Photon-beam radiotherapy in pregnant patients: can the fetal dose be limited to 10 cGy or less?

ESMO Expert Consensus Statements on the management of breast cancer during pregnancy (PrBC)

The management of breast cancer during pregnancy (PrBC) is a relatively rare indication and an area where no or little evidence is available since randomized controlled trials cannot be conducted. In general, advances related to breast cancer (BC) treatment outside pregnancy cannot always be translated to PrBC, because both the interests of the mother and of the unborn should be considered. Evidence remains limited and/or conflicting in some specific areas where the optimal approach remains controversial. In 2022, the European Society for Medical Oncology (ESMO) held a virtual consensus-building process on this topic to gain insights from a multidisciplinary group of experts and develop statements on controversial topics that cannot be adequately addressed in the current evidence-based ESMO Clinical Practice Guideline. The aim of this consensus-building process was to discuss controversial issues relating to the management of patients with PrBC. The virtual meeting included a multidisciplinary panel of 24 leading experts from 13 countries and was chaired by S. Loibl and F. Amant. All experts were allocated to one of four different working groups. Each working group covered a specific subject area with two chairs appointed: Planning, preparation and execution of the consensus process was conducted according to the ESMO standard operating procedures.

Analysis of fetal dose using Optically Simulated Luminescence Dosimeter and ion chamber in randophantom for various radiotherapy techniques

To analyse the fetal dose in all three trimesters in patients treated for brain tumors during pregnancy, a modified rando phantom representing three different trimesters was used with provisions for insertion of ion-chamber and Optically Simulated Luminescence Dosimeter (OSLD). The measurement regions were chosen at the level of fundus, umbilicus and pubis. Seven different treatment plans with 6FF and 6FFF beam energies were generated. Treating pregnant patients with brain tumors is safe irrespective of planning modalities except 3DCRT plan where the dose is 10.24 cGy.

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.

Cancer and Pregnancy: A Comprehensive Review

Cancer diagnosis and treatment in pregnant women is a challenging situation. A multidisciplinary network of specialists is required to guide both, the expecting mother and the unborn child through the diagnostic workup and the cytotoxic therapy, by balancing the respective risks and benefits. Tumor entity, stage, biology and gestational week at diagnosis determine the appropriate approach. As premature delivery emerged as one of the main risk factors for adverse long-term outcome of the progeny, it should be avoided, if reasonable from the oncological perspective. This article offers a comprehensive review with respect to the various aspects of cancer in pregnancy.

Measuring foetal dose from tomotherapy treatments

INTRODUCTION

Treating pregnant women in the radiotherapy clinic is a rare occurrence. When it does occur, it is vital that the dose received by the developing embryo or foetus is understood as fully as possible. This study presents the first investigation of foetal doses delivered during helical tomotherapy treatments. Six treatment plans were delivered to an anthropomorphic phantom using a tomotherapy machine. These included treatments of the brain, unilateral and bilateral head-and-neck, chest wall, and upper lung. Measurements of foetal dose were made with an ionisation chamber positioned at various locations longitudinally within the phantom to simulate a variety of patient anatomies. All measurements were below the established limit of 100 mGy for a high risk of damage during the first trimester. The largest dose encountered was 75 mGy (0.125% of prescription dose). The majority of treatments with measurement positions less than 30 cm fell into the range of uncertain risk (50 - 100 mGy). All treatments with measurement positions beyond 30 cm fell into the low risk category (< 50 mGy). For the cases in this study, tomotherapy resulted in foetal doses that are at least on par with, if not significantly lower than, similar 3D conformal or intensity-modulated treatments delivered with other devices. Recommendations were also provided for estimating foetal doses from tomotherapy plans.

Calculating and estimating second cancer risk from breast radiotherapy using Monte Carlo code with internal body scatter for each out-of-field organ

Out-of-field organs are not commonly designated as dose calculation targets during radiation therapy treatment planning, but they might entail risks of second cancer. Risk components include specific internal body scatter, which is a dominant source of out-of-field doses, and head leakage, which can be reduced by external shielding. Our simulation study quantifies out-of-field organ doses and estimates second cancer risks attributable to internal body scatter in whole-breast radiotherapy (WBRT) with or without additional regional nodal radiotherapy (RNRT), respectively, for right and left breast cancer using Monte Carlo code PHITS. Simulations were conducted using a complete whole-body female model. Second cancer risk was estimated using the calculated doses with a concept of excess absolute risk. Simulation results revealed marked differences between WBRT alone and WBRT plus RNRT in out-of-field organ doses. The ratios of mean doses between them were as large as 3.5-8.0 for the head and neck region and about 1.5-6.6 for the lower abdominal region. Potentially, most out-of-field organs had excess absolute risks of less than 1 per 10,000 persons-year. Our study surveyed the respective contributions of internal body scatter to out-of-field organ doses and second cancer risks in breast radiotherapy on this intact female model.

