Radiobiological and physical effects of patient setup errors during whole breast irradiation

Background: the dose-related effects of patient setup errors on bio-physical indices were evaluated for the conventional wedge (cw) and field-in-field (fif) whole breast irradiation techniques (wbi). materials and methods: the treatment plans of 10 patients receiving le' wbi were retrospectively selected for evaluation. the bio-physical effects of dose variations were evaluated by shi'ing the isocenters and gantry-angles of the treatment plans. dose-volume histograms of the planning target volume (ptv),heart,and lungs were generated,and the conformity index (ci),homogeneity index (hi),tumor control probability (tcp),and normal tissue complication probability (ntcp) were determined. results: the d95 of the ptv for an isocenter shi' plan with a posterior direction 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 for both techniques. increasing the gantry-angle decreased the tcps of the ptv by 24.4% (cw) and by 34% (fif). the ntcps of the lungs and heart for the two techniques differed by only 3%. the cis and his for the cw case were higher than the corresponding values obtained for the fif case. significant differences were observed between the two techniques (p<0.01). conclusion: our results revealed that the biophysical properties of the fif case were more sensitive to setup errors than those in the cw case. the radiobiological-based analysis could be detected significant dosimetric errors and provided a practical patient quality assurance method for guiding the bio-physical effects.