Room: ePoster Forums
Purpose: To evaluate the dosimetric changes in target volumes and organs at risk (OARs) of patients with left breast cancer who underwent intensity-modulated radiation therapy (IMRT) based on the deformable registration method.
Methods: Sixteen patients with left breast cancer treated with 6 MV X-ray IMRT were analyzed retrospectively. All targets included the lymph node drainage area and the chest wall. All patients underwent simulation of the primary positioning and repositioning to obtain CT series. The primary treatment plan and the secondary treatment plan were calculated on the primary positioning CT (CT1) and the repositioning CT (CT2) to obtain plan1 and plan2, respectively. The dose distribution of plan2 was registered rigidly to CT1 and to deformed CT1 and then added by the dose distribution of plan1 to obtain plan-rig and plan-def, respectively. The dosimetric differences between the targets and the OARs of the four plans were compared.
Results: The volume of CTV on CT2 was reduced by 8.74% comparing to CT1. The volume of PTV on CT2 was reduced by 11.20% comparing to CT1. The Dice similarity coefficients (DSCs) of the heart, left lung and right lung were lower than those before deformation registration accumulation (0.94Â±0.01vs.0.89Â±0.05,0.96Â±0.01vs.0.91Â±0.03,0.96Â±0.01vs.0.92Â±0.03), and the differences were statistically significant (t=3.83,7.28,6.70,P<0.05). There were no significant differences in the dose-volume indices of the heart or left lung between plan1 and the other plans, while the dose-volume indices in plan-rig were higher than those in plan-def (P>0.05).
Conclusion: Because of the small changes in the target volumes and OARs of left breast cancer patients after surgery during radiotherapy, we suggest using the first IMRT plan to evaluate the dose distribution of both lungs and the heart for patients with left breast cancer who have this complicated target.