Fetal Radiotherapy Dose Reduction with Lead Aprons In Pregnancy Associated H3-K28M Diffuse Midline Glioma of the Brainstem
Abstract
Purpose
To quantify the impact of lead aprons on reducing out-of-field fetal dose during external beam photon intracranial treatments.
Methods
A 34-year-old female at 22 weeks gestation underwent radiotherapy for H3-K28M diffuse midline glioma of the brainstem receiving 54Gy in 30 fractions with a volumetric modulated arc therapy technique. An anthropomorphic phantom was used for fetal dose measurements. Reference measurements characterized fetal dose as a function of beam energy, field size, and treatment geometry. Patient-specific measurements were performed using the clinically delivered treatment plan. A solid water insert representing the uterus was placed in the abdominal region of the phantom. Absolute dose was measured using a calibrated Farmer-type ionization chamber. Measurements were acquired under multiple shielding configurations, including no shielding, one to three anterior lead aprons, and combined anterior and posterior arrangements. Dose was measured at the phantom surface, mid-uterine location, and a superior conservative uterine position.
Results
Reference measurements demonstrated that 6 MV photons, smaller field sizes and 90° collimater angle produced the lowest out-of-field fetal dose. For the patient-specific plan delivered over 30 fractions, cumulative fetal dose without shielding exceeded 2 cGy at the phantom surface (2.09 cGy) and upper uterine location (2.13 cGy). Increasing anterior lead apron shielding produced stepwise dose reduction at all measurement locations. Use of two or more anterior aprons reduced upper uterine dose below 2 cGy (≤1.96 cGy), while mid-uterine dose remained below 2 cGy for all configurations. The lowest cumulative doses were observed with three anterior aprons (upper: 1.94 cGy; mid: 1.72 cGy).
Conclusion
Lead apron shielding effectively reduced fetal dose during intracranial radiotherapy. Combined anterior and posterior apron configurations provided no meaningful additional dose reduction compared with anterior shielding alone. Lower beam energy and reduced field size further minimizes fetal dose and should be considered during treatment planning for pregnant patients.