Triggered kV Imaging During Spine SBRT for Intrafraction Motion Management

Abstract

Purpose: To monitor intrafraction motion during spine stereotactic body radiotherapy(SBRT) treatment delivery with readily available technology, we implemented triggered kV imaging using the on-board imager(OBI) of a modern medical linear accelerator with an advanced imaging package. Methods: Triggered kV imaging for intrafraction motion management was tested with an anthropomorphic phantom and simulated spine SBRT treatments to the thoracic and lumbar spine. The vertebral bodies and spinous processes were contoured as the image guided radiotherapy(IGRT) structures specific to this technique. Upon each triggered kV image acquisition, 2D projections of the IGRT structures were automatically calculated and updated at arbitrary angles for display on the kV images. Various shifts/rotations were introduced in x, y, z, pitch, and yaw. Gantry-angle-based triggering was set to acquire kV images every 45°. A group of physicists/physicians(n = 10) participated in a survey to evaluate clinical efficiency and accuracy of clinical decisions on images containing various phantom shifts. This method was implemented clinically for treatment of 42 patients(94 fractions) with 15 second time-based triggering. Result: Phantom images revealed that IGRT structure accuracy and therefore utility of projected contours during triggered imaging improved with smaller CT slice thickness. Contouring vertebra superior and inferior to the treatment site was necessary to detect clinically relevant phantom rotation. From the survey, detectability was proportional to the shift size in all shift directions and inversely related to the CT slice thickness. Clinical implementation helped evaluate robustness of patient immobilization. Based on visual inspection of projected IGRT contours on planar kV images, appreciable intrafraction motion was detected in eleven fractions(11.7%). Discussion: Feasibility of triggered imaging for spine SBRT intrafraction motion management has been demonstrated in phantom experiments and implementation for patient treatments. This technique allows efficient, non-invasive monitoring of patient position using the OBI and patient anatomy as a direct visual guide.

Estimation of patient-size dependent imaging dose for stereoscopic/monoscopic real-time kV image guidance in lung and prostate SBRT

“…Although in this study we focused on lung and prostate sites, the results here can also apply to other treatment sites in pelvis (e.g. bladder) , or thorax for liver and spine SBRT (Koo et al 2021). As expected, the results show that bones received the highest average D2 (due to photoelectric effect) followed by the skin in both cases of thorax and pelvis tumor monitoring.…”

Optimized workflow to minimise intra-fractional motion during stereotactic body radiotherapy of spinal metastases

“…In contrast the ExacTrac imaging and matching procedure takes in the order of seconds, reducing the time during which the patient may move prior to the start or continuation of the dose delivery. Koo et al use triggered kV imaging during SBRT treatment and highlight the need to promptly detect and correct any movements that occur during spinal SBRT [6] . It is also plausible that the patient might move more at the beginning of the treatment, before “settling” into the treatment position.…”

“…SBRT for spinal metastases is established as an effective treatment modality with proven clinical efficacy [1] , [3] , [4] , [5] . A high degree of spatial accuracy is achieved by using image-guided radiotherapy (IGRT) to accurately irradiate the target, whilst minimizing the dose delivered to the healthy neighbouring tissues, thus avoiding potential toxicities, particularly to the spinal cord [2] , [6] , [13] . For high precision treatments techniques such as spinal SBRT, it is crucial to minimize positional errors in order to ensure a high dose gradient at the spinal cord and tumour interface [1] , [2] , [3] , [4] , [13] .…”

State-of-the-Art Imaging Techniques in Metastatic Spinal Cord Compression

“…Treatment can then be halted almost instantly for patient repositioning, which had been previously shown to correlate with positional changes of the spinal cord in the vertebral canal [140]. Previous methods to control intrafractional variation have mostly relied on periodic midtreatment imaging [125,141]. Another strategy to mitigate intrafractional motion employs the use of flattening filter free (FFF) SBRT to improve the dose rate and thereby reduce treatment time [142].…”