Intraoperative Electron Radiotherapy Research Articles

Monte Carlo dose calculations of shielding disks with different material combinations in intraoperative electron radiation therapy (IOERT)

PurposeShielding disks play an important role in intraoperative electron radiation therapy, and different designs are currently used in clinical practice. This paper investigates the dosimetric impact of the shielding disk used during intraoperative electron radiation therapy (IOERT). Materials and MethodsThis paper focuses on the study of four shielding disks types that have been used in our clinic: Aluminum (Al)/Lead (Pb), PMMA/Copper(Cu)/PMMA, Aluminum (Al)/Copper (Cu) and Aluminum (Al)/Steel with their specific thicknesses. The theoretical study was conducted with the EGSnrc Monte Carlo (MC) code. On the other hand, the measurements were carried out with gafchromic films for the four shielding disks for the same setup inside the water phantom. Finally, a comparison of the simulated and measured PDD curves was performed for the four material combinations. ResultsMC simulation and gafchromic measurements illustrated that dose values under the four shielding disks types were close to 0, whereas the backscattering enhancement of the disks were 103% with Al/Pb shielding disk, 102% with Al/Steel shielding disk, 102% with Al/Cu shielding disk, 95% with PMMA/Cu/PMMA shielding disk. The PDDs values of the gafchromic films in front of the disks were: 107%, 105%, 104%, and 94% for the Al/Pb, Al/Steel, Al/Cu, and PMMA/Cu/PMMA disks respectively. ConclusionsThe dose values above and under the shielding disks were acceptable for the four studied shielding types. Demonstrated it is possible to use any of them clinically, while the best shielding disk was the Al/Pb since it has minimum thickness and a small backscatter enhancement.

Evaluating the radiation contamination dose around a high dose per pulse intraoperative radiotherapy accelerator: a Monte Carlo study

AbstractAim:In this study, the radiation contamination dose (RCD) for different combinations of electron energy/distance, applicator and radius around the light intraoperative accelerator (LIAC), a high dose per pulse dedicated intraoperative electron radiotherapy machine, has been estimated. Being aware about the amount of RCDs is highly recommended for linear medical electron accelerators.Methods and methods:Monte Carlo Nuclear Particles (MCNP) code was used to simulate the LIAC® head and calculate RCDs. Experimental RCDs measurements were also done by Advanced Markus chamber inside a MP3-XS water phantom. Relative differences of simulations and measurements were calculated.Result:RCD reduction by distance from the machine follows the inverse-square law, as expected. The RCD was decreased by increasing angle from applicator walls opposed to the electron beam direction. The maximum differences between the simulation and measurement results were lower than 3%.Conclusions:The RCD is strongly dependent on electron beam energy, applicator size and distance from the accelerator head. Agreement between the MCNP results and ionometric dosimetry confirms the applicability of this simulation code in modelling the intraoperative electron beam and obtaining the dosimetric parameters. The RCD is a parameter that would restrict working with LIAC in an unshielded operative room.

Intraoperative computed tomography imaging for dose calculation in intraoperative electron radiation therapy: Initial clinical observations.

In intraoperative electron radiation therapy (IOERT) the energy of the electron beam is selected under the conventional assumption of water-equivalent tissues at the applicator end. However, the treatment field can deviate from the theoretic flat irradiation surface, thus altering dose profiles. This patient-based study explored the feasibility of acquiring intraoperative computed tomography (CT) studies for calculating three-dimensional dose distributions with two factors not included in the conventional assumption, namely the air gap from the applicator end to the irradiation surface and tissue heterogeneity. In addition, dose distributions under the conventional assumption and from preoperative CT studies (both also updated with intraoperative data) were calculated to explore whether there are other alternatives to intraoperative CT studies that can provide similar dose distributions. The IOERT protocol was modified to incorporate the acquisition of intraoperative CT studies before radiation delivery in six patients. Three studies were not valid to calculate dose distributions due to the presence of metal artefacts. For the remaining three cases, the average gamma pass rates between the doses calculated from intraoperative CT studies and those obtained assuming water-equivalent tissues or from preoperative CT studies were 73.4% and 74.0% respectively. The agreement increased when the air gap was included in the conventional assumption (98.1%) or in the preoperative CT images (98.4%). Therefore, this factor was the one mostly influencing the dose distributions of this study. Our experience has shown that intraoperative CT studies are not recommended when the procedure includes the use of shielding discs or surgical retractors unless metal artefacts are removed. IOERT dose distributions calculated under the conventional assumption or from preoperative CT studies may be inaccurate unless the air gap (which depends on the surface irregularities of the irradiated volume and on the applicator pose) is included in the calculations.

