Department of Radiation Oncology, Washington University School of Medicine in St. Louis, St. Louis, Missouri, USA.
Med Phys. 2024 Nov;51(11):8584-8596. doi: 10.1002/mp.17356. Epub 2024 Aug 26.
Radiochromic film (RCF) dosimeters with their high spatial resolution and tissue equivalent properties are conveniently used for two-dimensional and small-field dosimetry. OC-1 is a new model of RCF dosimeter that was commercially introduced recently. Due to its novelty there is a need to characterize its response in various radiation beam types.
To study the response of OC-1 RCFs to megavoltage clinical x-ray, electron, and proton beams, as well as kilovoltage x-ray beams used in a small animal research irradiator.
OC-1 RCFs were cut into ∼4 × 4 cm pieces. RCF samples were irradiated at various dose levels in the range 0.5-120 Gy using different modalities; a small animal radiation research platform (SARRP) (220 kVp), a medical linear accelerator (6 MV, 10 MV, 15 MV, 6 MV FFF, 10 MV FFF photon beams, as well as 6 and 20 MeV electron beams), and a gantry-mounted proton therapy synchrocyclotron. In order to study any dependency on the fractionation scheme, same dose was delivered at several fractions to a set of films. Different dose rates in the range 200-600 MU/min were delivered to a set of films to investigate any dose rate dependency. The films were scanned pre-irradiation and at 48 h post-irradiation using a flatbed scanner. The net optical density (OD) was measured for red, green, and blue color channel for each film. The orientation dependency was studied by scanning the films at eight different orientations. In order to study the temporal evolution of the response of the films, film samples were irradiated at 10 and 50 Gy using 6 MV photon beams and were scanned upon irradiation at certain time intervals up to 3 months. The spectral response of the films were studied over the visible range using a spectrometer.
For megavoltage photon, electron, and plateau region of the proton beams, we did not observe a significant dependency on the beam quality, dose rate, and fractionation scheme. At the kV beam, an unusual over-response was observed in the films' net OD. An orientation dependency in the response of the films with a sinusoidal trend was observed. The response of the films increased with time following a double or triple exponential trend. The spectral absorption peaks were blue-shifted with dose.
OC-1 RCFs were found to be reliable dosimeters with no significant energy dependency in MV range for photon and electron beams including the FFF beams. They over-respond when irradiated by kV x-ray beams compared to MV x-ray beams. Caution must be exercised to maintain the orientation of the films when scanning. Due to the temporal growth in the net OD of the films, same post-irradiation time interval must be used for scanning the calibration and test films.
放射色迹胶片（RCF）具有高空间分辨率和组织等效特性，非常适合二维和小野剂量测定。OC-1 是最近推出的新型 RCF 剂量计。由于其新颖性，需要对其在各种射线类型中的响应进行特征描述。
研究 OC-1 RCF 对兆伏临床 X 射线、电子和质子射线，以及小动物研究辐照器中使用的千伏 X 射线的响应。
将 OC-1 RCF 切割成约 4×4cm 的小块。使用不同的模式在 0.5-120Gy 的范围内将 RCF 样品照射到不同的剂量水平；小动物辐射研究平台（SARRP）（220kVp）、医用直线加速器（6MV、10MV、15MV、6MVFFF、10MVFFF 光子束，以及 6 和 20MeV 电子束）和安装在回旋加速器上的质子治疗同步回旋加速器。为了研究任何对分割方案的依赖性，对一组胶片进行了多次分割的相同剂量照射。将不同的剂量率（200-600MU/min）传递到一组胶片，以研究任何剂量率依赖性。在辐照前和辐照后 48 小时使用平板扫描仪对胶片进行扫描。为每张胶片的红色、绿色和蓝色通道测量净光密度（OD）。通过在八个不同方向上扫描胶片来研究方向依赖性。为了研究胶片响应的时间演变，使用 6MV 光子束在 10 和 50Gy 下辐照胶片样品，并在特定时间间隔内进行扫描，直到 3 个月。使用分光光度计研究胶片的光谱响应。
对于兆伏光子、电子和质子束的平台区域，我们没有观察到束质、剂量率和分割方案的显著依赖性。在千伏射束下，胶片的净 OD 观察到异常的过响应。在胶片的响应中观察到一种正弦趋势的方向依赖性。胶片的响应随时间呈双指数或三指数趋势增加。光谱吸收峰随剂量蓝移。
OC-1 RCF 被发现是可靠的剂量计，在兆伏范围内的光子和电子束（包括 FFF 束）中没有明显的能量依赖性。与兆伏 X 射线相比，它们在受到千伏 X 射线照射时会过度响应。在扫描时必须注意保持胶片的方向。由于胶片的净 OD 随时间增长，因此必须使用相同的辐照后时间间隔来扫描校准和测试胶片。
