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KMID : 0390320220320020019
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Chungbuk Medical Journal
2022 Volume.32 No. 2 p.19 ~ p.28
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Dosimetric Characteristics of Volumetric Modulated Arc Therapy, Static Field Intensity Modulated Radiation Therapy, and Field in Field Intensity Modulated Radiation Therapy for Whole Breast Irradiation in Patients with Early Breast Cancer
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Kim Won-Dong
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Abstract
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Purpose: In our department, three-dimensional conformal radiation therapy (3DCRT) using a physical wedge filter or field in field (FIF) intensity modulated radiation therapy (IMRT) has been used for whole breast irradiation therapy in patients with breast cancer. IMRT such as volumetric modulated arc therapy (VMAT) and static field IMRT (static IMRT), which have recently been developed, were proposed as an innovative methods to increase the dose homogeneity in the target volume and lower the dose to normal organs. In this study, static IMRT and VMAT are compared with the traditional FIF
technique based on the cumulative dose-volume histogram (DVH)
Materials and Methods: We produced the treatment plans of FIF, static IMRT, and VMAT in five patients with left breast cancer who underwent whole breast irradiation after breast-conserving surgery in 2019. Three treatment plans generated each a DVH. Regarding the target, distribution of 100% isodose curve in each cross section of planning target volume (PTV), Dmax, target volume receiving more than 98% of the prescribed dose (V98%), homogeneity index (HI), and conformity index (CI) were analyzed and concerning organ at risk (OAR), Dmim, Dmax, Dmean, V10Gy, and V20Gy of the heart and ipsilateral lung were calculated. Dosimetric parameters were compared with each other.
Results: In FIF, PTV Dmax (50.12 Gy) was significantly higher, while V98% (88.5%) was lower than that of other treatment plans. This led to the deterioration of the dose HI, which was significantly higher than VMAT and static IMRT (1.24 vs 1.07 p<0.05), and of the CI, which was significantly lower (0.65 vs 0.84, p<0.05). The distribution of dose to the heart did not differ according to the treatment plan in the high-dose region of more than 10 Gy on DVH, but the difference was significant in the low-dose region of less than 10 Gy. In VMAT and static IMRT, Dmin was above 1 Gy and Dmean was above 3
Gy, whereas in FIF, Dmin was 0.57 Gy and Dmean was 2.5 Gy, which were significantly lower (p<0.05). In the dose distribution of the left lung, Dmean showed a significant difference between treatment plans. In VMAT and static IMRT, Dmean was over 9.4 Gy, whereas, in FIF, it was 7.21 Gy which was significantly lower and V10Gy (19.1%) was also significantly lower (p<0.05).
Conclusion: While VMAT or static IMRT revealed a better target coverage than FIF for whole breast irradiation, the low dose to the ipsilateral lung and heart was relatively increased . Therefore, care must be taken for indiscriminate use of VMAT or static IMRT and it is necessary to find the most appropriate radiotherapy plan considering the patient’s comorbid lung and heart diseases, breast shape, and normal organ location.
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KEYWORD
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VMAT, IMRT, Whole breast irradiation, Breast cance
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