Kanda Daisuke, Hanada Takashi, Yoshida Kayo, Tanaka Tomoki, Eriguchi Takahisa, Yorozu Atsunori, Ohashi Toshio, Shigematsu Naoyuki
Department of Radiology, Tokyo Medical Center, National Hospital Organization, Higashigaoka 2-5-1, Meguro-ku, Tokyo 152-8902, Japan.
Department of Radiology, Keio University School of Medicine, Shinanomachi 35, Shinjuku-ku, Tokyo 160-8582, Japan.
J Radiat Res. 2023 May 5;64(3):590-8. doi: 10.1093/jrr/rrad023.
We investigated dose perturbations caused by 125I seeds in patients undergoing supplemental external beam radiotherapy (EBRT) for prostate cancer. We examined two types of nonradioactive seed models: model 6711 and model STM1251. All experiments were performed using a water-equivalent phantom. Radiochromic film was used to measure the dose distributions adjacent to the seeds upstream and downstream of the external beam source. Single and clusters of multiple seeds were placed in slots in a solid water (SW) slab to measure dose perturbations with separate versus dense seed placement at beam energies of 6 or 10 MV. Monte Carlo simulations (MCSs) were also performed to include the theoretical basis against film dosimetry. Distinct patterns of dose enhancement (buildup [BU]) were upstream, and dose reduction (builddown [BD]) were downstream of the radiation source. Model 6711 with lower photon beam energies produced larger dose perturbations of BU and BD than the model STM1251. The results showed the same tendency with different seed placements and beam energies. However, these differences were not observed in the rotational irradiation measurement, which replicated a clinical plan. Dose perturbations around seeds result in dose enhancement and dose reduction with varying impact depending on the photon beam energy and seed type. This has the potential to cancel out these perturbations using multiple beam direction fields.
我们研究了在接受前列腺癌补充外照射放疗（EBRT）的患者中，¹²⁵I 粒子引起的剂量扰动。我们检查了两种非放射性粒子模型：6711 型和 STM1251 型。所有实验均使用水等效体模进行。采用放射变色胶片测量外照射源上游和下游粒子附近的剂量分布。将单个和多个粒子簇放置在固体水（SW）平板的狭槽中，以测量在 6 或 10 MV 束能量下，粒子单独放置与密集放置时的剂量扰动。还进行了蒙特卡罗模拟（MCS），以纳入与胶片剂量测定相对的理论基础。剂量增强（积累[BU]）的明显模式出现在辐射源上游，而剂量降低（衰减[BD]）出现在辐射源下游。光子束能量较低的 6711 型产生的 BU 和 BD 剂量扰动比 STM1251 型更大。结果表明，不同的粒子放置方式和束能量具有相同的趋势。然而，在复制临床计划的旋转照射测量中未观察到这些差异。粒子周围的剂量扰动会导致剂量增强和剂量降低，其影响因光子束能量和粒子类型而异。这有可能利用多个射束方向场抵消这些扰动。
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