A study of the shielding used to reduce leakage and scattered radiation to the fetus in a pregnant patient treated with a 6-MV external X-ray beam

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.

Dose assessment for daily cone-beam CT in lung radiotherapy patients and its combination with treatment planning

With the increased use of X-ray imaging for patient alignment in external beam radiation therapy, particularly with cone-beam computed tomography (CBCT), the additional dose received by patients has become of greater consideration. In this study, we analysed the radiation dose from CBCT for clinical lung radiotherapy and assessed its relative contribution when combined with radiation treatment planning for a variety of lung radiotherapy techniques. The Monte Carlo simulation program ImpactMC was used to calculate the 3D dose delivered by a Varian TrueBeam linear accelerator to patients undergoing thorax CBCT imaging. The concomitant dose was calculated by simulating the daily CBCT irradiation of ten lung cancer patients. Each case was planned with a total dose of 50-60 Gy to the target lesion in 25-30 fractions using the 3DCRT or IMRT plan and retrospectively planned using VMAT. For each clinical case, the calculated CBCT dose was summed with the planned dose, and the dose to lungs, heart, and spinal cord were analysed according to conventional dose conformity metrics. Our results indicate greater variations in dose to the heart, lungs, and spinal cord based on planning technique, (3DCRT, IMRT, VMAT) than from the inclusion of daily cone-beam imaging doses over 25-30 fractions. The average doses from CBCT imaging per fraction to the lungs, heart and spinal cord were 0.52 ± 0.10, 0.49 ± 0.15 and 0.39 ± 0.08 cGy, respectively. Lung dose variations were related to the patient's size and body composition. Over a treatment course, this may result in an additional mean absorbed dose of 0.15-0.2 Gy. For lung V5, the imaging dose resulted in an average increase of ~ 0.6% of the total volume receiving 5 Gy. The increase in V20 was more dependent on the planning technique, with 3DCRT increasing by 0.11 ± 0.09% with imaging and IMRT and VMAT increasing by 0.17 ± 0.05% and 0.2 ± 0.06%, respectively. In this study, we assessed the concomitant dose for daily CBCT lung cancer patients undergoing radiotherapy. The additional radiation dose to the normal lungs from daily CBCT was found to range from 0.15 to 0.2 Gy when the patient was treated with 25-30 fractions. Consideration of potential variation in relative biological effectiveness between kilovoltage imaging and megavoltage treatment dose was outside the scope of this study. Regardless of this, our results show that the assessment of imaging dose can be incorporated into the treatment planning process and the relative effect on overall dose distribution was small compared to the difference among planning techniques.

Mobile shielding evaluation on the fetal dose during a breast radiotherapy using Monte Carlo simulation

PURPOSE

Evaluation of the out-of-field dose is an important aspect in radiotherapy. Due to the fetus radiosensitivity, this evaluation becomes even more conclusive when the patient is pregnant. In this work, a linear accelerator Varian Clinac 2100c operating at 6 MV, a pregnant anthropomorphic phantom (Maria), and different shields added above the abdominal region of the phantom were used for the analysis based on MCNPX.

METHODS

The simulations were performed for the medial and lateral projections, using either an open field collimation (10×16cm²) or a multileaf collimator. The added shields (M1 and M2) were designed based on models proposed by Stovall et al. [1], intending to reduce the deposited dose on the fetus and related structures.

RESULTS

The presence of the shields showed to be effective in reducing the doses on the fetus, amniotic sac, and placenta, for example. A reduction of about 43% was found in the dose on the fetus when M2 was added, using the open field collimation, in comparison with the situation with no shield, being the lateral projection the main responsible for the dose. The use of MLC significatively reduced the doses in different structures, including on the fetus and amniotic sac, for example, in comparison to the open field situation. A slight increment on the dose in organs such as the eyes, thyroid and brain was found in both collimation systems, due to the presence of the shields. The contribution of the leakage radiation from the tube head of the linear accelerator was found to be in the order of µGy, being reduced by the presence of the M2 shield.

CONCLUSION

Using the shields showed to be an essential feature in order to reduce the dose not only on the fetus, but also in important structures responsible to its development.

Radiotherapy in Pregnancy-Associated Breast Cancer

Breast radiotherapy during pregnancy is a matter of debate as both the efficacy of treatment and the safety of the developing fetus should be considered. Currently there is not enough data to support the safety of in-utero exposure to radiation even with modern radiotherapy techniques. So it is highly recommended that breast radiotherapy is postponed to after delivery, though it might be considered in very selected patients according to risk-benefit assessment.

