Paulsson Anna K, Braunstein Steve, Phillips Justin, Theodosopoulos Philip V, McDermott Michael, Sneed Patricia K, Ma Lijun
Radiation Oncology, University of California, San Francisco.
Department of Neurological Surgery, University of California, San Francisco.
Cureus. 2017 Jul 31;9(7):e1527. doi: 10.7759/cureus.1527.
A 42-year-old woman at 29 weeks gestation via in vitro fertilization who presented with eight metastatic brain lesions received Gamma Knife stereotactic radiosurgery (GKSRS) at our institution. In this study, we report our clinical experience and a general procedure of determining the fetal dose from patient-specific treatment plans and we describe quality assurance measurements to guide the safe practice of multi-target GKSRS of pregnant patients. To estimate fetal dose pre-treatment, peripheral dose-to-focal dose ratios (PFRs) were measured in a phantom at the distance approximating the fundus of uterus. Post-treatment, fetal dose was calculated from the actual patient treatment plan. Quality assurance measurements were carried out via the extrapolation dosimetry method in a head phantom at increasing distances along the longitudinal axis. The measurements were then empirically fitted and the fetal dose was extracted from the curve. The computed and measured fetal dose values were compared with each other and associated radiation risk was estimated. Based on low estimated fetal dose from preliminary phantom measurements, the patient was accepted for GKSRS. Eight brain metastases were treated with prescription doses of 15-19 Gy over 143 min involving all collimator sizes as well as composite sector mixed shots. Direct fetal dose computation based on the actual patient's treatment plan estimated a maximum fetal dose of 0.253 cGy, which was in agreement with surface dose measurements at the level of the patient's uterine fundus during the actual treatment. Later phantom measurements also estimated fetal dose to be in the range of 0.21-0.28 cGy (dose extrapolation curve R = 0.998). Using the National Council on Radiation Protection and Measurements (NCRP) population-based model, we estimate the fetal risk of secondary malignancy, which is the primary toxicity after 25 weeks gestation, to be less than 0.01%. Of note, the patient delivered the baby via scheduled cesarean section at 36 weeks without complications attributable to the GKSRS procedure. GKSRS of multiple brain metastases was demonstrated to be safe and feasible during pregnancy. The applicability of a general patient-specific fetal dose determination method was also demonstrated for the first time for such a treatment.
一名42岁、通过体外受精怀孕29周的女性，因出现8个脑转移瘤，在我院接受了伽玛刀立体定向放射外科治疗（GKSRS）。在本研究中，我们报告了我们的临床经验以及从患者特异性治疗计划确定胎儿剂量的一般程序，并描述了质量保证测量方法，以指导对孕妇进行多靶点GKSRS的安全操作。为了在治疗前估计胎儿剂量，在一个模体中于接近子宫底部的距离处测量外周剂量与焦点剂量之比（PFR）。治疗后，根据实际患者的治疗计划计算胎儿剂量。通过外推剂量测定法在头部模体中沿纵轴在不断增加的距离处进行质量保证测量。然后对测量值进行经验拟合，并从曲线中提取胎儿剂量。将计算得到的和测量得到的胎儿剂量值相互比较，并估计相关的辐射风险。基于初步模体测量估计的胎儿剂量较低，该患者被接受进行GKSRS治疗。8个脑转移瘤接受了15 - 19 Gy的处方剂量治疗，治疗时间为143分钟，涉及所有准直器尺寸以及复合扇形混合照射。基于实际患者治疗计划的直接胎儿剂量计算估计最大胎儿剂量为0.253 cGy，这与实际治疗期间患者子宫底部水平的表面剂量测量结果一致。后来的模体测量也估计胎儿剂量在0.21 - 0.28 cGy范围内（剂量外推曲线R = 0.998）。使用美国国家辐射防护与测量委员会（NCRP）基于人群的模型，我们估计胎儿继发恶性肿瘤的风险，这是妊娠25周后主要的毒性反应，小于0.01%。值得注意的是，患者在36周时通过计划剖宫产分娩婴儿，未出现归因于GKSRS手术的并发症。多个脑转移瘤的GKSRS在孕期被证明是安全可行的。首次证明了一种通用的患者特异性胎儿剂量测定方法对于此类治疗的适用性。
