元宫型宫内节育环对盆腔放射治疗剂量分布的影响

Impact of intrauterine contraceptive ring on pelvic radiotherapeutic dosage distribution

目的测量元宫型金属宫腔内节育环对放射治疗引起的密度效应及次级射线引起的散射效应对放射治疗剂量分布的影响。方法将元宫型金属节育环置于厚20cm的人体等效组织密度有机玻璃中间,分别用6MV和10MVX线垂直或平行于节育环分别进行10cm×10cm单野照射和二野对穿照射,用FARMER剂量仪电离室测量并比较节育环前1cm和0.5cm,环中间0cm,环后0.5cm和1cm及旁开0.5cm处的剂量。结果垂直或平行于节育环进行10cm×10cm单野照射时,各点与无环时比较,最大剂量变化为0.15%;对穿野照射时,最大剂量变化为0.13%。结论宫内节育器对放射治疗时剂量分布的影响远小于5%,在盆腔肿瘤需要放射治疗时,可以忽略节育环对剂量分布的影响。

Objective To determine the scattering and density effects of intrauterine contraceptive ring on pelvic radiotherapeutic dosage distribution. Methods A contraceptive ring was set into the middle of 20 cm thick plexiglass, an iso-human tissue, and irradiated in 10 cm × 10 cm single field and two parallel fields by 6 MV X ray as well as 10 MV X ray. The ionization measurement was performed by FARMER chamber, and measurement points were chosen in front of ring （0.5 and 1 cm） , in the centre of ring, behind ring （0.5 and 1 cm） , and on the side of ring （0.5 cm） in the presence or absence of ring. Results When 10 cm × 10 cm single field irradiated, the maximal dosage deviation was 0. 15% compared to that without ring. When two parallel fields irradiated, the dose maximal dosage deviation was 0. 13%. Conclusion The dosage change caused by scattering and density effects of contraceptive ring is far less than clinically limited 5% dosage deviation. The effects of contraceptive ring on pelvic radiotherapy can be ignored.