A New Workflow for Image-Guided Intraoperative Electron Radiotherapy Using Projection-Based Pose Tracking

A new workflow is proposed to update the intraoperative electron radiotherapy (IOERT) planning refreshing the position and orientation (pose) of a virtual applicator with respect to the preoperative computed tomography (CT) with the actual pose during surgery. The workflow proposed relies on a robust registration of the preoperative CT and intraoperative projection radiographs acquired with a C-arm system. The workflow initially performs a geometric calibration of the C-arm using fiducials placed on the applicator. In the next step, a point-based 2D–3D registration based on fiducials positioned on the patient’s skin is performed, followed by an intensity-based registration that refines the point-based registration result. The performance of the workflow has been evaluated using a realistic physical phantom consisting of a pig lower limb and its corresponding CT and 7 C-arm projections at different poses. The accuracy has been measured with respect to the applicator origin and axis before and after the registration refinement process. A feasibility study with human data is also included. Error analysis revealed angular accuracy of 0.9 ± 0.7 degrees and translational accuracy of 1.9 ± 1 mm. Our experiments demonstrated that the proposed workflow can achieve subdegree angular accuracy in locating the applicator with respect to the preoperative CT to update and supervise the IOERT planning right before radiation delivery. The proposed workflow could be easily implementable in a routine, corresponding to a significant improvement in quality assurance during IOERT procedures.

Electron radiotherapy (IOERT) for applications outside of the breast: Dosimetry and influence of tissue inhomogeneities

PurposeThe purpose of study is to investigate the dosimetry of electron intraoperative radiotherapy (IOERT) of the Intraop Mobetron 2000 mobile LINAC in treatments outside of the breast. After commissioning and external validation of dosimetry, we report in vivo results of measurements for treatments outside the breast in a large patient cohort, and investigate if the presence of inhomogeneities can affect in vivo measurements. Methods and materialsApplicator factors and profile curves were measured with a stereotactic diode. The applicators factors of the 6 cm flat and beveled applicators were also confirmed with radiochromic films, parallel-plate ion chamber and by an external audit performed with ThermoLuminescent Dosimeters (TLDs). The influence of bone on dose was investigated by using radiochromic films attached to an insert equivalent to cortical bone, immersed in the water phantom. In vivo dosimetry was performed on 126 patients treated with IOERT using metal oxide-silicon semiconductor field effect transistors (MOSFETs) placed on the tumor bed. ResultsRelatively small differences were found among different detectors for measurements of applicator factors. In the external audit, the agreement with the TLD was mostly within ±0.2%. The largest increase of dose due to the presence of cortical bone insert was +6.0% with energy 12 MeV and 3 cm applicator. On average, in vivo dose was significantly (+3.1%) larger than prescribed dose. ConclusionIOERT in applications outside the breast results in low discrepancies between in vivo and prescribed doses, which can be also explained with the presence of tissue inhomogeneity.

