Abstract
A technique for multiple breath-hold segmented volumetric modulated arc therapy (VMAT) has been proposed under real-time fluoroscopic image guidance with implanted fiducial markers. Fiducial markers were embedded as close as possible to a tumour and the patient was asked to breathe in slowly under fluoroscopy. Immediately after the marker positions on the fluoroscopic image moved inside the planned marker contours transferred from a digitally reconstructed radiographic image at each gantry start angle, the patient was asked to hold their breath and a segmented VMAT beam was delivered. During beam delivery, the breath-hold status was continuously monitored by viewing a pointer in a breath monitoring system, Abches (Apex Medical, Tokyo, Japan), with the aid of a video camera installed in the treatment room. As long as the pointer stayed still, the segmented VMAT delivery continued for a preset period of 15–30 s, depending on the breath-hold capability of each patient. As soon as each segmented delivery was completed, the beam interrupt button was pushed; subsequently, the patient was asked to breathe freely. Because the preset breath-hold period was determined in order for each patient to hold their breath without fail, an intermediate beam interrupt due to breath-hold failure during the segmented beam delivery was not observed. This procedure was repeated until all the segmented VMAT beams were delivered. A case of pancreatic cancer is reported here as a preliminary study. The proposed technique may be clinically advantageous for treating tumours that move with respiration, including pancreatic cancer, lung tumour and other abdominal cancers.
Highlights
Many techniques were proposed to manage respiratory motion during treatment
The tumour position may not be accurately reproduced among the three different periods of planning CT imaging, pre-treatment tumour localization and beam delivery, requiring additional treatment margin to compensate for position uncertainty
A single-arc volumetric modulated arc therapy (VMAT) plan was created, and the plan was exported to a linear accelerator (Synergy; Elekta AB), equipped with a kilovolt fluoroscopic and conebeam CT (CBCT) imager, X-ray volume imaging (XVI)
Summary
Many techniques were proposed to manage respiratory motion during treatment. The passive breath-hold technique may be the simplest. The tumour position may not be accurately reproduced among the three different periods of planning CT imaging, pre-treatment tumour localization and beam delivery, requiring additional treatment margin to compensate for position uncertainty. To reduce the tumour position uncertainty, a breath-hold monitor, Abches (Apex Medical, Tokyo, Japan), was developed, which had two fulcrums; one was placed on the abdomen and the other on the breast of a patient.[1,2] A pointer was mechanically connected to the two fulcrums, allowing the pointer to move along with the fulcrums during breathing. It was reported that a thoracoabdominal displacement of 1 mm would lead to a pointer rotation of 4.6°.1
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