART SBRT for liver tumors. Overlap between the PTV and OAR during treatment emerged in half of patients with separation between 0.1 and 1.5 cm at time of simulation. Among fractions with PTV-OAR overlap, adapted plans improved ability to meet PTV V100% goal while reducing Dmax to nearest OAR.