Dosimetric Study and Robustness Analysis of Base Note Intensive Locked Field Radiotherapy for Left Breast Cancer.

Background: The locked vision plan can make the left breast cancer heart and lung organs dose.

Objective: The aim of the present study was to compare the dosimetric differences between field-locked and field-split plans in intensity-modulated radiotherapy for left-sided breast cancer, to explore the effect of field-locking on the low-dose region, and to evaluate its robustness to the radiotherapy target, in order to provide a reference for the selection of clinical radiotherapy protocols.

Methods: A total of 30 patients were selected after radical left breast cancer surgery, and 7-field locked-field and split-field plans were developed to compare the dose difference (∆D) between the target area and each organ at risk, and to introduce offsets of 3, 5 and 7 mm in six directions and recalculate the perturbed dose distributions, and to compare the ∆D between the original and the perturbed plans according to the robustness of the plans.

Results: The results revealed that the D_98%, D_95% and D_mean values of the planning target volume (PTV) of the two plans differed little and were not statistically different. The locked field plan provided better protection for the left lung, right lung, heart, right breast and left anterior descending coronary artery. For PTV∆D_98%, PTV∆D_95%, PTV∆D_mean, the ∆D was higher for the Locked Fields plan, and for LungL∆5, LungL∆20 and Heart∆_mean, the ∆D was higher for the original plan.

Discussion: It was concluded that the field-locking plan could reduce the low-dose area of the affected lung and provide improved protection to the remaining critical organs, and the field-locking plan was more robust in protecting critical organs. Meanwhile, the field-locking plan showed higher sensitivity to positional deviation for target PTV.