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

Fetal dose assessment in a pregnant patient with brain tumor: A comparative study of proton PBS and 3DCRT/VMAT radiation therapy techniques

PURPOSE

The treatment of brain tumors in pregnant patients poses challenges, as the out-of-field dose exposure to the fetus can potentially be harmful. A pregnant patient with prior radiation treatment was presented with a brain tumor at our clinic. This work reports on our pre-treatment study that compared fetal dose exposure between intensity-modulated proton therapy (IMPT) using pencil beam scanning (PBS) and conventional photon 3D conformal radiation therapy (3DCRT) and volumetric-modulated arc therapy (VMAT), and the subsequent pregnant patient's radiation treatment.

MATERIALS AND METHODS

Pre-treatment measurements of clinical plans, 3DCRT, VMAT, and IMPT, were conducted on a phantom. Measurements were performed using a device capable of neutron detections, closely following AAPM guidelines, TG158. For photon measurements, fetus shielding was utilized. On patient treatment days, which was determined to be proton treatment, shielding was used only during daily imaging for patient setup. Additionally, an in vivo measurement was conducted on the patient.

RESULTS

Measurements showed that IMPT delivered the lowest fetal dose, considering both photon and neutron out-of-field doses to the fetus, even when shielding was implemented for photon measurements. Additionally, the proton plans demonstrated superior treatment for the mother, a reirradiation case.

CONCLUSION

The patient was treated with proton therapy, and the baby was subsequently delivered at full term with no complications. This case study supports previous clinical findings and advocates for the expanded use of proton therapy in this patient population.

Long-term neurocognitive, psychosocial, and physical outcomes after prenatal exposure to radiotherapy: a multicentre cohort study of the International Network on Cancer, Infertility, and Pregnancy

BACKGROUND

The main data available on the safety of radiation during pregnancy originate from animal studies and from studies of survivors of atomic or nuclear disasters. The effect of radiotherapy to treat maternal cancer on fetal development is uncertain. This report presents a unique cohort and aims to determine the long-term neurocognitive, psychosocial and physical outcomes of offspring of mothers treated with radiotherapy during pregnancy.

METHODS

In this international, multicentre, mixed retrospective-prospective cohort study, we recruited participants between Aug 5, 2006, and Aug 24, 2023, aged between 1·5 and 46 years, at three referral centres in Belgium, the Netherlands, and the USA. Participants were eligible if they were born from mothers treated with radiotherapy during pregnancy. Fetal radiation doses were obtained from medical records and participants were followed up at predefined ages (1·5, 3, 6, 9, 12, 15, and 18 years) and 5-yearly in adulthood, based on age at enrolment, using a neurocognitive test battery (measuring intelligence, attention, and memory), parent-reported executive function and psychosocial questionnaires, and a medical assessment. Results were compared with test-specific normative data. Linear regression models investigated associations between radiotherapy factors (fetal radiation dose, gestational age at the start and end of radiotherapy, and radiotherapy duration) and outcomes.

FINDINGS

68 maternal cases of radiotherapy during pregnancy were registered by the three participating centres, of which 61 resulted in a livebirth and were therefore eligible to participate in the child follow-up study. After excluding those who did not give consent, 43 participants born from 42 mothers treated with radiotherapy during pregnancy were included in the study (median age at first assessment 3 years [IQR 2-11]; median age at last assessment 12 years [9-18]; median number of assessments two [1-4]). 18 (42%) of the included participants were female and 25 (58%) male, and 37 (86%) were of White ethnicity. Mean neurocognitive outcomes of the entire cohort were within normal ranges. No associations were found with fetal radiation dose or timing of radiotherapy during pregnancy. Six (16%) of 38 participants with neurocognitive outcomes scored lower than one SD on at least one neurocognitive outcome, three (7%) reported chronic medical conditions (spasmophilia, spastic diplegia, and IgG deficiency), and three (7%) were diagnosed with attention-deficit hyperactivity disorder (of whom two scored lower on attention). Of ten (23%) participants with lower neurocognitive score(s), a chronic medical condition, or attention-deficit hyperactivity disorder, eight were born preterm. The remaining 33 (77%) participants showed no neurocognitive, psychosocial, or chronic physical problems.

INTERPRETATION

We show on average normal neurocognitive, psychosocial, and physical outcomes after prenatal exposure to radiotherapy. Differences in outcomes could not be explained by exposure to radiotherapy during pregnancy. These results suggest that extra-abdomino-pelvic radiotherapy exposure during pregnancy in general does not adversely affect outcomes of liveborn children. Further research with a larger sample is necessary to confirm these findings.

