Abstract
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 R2 = 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.
Highlights
Gamma Knife stereotactic radiosurgery (GKSRS) has been widely adopted as a definitive orHow to cite this article Paulsson A K, Braunstein S, Phillips J, et al (July 31, 2017) Patient-Specific Fetal Dose Determination for Multi-Target Gamma Knife Radiosurgery: Computational Model and Case Report
Substituting all the peripheral dose-to-focal dose ratios (PFRs) values as well as the focal dose rate from the patient’s treatment plan, the maximum fetal dose at the location of uterus fundus was calculated to be 0.253 cGy, which was in agreement with surface dose measurements using MOSFETs at the level of the patient’s uterine fundus during the actual treatment
Relative contributions from individual shots for the computed maximum fetal dose at the fundus of the uterus location based on the actual patient's treatment planning (a) and the fitting results for the direct extrapolation dose measurements
Summary
Gamma Knife stereotactic radiosurgery (GKSRS) has been widely adopted as a definitive or. We endeavored to determine a reliable method to estimate the patient-specific fetal dose, and whether it is practical and safe to treat pregnant patients in general with multiple brain tumors with Gamma Knife Perfexion To answer these questions, we developed an empirical computation method and concurrently performed in-phantom dose measurements to cross check the dose calculation results. At her two-month follow-up MRI with gadolinium contrast, there was significant decrease in five of the treated metastases, two areas of FLAIR hyperintensity which may represent treated metastases with resolution of enhancement, four new untreated metastases, and two lesions which in retrospect, were punctate dots of FLAIR abnormality at the time of her Gamma Knife planning MRI. Relative contributions from individual shots for the computed maximum fetal dose at the fundus of the uterus location based on the actual patient's treatment planning (a) and the fitting results for the direct extrapolation dose measurements.
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