(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: There is increasing interest in treating breast cancer with radiation in the preoperative setting, for which there is limited data regarding the optimal means of setting up patients to the intact breast tumor. When treating breast cancer patients with a preoperative boost, gross tumor volume (GTV), the ipsilateral breast, adjacent ribs, external radio-opaque markers and skin marks can all be used for aligning patients. This study prospectively investigated setup discrepancies when aligning patients to these distinct structures with CT on Rails (CTOR) on a phase II clinical trial.
Methods: Thirteen breast cancer patients treated with pre-operative boost were included in this IRB-approved protocol. Patients were treated with 3D conformal plans to the planning target volume (PTV). On the first fraction, patients were positioned to skin marks, shifted to treatment isocenter, imaged with CTOR, and further aligned to the CT-MRI defined GTV for treatment using an in-house image registration software. Off-line image alignments were performed to the ipsilateral breast, adjacent ribs, and external radio-opaque markers to compare with the alignment to GTV. The root mean square deviation (RMSD) and Wilcoxon matched-pairs signed rank test (T-test) were calculated to compare setup alignments.
Results: The study showed the differences between setting up patients to GTV and ipsilateral breast, adjacent ribs, external radio-opaque markers, and skin marks were 0.21 cm, 0.28 cm, 0.38 cm, 0.37 cm in RMSD, respectively. These differences were 0.60 cm, 0.50cm, 1.50 cm and 0.80 cm maximum, respectively. The P value was > 0.05 for all T-test comparisons.
Conclusion: There was modest differences (< 0.4 cm in RMSD) between setting up patients to GTV and other studied structures. Though the maximum difference can be as high as 1.5 cm if using external marks, these differences were not statistically significant in this small patient cohort.
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