Electron Beam Intraoperative Radiotherapy (ELIOT) in Pregnant Women with Breast Cancer: From in Vivo Dosimetry to Clinical Practice

Development and validation of the low-cost pregnant female physical phantom for fetal dosimetry in MV photon radiotherapy

BACKGROUND

Monte Carlo (MC) simulations or measurements in anthropomorphic phantoms are recommended for estimating fetal dose in pregnant patients in radiotherapy. Among the many existing phantoms, there is no commercially available physical phantom representing the entire pregnant woman.

PURPOSE

In this study, the development of a low-cost, physical pregnant female phantom was demonstrated using commercially available materials. This phantom is based on the previously published computational phantom.

METHODS

Three tissue substitution materials (soft tissue, lung and bone tissue substitution) were developed. To verify Tena's substitution tissue materials, their radiation properties were assessed and compared to ICRP and ICRU materials using MC simulations in MV radiotherapy beams. Validation of the physical phantom was performed by comparing fetal doses obtained by measurements in the phantom with fetal doses obtained by MC simulations in computational phantom, during an MV photon breast radiotherapy treatment.

RESULTS

Materials used for building Tena phantom are matched to ICRU materials using physical density, radiation absorption properties and effective atomic number. MC simulations showed that percentage depth doses of Tena and ICRU material comply within 5% for soft and lung tissue, up to 25 cm depth. In the bone tissue, the discrepancy is higher, but again within 5% up to the depth of 5 cm. When the phantom was used for fetal dose measurements in MV photon breast radiotherapy, measured fetal doses complied with fetal doses calculated using MC simulation within 15%.

CONCLUSIONS

Physical anthropomorphic phantom of pregnant patient can be manufactured using commercial materials and with low expenses. The files needed for 3D printing are now freely available. This enables further studies and comparison of numerical and physical experiments in diagnostic radiology or radiotherapy.

Evaluating the induced photon contamination by different breast IOERT shields using Monte Carlo simulation

BACKGROUND AND OBJECTIVE

Avoiding the underlying healthy tissue over-exposure during breast intraoperative electron radiotherapy (IOERT) is owing to the use of some dedicated radioprotection disks during patient irradiation. The originated contaminant photons from some widely used double-layered shielding disks including PMMA+Cu, PTFE+steel, and Al+Pb configurations during the breast IOERT have been evaluated through a Monte Carlo (MC) simulation approach.

METHODS

Produced electron beam with energies of 6, 8, 10, and 12 MeV by a validated MC model of Liac12 dedicated IOERT accelerator was used for disk irradiations. Each of above-mentioned radioprotection disks was simulated inside a water phantom, so that the upper disk surface was positioned at R90 depth of each considered electron energy. Simulations were performed by MCNPX (version 2.6.0) MC code. Then, the energy spectra of the contaminant photons at different disk surfaces (upper, middle, and lower one) and relevant contaminant dose beneath the studied disks were determined and compared.

RESULTS

None of studied shielding disks show significant photon contamination up to 10 MeV electron energy, so that the induced photon dose by the contaminant X-rays was lower than those observed in the disk absence under the same conditions. In return, the induced photon dose at a close distance to the lower disk surface exceeded from calculated values in the disk absence at 12 MeV electron energy. The best performance in contaminant dose reduction at the energy range of 6-10 MeV belonged to the Al+Pb disk, while the PMMA+Cu configuration showed the best performance in this regard at 12 MeV energy.

CONCLUSION

Finally, it can be concluded that all studied shielding disks not only don't produce considerable photon contamination but also absorb the originated X-rays from electron interactions with water at the electron energy range of 6-10 MeV. The only concern is related to 12 MeV energy where the induced photon dose exceeds the dose values in the disk absence. Nevertheless, the administered dose by contaminant photons to underlying healthy tissues remains beneath the tolerance dose level by these organs at the entire range of studied electron energies.

In vivodosimetry in cancer patients undergoing intraoperative radiation therapy

In vivodosimetry (IVD) is an important tool in external beam radiotherapy (EBRT) to detect major errors by assessing differences between expected and delivered dose and to record the received dose by individual patients. Also, in intraoperative radiation therapy (IORT), IVD is highly relevant to register the delivered dose. This is especially relevant in low-risk breast cancer patients since a high dose of IORT is delivered in a single fraction. In contrast to EBRT, online treatment planning based on intraoperative imaging is only under development for IORT. Up to date, two commercial treatment planning systems proposed intraoperative ultrasound or in-room cone-beam CT for real-time IORT planning. This makes IVD even more important because of the possibility for real-time treatment adaptation. Here, we summarize recent developments and applications of IVD methods for IORT in clinical practice, highlighting important contributions and identifying specific challenges such as a treatment planning system for IORT. HDR brachytherapy as a delivery technique was not considered. We add IVD for ultrahigh dose rate (FLASH) radiotherapy that promises to improve the treatment efficacy, when compared to conventional radiotherapy by limiting the rate of toxicity while maintaining similar tumour control probabilities. To date, FLASH IORT is not yet in clinical use.

Development of a computational pregnant female phantom and calculation of fetal dose during a photon breast radiotherapy

BACKGROUND

The incidence of carcinoma during pregnancy is reported to be 1:1000-1:1500 pregnancies with the breast carcinoma being the most commonly diagnosed. Since the fetus is most sensitive to ionizing radiation during the first two trimesters, there are mixed clinical opinions and no uniform guidelines on the use of radiotherapy during pregnancy. Within this study the pregnant female phantom in the second trimester, that can be used for radiotherapy treatment planning (as DICOM data), Monte Carlo simulations (as voxelized geometry) and experimental dosimetry utilizing 3D printing of the molds (as .STL files), was developed.