Breast Cancer during Pregnancy-Current Paradigms, Paths to Explore

Breast cancer is the most common form of malignancy in pregnant women. The prevalence of pregnancy-associated breast cancer (PABC) is up to 0.04% of pregnancies and is expected to rise in developed countries. PABC represents a unique clinical scenario which requires a delicate balance of risks and benefits for both maternal and fetal well-being. Currently, there is paucity of data regarding the short- and long-term outcomes of in-utero exposure to anti-neoplastic agents. In general, when possible, treatment for PABC should follow the same guidelines as in non-pregnant patients. Surgery, including sentinel lymph node biopsy, is possible during all trimesters of pregnancy. Radiotherapy is contraindicated during pregnancy, although it might be considered in highly selected patients based on risk-benefit assessment. Evidence supports that administration of chemotherapy may be safe during the second and third trimesters, with cessation of treatment three weeks prior to expected delivery. Currently, hormonal therapy and anti-HER2 agents are contraindicated during pregnancy and should be postponed until after delivery. Prematurity is associated with worse neonatal and long-term outcomes, and thus should be avoided. While current data on the long-term effects of anti-neoplastic treatments are reassuring, grade of evidence is lacking, hence additional large prospective studies with long-term follow-up are essential to rule out any treatment-induced adverse effects.

Excessive applicator radiation leakage for a common therapeutic kilovoltage system

OBJECTIVE:

The objective of this work is to characterise out- of- field leakage radiation emanating from clinical applicators of the WOmed T-200 kilovoltage therapy machine.

METHODS:

To identify points of leakage, radiosensitive film was affixed to the walls and base plate of each applicator. Quantitative assessment of leakage radiation was conducted with a 0.23 cm3 ionisation chamber following the International Electrotechnical Commission standard. Film was also used to illustrate leakage distribution in the patient plane. Angular and energy dependences of the leakage radiation were quantified as well as a two-dimensional leakage profile in the plane parallel to one applicator.

RESULTS:

Leakage was found when the diameter of primary collimator of the kV tube exceeded the external dimension of the applicator wall. In the patient plane all applicators showed similar leakage rates with the leakage distribution dependent upon applicator design. Mean patient plane leakage was 1.37% of central axis air kerma rate, exceeding the 0.5% limit specified in the standard. Leakage was shown to be profoundly energy dependent with maximum leakage of 11.8% for the 200 kV beam, 1.3% for 150 kV and 0.2% for 100 kV. Angular dependence measurements showed a 10.3% change in leakage between the minimum and maximum positions.

CONCLUSION

The combination of shielding thickness, primary collimator design and applicator dimensions permits unwanted radiation to contribute dose outside the treatment field when energies ≥150 kV are used.

ADVANCES IN KNOWLEDGE:

Even carefully designed modern kv therapy systems can exhibit leakage in some areas. Thorough assessment of leakage is needed prior to release for clinical use.

Management of musculoskeletal tumors during pregnancy: a retrospective study

Background

In recent years, scientific research has increasingly focused on malignancies during pregnancy. However, the development of musculoskeletal tumors during pregnancy has only been the subject of a few studies so far. The primary aim of this study was to identify the incidence of sarcomas during pregnancy at our musculoskeletal tumor center (MSTC). Secondarily we intended to analyze these cases and discuss possible recommendations regarding diagnostic work-up as well as therapy on the basis of the literature.

Methods

All female patients who had been treated for soft tissue or bone sarcoma at our academic MSTC in the period between the years 2002 and 2010 were screened retrospectively for anamnestic annotations of pregnancy or records of pregnancy in the obstetrical database of our university hospital. The patients who met the criteria for inclusion (diagnosed sarcoma and pregnancy) were enrolled. For every pregnant patient two age-matched female control patients that suffered from tumors with the same histologic type were included.

Results

In the period between 2002 and 2010, 240 female patients between the age of 16 and 45 were treated for sarcoma. In eight out of the 240 cases the tumor disease developed or progressed during pregnancy. The delay in diagnosis was approximately eight months and turned out to be significantly higher for pregnant patients compared to non- pregnant controls. Each woman’s tumor was misdiagnosed at least once.

Conclusions

Diagnostic follow-up of pregnant women presenting with a growing or painful mass, which is suspected to be a musculoskeletal tumor, should be performed at a specialized tumor center. We recommend a multidisciplinary approach and discussing all possible consequences for mother and child intensively in accordance with the available literature.

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

PURPOSE

To estimate fetal dose and its components from three-dimensional conformal radiotherapy for several malignancies presented during pregnancy.

MATERIALS AND METHODS

Fetal dose was measured from radiotherapy for Hodgkin's lymphoma and for tumors in the region of nasopharynx, breast and lung. Anthropomorphic phantoms were used to simulate an average pregnant patient at the first, second and third trimesters of gestation. Thermoluminescent dosemeters (TLD) were employed for fetal dose measurements. Phantom exposures were also performed to estimate fetal dose due to head leakage, scatter from collimators and beam modifiers and scatter generated inside the phantom (Din). All treatments were delivered for 6 MV photon beams.

