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Year : 2014  |  Volume : 10  |  Issue : 1  |  Page : 56-61

Implementation of a wedged-dynamic arc therapy technique for head and neck cancer

1 Department of Radiation Physics, Oncology and Hematology Hospital, Maadi Armed Forces Medical Compound, Cairo, Egypt
2 Department of Radiotherapy Physics, Beatson West of Scotland Cancer Centre, United Kingdom
3 Department of Physics, Faculty of Science, Ain Shams University, Cairo, Egypt

Correspondence Address:
Mohamed S Ibrahim
Radiotherapy Physicist, Department of Radiation Physics, Oncology and Hematology Hospital, Maadi Armed Forces Medical Compound, Cairo
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Source of Support: The work was primarily carried out at Radiation Physics Department, Oncology and Hematology Hospital, Maadi Armed Forces Medical Compound, Cairo, Egypt, Authors, Conflict of Interest: None

DOI: 10.4103/0973-1482.131369

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Introduction: In this study, we designed and evaluated a wedged dynamic arc therapy (W-DAT) to provide the desirable concaved-shape dose distribution to cover the target in the treatment of head and neck sequence cell carcinoma. Materials and Methods: Eight patients were treated using W-DAT. The dose prescriptions were 70 Gy and 54 Gy, in 35 fractions, to the sites of the gross planning target volume (PTV1) and the microscopic (PTV2) diseases respectively. This technique consists of four wedged half-arcs of moving multi-leaf collimator leaves to fit PTV1 and shield brain stem at all gantry rotations. These were combined with two anterior-posterior conformal fields of different weighing to improve the dose uniformity. Another two anterior-posterior conformal fields were designed to cover the PTV2. All of the eight fields were half blocked by the normal jaws so there is no dose overlap at the interface between the two targets. Results: Referring to radiation therapy oncology group protocol 0615, 95% of the PTV1 was covered by more than 95% (66.50 Gy) of the prescribed dose, with very low dose inhomogeneity index of 0.0670 ± 0.0007. The maximum dose to 1% of the planning organ at risk volumes-brainstem didn't exceed 56.10 ± 2.17 Gy while the two parotids were well spared as they received a mean dose of 21.97 ± 3.24 Gy. Isocentric ion chamber measurements showed good agreement with the treatment planning system calculated dose with the maximum deviation of 2.40% while film measurements yielded lesser than 4.20% of the pixels failed the acceptance gamma criteria of (3 mm, 3%). Conclusion: W-DAT technique was approved in our department as the standard choice for the radical treatment of head and neck sequence cell carcinoma.

Abstract in Chinese

头颈部肿瘤楔形动态电弧治疗技术 引言:本文中,我们设计和评估了一种楔形动态电弧疗法(W-DAT),提供了满意的凹面形状剂量分布用来治疗头颈部鳞癌。 材料和方法:8例病人用W-DAT治疗。处方剂量70Gy和54Gy,35次分割,分别作用于肉眼计划靶区(PTV1)和显微病灶(PTV2)。这个技术由移动的多叶准直器的四个楔形半弧形灯构成,适应PTV1并在机架转移时全方位保护脑干。这些装置与两个前后投影的装置相结合以改善剂量均匀性。另两个前后投影的装置用来覆盖PTV2。所有8个装置都是通过正常的狭窄口半联锁的,所以在两个靶区的交界不会有剂量重叠。 结果:参照肿瘤放射治疗学组研究方案0615,PTV1的95%被覆盖是通过实际超过95%(66.50Gy)处方剂量,不均一性指数非常低0.0670± 0.0007。脑干1%容量最大剂量不超过56.10± 2.17Gy,两侧腮腺也被保护,平均剂量21.97± 3.24Gy。中心离子室测量证实该系统的良好相符性,仅2.4%的最大偏差,而薄膜测量稍差,少于4.2%像素,不符合γ-标准的(3mm, 3%)。 结论:W-DAT技术在我部门证实是治疗头颈部肿瘤的标准选择。 关键词:动态弧,头颈部肿瘤,射线管电子束调节,辐射剂量测定法

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