监测器单位不能预测高能调强放疗中的中子剂量。
Monitor units are not predictive of neutron dose for high-energy IMRT.
机构信息
Institute for Radiotherapy, Radiotherapie Hirslanden AG, Aarau, Switzerland.
出版信息
Radiat Oncol. 2012 Aug 10;7:138. doi: 10.1186/1748-717X-7-138.
BACKGROUND
Due to the substantial increase in beam-on time of high energy intensity-modulated radiotherapy (>10 MV) techniques to deliver the same target dose compared to conventional treatment techniques, an increased dose of scatter radiation, including neutrons, is delivered to the patient. As a consequence, an increase in second malignancies may be expected in the future with the application of intensity-modulated radiotherapy. It is commonly assumed that the neutron dose equivalent scales with the number of monitor units.
METHODS
Measurements of neutron dose equivalent were performed for an open and an intensity-modulated field at four positions: inside and outside of the treatment field at 0.2 cm and 15 cm depth, respectively.
RESULTS
It was shown that the neutron dose equivalent, which a patient receives during an intensity-modulated radiotherapy treatment, does not scale with the ratio of applied monitor units relative to an open field irradiation. Outside the treatment volume at larger depth 35% less neutron dose equivalent is delivered than expected.
CONCLUSIONS
The predicted increase of second cancer induction rates from intensity-modulated treatment techniques can be overestimated when the neutron dose is simply scaled with monitor units.
背景
与传统治疗技术相比，高能强度调制放疗（>10MV）技术为实现相同靶剂量，其射束照射时间显著增加，从而向患者散射更多剂量的辐射，包括中子。因此，随着强度调制放疗的应用，未来可能会出现更多的第二恶性肿瘤。通常认为，中子剂量当量与监测器单位数量成正比。
方法
在四个位置（治疗野内外，分别为 0.2cm 和 15cm 深度）对开放式和强度调制式射野进行了中子剂量当量的测量。
结果
结果表明，患者在强度调制放疗过程中接受的中子剂量当量与相对于开放式照射应用的监测器单位的比值不成比例。在较大深度的治疗体积外，中子剂量当量比预期少 35%。
结论
当仅根据监测器单位来估算中子剂量时，可能会高估强度调制治疗技术引起第二癌症发生率的增加。
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