Treatment of a Pregnant Patient With a Brain Tumor Using Pencil Beam Scanning Proton Therapy

BackgroundRadiation therapy plays a crucial role in the treatment of patients with cancer, including those who are pregnant. 1However, balancing maternal prognosis and fetal risk can be challenging. 2,3The majority of fetal dose deposition is attributed to head leakage and patient scatter, necessitating specialized approaches to mitigate these contributions. 1,4In x-ray therapy (XRT), a lead fetal shield and planning modifications are often employed to reduce fetal exposure. 1,[5][6]][7] Traditionally, XRT has been the standard for treating pregnant patients when radiation therapy is medically necessary.Case studies have reported fetal dose estimates ranging from 0.5 to 2 cGy in patients with brain tumors. 6,8-10Some centers use a shielding device to achieve lower doses, albeit at the cost of practical challenges. 1,11,12Shield placement over the abdomen can pose clearance issues and restrict gantry rotation to partial anterior arcs to maintain the primary beam within the shielded region.These restrictions in beam angles can increase the dose to normal tissues and increase the risk of acute and late side effects in these young patients.Alternatively, certain centers forgo fetal shields, accepting a higher fetal dose.Pencil beam scanning proton therapy (PBS-PRT) emerges as a promising alternative for pregnant patients, and previous case studies have reported favorable results. [13][14]4][15][16][17] The main contributor to fetal exposure from PBS-PRT is internal neutrons, produced when protons interact with the patient. 4We previously conducted a retrospective study at our institution to determine the total fetal equivalent dose from PBS-PRT compared with XRT when treating brain and head and neck cancers. 18Fetal equivalent dose was reduced by a factor of 10 with PBS-PRT compared with XRT for all 7 cases that were investigated without making any compromises to the patient's treatment.These findings highlight the potential of PBS-PRT in effectively treating pregnant patients while minimizing fetal radiation exposure and led to a change of practice at our institution.Herein, we describe the case of the first pregnant woman with a brain tumor we treated with PBS-PRT after comparison with an XRT plan. CaseA 34-year-old pregnant woman initially presented with left-sided hearing loss and facial weakness at 17 weeks gestation.A brain magnetic resonance imaging (MRI) was performed (without contrast because of her pregnant status), which showed a T1 hypointense brain lesion at the left cerebellopontine angle.This was thought to most likely represent a schwannoma or meningioma given the