真空袋对等中心背斜野深度直接测定法的影响

Influence of Vacuum Bag on Direct Measurement of Depth for Isocentric Posterior Oblique Field

背景与目的:为了提高放射治疗的质量保证(qualityassurance,QA)及质量控制(qualitycontrol,QC)水平,定位和放疗中均使用个体化真空袋,逐渐成为放射治疗部门质量控制和质量保证的一项重要措施。胸、腹部肿瘤患者在模拟机中使用真空袋定位,是否影响等中心背斜野深度直接测定法的测量精确度仍有争议,本研究拟探讨真空袋对该测量方法的影响。方法:在29例使用真空袋固定体位、需仰卧位等中心放疗的胸、腹部肿瘤患者当中,分别用CT模拟和常规模拟定位测量45个背斜野照射深度并进行对比,把两者之差的绝对值作为误差值。结果:测量误差在5mm之内的有37个野,占82.2%;测量误差在5mm之上的有8个野,占17.8%,其中5个野属第二段放疗前复位,并在第一段治疗期间曾有真空袋轻度漏气,重抽真空的记录。结论:真空袋固定体位对等中心背斜野深度直接测定法的影响较小。

BACKGROUND &OBJECTIVE: In order to improve quality assurance (QA) and quality control (QC) of radiotherapy, individualized vacuum bag is used in t he localization of radiation treatment, gradually becoming one of the important steps for the QA and QC in the many departments of radiation oncology. It is con troversial whether localization with vacuum bags under the simulator influences the precision of direct measurement for tumor depth in the isocentric posterior oblique field in the patients with thoracic and abdominal tumors. This study was designed to explore the influence of vacuum bag on the direct measurement METHO DS: Twenty-nine patients with thoracic and abdominal carcinoma who had to need isocentric irradiation in the supine position were immobilized using vacuum bag. The irradiation depths of 45 posterior oblique fields were determined by CT-si mulator and conventional simulator, respectively; then the absolute value for th e difference of both depths was regarded as error value. RESULTS: There were 37 fields (82.2%) with error value of smaller than 5 mm; 8 fields (17.8%), more t han 5 mm. In the latter, 5 field were belonged to be repositioned in the phase Ⅱof radiotherapy because of light leaking air into the vacuum bag in the phase Ⅰof radiotherapy. CONCLUSION: Vacuum bag has a slight influence on direct measu rement for depths of isocentric posterior oblique field.