De Saint-Hubert Marijke, Majer Marija, Hršak Hrvoje, Heinrich Zdravko, Kneževic Željka, Miljanic Saveta, Porwol Paulina, Stolarczyk Liliana, Vanhavere Filip, Harrison Roger M
Belgium Nuclear Research Centre (SCK-CEN), Boeretang 200, Mol, Belgium.
Ruder Boškovic Institute, Bijenicka c. 54, Zagreb, Croatia.
Radiat Prot Dosimetry. 2018 Oct 1;181(2):100-110. doi: 10.1093/rpd/ncx301.
The purpose of this study was to measure out-of-field organ doses in two anthropomorphic child phantoms for the treatment of large brain arteriovenous malformations (AVMs) using hypofractionated gamma knife (GK) radiosurgery and to compare these with an alternative treatment using intensity-modulated radiation therapy (IMRT). Target volume was identical in size and shape in all cases. Radiophotoluminescent (RPL), thermoluminescent (TL) and optically stimulated luminescent (OSL) dosimeters were used for out-of-field dosimetry during GK treatment and a good agreement within 1-2% between results was shown. In addition, the use of multiple dosimetry systems strengthens the reliability of the findings. The number of GK isocentres was confirmed to be important for the magnitude of out-of-field doses. Measured GK doses for the same distance from the target, when expressed per target dose and isocentre, were comparable in both phantoms. GK out-of-field doses averaged for both phantoms were evaluated to be 120 mGy/Gy for eyes then sharply reduced to 20 mGy/Gy for mandible and slowly reduced up to 0.8 mGy/Gy for testes. Taking into account the fractionation regimen used to treat AVM patients, the total treatment organ doses to the out-of-field organs were calculated and compared with IMRT. The eyes were better spared with GK whilst for more distant organs doses were up to a factor of 2.8 and 4 times larger for GK compared to IMRT in 5-year and 10-year old phantoms, respectively. Presented out-of-field dose values are specific for the investigated AVM case, phantoms and treatment plans used for GK and IMRT, but provide useful information about out-of-field dose levels and emphasise their importance.
本研究的目的是测量使用大分割伽玛刀（GK）放射外科治疗大型脑动静脉畸形（AVM）时，两个儿童人体模型中靶区外器官的剂量，并将其与使用调强放射治疗（IMRT）的替代治疗进行比较。所有病例的靶区体积在大小和形状上均相同。在GK治疗期间，使用放射光致发光（RPL）、热释光（TL）和光激励发光（OSL）剂量计进行靶区外剂量测定，结果显示相互间的一致性良好，误差在1-2%以内。此外，使用多种剂量测定系统增强了研究结果的可靠性。已证实GK等中心点的数量对靶区外剂量的大小很重要。对于距靶区相同距离处测量的GK剂量，以每个靶区剂量和等中心点表示时，在两个模型中具有可比性。两个模型的GK靶区外剂量平均值经评估，眼睛为120 mGy/Gy，然后下颌骨急剧降至20 mGy/Gy，睾丸则缓慢降至0.8 mGy/Gy。考虑到用于治疗AVM患者的分割方案，计算了靶区外器官的总治疗器官剂量，并与IMRT进行比较。GK对眼睛的保护更好，而对于更远的器官，在5岁和10岁模型中，GK的剂量分别比IMRT大2.8倍和4倍。所呈现的靶区外剂量值特定于所研究的AVM病例、模型以及用于GK和IMRT的治疗计划，但提供了有关靶区外剂量水平的有用信息，并强调了它们的重要性。