FUNDING

Kom Op Tegen Kanker, KWF Kankerbestrijding, Stichting Tegen Kanker, Research Foundation Flanders.

A phantom study investigating effective strategies for reducing fetal dose in pregnant patients with head and neck cancer

PURPOSE

To measure the out-of-field doses for various treatment planning techniques and assess the impact on fetal dose with and without the use of custom shielding.

MATERIALS AND METHODS

A total of six treatment plans were generated with different treatment techniques such as 3-dimensional conformal radiation therapy (3DCRT), intensity modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT), utilizing both 6 MV flattened beams and flattening filter-free (FFF) beams. The measurements were carried out both out-of-field at the surface and at depth to assess the dose reduction achieved by removing the flattening filter and incorporating shielding.

RESULTS

The custom-made frame shielding can effectively reduce the surface dose with a maximum reduction of 15.2% observed in VMAT plans and achieve a maximum reduction of 100% for cone beam computed tomography (CBCT) imaging. Out-of-field dose measurements conducted at depth, positioned 58 cm inferior to the target isocenter, reveal that the shielding effectiveness consistently remains the greatest for 3DCRT technique. A maximum reduction of 21% is observed when utilizing a flattening filter-free beam.

CONCLUSION

The results of this study indicate that the 3DCRT technique exhibits the least amount of scatter radiation both near and far from the treatment isocenter, which is the most suitable approach for radiation therapy of pregnant patients. In cases where meeting dose constraints for critical organs becomes challenging, VMAT technique emerges as the most suitable treatment technique for reducing out-of-field doses. Additionally, a flattening filter-free beam significantly reduces out-of-field doses due to lower contributions from head scatter.

Challenges and opportunities for proton therapy during pregnancy

During pregnancy, the use of radiation therapy for cancer treatment is often considered impossible due to the assumed associated fetal risks. However, suboptimal treatment of pregnant cancer patients and unjustifiable delay in radiation therapy until after delivery can be harmful for both patient and child. In non-pregnant patients, proton-radiation therapy is increasingly administered because of its favorable dosimetric properties compared with photon-radiation therapy. Although data on the use of pencil beam scanning proton-radiation therapy during pregnancy are scarce, different case reports and dosimetric studies have indicated a more than 10-fold reduction in fetal radiation exposure compared with photon-radiation therapy. Nonetheless, the implementation of proton-radiation therapy during pregnancy requires complex fetal dosimetry for the neutron-dominated out-of-field radiation dose and faces a lack of clinical guidelines. Further exploration and standardization of proton-radiation therapy during pregnancy will be necessary to improve radiotherapeutic management of pregnant women with cancer and further reduce risks for their offspring.

Cancer during pregnancy: Twenty-two years of experience from a tertiary referral center

INTRODUCTION

Cancer complicating pregnancy is a rare but potentially life-threatening condition for both the mother and her child. The aim of the present study was to assess the outcomes for mothers and children after pregnancy complicated by malignancy and to investigate which parameters are important for their 1-year survival.

MATERIAL AND METHODS

The study included 84 pregnant women diagnosed with malignant tumors during pregnancy from 2001 to 2022. The pregnancy course and outcome, as well as parameters that could influence the survival and condition of the mother and child were evaluated. Mothers and children were followed up for 1 year after delivery to assess their condition/complications and overall survival.

RESULTS

Most malignancies were gynecological (31%) or hematological (23.8%) and were diagnosed and surgically treated in the second trimester. Most children (69%) showed adequate growth and development throughout pregnancy but were delivered before term (53.6%) to allow mothers to receive therapy. Adjuvant therapy during pregnancy mostly caused a transitory deterioration of the child's condition, while surgery did not significantly impact the pregnancy course. Deliveries, on average, occurred during the 33.01 ± 6.16 gestational week (range: 20-40) and mostly by cesarean section (76.2%). For mothers, the pregnancy survival rate was 95.2% and survival after 1 year was 87.5%. However, 37.5% of women were still ill and required additional therapy 1 year postpartum. The pregnancy survival rate for children was 94%, whereas the 1-year survival rate was 76.2%. Most children had a favorable condition (alive, adequately growing and developing, and without complications) at birth (81%) as well as at the 1-year follow-up (63.7%). Regression analysis identified the following predictors of favorable 1-year maternal condition: applying therapy during pregnancy, no progression of the malignancy during pregnancy, and delivery at a later gestational week. Predictors of favorable 1-year condition of children were lower histopathological grade of malignancy, surgery as therapy for malignancy, obtaining higher birthweight, and delivery by cesarean section.

