Dobler Barbara, Obermeier Tina, Hautmann Matthias G, Khemissi Amine, Koelbl Oliver
Department of Radiotherapy, Regensburg University Medical Center, Regensburg, Germany.
Radiat Oncol. 2017 Jul 5;12(1):114. doi: 10.1186/s13014-017-0850-8.
The aim of this study was to investigate if the flattening filter free (FFF) irradiation mode of a linear accelerator (linac) is advantageous as compared to the flat beam (FF) irradiation mode in intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) for carcinoma of the hypopharynx / larynx.
Four treatment plans were created for each of 10 patients for an Elekta Synergy linac with Agility collimating device, a dual arc VMAT and a nine field step and shoot IMRT each with and without flattening filter. Plan quality was compared considering target coverage and dose to the organs at risk. All plans were verified by a 2D-ionization-chamber-array and delivery times were compared. Peripheral point doses were determined as a measure of second cancer risk. The Wilcoxon test was used for statistical analysis with a significance level of 0.05.
Plan quality was similar for all four treatment plans without statistically significant differences of clinical relevance. The clinical goals were met in all plans for the PTV-SIB (V > 95%), the spinal cord (D < 45 Gy) and the brain stem (D < 48 Gy). For the parotids, the goal of D < 30 Gy was met in 70% and 60% of the plans for the left and right parotid respectively, and the V of the SIB reached an average of 94%. Delivery times were similar for FF and FFF and significantly decreased by around 70% for VMAT as compared to IMRT. Peripheral doses were significantly reduced by 18% in FFF mode as compared to FF and by 26% for VMAT as compared to IMRT. Lowest peripheral doses were found for VMAT FFF, followed by VMAT FF.
The FFF mode of a linear accelerator is advantageous for the treatment of hypopharynx/larynx carcinoma only with respect to reduction of second cancer induction in peripheral organs for the combination of Elekta Synergy linacs and Oncentra® External Beam v4.5 treatment planning system. This might be of interest in a therapy with curative intent.
本研究旨在探讨直线加速器的无均整器（FFF）照射模式与扁平射束（FF）照射模式相比，在下咽/喉癌的调强放射治疗（IMRT）和容积调强弧形治疗（VMAT）中是否具有优势。
为配备敏捷准直装置的医科达Synergy直线加速器的10例患者中的每例患者创建了四个治疗计划，一个双弧VMAT和一个九野静态调强放疗计划，均分别采用有均整器和无均整器的情况。从靶区覆盖和危及器官的剂量方面比较计划质量。所有计划均通过二维电离室阵列进行验证，并比较了治疗时间。确定周边点剂量作为继发癌症风险的指标。采用Wilcoxon检验进行统计分析，显著性水平为0.05。
所有四个治疗计划的计划质量相似，无临床相关的统计学显著差异。在所有计划中，PTV-SIB（V＞95%）、脊髓（D＜45 Gy）和脑干（D＜48 Gy）均达到临床目标。对于腮腺，左右腮腺分别在70%和60%的计划中达到D＜30 Gy的目标，SIB的V平均达到94%。FF和FFF的治疗时间相似，与IMRT相比，VMAT的治疗时间显著减少约70%。与FF相比，FFF模式下周边剂量显著降低18%，与IMRT相比，VMAT降低26%。VMAT FFF的周边剂量最低，其次是VMAT FF。
对于医科达Synergy直线加速器和Oncentra®外照射v4.5治疗计划系统的组合，直线加速器FFF模式仅在减少周边器官继发癌症诱导方面对下咽/喉癌治疗具有优势。这在根治性治疗中可能具有意义。
