Radiation therapy and cancer during pregnancy - Current practice in the Netherlands

Cancer during pregnancy is rare, and radiation therapy is initiated in pregnancy in only a few cases. In situations where it would usually be indicated outside pregnancy, an alternative treatment plan is usually developed, often by reversing sequences of multidisciplinary treatments. The reasons for doing so can be associated with the stage of the pregnancy, the estimated dose to the foetus and a perceived reluctance to administer radiotherapy during pregnancy. This paper summarises current practice in the Netherlands with respect to foetal dose assessment, abdominal shielding strategies, and emerging technologies, supported by the experience of the Dutch Advisory Board on Cancer, Infertility and Pregnancy (Dutch ABCIP).

A scoping review was conducted to determine the physical determinants of peripheral dose in photon radiation therapy, biological effects of foetal radiation exposure, methods for foetal dose estimation, and the role and limitations of abdominal shielding. Advances in proton therapy are discussed, illustrated by recent phantom and clinical studies. In addition, the organisation and activity of the Dutch ABCIP are described. The database of the Dutch ABCIP is used to estimate the number of pregnant patients who received radiation therapy.

Close to the treatment fields, peripheral dose from photon radiation therapy is dominated by patient scatter and may result in clinically relevant foetal exposure. Foetal dose estimation is associated with several uncertainties and imaging procedures may contribute significantly to cumulative dose. Abdominal shielding can reduce collimator scatter and head leakage radiation but has no effect on patient scatter and is constrained by practical considerations. Accumulating evidence demonstrates that pencil beam scanning proton therapy consistently reduces foetal dose by one to two orders of magnitude compared with photon radiation therapy, without compromising maternal treatment quality. Since 2012, the Dutch ABCIP has reviewed 420 cases of cancer during pregnancy; radiation therapy during pregnancy was advised in only selected cases, which contributes to the limited experience with such situations.

Radiation therapy during pregnancy is rare but requires highly specialised, multidisciplinary decision-making. The low number of cases found is in agreement with literature and personal experiences of experts involved. Proton therapy offers a substantial and consistent reduction in foetal dose and should be strongly considered when radiation therapy during pregnancy cannot be avoided. Centralised advisory boards such as the Dutch ABCIP provide an effective framework to support clinicians managing these complex cases. Pregnant cancer patients are not yet a standard indication for reimbursement, which is currently under development.