Yoshihiro Ueda, Shingo Ohira, Masaru Isono, Masayoshi Miyazaki, Koji Konishi, Shoji Kamiura, Iori Sumida, Kazuhiko Ogawa, Teruki Teshima
1 Department of Radiation Oncology, Osaka International Cancer Institute, Osaka Japan.
2 Department of Radiation Oncology, Graduate School of Medicine, Osaka University, Osaka, Japan.
Br J Radiol. 2018 Jan;91(1081):20160777. doi: 10.1259/bjr.20160777. Epub 2017 Nov 3.
To reduce the ovarian dose with volumetric modulated arc therapy (VMAT), an original VMAT was designed with two types of arcs to restrict angles and fields (R-VMAT).
The subjects were 11 patients who underwent ovarian transposition with clips left by a surgeon. Three methods, intensity-modulated radiotherapy (IMRT), standard VMAT (S-VMAT) and R-VMAT, were optimized for assessment of the ovarian dose with the target coverage kept high.
The homogeneity and conformity indexes for the planning target volume (PTV) were similar for the three methods. However, the average ± SD of the ovarian mean dose (OMD) was 5.0 ± 1.5, 4.9 ± 1.9 and 3.5 ± 1.4 Gy, and the percentage of ovarian volume exceeding 5 Gy (V5) was 41.5 ± 34.1%, 34.1 ± 38.05% and 8.4 ± 20.5% for IMRT, S-VMAT and R-VMAT, respectively. The OMD and V5 were significantly smaller for R-VMAT than for the other plans (p < 0.01). Correlation values between the OMD and the lateral distance from the ovaries to the PTV surface were 0.86, 0.81 and 0.82 for IMRT, S-VMAT and R-VMAT, respectively.
These findings suggest that R-VMAT delivered the lowest dose to the ovaries. To reduce the OMD to less than 3 Gy, ovaries should be transposed laterally 6.1 cm away from the PTV surface when R-VMAT is used. Advances in knowledge: When organs with high susceptibility to radiation, such as ovaries, are near the PTV, R-VMAT is superior to IMRT and S-VMAT.
为了使用容积调强弧形放疗（VMAT）降低卵巢剂量，设计了一种原始的VMAT，采用两种弧形来限制角度和射野（R-VMAT）。
研究对象为11例接受了卵巢移位术且外科医生留置了夹子的患者。对三种方法，即调强放疗（IMRT）、标准VMAT（S-VMAT）和R-VMAT进行优化，以在保持高靶区覆盖的情况下评估卵巢剂量。
三种方法的计划靶区（PTV）的均匀性和适形指数相似。然而，IMRT、S-VMAT和R-VMAT的卵巢平均剂量（OMD）的平均值±标准差分别为5.0±1.5、4.9±1.9和3.5±1.4 Gy，卵巢体积超过5 Gy（V5）的百分比分别为41.5±34.1%、34.1±38.05%和8.4±20.5%。R-VMAT的OMD和V5显著低于其他计划（p<0.01）。IMRT、S-VMAT和R-VMAT的OMD与卵巢到PTV表面的横向距离之间的相关值分别为0.86、0.81和0.82。
这些结果表明R-VMAT对卵巢的剂量最低。当使用R-VMAT时，为了将OMD降低到3 Gy以下，卵巢应横向移位至距离PTV表面6.1 cm处。知识进展：当对辐射敏感的器官，如卵巢，靠近PTV时，R-VMAT优于IMRT和S-VMAT。
