Zhu X R, Jursinic P A, Grimm D F, Lopez F, Rownd J J, Gillin M T
Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee 53226, USA.
Med Phys. 2002 Aug;29(8):1687-92. doi: 10.1118/1.1493781.
A new type of radiographic film, Kodak EDR2 film, was evaluated for dose verification of intensity modulated radiation therapy (IMRT) delivered by a static multileaf collimator (SMLC). A sensitometric curve of EDR2 film irradiated by a 6 MV x-ray beam was compared with that of Kodak X-OMAT V (XV) film. The effects of field size, depth and dose rate on the sensitometric curve were also studied. It is found that EDR2 film is much less sensitive than XV film. In high-energy x-ray beams, the double hit process is the dominant mechanism that renders the grains on EDR2 films developable. As a result, in the dose range that is commonly used for film dosimetry for IMRT and conventional external beam therapy, the sensitometric curves of EDR2 films cannot be approximated as a linear function, OD = c * D. Within experimental uncertainty, the film sensitivity does not depend on the dose rate (50 vs 300 MU/min) or dose per pulse (from 1.0 x 10(-4) to 4.21 x 10(-4) Gy/pulse). Field sizes and depths (up to field size of 10 x 10 cm2 and depth = 10 cm) have little effect on the sensitometric curves. Percent depth doses (PDDs) for both 6 and 23 MV x rays were measured with both EDR2 and XV films and compared with ion chamber data. Film data are within 2.5% of the ion chamber results. Dose profiles measured with EDR2 film are consistent with those measured with an ion chamber. Examples of measured IMRT isodose distributions versus calculated isodoses are presented. We have used EDR2 films for verification of all IMRT patients treated by SMLC in our clinic. In most cases, with EDR2 film, actual clinical daily fraction doses can be used for verification of composite isodose distributions of SMLC-based IMRT.
一种新型的放射成像胶片——柯达EDR2胶片，被用于评估由静态多叶准直器（SMLC）实施的调强放射治疗（IMRT）的剂量验证。将6兆伏X射线束照射下的EDR2胶片的感光曲线与柯达X-OMAT V（XV）胶片的感光曲线进行了比较。还研究了射野大小、深度和剂量率对感光曲线的影响。结果发现，EDR2胶片的敏感度远低于XV胶片。在高能X射线束中，双打击过程是使EDR2胶片上的颗粒可显影的主要机制。因此，在IMRT和传统外照射治疗中通常用于胶片剂量测定的剂量范围内，EDR2胶片的感光曲线不能近似为线性函数OD = c * D。在实验不确定度范围内，胶片敏感度不取决于剂量率（50与300 MU/min）或每脉冲剂量（从1.0×10⁻⁴到4.21×10⁻⁴ Gy/脉冲）。射野大小和深度（最大射野大小为10×10平方厘米且深度 = 10厘米）对感光曲线影响很小。使用EDR2和XV胶片测量了6和23兆伏X射线的百分深度剂量（PDD），并与电离室数据进行了比较。胶片数据在电离室结果的2.5%以内。用EDR2胶片测量的剂量分布与用电离室测量的结果一致。给出了测量的IMRT等剂量分布与计算等剂量的示例。我们已在临床中使用EDR2胶片对所有由SMLC治疗的IMRT患者进行验证。在大多数情况下，使用EDR2胶片时，实际临床每日分次剂量可用于验证基于SMLC的IMRT的复合等剂量分布。
