Cone-Beam Computed Tomography (CB-CT) internal motion tracking should be used to validate 4-Dimensional CT for abdominal radiotherapy patients

Publication date: Available online 2 February 2016
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Leith Rankine, Hanlin Wan, Parag Parikh, Nichole Maughan, Per Poulsen, Todd DeWees, Eric Klein, Lakshmi Santanam
Purpose/Objective(s)Although 4-Dimensional Computed Tomography (4DCT) is often used for motion management in radiation therapy, research shows it does not adequately predict on-table tumor motion for abdominal radiotherapy. In this study, we demonstrate that tumor motion should be measured using fiducial tracking during pre-treatment Cone-Beam CT (CBCT) and used to validate the 4DCT margins before treatment.Materials/MethodsFor 31 patients with abdominal tumors and implanted fiducial markers, tumor motion was measured daily with CBCT and fluoroscopy for 202 treatment fractions. Fiducial tracking and maximum-likelihood algorithms extracted three-dimensional fiducial trajectories from CBCT projections. The daily internal margin (IM), i.e, range of fiducial motion, was calculated for CBCT and fluoroscopy as the 5^th-95^th percentiles of displacement in each cardinal direction. The planning IM from simulation 4DCT (IM4DCT) was considered adequate when within ±1.2mm (AP, LR) and ±3mm (SI) of the daily measured IM. We validated CBCT fiducial-tracking as an accurate predictive measure of intrafraction motion by comparing the daily measured IMCBCT to the daily IM measured by pre-treatment fluoroscopy (IMpre-fluoro); these were compared to pre- and post-treatment fluoroscopy (IMfluoro) to identify those patients who could benefit from imaging during treatment.Results4DCT could not accurately predict intrafractional tumor motion for ≥80% of fractions in 94% (IMCBCT), 97% (IMpre-fluoro), and 100% (IMfluoro) of patients. IMCBCT was significantly closer to IMpre-fluoro than IM4DCT (p<0.01). For patients with median treatment time t<7.5min, IMCBCT agreed with or exceeded IMfluoro for 97.3% of fractions (superior-inferior), compared to 82.3% for the t>7.5min group, demonstrating the need for patient-specific intra-treatment imaging.ConclusionTumor motion determined from 4DCT-simulation does not accurately predict the daily motion observed on CBCT or fluoroscopy. CBCT could replace fluoroscopy for pre-treatment verification of simulation IM4DCT, reducing patient setup time and imaging dose. Patients with treatment time t>7.5min could benefit from the addition of intra-treatment imaging.

Teaser

The intrafractional tumor motion of 31 patients with abdominal tumors was measured over 202 treatment fractions by fiducial marker tracking in cone-beam computed tomography (CBCT) projections. Tumor motion from CBCT was compared to pre- and post- treatment kV fluoroscopy and to the corresponding 4-dimensional computed tomography (4DCT) simulation. In >90% of patients, tumor motion measured from the planning 4DCT did not accurately predict intrafractional tumor motion observed during CBCT and fluoroscopy in ≥80% of fractions. Tumor motion observed during CBCT more accurately reflects the motion observed on fluoroscopy, indicating that CBCT fiducial tracking could replace fluoroscopy for on-treatment verification of tumor motion.


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