Development of a real-time monitoring system for intra-fractional motion in intracranial treatment using pressure sensors

Abstract

This study developed a dedicated real-time monitoring system to detect intra-fractional head motion in intracranial radiotherapy using pressure sensors. The dedicated real-time monitoring system consists of pressure sensors with a thickness of 0.6 mm and a radius of 9.1 mm, a thermoplastic mask, a vacuum pillow, and a baseplate. The four sensors were positioned at superior-inferior and right-left sides under the occipital area. The sampling rate of pressure sensors was set to 5 Hz. First, we confirmed that the relationship between the force and the displacement of the vacuum pillow follows Hook's law. Next, the spring constant for the vacuum pillow was determined from the relationship between the force given to the vacuum pillow and the displacement of the head, detected by Cyberknife target locating system (TLS) acquisitions in clinical application. Finally, the accuracy of our system was evaluated by using the 2 × 2 confusion matrix. The regression lines between the force, y, and the displacement, x, of the vacuum pillow were given by y = 3.8x, y = 4.4x, and y = 5.0x when the degree of inner pressure was -12 kPa,-20 kPa, and -27 kPa, respectively. The spring constant of the vacuum pillow was 1.6 N mm(-1) from the 6D positioning data of a total of 2999 TLS acquisitions in 19 patients. Head motions of 1 mm, 1.5 mm, and 2 mm were detected in real-time with the accuracies of 67%, 84%, and 89%, respectively. Our system can detect displacement of the head continuously during every interval of TLS with a resolution of 1-2 mm without any radiation exposure.

Effects of respiratory motion on volumetric and positional difference of GTV in lung cancer based on 3DCT and 4DCT scanning

“…The respiratory movement has a significant effect on the radiation dose distribution and radiotherapy effect of lung cancer, which is one of the important factors to be considered when the target region expands outside (11). Therefore, many scholars have carried out relevant research to reduce the influence of tumor displacement on the target area (12).…”

Estimation of imaging intervals and intrafraction displacement in CyberKnife image‐guided radiotherapy for intracranial lesions

“…This monitoring system can detect force within the occipital region using pressure sensors (FSR402; Interlink Electronics) and can measure displacement according to changes in force by following Hook's law. Briefly, the force for the occipital region ( F (N)), head displacement (∆ d (mm)), and the spring constant of the vacuum pillow k (N/mm) can be expressed by Hook's law as follows: ∆ d is expressed in the next expression by transforming Equation () as follows: The displacement of the vacuum pillow can be obtained from measurements of sensor pressure P (kPa) and the sensor area A (mm 2 ) as follows: The pressure sensor has high sensitivity that facilitates direct contact with the occipital region of the head, and our system can theoretically detect head displacement with a resolution of 1.3 × 10 −4 mm 12 …”

“…20 Therefore, we inserted a foam sheet (made from natural rubber origin, with a thickness of 3 mm and a density of 0.100 ± 0.03 kg/m 3 ) under the pressure sensors to improve the sensitivity and equalization of pressure in the occipital region as compared to the procedure followed in our previous study. 12 As the pressure sensors in this system make angles that reflect the shape of the back of the head in a horizontal direction, the displacement could measure pressure based on Equation (3) (unless head displacement moved in parallel for each axis). Briefly, a displacement in the superior-inferior (SI) direction (Δd SI (t)) was proportional to the mean value of the pressure in the superior side, whereas P s (N) and the pressure in the inferior side (P i (N)) (with a displacement in the right-left (RL) direction (Δd RL (t)) was proportional to the mean value of the pressure in the right side (P r (N)) and the pressure in the left side (P l (N)); a displacement in the posterioranterior (PA) direction (Δd PA (t)) was proportional to the mean value of the pressure in each of the four sensors.…”

“…In a previous study, we developed a dedicated real-time monitoring system using pressure sensors without radiation exposure to detect intracranial head movements during intracranial radiotherapy. 12 TLS can only specify the imaging interval in seconds, whereas this novel system can continuously detect head displacement at the subsecond level with a resolution of less than 1 mm. In the current study, the system was simulated to retrospectively analyze the association between imaging intervals and intrafraction displacements (instead of the TLS).…”

Relationship between pressure levels on the occipital region and intrafraction motion using an individualized head support for intracranial treatment

“…The vacuum pillow could be customized to the patient’s occipital shape to create uniform pressure on the patient’s head. We also used a dedicated real-time monitoring system [ 16 ] that consisted of pressure sensors (FSR®402, Interlink Electronics, CA, USA) with a thickness of 0.6 mm and a radius of 9.1 mm to detect the pressure on the patient’s head. Four sensors are able to detect the absolute pressures at the occipital region as voltages, with a sampling rate of 15 .…”