Department of Medical Physics in Radiation Therapy (E040), German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, Heidelberg, Germany. National Center for Radiation Research in Oncology (NCRO), Heidelberg Institute for Radiation Oncology (HIRO), Im Neuenheimer Feld 280, Heidelberg, Germany. Author to whom any correspondence should be addressed. These authors contributed equally to this study.
Phys Med Biol. 2019 Feb 11;64(4):045010. doi: 10.1088/1361-6560/aafd41.
Absolute dosimetry in 3D with polymer gels (PG) is generally complicated and usually requires a second independent measurement with conventional detectors. This is why, PG are often used only for relative dosimetry. To overcome this drawback, we combine PG with a 1D thermoluminescence (TL) detector within the same measurement. The TL detector information is then used as additional information for calibration of the gel.
The PAGAT dosimetry gel was used in combination with TLD600 (LiF:Mg,Ti). TL detectors were attached on the surface of the PG container placed inside a cylindrical phantom. To test the usability of this setup, two irradiation geometries were carried out: (a) homogeneous target coverage and (b) small-field irradiation. PG was evaluated with magnetic resonance imaging (MRI) and the TL detectors with a Harshaw 5500 hot gas reader.
PG dosimetry alone showed deviations of up to 4% as compared to calculations. Including additionally the dose information of the TL detectors for PG calibration, this deviation was decreased to less than 1% for both irradiation geometries. This is also reflected by the very high [Formula: see text]-passing rates of > 96% (3%/3 mm) and >93% (2%/2 mm), respectively.
This study presents a novel method combining 3D PG and TL dose measurements for the purpose of absolute 3D dose measurements that can also be applied in complex anthropomorphic phantoms using only a single measurement. The method was validated for two different irradiation geometries including a homogeneous large field as well as a small field irradiation with sharp dose gradients.
使用聚合物凝胶（PG）进行三维绝对剂量测定通常较为复杂，通常需要使用传统探测器进行第二次独立测量。这就是为什么 PG 通常仅用于相对剂量测定的原因。为了克服这一缺点，我们在同一测量中结合了 PG 和一维热释光（TL）探测器。然后，TL 探测器的信息将被用作凝胶校准的附加信息。
PAGAT 剂量凝胶与 TLD600（LiF：Mg，Ti）结合使用。TL 探测器附着在放置在圆柱形体模内的 PG 容器的表面上。为了测试此设置的可用性，进行了两种辐照几何形状的测试：（a）均匀靶覆盖和（b）小场辐照。PG 通过磁共振成像（MRI）进行评估，TL 探测器通过 Harshaw 5500 热气体阅读器进行评估。
与计算值相比，单独进行 PG 剂量测定会产生高达 4%的偏差。通过另外将 TL 探测器的剂量信息用于 PG 校准，这两种辐照几何形状的偏差都降低到了 1%以下。这也反映在非常高的通过率上，分别为>96%（3%/3mm）和>93%（2%/2mm）。
本研究提出了一种新的方法，将 3D PG 和 TL 剂量测量结合起来，用于绝对 3D 剂量测量的目的，该方法仅使用单次测量即可应用于复杂的人体模型。该方法已针对两种不同的辐照几何形状进行了验证，包括均匀大场以及具有陡峭剂量梯度的小场辐照。
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