Technical and dosimetric aspects of respiratory gating using a pressure‐sensor motion monitoring system

Abstract

This work introduces a gating technique that uses 4DCT to determine gating parameters and to plan gated treatment, and employs a Siemens linear accelerator to deliver the gated treatment. Because of technology incompatibility, the 4DCT scanner (LightSpeed, GE) and the Siemens accelerator require two different motion-monitoring systems. The motion monitoring system (AZ-773V, Anzai Med.) used for the gated delivery utilizes a pressure sensor to detect the external respiratory motion (pressure change) in real time. Another system (RPM, Varian) used for the 4DCT scanner (LightSpeed, GE) is based on an infrared camera to detect motion of external markers. These two motion monitoring systems (RPM and Anzai systems) were found to correlate well with each other. The depth doses and profile measured for gated delivery (with a duty cycle of 25% or 50%) were found to agree within 1.0% with those measured for ungated delivery, indicating that gating did not significantly alter beam characteristics. The measurement verified also that the MU linearity and beam output remained unchanged (within 0.3%). A practical method of using 4DCT to plan a gated treatment was developed. The duty cycle for either phase or amplitude gating can be determined based on 4DCT with consideration of set-up error and delivery efficiency. The close-loop measurement involving the entire gating process (imaging, planning, and delivery) showed that the measured isodose distributions agreed with those intended, validating the accuracy and reliability of the gating technique. Based these observations, we conclude that the gating technique introduced in this work, integrating Siemens linear accelerator and Anzai pressure sensor device with GE/Varian RPM 4DCT, is reliable and effective, and it can be used clinically to account for respiratory motion during radiation therapy.

Evaluation of the combined use of two different respiratory monitoring systems for 4D CT simulation and gated treatment

“…In the scenario of mixed use of the ANZAI system for 4D CT and RPM for treatment gating, the differences between the two systems may be detrimental to the desired clinic outcome. Previous studies14, 15, 16 compare different types of surrogates based on phantom experiments and show high agreement achievable for both regular and irregular breathing patterns. However, human respiratory motion involves movement in three dimensions rather than the 1D movement as designed in the phantom studies.…”

“…Several respiratory monitoring systems using external surrogates are available in the market for the purposes of measuring respiratory motion for 4D CT imaging and gated treatment 5. These systems measure the respiratory motion as the surface movement of abdomen or chest wall (eg, Real‐Time Position Management [RPM],4 C‐RAD,13 GateCT14), or the pressure change in a belt wrapped around the abdomen (eg, ANZAI,15 Bellows16), etc. There is no consensus of which is the best external surrogate with respect to the correlation with the internal tumor motion.…”

Expanding the use of real‐time electromagnetic tracking in radiation oncology

“…Such devices include, but are not limited to, external marker blocks, ( 13 ) infrared reflector body markers, ( 14 ) as well as strain gauge belts. ( 15 ) Studies have shown that the correlation between internal anatomy markers and external markers are valid, but in extremely limited cases. ( 16 – 20 ) This correlation was reported to be poor or nonexistent unless the external surrogate measuring the skin surface was near the target volume.…”

Implementation of respiratory‐gated VMAT on a Versa HD linear accelerator

“…One such system, the AZ‐733VI by Anzai Medical Systems (Tokyo, Japan), uses a load cell and elastic belt wrapped around the patient's abdomen to monitor respiration 6. During inhalation, the elastic belt stretches with expansion of the patient's abdomen and the compressive forces are registered on the load cell.…”