CONCLUSIONS

If the malignancy is not progressing, pregnancy should be continued as long as possible for the child to obtain adequate birthweight. Both surgery and chemotherapy were safe therapeutic choices, as most pregnancies continued successfully after therapy.

Cancer in pregnancy - The obstetrical management

Cancer in pregnancy, defined as a cancer diagnosed during pregnancy, is a rare but severe condition presenting both clinical and ethical challenges. During the last two decades a paradigm shift has occurred towards recommending similar staging and treatment regimens of pregnant and non-pregnant cancer patients. This strategy is a result of an increasing number of reassuring reports on chemotherapy treatment in pregnancy after the first trimester. The management of cancer in pregnancy should be managed in a multidisciplinary team where staging, oncological treatment, social and mental care, timing of delivery, and follow-up of the infant should be planned. Due to the rarity, centralization is recommended to allow experience accumulation. Furthermore, national and international advisory boards are supportive when there is a lack of expertise.

The effect of ionizing radiation on the fetal bone development in pregnant rats: Role of melatonin

Radiation has been widely used in many business sectors over the last century. Our study investigated the possible teratogenic effects of radiation on the bones of rat fetuses and the protective effect of melatonin against these effects. In this study, 15 pregnant female Wistar albino rats were used. These rats were divided into four groups: the control group, melatonin group (10 mg/kg/day), radiation group (0.5 gray), radiation (0.5 gray) + melatonin group (10 mg/kg/day), and sham group (1 mm hanks/day). The skeletal system development of fetuses was examined with double skeletal and scanning electron microscope (SEM), histopathological methods. In our study, fetal weight, placental weight, and fetal morphometric values were found to be statistically significantly decreased in the radiation group compared to the control group (p < .05). In immünohistochemistry (IHC) analysis, alkaline phosphatase, and tartrate-resistant acid phosphatase) concentrations were found to be significantly lower in the radiation group compared to the other groups. In the SEM analysis, it was observed that the amount of calcium and sodium decreased when the radiation group was compared with the other groups. As a result, when exposed to ionizing radiation during pregnancy, melatonin has a protective feature against the negative effects of radiation on the bone development of fetuses. RESEARCH HIGHLIGHTS: In our study, fetuses obtained from pregnant rats exposed to ionizing radiation were examined. In this study, the effect of melatonin on bone development in fetuses exposed to gray ionizing radiation was investigated. There are few studies on our subject in the literature. We believe that our findings will contribute to other planned studies.

Thermal neutron detection and track recognition method in reference and out-of-field radiotherapy FLASH electron fields using Timepix3 detectors

Objective.This work presents a method for enhanced detection, imaging, and measurement of the thermal neutron flux.Approach. Measurements were performed in a water tank, while the detector is positioned out-of-field of a 20 MeV ultra-high pulse dose rate electron beam. A semiconductor pixel detector Timepix3 with a silicon sensor partially covered by a6LiF neutron converter was used to measure the flux, spatial, and time characteristics of the neutron field. To provide absolute measurements of thermal neutron flux, the detection efficiency calibration of the detectors was performed in a reference thermal neutron field. Neutron signals are recognized and discriminated against other particles such as gamma rays and x-rays. This is achieved by the resolving power of the pixel detector using machine learning algorithms and high-resolution pattern recognition analysis of the high-energy tracks created by thermal neutron interactions in the converter.Main results. The resulting thermal neutrons equivalent dose was obtained using conversion factor (2.13(10) pSv·cm2) from thermal neutron fluence to thermal neutron equivalent dose obtained by Monte Carlo simulations. The calibrated detectors were used to characterize scattered radiation created by electron beams. The results at 12.0 cm depth in the beam axis inside of the water for a delivered dose per pulse of 1.85 Gy (pulse length of 2.4μs) at the reference depth, showed a contribution of flux of 4.07(8) × 103particles·cm-2·s-1and equivalent dose of 1.73(3) nSv per pulse, which is lower by ∼9 orders of magnitude than the delivered dose.Significance. The presented methodology for in-water measurements and identification of characteristic thermal neutrons tracks serves for the selective quantification of equivalent dose made by thermal neutrons in out-of-field particle therapy.