Implementation of free breathing respiratory amplitude‐gated treatments

Abstract

The purpose of this study was to provide guidance in developing and implementing a process for the accurate delivery of free breathing respiratory amplitude-gated treatments.Methods: A phase-based 4DCT scan is acquired at time of simulation and motion is evaluated to determine the exhale phases that minimize respiratory motion to an acceptable level. A phase subset average CT is then generated for treatment planning and a tracking structure is contoured to indicate the location of the target or a suitable surrogate over the planning phases. Prior to treatment delivery, a 4DCBCT is acquired and a phase subset average is created to coincide with the planning phases for an initial match to the planning CT. Fluoroscopic imaging is then used to set amplitude gate thresholds corresponding to when the target or surrogate is in the tracking structure. The final imaging prior to treatment is an amplitude-gated CBCT to verify both the amplitude gate thresholds and patient positioning. An amplitude-gated treatment is then delivered. This technique was commissioned using an in-house lung motion phantom and film measurements of a simple two-field 3D plan.Results: The accuracy of 4DCBCT motion and target position measurements were validated relative to 4DCT imaging. End to end testing showed strong agreement between planned and film measured dose distributions. Robustness to interuser variability and changes in respiratory motion were demonstrated through film measurements. Conclusions:The developed workflow utilizes 4DCBCT, respiratory-correlated fluoroscopy, and gated CBCT imaging in an efficient and sequential process to ensure the accurate delivery of free breathing respiratory-gated treatments. | INTRODUCTIONRespiratory motion management is an important strategy to account for breathing-induced target motion during radiation therapy. 1 If not considered during both the treatment planning and delivery processes, respiratory motion can lead to artifacts and target volumes that do not adequately encompass the target. Active respiratory motion management techniques can be used to minimize target motion during treatment delivery, allowing for a reduction in target volumes and improved normal tissue sparing. Such techniques include abdominal compression, 2 breath hold, 3 and free breathing phase or amplitude gating. 4 Many thoracic and abdominal sites are susceptible to substantial motion, with abdominal and lower lung lesion motion often measured to be greater than 1 cm. 5,6 Inter-and intrafraction changes in target motion magnitude greater than 5 mm have been

A simple method to measure the gating latencies in photon and proton based radiotherapy using a scintillating crystal

“…5 Gated delivery performed while the patient is breathing freely is known as respiratory gating and is used for tumor sites highly affected by respiratory motion such as the liver, lung, and pancreas. [6][7][8][9][10][11][12] Other candidates for gated radiotherapy are patients with tumors that represent a favorable anatomy in specific breathing phases, for example with increased distance between the tumor and organs at risk. This group includes lung, lymphoma, and breast cancer patients often treated in deep-inspiration breath hold.…”

“…Gating relies on the ability to turn the treatment beam on and off such that the tumor is irradiated only in specific positions, for example only in specific phases of the breathing cycle, thereby effectively limiting the motion during irradiation 5 . Gated delivery performed while the patient is breathing freely is known as respiratory gating and is used for tumor sites highly affected by respiratory motion such as the liver, lung, and pancreas 6–12 . Other candidates for gated radiotherapy are patients with tumors that represent a favorable anatomy in specific breathing phases, for example with increased distance between the tumor and organs at risk.…”

Adoption of respiratory motion management in radiation therapy

“…Given that FBG and BHG have similar hardware requirements, the low interest in FBG may simply be related to its worse duty cycle, rather than a lack of access to technology [11] . Longer duty cycles and more gating events may exacerbate the internal-external correlation uncertainty for facilities relying on external markers for monitoring/gating on [36] , however, too few responses for FBG were collected to determine whether this was a concern amongst survey respondents.…”

“…Changes in respiration between simulation and treatment may lead to target under- or over-doses depending on the nature of the change [8] , [9] , [10] . Such changes may not be obvious during the patient set-up and image guidance procedures, adding further scope for geographic miss [11] , [12] , [13] . During treatment planning, dose accumulation in the moving anatomy is commonly estimated using a single static image, leading to increased uncertainty in the 3D dose calculation [1] , [14] , [15] , [16] .…”

A standardized workflow for respiratory‐gated motion management decision‐making

“…While several groups have published on general aspects of respiratory gating, including development of processes, commissioning of equipment, 13 and guidelines for clinical implementation, 7,14,15 there are very few resources to guide patient-specific respiratory gating decision-making. 16,17 Large centers, in particular, can benefit from standardized guidelines and workflows to ensure consistency of practice and to F I G U R E 2 Depiction of a tumor position in each phase of the breathing cycle and corresponding amplitude of the respiratory trace reduce errors when multiple hand-offs are made between team members.…”