Abstract
Before treatment delivery of respiratory‐gated radiation therapy (RT) in patients with implanted fiducials, both the patient position and the gating window thresholds must be set. In linac‐based RT, this is currently done manually and setup accuracy will therefore be dependent on the skill of the user. In this study, we present an automatic method for finding the patient position and the gating window thresholds. Our method uses sequentially acquired anterior–posterior (AP) and lateral fluoroscopic imaging with simultaneous breathing amplitude monitoring and intends to reach 100% gating accuracy while keeping the duty cycle as high as possible. We retrospectively compared clinically used setups to the automatic setups by our method in five pancreatic cancer patients treated with hypofractionated RT. In 15 investigated fractions, the average (±standard deviation) differences between the clinical and automatic setups were −0.4 ± 0.8 mm, −1.0 ± 1.1 mm, and 1.8 ± 1.3 mm in the left–right (LR), the AP, and the superior–inferior (SI) direction, respectively. For the clinical setups, typical interfractional setup variations were 1–2 mm in the LR and AP directions, and 2–3 mm in the SI direction. Using the automatic method, the duty cycle could be improved in six fractions, in four fractions the duty cycle had to be lowered to improve gating accuracy, and in five fractions both duty cycle and gating accuracy could be improved. Our automatic method has the potential to increase accuracy and decrease user dependence of setup for patients with implanted fiducials treated with respiratory‐gated RT. After fluoroscopic image acquisition, the calculated patient shifts and gating window thresholds are calculated in 1–2 s. The method gives the user the possibility to evaluate the effect of different patient positions and gating window thresholds on gating accuracy and duty cycle. If deemed necessary, it can be used at any time during treatment delivery.
Highlights
Fiducial markers are commonly used in respiratory-gated stereotactic body radiation therapy (SBRT) of pancreatic cancer[1,2,3,4] to assist in the visualization of the treatment area
SBRT of the pancreas needs a very accurate patient setup because small margins are used around the target to minimize dose and toxicity to surrounding organs at risk (OARs) such as the duodenum
We present a userindependent automatic method of simultaneously finding an optimized patient position and gating window thresholds in patients with implanted fiducial markers for pancreatic treatments treated on a linear accelerator with a single kV imager
Summary
Fiducial markers are commonly used in respiratory-gated stereotactic body radiation therapy (SBRT) of pancreatic cancer[1,2,3,4] to assist in the visualization of the treatment area. Fiducials are used together with monitoring of patient breathing during patient setup and treatment.[5] In gated treatments, proper setup of the patient requires that patient’s position and the gating window thresholds agree with the treatment plan. Different commercial treatment systems use various motion management methods for patient setup and/or intrafractional position monitoring.[6,7,8,9] current linear accelerators do not have the functionality to perform automatic setup of the patients and gating window based on fiducials, and rather rely on a manual patient setup.[10] SBRT treatments, could benefit from the assistance of automatic, user-independent methods
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