Bayoumi Y, Al-Amro A, Moniem R A, Sohaibani I, Al-Hanafy O, Alawadi A S, Asiri M
Radiation Oncology Department, King Fahad Medical City, Riyadh, Saudi Arabia.
Gulf J Oncolog. 2009 Jul(6):35-40.
Set-up errors are an inherent part of radiation treatment process. Coverage of target volume is a direct function of set-up margins, which should be optimized to prevent inadvertent irradiation of adjacent normal tissues. The aim of this study is to evaluate set-up errors and propose optimum margins for target volume coverage in head and neck radiotherapy.
Twenty six head and neck cancer patients received intensity modulated radiation therapy (IMRT) included in the study. The weekly portal images taken after correction of the systematic error -if any- were evaluated. The systematic error tested and corrected by taking portal images in the 1st 3 days of treatment by using the VARIS offline review system. Three hundred sixty four portal images matched anatomically with anterior and lateral digitally reconstructed radiographs (DRRs). Five hundred forty six points used to evaluate isocenter displacement in antero-posterior direction (AP), supero-inferior direction (SI) and right-left direction (RL).
The mean isocenter displacement in AP, RL, and SI directions were 1.5 +/- 1.6 mm, 1.3 +/-1.4 mm and 2.13 +/- 1.6 mm. Ninety six percent of the isocenter deviations were within 4 mm in all three directions. The displacement more than 4 mm (negative or positive) was 4% in the vertical direction, 7% in the longitudinal direction and 1.6% in the lateral direction. There is insignificant increase of the isocenter shift in the last weeks of radiotherapy especially in the vertical and longitudinal directions.
The current setup for irradiating head and neck cancer patients using IMRT in our department is accurate. The 4 mm CTV-PTV margin is enough.
摆位误差是放射治疗过程中固有的一部分。靶区的覆盖范围是摆位边界的直接函数，应优化摆位边界以防止对相邻正常组织的意外照射。本研究的目的是评估头颈部放疗中的摆位误差，并提出靶区覆盖的最佳边界。
本研究纳入了26例接受调强放射治疗（IMRT）的头颈部癌患者。对校正系统误差（如有）后每周拍摄的射野图像进行评估。在治疗的前3天使用VARIS离线复查系统拍摄射野图像来检测和校正系统误差。364张射野图像与前后位和侧位数字重建X线片（DRR）进行解剖学匹配。546个点用于评估等中心在前后方向（AP）、上下方向（SI）和左右方向（RL）的位移。
等中心在AP、RL和SI方向的平均位移分别为1.5±1.6mm、1.3±1.4mm和2.13±1.6mm。在所有三个方向上，96%的等中心偏差在4mm以内。垂直方向上位移超过4mm（正负）的占4%，纵向方向占7%，横向方向占1.6%。在放疗的最后几周，等中心移位无明显增加，尤其是在垂直和纵向方向。
我们科室目前对头颈部癌患者使用IMRT的摆位是准确的。4mm的临床靶区（CTV）到计划靶区（PTV）边界足够。