Organ at risk dose calculation for left sided breast cancer treatments using intraoperative electron radiotherapy: A Monte Carlo-based feasibility study

The present study aims to calculate the received dose by lungs and heart, as organs at risk (OAR), during intraoperative electron radiotherapy (IOERT) of left breast cancer at the presence and absence of shielding disk using Monte Carlo (MC) simulation. LIAC 12, a dedicated IOERT Linac, and an anthropomorphic phantom were considered in this study to simulate particle tracks of 6, 8, 10, and 12 MeV nominal electron energies using EGSnrc MC particle transport simulation code. The results showed that for increasing electron beam energies in the absence of shielding disk, left lung and heart dose would also be increasing so that, maximum left lung and heart dose respectively increases from 0.512 to 9.920 Gy and from 0 to 0.506 Gy with increment of electron energy from 6 to 12 MeV. Employing the shielding disk in 6 and 8 MeV energy can reduce the heart and left lung maximum dose to zero. On the other hand, this dose reduction at 10 and 12 MeV energy was respectively about 99% and 93.5% for heart and 99.9% and 92.9% for left lung. Right lung did not receive a remarkable dose both in presence and absence of shielding disk. From the results, it can be concluded that employing the shielding disk can effectively reduce the received dose to OARs.

In-field radiation contamination during intraoperative electron radiation therapy with a dedicated accelerator

The in-field radiation contamination including photons and neutrons originated from a dedicated intraoperative electron radiotherapy (IOERT) accelerator, LIAC12, at different electron energies (6–12 MeV) and applicator sizes (3, 5 and 10 cm diameter) were quantitatively evaluated in the current study. A validated MC model of LIAC12 head in conjunction with different applicator diameters was employed for this purpose. The results showed that the fluence of in-field photon contamination is highly dependent on the electron energy and field size so that it would be increased by the factors of about 3 and 10 with an increment of electron energy and decrement of field size, respectively. Neutron contamination was found only at 12 MeV electron energy and zero neutron fluence was obtained at lower electron energies. The same trend with the field size was observed for neutron contamination fluence that increased about 7 times by decreasing the applicator diameter from 10 cm to 3 cm. The maximum contaminant neutron dose and photon dose per one Gy delivered electron dose were obtained about 0.3 μSv and 7.24 mSv, respectively. The produced neutron contamination by this dedicated IOERT accelerator was approximately 10−3 times lower than those originated from a conventional radiotherapy accelerator.

Clinical Results of Intraoperative Electron Radiation Therapy Combined with Narrow-Margin Hepatectomy for Centrally Located Hepatocellular Carcinoma

Clinical Results of Intraoperative Electron Radiation Therapy Combined with Narrow-Margin Hepatectomy for Centrally Located Hepatocellular Carcinoma

Effect of intraoperative radiotherapy on wound healing in breast cancer patient post breast conserving surgery, KSUMC, Riyadh, Saudi Arabia: Case series and review of literature.

Intraoperative radiotherapy during breast-conserving surgery is being studied as an alternative to 6 weeks of external beam radiotherapy (EBRT) for low-risk women; it can be delivered using electrons (intraoperative electron radiotherapy, IOERT) or 50-kV X-rays. Intraoperative radiation therapy (IORT) may pose a risk for wound complications. Between March 2018 and June 2018, 5 breast cancer patients, all eligible for breast conserving surgery (BCS), were treated at the King Saud Medical city with IORT using the IOERT. Complete data sets for age, stage (T, N, and M), and histology and hormone receptor status were available in 5 cases. Parameters to identify eligible patients are as follows: ESTRO: >50 years, invasive ductal carcinoma/other favourable histology (IDC), T1-2 (≤3 cm), N0, any hormone receptor status, M0; ASTRO: ≥60 years, IDC, T1, N0, positive estrogen hormone receptor status, M0; TARGIT E “elderly”, risk adapted radiotherapy with IORT followed by external beam radiotherapy in case of risk factors in final histopathology. Consecutive patients operated on with the same surgical technique and given IORT were included. Wound complications were evaluated.

