Kortmann R D, Hess C F, Hoffmann W, Jany R, Bamberg M
Department of Radiotherapy, University of Tübingen, Germany.
Int J Radiat Oncol Biol Phys. 1995 Apr 30;32(1):241-4. doi: 10.1016/0360-3016(94)00411-D.
To evaluate whether the standardized helmet technique is adequate to reliably cover the clinical target volume (whole brain including cranial meninges) during treatment planning and treatment delivery.
In 21 patients undergoing irradiation of the brain in acute lymphoblastic leukemia or primary cerebral lymphoma, the coverage of the clinical target volume was checked with a repeat computed tomography (CT) in the treatment position (head fixation with face mask). The accuracy of field alignment was quantitatively assessed with sequential verification films. For each patient, linear and rotational discrepancies were measured between the simulation and first check film, and between five consecutive verification films.
Coverage of clinical target volume. In 11 cases (52%), the CT examinations showed that parts of the subfrontal region and midcranial fossa were not included by the field assigned under simulation. Accuracy of field alignment. For the total group of patients, all deviations were normally distributed with mean values between -1.2 mm and 1.5 mm and standard deviations of 2.9 mm to 3.7 mm for linear discrepancies, and 0.3 degrees +/- 3.2 degrees for rotational discrepancies. For all patients, deviations were similar for the transition from simulation to the treatment machine and for subsequent treatment delivery, with 50% and 95% of absolute differences being less than 2.0 mm and 6.5 mm, respectively. Maximum linear deviations were less than 9.5 mm.
The currently used helmet technique is inadequate to cover the clinical target volume. Repeat CT examinations are a useful method to delineate the clinical target volume on an individual patient basis. In addition, statistical fluctuations of field displacements up to 1.0 cm have to be considered when prescribing safety margins for reliable coverage of the clinical target volume during treatment planning and delivery.
评估标准化头盔技术在治疗计划制定和治疗实施过程中能否可靠地覆盖临床靶区（包括颅脑膜的全脑）。
对21例急性淋巴细胞白血病或原发性脑淋巴瘤接受脑部放疗的患者，在治疗体位（使用面罩固定头部）下通过重复计算机断层扫描（CT）检查临床靶区的覆盖情况。使用连续验证片定量评估射野对准的准确性。对每位患者，测量模拟定位与首次检查片之间以及五张连续验证片之间的线性和旋转偏差。
临床靶区的覆盖情况。11例（52%）CT检查显示，模拟定位时所设射野未包括额下区域和颅中窝的部分区域。射野对准的准确性。对于所有患者，所有偏差均呈正态分布，线性偏差的平均值在-1.2毫米至1.5毫米之间，标准差为2.9毫米至3.7毫米，旋转偏差为0.3度±3.2度。对于所有患者，从模拟定位到治疗机器以及后续治疗实施过程中的偏差相似，绝对差值的50%和95%分别小于2.0毫米和6.5毫米。最大线性偏差小于9.5毫米。
目前使用的头盔技术不足以覆盖临床靶区。重复CT检查是在个体患者基础上勾画临床靶区的有用方法。此外，在制定治疗计划和实施过程中为可靠覆盖临床靶区规定安全边界时，必须考虑高达1.0厘米的射野位移统计波动。
