Abstract:
Objective To compare the dosimetry difference between flattening filter free (FFF) mode and flattening filter (FF) mode in deep inspiration breath-hold(DIBH) treatments of left-sided breast cancer after modified radical mastectomy with volumetric modulated arc therapy (VMAT).
Methods Retrospectively analyzed the clinical data of 16 female patients with left breast cancer after modified radical mastectomy with DIBH radiotherapy in the First Affiliated Hospital of Xi'an Jiaotong University from December 2020 to May 2021, aged 37 to 61 (43.5±5.7) years old. VMAT plans of FFF and FF modes were designed for the same patient, and the same prescription dose of 50 Gy/25 times was set in the planning target volume (PTV). Under the same dose normalization, the dosimetric parameters of the target and the organs at risk(OAR) and treatment efficiency were compared between the two plans. Paired t-test was used to compare the data between groups.
Results No significant differences in D2%, D50%, D98%, CI , HI and GI were found in the target area between the two modes (t=−1.519-1.644; all P>0.05). FFF mode was superior to FF mode in protection of OAR, such as V5 Gy, V30 Gy (Vx Gy: ≥x Gy volume as a percentage of total volume) and mean dose (Dmean) of heart; V5 Gy, V10 Gy and Dmean of ipsilateral lung; V5 Gy, V10 Gy, V20 Gy and Dmean of whole lung; and V5 Gy of patient dose, and the differences between the two modes were statistically significant (t=−4.741 to−2.156; all P<0.05). The total monitor units of FFF mode was 1.32 times of that in FF mode ((1073.41±143.79) MU vs.(815.70±87.69) MU), but the total delivery time was reduced to 88.9% of that in FF mode((128.00±11.64) s vs.(144.75±11.45) s), and the differences between the two modes were statistically significant (t=8.665, −4.373; both P<0.05).
Conclusion The target dose between the two modes were similar. The FFF mode can remarkably reduce the radiation dose of OAR and normal tissues, and can significantly shorten the time of DIBH therapy.