Department of Physics, University of British Columbia-Okanagan campus, Kelowna BC, V1V 1V7, Canada.
Medical Physics, BC Cancer-Victoria, Victoria BC, V8R 6V5, Canada.
Phys Med Biol. 2020 Nov 24;65(22):225030. doi: 10.1088/1361-6560/abbb76.
X-ray CT polymer gel dosimetry (PGD) remains a promising tool for three dimensional verification of high-dose treatment deliveries such as non-coplanar stereotactic irradiations. Recent demonstrations have shown a proof-of-principle application of linac-integrated cone beam CT-imaged (LI-CBCT) PGDs for 3D dose verification. LI-CBCT offers advantages over previous CT based PGD, including close to real-time imaging of the irradiated dosimeter, as well as the ability to maintain the dosimeter in the same physical location for irradiation and imaging, thereby eliminating spatial errors due to dosimeter re-positioning for read-out that may occur for other systems. However the dosimetric characteristics of a LI-CBCT PGD system remain to be established. The work herein determines the dosimetric properties and critical parameters needed to perform cone beam PGD. In particular, we show that imaging the dosimeter 20-30 min post irradiation offers excellent recovery of maximum polymerization yield ([Formula: see text]90%), averaging with as few as 10 image averages can provide ∼90% gamma pass rates (3%, 3 mm) as compared to treatment planning, and that eliminating outlier averaging points can improve the precision and signal to noise ratio of resultant images. In summary, with appropriate methodology LI-CBCT PGD can provide dosimetric data capable of verification of complex high dose radiation deliveries in three dimensions and may find use in commissioning and validation of novel complex treatments.
X 射线 CT 聚合物凝胶剂量测定（PGD）仍然是一种很有前途的工具，可用于验证非共面立体定向照射等高剂量治疗的三维剂量分布。最近的研究已经证明了将 LINAC 集成锥形束 CT 成像（LI-CBCT）PGD 用于 3D 剂量验证的原理验证应用。LI-CBCT 相较于之前基于 CT 的 PGD 具有优势，包括可以实时成像辐照后的剂量计，并且能够将剂量计保持在相同的物理位置进行辐照和成像，从而消除了由于其他系统可能需要重新定位剂量计进行读出而导致的空间误差。然而，LI-CBCT PGD 系统的剂量学特性仍有待确定。本文旨在确定进行锥形束 PGD 所需的剂量学特性和关键参数。特别是，我们证明了在辐照后 20-30 分钟对剂量计进行成像可以极好地恢复最大聚合产率（[Formula: see text]90%），仅使用 10 次左右的图像平均即可获得与治疗计划相比约 90%的伽马通过率（3%，3 mm），并且消除异常值平均点可以提高图像的精度和信噪比。总之，通过适当的方法，LI-CBCT PGD 可以提供能够验证复杂高剂量辐射三维分布的剂量学数据，并且可能有助于新型复杂治疗的调试和验证。
