MRI quantification of pancreas motion as a function of patient setup for particle therapy —a preliminary study

Abstract

Particle therapy (PT) has shown positive therapeutic results in local control of locally advanced pancreatic lesions. PT effectiveness is highly influenced by target localization accuracy both in space, since the pancreas is located in proximity to radiosensitive vital organs, and in time as it is subject to substantial breathing‐related motion. The purpose of this preliminary study was to quantify pancreas range of motion under typical PT treatment conditions. Three common immobilization devices (vacuum cushion, thermoplastic mask, and compressor belt) were evaluated on five male patients in prone and supine positions. Retrospective four‐dimensional magnetic resonance imaging data were reconstructed for each condition and the pancreas was manually segmented on each of six breathing phases. A k‐means algorithm was then applied on the manually segmented map in order to obtain clusters representative of the three pancreas segments: head, body, and tail. Centers of mass (COM) for the pancreas and its segments were computed, as well as their displacements with respect to a reference breathing phase (beginning exhalation). The median three‐dimensional COM displacements were in the range of 3 mm. Latero–lateral and superior–inferior directions had a higher range of motion than the anterior–posterior direction. Motion analysis of the pancreas segments showed slightly lower COM displacements for the head cluster compared to the tail cluster, especially in prone position. Statistically significant differences were found within patients among the investigated setups. Hence a patient‐specific approach, rather than a general strategy, is suggested to define the optimal treatment setup in the frame of a millimeter positioning accuracy.PACS number(s): 87.55.‐x, 87.57.nm, 87.61

Image‐based retrospective 4D MRI in external beam radiotherapy: A comparative study with a digital phantom

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“…Other strategies rely on the extraction of the internal surrogates directly from the acquired image slices, without the need of adding a navigator frame and therefore result in a lower acquisition time. Surrogates able to capture the anatomic variation due to breathing motion can be derived, such as the so‐called body area, as well as the use of image similarity measures between slices …”

“…Surrogates able to capture the anatomic variation due to breathing motion can be derived, such as the so-called body area, [20][21][22] as well as the use of image similarity measures between slices. 23,24 K-space under-sampling strategies can be an alternative in 4D reconstruction. [25][26][27][28][29] However, k-space methods are not always available in MR clinical scanners, thus requiring tailored pulse sequences and reconstruction algorithms.…”

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Comparison of pancreatic respiratory motion management with three abdominal corsets for particle radiation therapy: Case study

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