Radiotherapy beyond cancer: Target localization in real‐time MRI and treatment planning for cardiac radiosurgery. Issue 12 (17th November 2014)

• Record Type: Journal Article
• Authors: Ipsen, S.; Blanck, O.; Oborn, B.; Bode, F.; Liney, G.; Hunold, P.; Rades, D.; Schweikard, A.; Keall, P. J.
• Is Part Of: Medical physics. Volume 41:Issue 12(2014)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2014-11-17
• Subjects: biomedical MRI -- cardiology -- medical image processing -- Monte Carlo methods -- motion compensation -- radiation therapy -- real‐time systems; Applications -- Clinical applications -- Monte Carlo simulations -- Cardiac dynamics; Involving electronic [emr] or nuclear [nmr] magnetic resonance, e.g. magnetic resonance imaging -- Radiation therapy -- Biological material, e.g. blood, urine; Haemocytometers -- Digital computing or data processing equipment or methods, specially adapted for specific applications -- Image data processing or generation, in general -- Analysis of motion; atrial fibrillation -- cardiac radiosurgery -- real‐time tracking -- image guidance -- MRI‐Linac; Heart -- Magnetic resonance imaging -- Medical imaging -- Radiosurgery -- Dosimetry -- Medical treatment planning -- Magnetic fields -- Radiation treatment -- Cardiac dynamics; Medical physics -- Periodicals; Medical physics; Geneeskunde; Natuurkunde; Toepassingen; Biophysics; Periodicals; Periodicals; Electronic journals; 610.153
• DOI: 10.1118/1.4901414
• Languages: English
• ISSNs: 0094-2405

Abstract

Abstract : Purpose: Atrial fibrillation (AFib) is the most common cardiac arrhythmia that affects millions of patients world‐wide. AFib is usually treated with minimally invasive, time consuming catheter ablation techniques. While recently noninvasive radiosurgery to the pulmonary vein antrum (PVA) in the left atrium has been proposed for AFib treatment, precise target location during treatment is challenging due to complex respiratory and cardiac motion. A MRI linear accelerator (MRI‐Linac) could solve the problems of motion tracking and compensation using real‐time image guidance. In this study, the authors quantified target motion ranges on cardiac magnetic resonance imaging (MRI) and analyzed the dosimetric benefits of margin reduction assuming real‐time motion compensation was applied. Methods: For the imaging study, six human subjects underwent real‐time cardiac MRI under free breathing. The target motion was analyzed retrospectively using a template matching algorithm. The planning study was conducted on a CT of an AFib patient with a centrally located esophagus undergoing catheter ablation, representing an ideal case for cardiac radiosurgery. The target definition was similar to the ablation lesions at the PVA created during catheter treatment. Safety margins of 0 mm (perfect tracking) to 8 mm (untracked respiratory motion) were added to the target, defining the planning target volume (PTV). For each margin, a 30 Gy single fraction IMRT plan was generated. Additionally, the influence of 1 and 3 T magnetic fields on the treatment beam delivery was simulated using Monte Carlo calculations to determine the dosimetric impact of MRI guidance for two different Linac positions. Results: Real‐time cardiac MRI showed mean respiratory target motion of 10.2 mm (superior–inferior), 2.4 mm (anterior–posterior), and 2 mm (left–right). The planning study showed that increasing safety margins to encompass untracked respiratory motion leads to overlapping structures even in the ideal scenario, compromising either normal tissue dose constraints or PTV coverage. The magnetic field caused a slight increase in the PTV dose with the in‐line MRI‐Linac configuration. Conclusions: The authors' results indicate that real‐time tracking and motion compensation are mandatory for cardiac radiosurgery and MRI‐guidance is feasible, opening the possibility of treating cardiac arrhythmia patients completely noninvasively.