Harrison R M, Wilkinson M, Shemilt A, Rawlings D J, Moore M, Lecomber A R
Regional Medical Physics Department, Newcastle General Hospital, Newcastle upon Tyne NE4 6BE, UK.
Br J Radiol. 2006 Jun;79(942):487-96. doi: 10.1259/bjr/16187818.
In addition to the therapeutic exposure, a course of radiotherapy will involve the additional (concomitant) irradiation of the patient using CT, simulator or portal imaging systems, for localization of the target volume and subsequent verification of treatment delivery. The number of concomitant exposures is likely to increase as the developing technical capabilities for conformal, image-guided radiotherapy make target and critical organ definition an increasingly important aspect of radiotherapy. Estimation of doses and risks to critical organs in the body from all sources is thus necessary to provide the basis for adequate justification of the exposures as required by ICRP. In this paper, doses to selected organs and tissues for which ICRP have identified fatal cancer probabilities have been measured using a realistic anthropomorphic phantom loaded with thermoluminescent dosemeters and irradiated using a treatment protocol for radical radiotherapy of the prostate. Independently, doses to the same organs and tissues have been measured from concomitant CT and portal imaging exposures given for localization and verification purposes. Although negligible in comparison with the target dose, realistic numbers of concomitant exposures give a small but significant contribution to the total dose to most organs and tissues outside the target volume. Generally, this is in the range 5-10% of the total organ dose, but can be as high as 20% for bone surfaces. These data may be used to estimate concomitant doses from any combination of CT and portal imaging and may help in the justification process, especially when additional verification exposures may be required during treatment.
除了治疗性照射外，一个疗程的放射治疗还将包括使用CT、模拟定位机或射野成像系统对患者进行额外的（同步）照射，用于靶区定位以及后续治疗实施的验证。随着适形、图像引导放射治疗技术能力的发展，使靶区和危及器官的定义成为放射治疗中越来越重要的方面，同步照射的次数可能会增加。因此，有必要估计身体中所有来源对危及器官的剂量和风险，以便为国际放射防护委员会（ICRP）要求的照射充分正当性提供依据。在本文中，使用装有热释光剂量计的逼真人体模型，并按照前列腺癌根治性放射治疗的治疗方案进行照射，测量了ICRP已确定其致命癌症概率的选定器官和组织的剂量。另外，还测量了为定位和验证目的而进行的同步CT和射野成像照射对相同器官和组织的剂量。尽管与靶区剂量相比可以忽略不计，但实际数量的同步照射对靶区外大多数器官和组织的总剂量有微小但显著的贡献。一般来说，这在总器官剂量的5%至10%范围内，但骨表面的这一比例可能高达20%。这些数据可用于估计CT和射野成像任意组合产生的同步剂量，并可能有助于正当性论证过程，特别是在治疗期间可能需要额外验证照射的情况下。
