Analysis of fetal dose exposure by modern radiation therapy in pregnant patients with supradiaphragmatic Hodgkin lymphoma-a phantom-based simulation.

Purpose: Modern involved-site radiotherapy (ISRT) for Hodgkin lymphoma decreases toxicity through reduced field sizes and radiation doses. However, in pregnancy, the therapeutic benefit has to be weighed against putative harm to the mother and the fetus, as even small doses may have deleterious effects. We conducted a phantom-based simulation to analyze uterine dose exposure from cervical and mediastinal ISRT.

Methods: Cervical and mediastinal ISRT target volumes were contoured to calculate three comparison plans (3D-conformal radiotherapy [3D-CRT], intensity-modulated radiotherapy [IMRT], volumetric intensity-modulated arc therapy [VMAT]). Thermoluminescent dosimeters (TLD) were placed within a humanoid Alderson phantom to simulate early and late pregnancy. Overall, six measurements (two for every radiotherapy plan) with 38 TLD were conducted.

Results: In early pregnancy, cervical ISRT treatment of 19.8 Gray (Gy) resulted in median fetal exposures of 8.8 mGy, 15.4 mGy, and 9.9 mGy for 3D-CRT, IMRT, and VMAT, respectively, with significant differences between the three techniques (p < 0.001) and increased doses in late pregnancy (p < 0.001). For mediastinal ISRT (19.8 Gy), early pregnancy doses were 44 mGy, 63.8 mGy, and 60.5 mGy for 3D-CRT, IMRT, and VMAT, respectively, again with significant differences (p < 0.001) and a significant increase (p < 0.001) in late pregnancy. In comparison, values of 214.2 mGy (3D-CRT), 249.9 mGy (IMRT), and 249.9 mGy (VMAT) were reached using 30.6 Gy, with significant differences between 3D-CRT and VMAT (p < 0.001), 3D-CRT and IMRT (p < 0.001), and IMRT and VMAT (p = 0.004).

Conclusion: Using RT during pregnancy may have deleterious effects on the fetus and should be deferred until after birth whenever possible. Theoretical uterine RT doses are low overall and only exceeded safety thresholds with higher-dose intensity-modulated plans. The indication for RT in pregnancy always requires careful risk-benefit consideration and individualized planning.