On the study of effective electron source position for a dedicated beam shaper IOERT applicator

Intra-Operative electron radiotherapy (IOERT) is a technique based on the delivery of a high single electron dose to the patient during the surgery. To overcome the field matching problems related to the standard cylindrical electron applicators, which are commonly used in this technique, a dedicated beam shaper applicator is also introduced for IOERT. Due to the high weight of this dedicated applicator, it cannot be directly located on the patient body. So, an air gap always exists between the applicator and treatment surface which can lead to the variation of applicator output respect to the reference condition (zero air gap during applicator commissioning). To consider this change in the applicator output, one needs to know the effective electron source position (SSD eff ) to correct the output variations. In this study, the SSD eff for beam shaper applicator has been evaluated through ionometric measurement and Monte Carlo simulation at the various combinations of electron energy/field size. Variations of dosimetric parameters of emerging electron beam from beam shaper applicator were also evaluated at different air gaps. The results showed that the SSD eff substantially changes with the variations of electron energy and field size. The air gap between applicator and treatment surface has a measurable effect on the output of beam shaper applicator which should be corrected through SSD eff . Furthermore, the presence of air gap can considerably affect the dosimetric parameters of electron beam respect to the reference condition which should be taken into account during the treatment planning to assure an accurate electron dose delivery.

Recurrence rates for patients with early-stage breast cancer treated with IOERT at a community hospital per the ASTRO consensus statement for APBI

PurposeTo report the recurrence rates after single-fraction intraoperative electron radiotherapy (IOERT) in patients with early-stage breast cancer treated on a single institution prospective Phase I/II protocol at a community hospital. Results were retrospectively analyzed according to suitability criteria from the updated American Society for Radiation Oncology (ASTRO) consensus statement for accelerated partial breast irradiation (APBI). Methods and MaterialsPatients over 40 years with early-stage invasive or in situ breast cancer (<2.5 cm and node negative) were enrolled. IOERT 2100 cGy was delivered during breast conservation surgery, and patients were followed up for a median of 3 years (0.8–6.5 years) to determine toxicity and recurrence rates. ResultsSingle-fraction IOERT was performed in 215 cases (6 bilateral treatments, 196 patients) with 13 patients receiving whole-breast radiation (WBR) after IOERT for adverse pathologic features. Of 202 cases of IOERT without WBR, 89 patients experienced an ipsilateral breast tumor recurrence (IBTR) giving a cumulative incidence of 3.96%. When the ASTRO APBI suitability criteria were applied, the IBTR rate was significantly lower for suitable patients vs. cautionary or unsuitable patients (1.6% vs. 3.4% vs. 21.0%, p = 0.0002). 3-year progression-free survival after IOERT alone was 93.4%. For patients who received standard WBR (4500–5040 cGy) after IOERT, no Grade 3 or 4 toxicities (acute or late) occurred and all patients are disease-free. ConclusionsSingle-fraction IOERT results in a low rate of IBTR when strictly adhering to ASTRO criteria for APBI suitability. Standard dose WBR for unfavorable pathologic results after 2100 cGy IOERT is well tolerated.

Breast Conserving Surgery and Intraoperative Electron Radiotherapy (IOERT) Among Cases of Ductal Carcinoma In Situ

Background: Ductal Carcinoma In Situ (DCIS) which has recently been renamed into Ductal Intraepithelial Neoplasia (DIN), is a malignant cell proliferation without invasion to basement membrane of ducts or lobules of breast. DCIS consists 20-30% of newly diagnosed breast cancers in some Western countries due to higher diagnosis resulting from screening by mammography. Relative Risk (RR) of invasive ductal carcinoma is 8-10 times in DCIS, although high grading lesions and positive or close surgical margins are two important predictive factors in DCIS recurrences. The adjuvant radiotherapy has decreased the rate of ipsilateral local recurrence about 60%. In this article, we evaluated the recurrence rate as DCIS as well as invasive breast cancer in patients with DCIS undergoing breast conserving surgery (BCS) and intraoperative electron radiotherapy (IOERT).Methods: Data were derived from Cancer Research Center database from 38 pure DCIS cases who had received intraoperative radiation therapy between 2012–2017. Intraoperative electron radiotherapy (IOERT) was performed according to Iran's intraoperative radiation therapy consensus.Results: The median age of the patients was 55 years and median histological lesion size was 1.8 centimeters. Number of extracted lymph nodes had a median of 1 and all extracted nodes were negative. Hormonal therapy was performed in 42.1% of patients. IOERT was done as radical full exposure for 86.9% of cases and as boost dose for 13.1% of cases, who needed to complete radiotherapy by external beam. One case in the group received boost dose and 4 cases in the group received full dose had recurrence. The median follow-up of patients was 31 months. Pathology of recurrence was reported as DCIS in 3 cases and invasive breast cancer in 2 of them.Conclusion: There is not a lot of data on the effectiveness of IOERT in DCIS management. Although there are not large number of cases in our study, the local recurrence (13.1%) was only event in our study with 31 months median follow up with no contralateral metastasis, distant metastasis, or death.

