External photon beam radiotherapy of pregnant patients with brain tumors: Reducing fetal dose through treatment parameter adjustment

Although the lowest fetal dose was obtained with 3D-CRT, adjusting beam collimator angle and beam modulation in VMAT FFF plans with a Truebeam machine resulted in a comparable fetal dose and better dose distribution to the primary tumor. This study provides indications on how to improve the benefit-risk ratio between minimal fetal dose and optimal target dose delivery through treatment plan parameter adjustment and highlights the need to characterize the out-of-field dose of the machine used.