PURPOSE:To investigate robust margin strategies in intensity modulated proton therapy to account for interfractional organ motion in prostate cancer.
METHODS AND MATERIALS: For 9 patients, one planning computed tomography (CT) scan and daily and weekly cone beam CTs (CBCTs) were acquired and coregistered. The following planning target volume (PTV) approaches were investigated: a clinical target volume (CTV) delineated on the planning CT (CTVct) plus 10-mm margin (PTV10mm); a reduced PTV (PTVRed): CTVct plus 5 mm in the left-right (LR) and anterior-posterior (AP) directions and 8 mm in the inferior-superior (IS) directions; and a PTVHull method: the sum of CTVctand CTVs from 5 CBCTs from the first week plus 3 mm in the LR and IS directions and 5 mm in the AP direction. For each approach, separate plans were calculated using a spot-scanning technique with 2 lateral fields.
RESULTS: Each approach achieved excellent target coverage. Differences were observed in volume receiving 98% of the prescribed dose (V98%) where PTVHull and PTVRed results were superior to the PTV10mm concept. The PTVHull approach was more robust to organ motion. The V98% for CTVs was 99.7%, whereas for PTVRed and PTV10mm plans, V98% was 98% and 96.1%, respectively. Doses to organs at risk were higher for PTVHull and PTV10mm plans than for PTVRed, but only differences between PTV10mm and PTVRedwere significant.
CONCLUSIONS: In terms of organ sparing, the PTV10mm method was inferior but not significantly different from the PTVRed and PTVHull approaches. PTVHull was most insensitive to target motion.
Written by:
Góra J, Stock M, Lütgendorf-Caucig C, Georg D. Are you the author?
Division of Medical Radiation Physics, Department of Radiation Oncology, Medical University Vienna/AKH Wien, Austria; EBG MedAustron GmbH, Wiener Neustadt, Austria.
Reference: Int J Radiat Oncol Biol Phys. 2012 Jul 17. Epub ahead of print.
doi: 10.1016/j.ijrobp.2012.05.046
PubMed Abstract
PMID: 22818417
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