Acute Toxicity and Early Oncological Outcomes After Intraoperative Electron Radiotherapy (IOERT) as Boost Followed by Whole Breast Irradiation in 157 Early Stage Breast Cancer Patients-First Clinical Results From a Single Center.

Introduction: Breast conserving surgery (BCS) followed by postoperative whole breast irradiation (WBI) is the current standard of care for early stage breast cancer patients. Boost to the tumor bed is recommended for patients with a higher risk of local recurrence and may be applied with different techniques. Intraoperative electron radiotherapy (IOERT) offers several advantages compared to other techniques, like direct visualization of the tumor bed, better skin sparing, less inter- and intrafractional motion, but also radiobiological effects may be beneficial. Objective of this retrospective analysis of IOERT as boost in breast cancer patients was to assess acute toxicity and early oncological outcomes.Material and Methods: All patients, who have been irradiated between 11/2014 and 01/2018 with IOERT during BCS were analyzed. IOERT was applied using the mobile linear accelerator Mobetron with a total dose of 10 Gy, prescribed to the 90% isodose. After ensured woundhealing, WBI followed with normofractionated or hypofractionated regimens. Patient reports, including diagnostic examinations and toxicity were analyzed after surgery and 6–8 weeks after WBI. Overall survival, distant progression-free survival, in-breast and contralateral breast local progression-free survival were calculated using the Kaplan-Meier method. Furthermore, recurrence patterns were assessed.Results: In total, 157 patients with a median age of 57 years were evaluated. Postoperative adverse events were mild with seroma and hematoma grade 1–2 in 26% and grade 3 in 0.6% of the patients. Wound infections grade 2–3 occurred in 2.2% and wound dehiscence grade 1–2 in 1.9% of the patients. Six to eight weeks after WBI radiotherapy-dependent acute dermatitis grade 1–2 was most common in 90.9% of the patients. Only 4.6% of the patients suffered from dermatitis grade 3. No grade 4 toxicities were documented after surgery or WBI. 2- and 3-year overall survival and distant progression-free survival, were 97.5 and 93.6, and 0.7 and 2.8%, respectively. In-breast recurrence and contralateral breast cancer rates after 3 years were 1.9 and 2.8%, respectively.Conclusion: IOERT boost during BCS is a safe treatment option with low acute toxicity. Short-term recurrence rates are comparable to previously published data and emphasize, that IOERT as boost is an effective treatment.

Performance evaluation and secondary monitor unit checkout for a dedicated accelerator in intraoperative electron radiotherapy

Quality assurance in intraoperative electron radiotherapy (IOERT) is a mandatory issue, because of single shot nature. Employed equipment for IOERT implementation, especially the treatment machine, should have a very stable performance for reliable treatment delivery. Calculated MUs is also an important factor which can affect the treatment quality. The aim of this study is to evaluate the performance characteristics of a dedicated accelerator in IOERT as well as a secondary MU check to ensure the validity of employed software for such purpose.The LIAC12 accelerator was considered in this study. The performance characteristics of accelerator including linearity, short term repeatability (STR) and Long term repeatability (LTR) were measured by ionometric dosimetry over a long time period of 48 weeks. LIAC Monitor Unit calculation (LMUCalculation) software is currently used for MU calculations of LIAC in IOERT. The validity of this software was evaluated through development of a secondary MU calculation worksheet and comparing the obtained results by two methods.The results showed that the LIAC accelerator fulfils the desired performance for IOERT. A perfect linear response was observed at different electron energies. The STR and LTR of LIAC response were less than 1% and 4%, respectively, at all of studied electron energies. The mean difference between calculated MUs by LMUCalculation and the developed manual approach was 1.23%.The obtained results guarantee the validity of LIAC performance for intraoperative radiotherapy purposes. Furthermore, accuracy of calculated MUs by LMUCalculation software was confirmed according to the recommended action level (2%) by AAPM TG-40 protocol.

