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Reducing monitor units for robotic radiosurgery by optimized use of multiple collimators
Author(s) -
Pöll Johan J.,
Hoogeman Mischa S.,
Prévost JeanBriac,
Nuyttens Joost J.,
Levendag Peter C.,
Heijmen Ben J.
Publication year - 2008
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2919090
Subject(s) - radiosurgery , medical physics , dosimetry , computer science , nuclear medicine , physics , medicine , radiation therapy , radiology
Advances in image guidance and dose delivery techniques, and increased use of hypofractionation, have led to prolonged radiotherapy fraction duration. This is also the case with robotic radiosurgery, as extensive on‐line image guidance procedures, many beams, and usually high fraction doses are used for tumor irradiation. At this institution, early stage non‐small‐cell lung cancer patients are treated with image guided tumor tracking for respiratory motion compensation. Approximately 130 circular beams and up to ∼ 39 000 monitor units (MUs) are used for delivery of a total treatment dose of 60 Gy. The large number of MUs leads to long treatment times and the radiation leakage increases with the number of MUs. Generally, per patient, a single (small) cone is used. To substantially reduce the number of MUs, the authors have developed a new planning strategy for combined use of a small and a large cone. The large cone aims at dose delivery around the PTV center, while the small cone shapes the dose around the (irregular) PTV edges. The authors systematically investigated relationships between the number of MUs, the plan quality, the selected cone diameters, and the beam‐direction setup. Plan quality was assessed with the conformity index, mean lung dose (MLD), V20 of the lungs, and by visual inspection. The reduction in MUs was determined by comparing two‐cone plans with corresponding one‐cone plans that yielded equal MLD, i.e., equal predicted lung toxicity. With the proposed two‐cone approach, the required number of MUs reduced by on average 31 % (range 4 % − 56 % ). The beam‐on time per treatment fraction reduced by on average 8 min (range 1–15.2 min). All plans obeyed the clinically applied constraints and were considered clinically acceptable by an involved physician.