RESULTS

Radiotherapy of Hodgkin's lymphoma resulted in a fetal dose of 5.6-57.9 cGy depending upon the gestational age and the distance between the fetal level and the field edge. The corresponding dose ranges for treatment of nasopharyngeal, breast and lung cancer was 4.0-17.1 cGy, 3.9-24.8 cGy and 5.7-74.3 cGy, respectively. The Din at the first trimester of gestation was always smaller than 10 cGy for all examined malignancies. Pregnancy progression resulted in Din values above or below 10 cGy depending upon the treatment site and gestational age.

CONCLUSION

This study provides data about the fetal exposure and the contribution of Din to the total fetal dose from conformal radiation therapy. The Din knowledge prior to patient's irradiation enables radiation oncologists and medical physicists to decide whether fetal dose may be limited to 10 cGy or less with or without the introduction of special shielding materials.

Locoregional treatment of breast cancer during pregnancy

The management of patients with breast cancer during pregnancy is very demanding and it should be better performed in highly qualified and experienced centers. Referral to institutes and physicians trained in this special clinical scenario allows reducing the risk of both overtreating and undertreating the patients. Moreover, patients can receive appropriate information regarding safety of treatments without old-fashioned taboo. The purpose of the current paper is to discuss the main issues concerning surgical management and in general locoregional treatment of patients diagnosed with breast cancer and treated during gestation, focusing on those women who chose to continue their pregnancy. We cover the issues regarding type of breast surgery, radiation therapy, immediate reconstruction during mastectomy, and management of the axilla.

Fear of the unknown: ionizing radiation exposure during pregnancy

Ionizing radiation during pregnancy can negatively impact a fetus. In light of the Fukushima nuclear plant disaster in Japan, we discuss existing knowledge on the health effects of radiation and preventive measures for pregnant women. Overall, the risk of exposure to radiation is limited but severe defects can result from fetal radiation exposure >100 mGy equivalent to 10 rad (>1000 chest x-rays). While such high-level exposure rarely occurs during single medical diagnostic procedures, caution should be exercised for pregnant women. As a protective public health measure in light of a disaster, evacuation, shielding, and elimination of ingested radioactive isotopes should all be considered. Detailed radiation reports with health effects and precautionary measures should be available for a population exposed to more than background radiation.

Breast cancer in pregnancy

Breast cancer staging and treatment are possible during pregnancy, and should be defined in a multidisciplinary setting. Tumour biology, tumour stage, and gestational stage at diagnosis determine the appropriate approach. Surgery for breast cancer is possible during all trimesters of pregnancy. Radiotherapy is possible during pregnancy but, dependent on the fetal dose received, can result in poor fetal outcomes. The decision to give radiotherapy should be made on an individual basis. Evidence increasingly supports administration of chemotherapy from 14 weeks' gestation onwards. New breast cancer treatments might be applicable to pregnant patients, but tamoxifen and trastuzumab are contraindicated during pregnancy. Cancer treatment during pregnancy will decrease the need for early delivery and thus prematurity, which is a major concern in management of breast cancer in pregnancy.

Breast cancer in pregnancy: recommendations of an international consensus meeting

PURPOSE

To provide guidance for clinicians about the diagnosis, staging and treatment of breast cancer occurring during an otherwise uncomplicated pregnancy.

METHODS

An international expert Panel convened to address a series of questions identified by a literature review and personal experience. Issues relating to the diagnosis and management of breast cancer after delivery were outside the scope.

RESULTS

There is a paucity of large and/or randomized studies. Based on cohort studies, case series and case reports, the recommendations represent the best available evidence, albeit of a lower grade than is optimal.

RECOMMENDATIONS

In most circumstances, serious consideration should be given to the option of treating breast cancer whilst continuing with the pregnancy. Each woman should ideally be referred to a centre with sufficient expertise, given a clear explanation of treatment options. Most diagnostic and staging examinations can be performed adequately and safely during pregnancy. Treatment should however be adapted to the clinical presentation and the trimester of the pregnancy: surgery can be performed during all trimesters of pregnancy; radiotherapy can be considered during the first and second trimester but should be postponed during the third trimester; and standard chemotherapies can be used during the second and third trimester. Since neonatal morbidity mainly appears to be related to prematurity, delivery should not be induced before 37 weeks, if at all possible.

CONCLUSIONS

The treatment of breast cancer in pregnancy should be executed by experienced specialists in a multidisciplinary setting and should adhere as closely as possible to standard protocols.