Health-related quality of life of breast cancer patients after accelerated partial breast irradiation using intraoperative or external beam radiotherapy technique

PurposeTo compare health-related quality of life (HRQL) in elderly breast cancer patients between two types of Accelerated Partial Breast Irradiation: intraoperative radiotherapy (IORT) and external beam APBI (EB-APBI). MethodsBetween 2011 and 2016 women ≥60 years undergoing breast conserving therapy for early stage breast cancer were included in a prospective multi-centre cohort study. Patients were treated with electron IORT (1 × 23.3 Gy) or photon EB-APBI (10 × 3.85 Gy daily). HRQL was measured by the EORTC-QLQ C30 and BR23 questionnaires before surgery and at several time points until 1 year. ResultsHRQoL data was available of 204 IORT and 158 EB-APBI patients. In longitudinal analyses emotional functioning and future perspective were significantly, but not clinically relevantly, worse in IORT-treated patients, and improved significantly during follow-up in both groups. All other aspects of HRQL slightly worsened after treatment and recovered within 3 months with an improvement until 1 year. Cross-sectional analysis showed that postoperatively fatigue and role functioning were significantly worse in IORT patients compared to EB-APBI patients who were not yet irradiated, but the difference was not clinically relevant. At other timepoints there were no significant differences. Multivariable analysis at 1 year identified comorbidity and systemic therapy as risk factors for a worse global health score (GHS). ConclusionsEB-APBI and IORT were well tolerated. Despite a temporary deterioration after treatment, all HRQL scales recovered within 3 months resulting in no clinically relevant differences until 1 year between groups nor compared to baseline levels.

Breast intraoperative electron radiotherapy: Image-based setup verification and in-vivo dosimetry

IntroductionSingle fraction nature of intraoperative radiotherapy highly demands a quality assurance procedure to qualify both beam setup and treatment delivery. The aim of this study is to evaluate the treatment setup during breast intraoperative electron radiotherapy (IOERT) and in-vivo dose delivery verification. Materials and methodsTwenty-five breast cancer patients were enrolled and setup verification for each case was performed using C-arm imaging. The received dose by surface and distal end of target was measured by EBT2 film. The significance level of difference between obtained dosimetry results and predicted ones was evaluated by the T statistical test. ResultsAcquired C-arm images in two different oblique views revealed any misalignment between the applicator and shielding disk. The mean difference between the measured surface dose and expected one was 1.8% ± 1.2 (p = 0.983) while a great disagreement, 11.1% ± 1.5 (p < 0.001), was observed between the measured distal end dose and expected one. This discrepancy is mainly correlated to the backscattering effect from the shielding disk. Target depth nonuniformities can also contribute to this remarkable difference. ConclusionEmploying the intraoperative imaging for IOERT setup verification can considerably improve the treatment quality. Therefore, it is suggested to implement this imaging procedure as a part of treatment quality assurance. Favorable agreement between the predicted and measured surface doses demonstrates the applicability of EBT2 film for dose delivery verification. The results of in-vivo dosimetry showed that the electron backscattering from employed shielding disk can affect the received dose by the distal end of tumor bed.

A new proposal of utilizing intraoperative electron radiation therapy on the surface of liver to prevent postoperative liver metastasis of pancreatic cancer

