Oldham M, Siewerdsen J H, Shetty A, Jaffray D A
Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, Michigan 48073, USA.
Med Phys. 2001 Jul;28(7):1436-45. doi: 10.1118/1.1380430.
The increased intricacy of Intensity-Modulated-Radiation-Therapy (IMRT) delivery has created the need for a high-resolution 3D-dosimetry (three-dimensional) system capable of measuring and verifying the complex delivery. Present clinical methods are inadequate being restricted to single points (e.g., ion-chambers) or to 2D planes (e.g., film), and are labor intensive. In this paper we show that gel-dosimetry in conjunction with optical-CT scanning can yield maps of dose that are of sufficient accuracy, resolution and precision to allow verification of complex radiosurgery deliveries, and by extension IMRT deliveries. The radiosurgery dose-distribution represents the most challenging case encountered in external beam therapy by virtue of the steep dose-gradients and high resolution of delivery. We characterize the stringent radiosurgery requirements by the RTAP (Resolution-Time-Accuracy-Precision) criteria defined as < or = 1 mm3 spatial resolution, < or = 1 hour imaging time, accurate to within 3%, and within -1% precision. The RTAP criteria is applied to an in-house laser-based optical-CT scanning system presented here, and evaluated using gel-flasks containing BANG3 gel. The same gel flasks were subsequently imaged using the MR imaging protocol recommended by the gel manufacturer, but modified to match as closely as possible the RTAP. The resulting dose-maps demonstrate the high precision (< 1.3% noise at high dose) achievable with optical CT scanning while preserving high spatial resolution (<1 mm3). Using the sequence above, the MR gel-dose maps were found to have poorer precision by a factor of 5, under the strict conditions of the RTAP. The optical CT gel-dosimetry system was further evaluated for the verification of a complex 3-isocenter radiosurgery delivery. In conclusion, this work demonstrates that gel-dosimetry and optical-CT scanning approach an important long-term goal of radiation dosimetry, as specified by the RTAP criteria, and have potential to impact the clinic by improving and facilitating clinical dose verification for the most complex external beam radiation treatments.
调强放射治疗（IMRT）实施过程的复杂性不断增加，因此需要一种高分辨率三维剂量测定系统，以测量和验证这种复杂的治疗过程。目前的临床方法存在不足，仅限于单点测量（如电离室）或二维平面测量（如胶片），且劳动强度大。在本文中，我们表明，凝胶剂量测定法与光学CT扫描相结合，可以生成具有足够准确性、分辨率和精度的剂量图，以验证复杂的放射外科治疗过程，进而验证IMRT治疗过程。放射外科治疗的剂量分布是外照射治疗中最具挑战性的情况，因为其剂量梯度陡峭且治疗分辨率高。我们通过定义为≤1立方毫米空间分辨率、≤1小时成像时间、精确到±3%以内且精度在±1%以内的RTAP（分辨率-时间-准确性-精度）标准来描述严格的放射外科治疗要求。将RTAP标准应用于此处介绍的基于激光的内部光学CT扫描系统，并使用装有BANG3凝胶的凝胶瓶进行评估。随后，使用凝胶制造商推荐的磁共振成像协议对相同的凝胶瓶进行成像，但进行了修改以尽可能符合RTAP标准。所得的剂量图表明，光学CT扫描在保持高空间分辨率（<1立方毫米）的同时，可实现高精度（高剂量时噪声<1.3%）。按照上述顺序，发现在RTAP的严格条件下，磁共振凝胶剂量图的精度要差5倍。对光学CT凝胶剂量测定系统进行了进一步评估，以验证复杂的三等中心放射外科治疗过程。总之，这项工作表明，凝胶剂量测定法和光学CT扫描达到了放射剂量测定的一个重要长期目标，即RTAP标准所规定的目标，并且有潜力通过改进和促进最复杂的外照射放射治疗的临床剂量验证来影响临床实践。
