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Investigation of interfractional shape variations based on statistical point distribution model for prostate cancer radiation therapy
Author(s) -
Shibayama Yusuke,
Arimura Hidetaka,
Hirose Takaaki,
Nakamoto Takahiro,
Sasaki Tomonari,
Ohga Saiji,
Matsushita Norimasa,
Umezu Yoshiyuki,
Nakamura Yasuhiko,
Honda Hiroshi
Publication year - 2017
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 - 10.1002/mp.12217
Subject(s) - standard deviation , medicine , radiation therapy , prostate cancer , cone beam computed tomography , radiation treatment planning , nuclear medicine , point distribution model , prostate , image guided radiation therapy , mathematics , statistics , computed tomography , radiology , computer science , cancer , artificial intelligence
Purpose The setup errors and organ motion errors pertaining to clinical target volume ( CTV ) have been considered as two major causes of uncertainties in the determination of the CTV ‐to‐planning target volume ( PTV ) margins for prostate cancer radiation treatment planning. We based our study on the assumption that interfractional target shape variations are not negligible as another source of uncertainty for the determination of precise CTV ‐to‐ PTV margins. Thus, we investigated the interfractional shape variations of CTV s based on a point distribution model ( PDM ) for prostate cancer radiation therapy. Materials and methods To quantitate the shape variations of CTV s, the PDM was applied for the contours of 4 types of CTV regions (low‐risk, intermediate‐ risk, high‐risk CTV s, and prostate plus entire seminal vesicles), which were delineated by considering prostate cancer risk groups on planning computed tomography ( CT ) and cone beam CT ( CBCT ) images of 73 fractions of 10 patients. The standard deviations ( SD s) of the interfractional random errors for shape variations were obtained from covariance matrices based on the PDM s, which were generated from vertices of triangulated CTV surfaces. The correspondences between CTV surface vertices were determined based on a thin‐plate spline robust point matching algorithm. The systematic error for shape variations was defined as the average deviation between surfaces of an average CTV and planning CTV s, and the random error as the average deviation of CTV surface vertices for fractions from an average CTV surface. Results The means of the SD s of the systematic errors for the four types of CTV s ranged from 1.0 to 2.0 mm along the anterior direction, 1.2 to 2.6 mm along the posterior direction, 1.0 to 2.5 mm along the superior direction, 0.9 to 1.9 mm along the inferior direction, 0.9 to 2.6 mm along the right direction, and 1.0 to 3.0 mm along the left direction. Concerning the random errors, the means of the SD s ranged from 0.9 to 1.2 mm along the anterior direction, 1.0 to 1.4 mm along the posterior direction, 0.9 to 1.3 mm along the superior direction, 0.8 to 1.0 mm along the inferior direction, 0.8 to 0.9 mm along the right direction, and 0.8 to 1.0 mm along the left direction. Conclusions Since the shape variations were not negligible for intermediate and high‐risk CTV s, they should be taken into account for the determination of the CTV ‐to‐ PTV margins in radiation treatment planning of prostate cancer.