Fetal radiation monitoring and dose minimization during intensity modulated radiation therapy for glioblastoma in pregnancy

A review on fetal dose in Radiotherapy: A historical to contemporary perspective

This paper aims to review on fetal dose in radiotherapy and extends and updates on a previous work¹ to include proton therapy. Out-of-field doses, which are the doses received by regions outside of the treatment field, are unavoidable regardless of the treatment modalities used during radiotherapy. In the case of pregnant patients, fetal dose is a major concern as it has long been recognized that fetuses exposed to radiation have a higher probability of suffering from adverse effects such as anatomical malformations and even fetal death, especially when the 0.1Gy threshold is exceeded. In spite of the low occurrence of cancer during pregnancy, the radiotherapy team should be equipped with the necessary knowledge to deal with fetal dose. This is crucial so as to ensure that the fetus is adequately protected while not compromising the patient treatment outcomes. In this review paper, various aspects of fetal dose will be discussed ranging from biological, clinical to the physics aspects. Other than fetal dose resulting from conventional photon therapy, this paper will also extend the discussion to modern treatment modalities and techniques, namely proton therapy and image-guided radiotherapy, all of which have seen a significant increase in use in current radiotherapy. This review is expected to provide readers with a comprehensive understanding of fetal dose in radiotherapy, and to be fully aware of the steps to be taken in providing radiotherapy for pregnant patients.

Clinical management of brain tumors in pregnancy

PURPOSE OF REVIEW

We review the diagnostic tools, treatment options, and clinical management for brain tumors diagnosed in pregnancy with consideration for management approaches that are best suited to preserve maternal and fetal health.

RECENT FINDINGS

Women of child-bearing age are at risk of developing brain tumors and are at increased risk compared with male counterparts for tumors that are hormonally driven. Brain tumors are rare neoplasms, and diagnosis of brain tumors in pregnancy is uncommon, such that management guidelines and treatment recommendations are lacking for most tumor types. We discuss the standard treatment options for brain tumors and the relative risks and safety when these treatments are considered during pregnancy. We review the neoplasms most commonly affecting pregnant women and the existing literature and guidelines.

SUMMARY

Pregnancy is a unique phase of life in which hormonal, immunologic, and vascular changes may impact tumor growth and presentation. Treatment decisions should consider the symptoms and stability of the pregnant patients, the gestational age and health of the fetus, and the location and behavior of the neoplasm.

Radiotherapy and pregnancy

We present the updated recommendations of the French society for radiation oncology on radiotherapy and pregnancy. The occurrence of cancer during pregnancy is a rare event (approximately 1 in 1000 pregnancies). The risks for the embryo or the foetus depend on the gestational age at the time of irradiation. The main risks are malformations with microcephaly and mental retardation. There is also a risk of radiation-induced cancer in the unborn child. In the case of only supradiaphragmatic irradiation, radiotherapy can be performed most often in pregnant women without risk to the foetus. On the other hand, in the case of an indication for subdiaphragmatic irradiation, therapeutic termination of the pregnancy should be proposed. In all cases, when radiotherapy is chosen, a phantom estimation of the dose delivered to the foetus, confirmed by in vivo measurement, is recommended. Conformational radiotherapy is the preferred technique because of the lower dose delivered to the foetus (except in tumour locations where other techniques such as IMRT are recommended).

Evaluation of a new foetal shielding device for pregnant brain tumour patients

Background

The present study aimed to propose a new foetal shielding device for pregnant cancer patients to reduce the foetal dose associated with treatment techniques using multiple gantry angles, such as intensity-modulated radiation therapy (IMRT) or volumetric modulated arc therapy (VMAT).

Methods

Three shielding structures were designed to minimise the scattered and leaked radiation from various gantry angles and radiation scattering within the patient. The base-plate part that can be placed on the treatment couch was designed to reduce the scattered and leaked radiation generated at gantry angles located near 180°. A body shielding part that can cover the lower chest and abdomen was designed, and a neck-shielding structure was added to reduce the internal and external radiation scattering from the treatment area. Evaluation plans were generated to assess the foetal dose reduction by the foetal shielding device in terms of the shielding material thickness, distance from the field edge, and shielding component using the flattened 6 MV photon beam (6MV) and flattening filter-free 6 MV photon beam (6MV-FFF). In addition, the effectiveness of the foetal shielding device was evaluated in a pregnant brain tumour patient.

Results

The shielding material consisting of three parts was placed on frames composed of four arch shapes with a vertical curved structure, connection bar at the top position, and base plate. Each shielding part resulted in reductions in the radiation dose according to the treatment technique, as the thickness of the shielding material increased and the foetal dose decreased. In addition, a foetal dose reduction of approximately 50% was confirmed at 50 cm from the field edge by using the designed shielding device in most delivery techniques. In patients, the newly designed shielding structures can effectively eliminate up to about 49% of the foetal dose generated from various gantry angles used in VMAT or IMRT.

Conclusions

We designed a foetal shielding device consisting of three parts to effectively reduce the dose delivered to the foetus, and evaluated the device with various treatment techniques for a pregnant patient with brain tumour. The foetal shielding device shielded the scattered/leaked radiation from the treatment machine, and also effectively reduced internal scattering from the treatment area in the patient.

