Computational analysis of interfractional anisotropic shape variations of the rectum in prostate cancer radiation therapy. (February 2018)

• Record Type: Journal Article
• Authors: Haekal, Mohammad; Arimura, Hidetaka; Hirose, Taka-aki; Shibayama, Yusuke; Ohga, Saiji; Fukunaga, Junichi; Umezu, Yoshiyuki; Honda, Hiroshi; Sasaki, Tomonari
• Is Part Of: Physica medica. Volume 46(2018)
• Page Start: 168
• Page End: 179
• Publication Date: 2018-02
• Subjects: Point distribution model -- Prostate cancer radiation therapy -- Rectum shape variation -- Rectum overlap region; Medical physics -- Periodicals; Biophysics -- Periodicals; Biophysics -- Periodicals; Imagerie médicale -- Périodiques; Radiothérapie -- Périodiques; Rayons X -- Sécurité -- Mesures -- Périodiques; Physique -- Périodiques; Médecine -- Périodiques; 610.153
• DOI: 10.1016/j.ejmp.2017.12.019
• Languages: English
• ISSNs: 1120-1797

Abstract

Highlights: The shape variations of the rectum varies in every part of the rectum. The shape variations of the overlap (ROP) region of rectum with PTV were analyzed. The dose evaluation indices of the rectum were investigated. The rectum V75 was smaller when using PRV-based plan. Abstract: Purpose: To analyze the uncertainties of the rectum due to anisotropic shape variations by using a statistical point distribution model (PDM). Materials and methods: The PDM was applied to the rectum contours that were delineated on planning computed tomography (CT) and cone-beam CT (CBCT) at 80 fractions of 11 patients. The standard deviations (SDs) of systematic and random errors of the shape variations of the whole rectum and the region in which the rectum overlapped with the PTV (ROP regions) were derived from the PDMs at all fractions of each patient. The systematic error was derived by using the PDMs of planning and average rectum surface determined from rectum surfaces at all fractions, while the random error was derived by using a PDM-based covariance matrix at all fractions of each patient. Results: Regarding whole rectum, the population SDs were larger than 1.0 mm along all directions for random error, and along the anterior, superior, and inferior directions for systematic error. The deviation is largest along the superior and inferior directions for systematic and random errors, respectively. For ROP regions, the population SDs of systematic error were larger than 1.0 mm along the superior and inferior directions. The population SDs of random error for the ROP regions were larger than 1.0 mm except along the right and posterior directions. Conclusions: The anisotropic shape variations of the rectum, especially in the ROP regions, should be considered when determining a planning risk volume (PRV) margins for the rectum associated with the acute toxicities.