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Bio-Physical Effects of Patients Set-Up Errors According to Whole Breast Irradiation Techniques

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S Lee

S Lee1*, T Suh1 , S Park1 , M Kim1 , J Park2 , M Lee1 , (1) Research Institute of Biomedical Engineering,The Catholic University of Korea, Seoul, (2) Stanford University School of Medicine, Stanford, CA


SU-E-J-172 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The dose-related effects of patient setup errors on biophysical indices were evaluated for conventional wedge (CW) and field-in-field (FIF) whole breast irradiation techniques.
Methods: The treatment plans for 10 patients receiving whole left breast irradiation were retrospectively selected. Radiobiological and physical effects caused by dose variations were evaluated by shifting the isocenters and gantry angles of the treatment plans. Dose-volume histograms of the planning target volume (PTV), heart, and lungs were generated, and conformity index (CI), homogeneity index (HI), tumor control probability (TCP), and normal tissue complication probability (NTCP) were determined.
Results: For “isocenter shift plan” with posterior direction, the D95 of the PTV decreased by approximately 15% and the TCP of the PTV decreased by approximately 50% for the FIF technique and by 40% for the CW; however, the NTCPs of the lungs and heart increased by about 13% and 1%, respectively, for both techniques. Increasing the gantry angle decreased the TCPs of the PTV by 24.4% (CW) and by 34% (FIF). The NTCPs for the two techniques differed by only 3%. In case of CW, the CIs and HIs were much higher than that of the FIF in all cases. It had a significant difference between two techniques (p<0.01). According to our results, however, the FIF had more sensitive response by set up errors rather than CW in bio-physical aspects.
Conclusions: The radiobiological-based analysis can detect significant dosimetric errors then, can provide a practical patient quality assurance method to guide the radiobiological and physical effects.

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