Elsevier

The Lancet Oncology

Volume 6, Issue 5, May 2005, Pages 328-333
The Lancet Oncology

Review
Radiotherapy during pregnancy: fact and fiction

https://doi.org/10.1016/S1470-2045(05)70169-8Get rights and content

Summary

Radiotherapy during pregnancy might cause harm to the developing fetus. Generally, pregnant women with malignant diseases are advised to delay radiotherapy until after delivery. However, this advice is not based on knowledge of the risks of radiation to the unborn child. In general, the expected radiation effects, such as mental retardation and organ malformations probably only arise above a threshold dose of 0·1–0·2 Gy. This threshold dose is not generally reached with curative radiotherapy during pregnancy, provided that tumours are located sufficiently far from the fetus and that precautions have been taken to protect the unborn child against leakage radiation and collimator scatter of the teletherapy machine; such precautions also reduce the risk of radiation-induced childhood cancer and leukaemia in the unborn child.

Introduction

Cancer in pregnancy is uncommon, with an incidence of about one in 1000.1, 2 Breast and cervical cancer, Hodgkin's disease, malignant melanoma, and leukaemia are the most frequently diagnosed malignant disorders during pregnancy. The incidence of breast cancer is between one in 3000 and one in 10 000 pregnancies.2, 3 The proportion of women destined to develop breast cancer who might do so during pregnancy could increase because the average age of women at first pregnancy is rising. The incidence of Hodgkin's disease is between one in 1000 and one in 6000 and that of cervical cancer is 1·2 in 10 000.2 The frequencies of brain tumours and head and neck tumours are probably lower. Overall, the probability that a pregnant woman will be diagnosed with cancer is very low. For instance, for an obstetrician delivering about 250 babies a year, to diagnose two or three patients with pregnancy-associated breast cancer would take at least 40 years of clinical practice.2

When cancer is diagnosed during pregnancy and treatment cannot be delayed until delivery, there are concerns as to whether radiotherapy can be given safely (figure 1). A potential conflict exists between the mother and fetus, since the mother would be the major beneficiary whereas the fetus could be at substantial risk.4 The clinician has to achieve an ethical balance in terms of responsibility to the fetus and to the mother. The radiation oncologist can advise on whether to give the patient radiotherapy before delivery. For instance, several commentators have stated that radiotherapy should be avoided in patients who are pregnant and have breast cancer and should be given after delivery, because of the expected risks associated with fetal exposure to radiation.2, 5, 6 Kaufmann and colleagues7 stated that sentinel-lymph-node procedures should not be undertaken because of the expected adverse effects to the unborn child of the radioactive drug injected for lymph-node mapping. Some clinicians recommend termination of pregnancy when doses higher than 0·05–0·10 Gy are to be received by the fetus.8, 9 However, this advice is not based on sufficient knowledge of the radiation risks to the unborn child. We review published work on the risks of medical irradiation of pregnant women with malignant disorders and the fetal dose as a result of the radiotherapy. We did not review studies on pregnancy in patients who had previously undergone radiotherapy for cancer. Upponi and colleagues10 have reviewed pregnancy after treatment for breast cancer.

Section snippets

Risks

The risks of medical irradiation of pregnant women have been reviewed in two reports by the International Commission on Radiological Protection.4, 11 The study11 from which the risks were derived mentions results of animal studies, data from survivors of nuclear explosions, data from children exposed in utero to diagnostic X-rays, and data on children who were exposed to radiation from the Chernobyl accident in utero. In general, the expected radiation effects are lethality, malformations,

Diagnostic radiology

If a diagnostic radiology examination is medically indicated, in general the risk to the pregnant woman of not doing the procedure is greater than that of potential harm to the fetus. The dose to the fetus resulting from most conventional radiograph examinations is less than 0·01 Gy. For fluoroscopic examinations, the dose resulting from barium enema can exceed 0·01 Gy, but with proper tailoring of the examination the dose can be reduced. For CT of the pelvis and abdomen, the dose to the fetus

Nuclear medicine

Most diagnostic nuclear-medicine procedures use short-lived radionuclides such as technetium-99m that do not expose the fetus to large doses of radiation; the dose to the fetus is generally less than 0·01 Gy.4, 18 The role of sentinel-lymph-node biopsy as an alternative staging procedure for the axilla in breast cancer is unknown. Likewise, whether lymphatic pathways are altered in pregnancy is unclear.19 The panel of the Consensus Conference on the Role of Sentinel-Lymph-Node Biopsy advised

Radiotherapy

In patients who are pregnant, most cancers that are remote from the pelvis can be treated with radiation; However, careful planning is necessary. The dose to the fetus is from internal scatter, leakage radiation from the tube head of the linear accelerator, scatter from the collimator, and blocks, as well as other objects. Internal scatter depends largely on the source of irradiation and on the size of the treatment fields and their proximity to the fetus.25 The fetal dose from leakage

Conclusions

The dose to the fetus resulting from most conventional radiographic and nuclear-medicine examinations is less than 0·01 Gy. In patients who are pregnant, most cancers that are remote from the pelvis can be safely treated with radiotherapy. The use of supplemental shielding can substantially reduce the fetal exposure. Pretreatment dose measurements by a qualified medical physicist are necessary for reliable prediction of side-effects and, hence, adequate provision of information to parents. For

Search strategy and selection criteria

Published data were identified by searches of PubMed, Medscape, and the Cochrane library with the search terms “pregnancy”, “irradiation”, “tumours”, and “fetus”. Reference lists in selected papers were also searched. Only papers published in English between 1980 and 2004 were selected.

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