Pancreatic cancer is a lethal cancer with high rate of liver metastasis worldwide, whereas its treatment choices are limited to a large extent. The limitation of current therapeutic strategies calls for an effective approach which can lower the postoperative liver metastasis rate in order to improve the overall prognosis and survival rate. Comprehensively considering the basic knowledge and clinical practice of tumor treatment worldwide, we proposed three points of hypotheses. Basically, the existing evidences indicated that tumor cells shedding from pancreatic cancer localized in the marginal liver preferentially through the Portal vein. Then, the percentage depth dose distribution of electron radiation is consistent with the marginal distribution of liver metastasis from pancreatic cancer. Based on the characteristics of liver metastasis of pancreatic cancer and the percentage depth dose of electron radiation, we provide a new propose of preventing postoperative liver metastasis in a way of prophylactic intraoperative electron radiation therapy on the surface of liver. Intraoperative electron radiation is relatively easy to control radiation dose and treatment area under direct vision, effectively inhibiting the metastasis and growth of cancer cells and preventing further deterioration of pancreatic cancer patients’ condition. Therefore, this hypothesis has an important clinical significance for postoperative rehabilitation and improvement of patients’ survival.

Measurement of peripheral dose to the pelvic region and the associated risk for cancer development after breast intraoperative electron radiation therapy

This study aimed to measure the received dose to the pelvic region of patients during breast intraoperative electron radiation therapy (IOERT). Furthermore, we compared the findings with those of external beam radiation therapy. Finally, secondary ovarian and uterus cancer risks following breast IOERT were estimated. In the current study, the received dose to the pelvic surface of 18 female patients during breast IOERT boosts were measured by thermoluminescent dosimeter (TLD-100) chips. All patients were treated with 12 Gy given in a single fraction. To estimate the dose to the ovary and uterus of the patients, conversion coefficients for depth from the surface dose were obtained in a Rando phantom. Given the received dose to the pelvic region of the patients, secondary ovarian and uterus cancer risks following breast IOERT were estimated. The received doses to the ovary and uterus surface of the patients were 0.260 ± 0.155 mGy to 31.460 ± 6.020 mGy and 0.485 ± 0.122 mGy to 22.387 ± 15.476 mGy, respectively. Corresponding intra-pelvic (ovary and uterus) regional doses were 0.012 ± 0.007 mGy to 1.479 ± 0.283 mGy and 0.027 ± 0.001 mGy to 1.164 ± 0.805 mGy, respectively. Findings demonstrated that the ratio of the received dose by the pelvic surface to the regional dose during breast IOERT was much less than external beam radiation therapy. The mean of the secondary cancer risks for the ovary in 8 and 10 MeV electron beam energies were 135.722 ± 117.331 × 10−6 and 69.958 ± 28.072 × 10−6, and for the uterus were 17.342 ± 10.583 × 10−6 and 2.971 ± 3.604 × 10−6, respectively. According to our findings, the use of breast IOERT in pregnant patients can be considered as a safe radiotherapeutic technique, because the received dose to the fetus was lower than 50 mGy. Furthermore, IOERT can efficiently reduce the unnecessary dose to the pelvic region and lowers the risk of secondary ovarian and uterus cancer following breast irradiation.

Abstract OT2-04-04: Multi-institution phase II trial of intraoperative electron beam radiotherapy boost at the time of breast conserving surgery with oncoplastic reconstruction in women with early-stage breast cancer

