Determining parameters for respiration‐gated radiotherapy

Abstract

Respiration-gated radiotherapy for tumor sites affected by respiratory motion will potentially improve radiotherapy outcomes by allowing reduced treatment margins leading to decreased complication rates and/or increased tumor control. Furthermore, for intensity-modulated radiotherapy (IMRT), respiratory gating will minimize the hot and cold spot artifacts in dose distributions that may occur as a result of interplay between respiratory motion and leaf motion. Most implementations of respiration gating rely on the real time knowledge of the relative position of the internal anatomy being treated with respect to that of an external marker. A method to determine the amplitude of motion and account for any difference in phase between the internal tumor motion and external marker motion has been developed. Treating patients using gating requires several clinical decisions, such as whether to gate during inhale or exhale, whether to use phase or amplitude tracking of the respiratory signal, and by how much the intrafraction tumor motion can be decreased at the cost of increased delivery time. These parameters may change from patient to patient. A method has been developed to provide the data necessary to make decisions as to the CTV to PTV margins to apply to a gated treatment plan.

Initial evaluation of a four‐dimensional computed tomography system, using a programmable motor

“…The RPM system has been described in the literature. ( 12 , 13 ) It is based on an external reflecting tape stuck on a small, lightweight cube and followed by an infrared camera. The cube is usually positioned on the patient's chest and is considered a surrogate of tumor motion.…”

“…Generally, these new techniques that manage the patient's respiratory motion during treatment are separated into two groups: breath‐hold techniques ( 6 , 11 ) and gating techniques (12) . In the breath‐hold technique, the patient is imaged and treated during a monitored breath‐hold.…”

“…In the gating technique, the patient is treated at a particular phase of free breathing, generally by placing an external marker on the patient's chest and synchronizing beam delivery with the motion of the marker. ( 12 – 14 ) For this group of patients, the treatment plan should be based on a breathing‐adapted imaging technique. Four‐dimensional computed tomography (4D‐CT) is such a technique ( 15 – 19 ) and the focus of the present work.…”

Feasibility Study of Robotics-based Patient Immobilization Device for Real-time Motion Compensation

“…In the gating method, the treatment beam is irradiated during a specific phase of the respiratory cycle, calculated by monitoring the breathing pattern, but this method is likely to be less accurate when the breathing pattern becomes irregular owing to prolonged treatment time. [3][4][5][6] On the other hand, with the real-time tumor tracking method the treatment time can be shorter; however, this method requires sophisticated operation and technology for changing the position and shape of the treatment beam in real time, by monitoring the three-dimensional (3D) location of a tumor. One well-known tumor tracking method uses a dynamic multi-leaf collimator (DMLC) for aligning the treatment beam to a moving tumor.…”

A study of longitudinal tumor motion in helical tomotherapy using a cylindrical phantom

“…Respiratory gating is a technique used in IMRT in which radiation delivery is shut off when the tumor is not within a predefined area. ( 15 , 16 ) Unfortunately, in HT, the constant couch translation and gantry rotation do not allow for a pause in radiation delivery. Some HT‐specific solutions include several deliveries with a large pitch factor, ( 17 ) rearranging sinogram projections to account for target motion, ( 18 ) incorporating CT images from different breathing phases into the plan optimization process, ( 19 ) and creating intensity maps with increased intensity near the edges of the tumor, in addition to margins.…”