Multidisciplinary Therapy Managed Recurrent Glioblastoma in a BRAF-V600E Mutant Pregnant Female: A Case Report and Review of the Literature

Background: Glioblastoma (GBM) is the most malignant intracranial tumor in adults. However, the overall management of GBM in pregnancy is rarely reported. How to balance the therapeutic benefits to the mother and risks to the fetus remains hugely challenging for clinicians. The application of specific targeting therapy combined with conventional treatment sheds light on a longer lifetime for the patients suffering from GBM. Case Presentation: We present a pregnant female at 20 weeks gestation diagnosed with GBM. Surgical resection was initially performed without adjuvant therapy, and the tumor recurred de novo 2 months later. A secondary craniotomy and cesarean section were performed simultaneously at 32 weeks gestation, both the patient and infant were survived. She was subsequently treated with traditional chemo-radiotherapy. No other identified genetic alterations indicating an optimistic prognosis were detected except for BRAF V600E mutation. Thus, the BRAF inhibitor was placed on her with achieving a good clinical outcome of more than 2-year survival without recurrence. Conclusion: Personalized multidisciplinary therapy should be considered when GBMs occur in pregnancy. Response to the therapy in this presenting case suggests that BRAF V600E mutation is a favorable biomarker for GBM. The mortality of GBM might be reduced through genetic testing and targeted treatment. However, more studies must be conducted to confirm our observation.

Radiation treatment planning and delivery strategies for a pregnant brain tumor patient

The management of a pregnant patient in radiation oncology is an infrequent event requiring careful consideration by both the physician and physicist. The aim of this manuscript was to highlight treatment planning techniques and detail measurements of fetal dose for a pregnant patient recently requiring treatment for a brain cancer. A 27-year-old woman was treated during gestational weeks 19-25 for a resected grade 3 astrocytoma to 50.4 Gy in 28 fractions, followed by an additional 9 Gy boost in five fractions. Four potential plans were developed for the patient: a 6 MV 3D-conformal treatment plan with enhanced dynamic wedges, a 6 MV step-and-shoot (SnS) intensity-modulated radiation therapy (IMRT) plan, an unflattened 6 MV SnS IMRT plan, and an Accuray TomoTherapy HDA helical IMRT treatment plan. All treatment plans used strategies to reduce peripheral dose. Fetal dose was estimated for each treatment plan using available literature references, and measurements were made using thermoluminescent dosimeters (TLDs) and an ionization chamber with an anthropomorphic phantom. TLD measurements from a full-course radiation delivery ranged from 1.0 to 1.6 cGy for the 3D-conformal treatment plan, from 1.0 to 1.5 cGy for the 6 MV SnS IMRT plan, from 0.6 to 1.0 cGy for the unflattened 6 MV SnS IMRT plan, and from 1.9 to 2.6 cGy for the TomoTherapy treatment plan. The unflattened 6 MV SnS IMRT treatment plan was selected for treatment for this particular patient, though the fetal doses from all treatment plans were deemed acceptable. The cumulative dose to the patient's unshielded fetus is estimated to be 1.0 cGy at most. The planning technique and distance between the treatment target and fetus both contributed to this relatively low fetal dose. Relevant treatment planning strategies and treatment delivery considerations are discussed to aid radiation oncologists and medical physicists in the management of pregnant patients.

Evaluation of surface and shallow depth dose reductions using a Superflab bolus during conventional and advanced external beam radiotherapy

The purpose of this study was to evaluate a methodology to reduce scatter and leakage radiations to patients’ surface and shallow depths during conventional and advanced external beam radiotherapy. Superflab boluses of different thicknesses were placed on top of a stack of solid water phantoms, and the bolus effect on surface and shallow depth doses for both open and intensity‐modulated radiotherapy (IMRT) beams was evaluated using thermoluminescent dosimeters and ion chamber measurements. Contralateral breast dose reduction caused by the bolus was evaluated by delivering clinical postmastectomy radiotherapy (PMRT) plans to an anthropomorphic phantom. For the solid water phantom measurements, surface dose reduction caused by the Superflab bolus was achieved only in out‐of‐field area and on the incident side of the beam, and the dose reduction increased with bolus thickness. The dose reduction caused by the bolus was more significant at closer distances from the beam. Most of the dose reductions occurred in the first 2‐cm depth and stopped at 4‐cm depth. For clinical PMRT treatment plans, surface dose reductions using a 1‐cm Superflab bolus were up to 31% and 62% for volumetric‐modulated arc therapy and 4‐field IMRT, respectively, but there was no dose reduction for Tomotherapy. A Superflab bolus can be used to reduce surface and shallow depth doses during external beam radiotherapy when it is placed out of the beam and on the incident side of the beam. Although we only validated this dose reduction strategy for PMRT treatments, it is applicable to any external beam radiotherapy and can potentially reduce patients’ risk of developing radiation‐induced side effects.

Melanoma and pregnancy

Melanoma is the most common cancer in women during their reproductive years and kills more young Australians than any other single cancer. Care of women whose pregnancy is complicated by a diagnosis of malignancy is complex. The risk of delaying treatment to the mother, the short-term and long-term risks of premature delivery to the child, and the immediate risks to the foetus and long-term risks to the child of maternal treatment with surgery, radiotherapy or medical therapies must be considered.