Synchronized moving aperture radiation therapy (SMART): improvement of breathing pattern reproducibility using respiratory coaching

Abstract

Recently, at Massachusetts General Hospital (MGH) we proposed a new treatment technique called synchronized moving aperture radiation therapy (SMART) to account for tumour motion during radiotherapy. The basic idea of SMART is to synchronize the moving radiation beam aperture formed by a dynamic multileaf collimator with the tumour motion induced by respiration. The two key requirements for being able to successfully use SMART in clinical practice are the precise and fast detection of tumour position during the simulation/treatment and the good reproducibility of the tumour motion pattern. To fulfil the first requirement, an integrated radiotherapy imaging system is currently being developed at MGH. The results of a previous study show that breath coaching techniques are required to make SMART an efficient technique in general. In this study, we investigate volunteer and patient respiratory coaching using a commercial respiratory gating system as a respiration coaching tool. Five healthy volunteers, observed during six sessions, and 33 lung cancer patients, observed during one session when undergoing 4D CT scans, were investigated with audio and visual promptings, with free breathing as a control. For all five volunteers, breath coaching was well tolerated and the intra- and inter-session reproducibility of the breathing pattern was greatly improved. Out of 33 patients, six exhibited a regular breathing pattern and needed no coaching, four could not be coached at all due to the patient's medical condition or had difficulty following the instructions, 13 could only be coached with audio instructions and 10 could follow the instructions of and benefit from audio-video coaching. We found that, for all volunteers and for those patients who could be properly coached, breath coaching improves the duty cycle of SMART treatment. However, about half of the patients could not follow both audio and video instructions simultaneously, suggesting that the current coaching technique requires improvements.

Measurement of the interplay effect in lung IMRT treatment using EDR2 films

“…In order to ensure regularity, a method of breath coaching may have to be used with patients. ( 21 , 22 ) These conclusions are in agreement with our previous study using an ion chamber for measurement.…”

Development of a geometry‐based respiratory motion– simulating patient model for radiation treatment dosimetry

“…The results demonstrate the importance of using accurate “gating” to improve the dose distribution. The results also suggest that, during 4D image‐guided treatment delivery, monitoring of the patient's breathing pattern is critical and that accuracy‐improvement technologies such as SMART may be useful (52) . Currently, we are refining our model and considering more dosimetry cases in the hope of providing insights into ways of refining strategies for the management of respiratory motion during radiation treatment.…”

The role of image guidance in respiratory gated radiotherapy

“…Respiratory beam gating is the most commonly used breathing adaptation technique, and is offered in several commercially available systems. Other breathing adaptation techniques include breath-hold techniques (voluntary and controlled) [41] and dynamic motion tracking in which the beam ''chases'' the target during its respiratory motion [12,24]. In the simpler end, motion inclusion techniques can be based on 4DCT scans to cover the target respiratory motion with treatment field margins on a patient individual basis [40].…”