MATERIALS AND METHODS

The developed phantom is based on MRI images of a female patient in her 18th week of pregnancy and CT images after childbirth. Phantom was developed in such a manner that a pregnant female was scanned "in vivo" using MRI during pregnancy and CT after childbirth. For the treatment of left breast carcinoma, 3D conformal radiotherapy was used. The voxelized geometry of the phantom was used for Monte Carlo (MC) simulations using Monte Carlo N-Particle transport code^TM 6.2 (MCNP).

CONCLUSIONS

The modeled photon breast radiotherapy plan, applied to the phantom, indicated that the fetus dose is 59 mGy for 50 Gy prescribed to the breast. The results clearly indicate that only 9.5% of the fetal dose is caused by photons that are generated in the accelerator head through scattering and leakage, but the dominant component is scattered radiation from the patient's body.

Early Breast Cancers During Pregnancy Treated With Breast-Conserving Surgery in the First Trimester of Gestation: A Feasibility Study

Breast cancer is the most common malignancy occurring during gestation. In early-stage breast cancer during pregnancy (PrBC), breast-conserving surgery (BCS) with delayed RT is a rational alternative to mastectomy, for long considered the standard-of-care. Regrettably, no specific guidelines on the surgical management of these patients are available. In this study, we investigated the feasibility and safety of BCS during the first trimester of pregnancy in women with early-stage PrBC. All patients with a diagnosis of PrBC during the first trimester of pregnancy jointly managed in two PrBC-specialized Centers were included in this study. All patients underwent BCS followed by adjuvant radiotherapy to the ipsilateral breast after delivery. Histopathological features and biomarkers were first profiled on pre-surgical biopsies. The primary outcome was the isolated local recurrence (ILR). Among 168 PrBC patients, 67 (39.9%) were diagnosed during the first trimester of gestation. Of these, 30 patients (age range, 23-43 years; median=36 years; gestational age, 2-12 weeks; median=7 weeks; median follow-up time=6.5 years) met the inclusion criteria. The patients that were subjected to radical surgery (n=14) served as controls. None of the patients experienced perioperative surgical complications. No ILR were observed within three months (n=30), 1 year (n=27), and 5 years (n=18) after surgery. Among the study group, 4 (12.3%) patients experienced ILR or new carcinomas after 6-13 years, the same number (n=4) had metastatic dissemination after 3-7 years. These patients are still alive and disease-free after 14-17 years of follow-up. The rate of recurrences and metastasis in the controls were not significantly different. The findings provide evidence that BCS in the first trimester PrBC is feasible and reasonably safe for both the mother and the baby.

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.

Cancer in Pregnancy

Cancer in pregnancy may be increasing in incidence with advancing maternal age and higher rates of obesity. The diagnosis of cancer in pregnancy provokes complex management issues balancing short- and long-term risks for both mother and baby. Every case needs to be individualized, with a multidisciplinary team of midwives, obstetricians, oncologists, surgeons, radiation oncologists, and neonatologists assisting the family to make informed decisions regarding the best treatment course for the mother and baby. The present article reviews the evidence regarding the safety of diagnostic imaging, procedures and treatment modalities for cancer for the pregnant woman and fetus. The efficacy of novel anticancer therapies highlight the need for International Registries to accumulate safety data for these agents in pregnancy as expeditiously as possible.

Modern radiotherapy in cancer treatment during pregnancy

Breast cancer, gynecological malignancies and lymphomas are the most frequently diagnosed tumors in pregnant women. The feasibility of radiotherapy during pregnancy remains a subject of debate and clinicians continue to hesitate on this approach, trying to avoid radiotherapy in most cases. Since the 1990s, several technological advances, including intensity modulated and image guided radiation delivery, have been implemented in radiation oncology to improve the radiation treatment in terms of effectiveness and tolerability. It remains uncertain which short- and long-term health effects the radiation exposure of the fetus may have through advanced radiotherapy techniques. The present systematic literature review aims to summarize the limited current evidences of the feasibility and clinical results of "modern" radiotherapy procedures for the treatment of the most frequently diagnosed tumors in pregnant women.

Dosimetric study to assess the feasibility of intraoperative radiotherapy with electrons (ELIOT) as partial breast irradiation for patients with cardiac implantable electronic device (CIED)

PURPOSE

To report in-vivo dosimetry in the infraclavicular region, a potential site of a cardiac implantable electronic device (CIED) and to evaluate the absorbed dose from intraoperative radiotherapy with electrons (ELIOT).

METHODS

27 non-cardiopathic breast cancer (BC) patients without CIED received quadrantectomy and ELIOT as partial breast irradiation. Before delivering ELIOT, two catheters, each containing eight thermoluminescent dosimeters (TLDs), were positioned in the infraclavicular region. TLDs internal catheter was located deep in the tumor bed while the external catheter was placed on patient's skin.

RESULTS

Data were available for 24/27 patients. The absorbed doses were referred to the dose of 21 Gy. Values measured by the external catheter were low, although statistically significant higher doses were found close to the applicator (mean values 0.26-0.49 Gy). External TLD doses in proximity of the applicator were lower than those detected by their internal counterparts. Values measured by the internal catheter TLDs varied according to the distance from the applicator while no correlation with tumor site and beam energy was found. The distance from the applicator to deliver < 2 Gy to a CIED was 2 cm, while from 2.5 cm the dose measured in all the patients became negligible.

CONCLUSIONS

This dosimetric study provided data to support the clinical use of ELIOT in BC patients having CIEDs as long as the suggested minimum safe distance of 2.5 cm is taken from the RT field in case of ELIOT single dose of 21 Gy, in the energy range of 6-10 MeV.