Interfractional target variations for partial breast irradiation. Int J Radiat Oncol Biol Phys 2012 Apr 01;82(5):1594-604
Date
05/17/2011Pubmed ID
21570200DOI
10.1016/j.ijrobp.2011.01.041Scopus ID
2-s2.0-84858698956 (requires institutional sign-in at Scopus site) 13 CitationsAbstract
PURPOSE: In this work, we quantify the interfractional variations in the shape of the clinical target volume (CTV) by analyzing the daily CT data acquired during CT-guided partial breast irradiation (PBI) and compare the effectiveness of various repositioning alignment strategies considered to account for the variations.
METHODS AND MATERIALS: The daily CT data for 13 breast cancer patients treated with PBI in either prone (10 patients) or supine (3 patients) with daily kV CT guidance using CT on Rails (CTVision, Siemens, Malvern, PA) were analyzed. For approximately 25 points on the surface of the CTV, deformation vectors were calculated by means of deformable image registration and verified by visual inspection. These were used to calculate the distances along surface normals (DSN), which directly related to the required margin expansions for each point. The DSN values were determined for seven alignment methods based on volumetric imaging and also two-dimensional projections (portal imaging).
RESULTS: The margin expansion necessary to cover 99% of all points for all days was 2.7 mm when utilizing the alignment method based on deformation field data (the best alignment method). The center-of-mass based alignment yielded slightly worse results (a margin of 4.0 mm), and shifts obtained by operator placement (7.9 mm), two-dimensional-based methods (7.0-10.1 mm), and skin marks (13.9 mm) required even larger margin expansions. Target shrinkage was evident for most days by the negative values of DSN. Even with the best alignment, the range of DSN values could be as high as 7 mm, resulting in a large amount of normal tissue irradiation, unless adaptive replanning is employed.
CONCLUSION: The appropriate alignment method is important to minimize the margin requirement to cover the significant interfractional target deformations observed during PBI. The amount of normal tissue unnecessarily irradiated is still not insignificant, and can be minimized if adaptive radiotherapy is applied.
Author List
Ahunbay EE, Robbins J, Christian R, Godley A, White J, Li XAAuthor
Ergun Ahunbay PhD Professor in the Radiation Oncology department at Medical College of WisconsinMESH terms used to index this publication - Major topics in bold
Anatomic LandmarksBreast Neoplasms
Female
Humans
Mastectomy, Segmental
Movement
Organs at Risk
Patient Positioning
Radiation Oncology
Radiotherapy Planning, Computer-Assisted
Radiotherapy Setup Errors
Radiotherapy, Image-Guided
Retrospective Studies
Tomography, X-Ray Computed
Tumor Burden