Open AccessAccuracy and sensitivity of four‐dimensional dose calculation to systematic motion variability in stereotatic body radiotherapy (SBRT) for lung cancer
Author(s) -
Chan Mark K.H.,
Kwong Dora L.W.,
Ng Sherry C.Y.,
Tong Anthony S.M.,
Tam Eric K.W.
Publication year - 2012
Publication title -
journal of applied clinical medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.83
H-Index - 48
ISSN - 1526-9914
DOI - 10.1120/jacmp.v13i6.3992
Subject(s) - cyberknife , imaging phantom , monte carlo method , radiation treatment planning , nuclear medicine , pixel , sensitivity (control systems) , radiosurgery , tracking (education) , computer science , dosimetry , radiation therapy , physics , medicine , mathematics , computer vision , radiology , statistics , psychology , pedagogy , electronic engineering , engineering
The dynamic movement of radiation beam in real‐time tumor tracking may cause overdosing to critical organs surrounding the target. The primary objective of this study was to verify the accuracy of the 4D planning module incorporated in CyberKnife treatment planning system. The secondary objective was to evaluate the error that may occur in the case of a systematic change of motion pattern. Measurements were made using a rigid thorax phantom. Target motion was simulated with two waveforms (sin andcos 4 ) of different amplitude and frequency. Inversely optimized dose distributions were calculated in the CyberKnife treatment planning system using the 4D Monte Carlo dose calculation algorithm. Each plan was delivered to the phantom assuming (1) reproducible target motion, and (2) systematic change of target motion pattern. The accuracy of 4D dose calculation algorithm was assessed using GAFCHROMIC EBT2 films based on 5 % / 3 mm γ criteria. Treatment plans were considered acceptable if the percentage of pixels passing the 5 % / 3 mm γ criteria was greater than 90%. The mean percentages of pixels passing were 95% for the target and 91% for the static off‐target structure, respectively, with reproducible target motion. When systematic changes of the motion pattern were introduced during treatment delivery, the mean percentages of pixels passing decreased significantly in the off‐target films (48%; p < 0.05 ), but did not change significantly in the target films (92%; p = 0.324 ) compared to results of reproducible target motion. These results suggest that the accuracy of 4D dose calculation, particularly in off‐target stationary structure, is strongly tied to the reproducibility of target motion and that the solutions of 4D planning do not reflect the clinical nature of nonreproducible target motion generally. PACS numbers: 87.53.Ly, 87.55.km