Postoperative radiotherapy for synovial sarcoma of the head and neck during pregnancy: clinical and technical management and fetal dose estimates.

Aims and Background: In vivo and phantom dosimetry is reported to estimate the fetal dose and evaluate the effectiveness of a special shielding device to reduce fetal exposure in a woman undergoing postoperative radiation therapy for synovial oral cavity sarcoma at the 30th week of pregnancy.
Methods: In vivo measurements were performed by placing thermoluminescent dosimeters on 3 points for fetal dose estimation: uterine fundus, umbilicus and pubis. A Rando anthropomorphic phantom was used to simulate radiotherapy. We also performed off-axis dose measurements for wedged beams to estimate the dose contribution of this accessory used in the treatment.
Results: The special shielding device reduced the fetal dose by 70% on average, despite the presence of wedges, which increased the dose by a factor of about 2.5. Before delivery the patient received 48 Gy, and from the in vivo measurements a fetal dose of 8.5, 1.7 and 0.7 cGy was estimated to the uterine fundus, umbilicus and pubis, respectively.
Conclusions: Pre-treatment simulation in the same irradiation conditions is the only reliable approach to predict the fetal dose. By using a special shielding device, radiotherapy can be optimized while keeping the fetal exposure below the risk of deterministic damage.