Monte Carlo Simulation of Radiotherapy for Breast Cancer in Pregnant Patients: How to Reduce the Radiation Dose and Risks to Fetus?

This study estimated the fetal dose and risks from radiotherapy for breast cancer with 6 MV X-rays. Breast irradiation was simulated with the MCNP code using two mathematical phantoms corresponding to patients in the early and middle periods of pregnancy. Monte Carlo simulations were performed to determine the appropriate fetal shielding. For a 50-Gy tumor dose, the unshielded fetal dose reached up to 133.1 mGy. Fetal protection with a lead shield of dimensions 30 × 30 × 5 cm3 placed besides the treatment couch resulted in maximum doses of 22.0 and 70.3 mGy at the first and second trimesters of gestation, respectively. These shielded fetal doses may be associated with a fatal cancer risk during childhood up to 0.42% and a maximum probability for the appearance of heritable effects of 0.17%. The use of fetal shielding ensures the absence of deterministic effects from radiotherapy during the first 24 weeks of gestation.

Investigation of conformal and intensity-modulated radiation therapy techniques to determine the absorbed fetal dose in pregnant patients with breast cancer

The aim of this research was to investigate the fetal doses of pregnant patients undergoing conformal radiotherapy or intensity-modulated radiation therapy (IMRT) for breast cancers. An Alderson Rando phantom was chosen to simulate a pregnant patient with breast cancer who is receiving radiation therapy. This phantom was irradiated using the Varian Clinac DBX 600 system (Varian Medical System, Palo Alto, CA) linear accelerator, according to the standard treatment plans of both three-dimensional conformal radiation therapy (3-D CRT) and IMRT techniques. Thermoluminescent dosimeters were used to measure the irradiated phantom׳s virtually designated uterus area. Thermoluminescent dosimeter measurements (in the phantom) revealed that the mean cumulative fetal dose for 3-D CRT is 1.39cGy and for IMRT it is 8.48cGy, for a pregnant breast cancer woman who received radiation treatment of 50Gy. The fetal dose was confirmed to increase by 70% for 3-D CRT and 40% for IMRT, if it is closer to the irradiated field by 5cm. The mean fetal dose from 3-D CRT is 1.39cGy and IMRT is 8.48cGy, consistent with theoretic calculations. The IMRT technique causes the fetal dose to be 5 times more than that of 3-D CRT. Theoretic knowledge concerning the increase in the peripheral doses as the measurements approached the beam was also practically proven.

Fetal dose measurements and shielding efficiency assessment in a custom setup of (192)Ir brachytherapy for a pregnant woman with breast cancer

PURPOSE

To assess the radiation dose to the fetus of a pregnant patient undergoing high-dose-rate (HDR) (192)Ir interstitial breast brachytherapy, and to design a new patient setup and lead shielding technique that minimizes the fetal dose.

METHODS

Radiochromic films were placed between the slices of an anthropomorphic phantom modeling the patient. The pregnant woman was seated in a chair with the breast over a table and inside a leaded box. Dose variation as a function of distance from the implant volume as well as dose homogeneity within a representative slice of the fetal position was evaluated without and with shielding.

RESULTS

With shielding, the peripheral dose after a complete treatment ranged from 50 cGy at 5 cm from the caudal edge of the breast to <0.1 cGy at 30 cm. The shielding reduces absorbed dose by a factor of two near the breast and more than an order of magnitude beyond 20 cm. The dose is heterogeneous within a given axial plane, with variations from the central region within 50%. Interstitial HDR (192)Ir brachytherapy with breast shielding can be more advantageous than external-beam radiotherapy (EBRT) from a radiation protection point of view, as long as the distance to the uterine fundus is higher than about 10 cm. Furthermore, the weight of the shielding here proposed is notably lower than that needed in EBRT.

CONCLUSIONS

Shielded breast brachytherapy may benefit pregnant patients needing localized radiotherapy, especially during the early gestational ages when the fetus is more sensitive to ionizing radiation.