Abstract Background: In women amenable to breast conserving therapy, lumpectomy followed by adjuvant whole breast irradiation (WBI) remains the standard of care. Randomized trials demonstrate that addition of a lumpectomy cavity boost significantly reduces the risk of ipsilateral breast tumor recurrences but also increases the risk of breast fibrosis. Contemporary randomized trials define the lumpectomy cavity boost volume as a 1.7 cm isometric expansion on the lumpectomy cavity as delineated on CT. However, identifying the lumpectomy cavity can be challenging, especially in women that receive adjuvant chemotherapy and in cases in which surgical clips are not present. Recently, the use of oncoplastic techniques in breast conserving surgery has increased. These techniques are used to prevent the poor cosmetic results that can occur when a large volume of breast tissue is resected. Women that undergo oncoplastic reconstruction represent especially difficult cases for lumpectomy cavity delineation. Retrospective series have evaluated the use of intraoperative electron radiotherapy (IOERT) as a boost prior to WBI in women receiving lumpectomy without oncoplastic reconstruction. In the largest series of IOERT boost prior to WBI the local control rate of this approach was &amp;gt;99%. Prospective data regarding IOERT boost in women undergoing oncoplastic reconstruction are limited. The advantages of this approach include direct visualization/irradiation of the tumor bed, sparing the skin of irradiation, and reducing the treatment time by ˜1 week. We hypothesize that IOERT boost followed by WBI will result in acceptably low rates of grade 3 fibrosis in women undergoing lumpectomy with oncoplastic reconstruction. Trial Design: This is a single-arm, prospective study to evaluate the safety, toxicity and efficacy of IOERT boost at the time of breast conserving surgery in women with early-stage breast cancer undergoing oncoplastic reconstruction. Eligible women will receive 1 dose of 8 Gy to the surgical bed after lumpectomy but prior to oncoplastic reconstruction. Women will then receive adjuvant WBI of 40 Gy in 15 fractions or 50 Gy in 25 fractions. Eligibility: Key criteria include age≥18 yo, clinically node-negative stage I/II, any breast cancer subtype. Specific Aims: To determine the rate of grade 3 breast fibrosis at 1 year. Additional aims include surgical complication rates, cosmesis, and local regional cancer control. Statistical Methods: Safety will be evaluated by the rate of surgical complications necessitating hospital readmission or return to the operating room within 30 days of surgery+IOERT. If ≥4 events in the first 10 patients, ≥7 events in the first 20 patients, or ≥9 events in the first 30 patients are seen, the study will be halted. We hypothesize that the grade 3 fibrosis rate in our study will be ≤5%. Assuming an actual rate of 4%, an unacceptable rate of 9%, and a drop-out rate of 10%, the expected sample size is 176. Sites: Ohio State University, Avera Medical Group, University of North Carolina-Chapel Hill Patient Accrual: Current accrual is 5/176. Contact Information: Jose Bazan (jose.bazan2@osumc.edu) Funding Source: Intraop Medical Citation Format: Bazan JG, Stephens J, Agnese D, Skoracki R, Arneson K, Reiland J, Gupta G, Gallagher K, McElroy S, Gupta N, White JR. Multi-institution phase II trial of intraoperative electron beam radiotherapy boost at the time of breast conserving surgery with oncoplastic reconstruction in women with early-stage breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr OT2-04-04.

Abstract ES4-3: Techniques and technical considerations

Abstract Purpose: Partial breast irradiation (PBI) treats the lumpectomy cavity and a margin of adjacent breast tissue allowing for a reduction in treatment volume, duration and potentially toxicity. Body: Multiple PBI techniques are available. Interstitial brachytherapy (IB) represents the oldest PBI technique; mature data from randomized trials are available with 5-10 year follow-up and demonstrate comparable local control and toxicity profiles. Technically, multiple target volume definitions are currently utilized. Applicator based brachytherapy has evolved from single-lumen applicators, increasing the degrees of freedom for treatment planning. Prospective, non-randomized 5 year data are available with applicator based brachytherapy, demonstrating low rates of recurrence, comparable rates of toxicity, and high rates of excellent/good cosmetic outcomes. The treatment volume for applicator based brachytherapy is 1 cm surrounding the device, with adjustments for the skin and chest wall. External beam radiation therapy includes 3D-CRT, IMRT and proton based techniques. Data from 3D-CRT studies have suggested higher toxicities and inferior cosmetic outcomes. However, randomized studies evaluating IMRT PBI have not, demonstrating comparable or improved toxicity and cosmetic outcomes. Intraoperative radiation therapy (IORT) is unique as two randomized trials have evaluated IORT and found higher rates of local recurrence as compared to WBI. Low-energy IORT delivers 25-30% of prescription at 1 cm, different from other PBI techniques while electron IORT allows for modulation of energy/depth. Currently, ASTRO PBI guidelines do not recommend low-energy IORT off protocol and electron IORT only for suitable risk patients, while ABS guidelines do not recommend IORT off trial. Finally, newer PBI techniques include non-invasive image-guided breast brachytherapy and permanent seed implants. As with all PBI techniques, use of guidelines for the application of PBI is encouraged for patient selection and the application of well-established dosimetric criteria for target coverage and normal tissue tolerances. Partial Breast TechniquesTechniqueRandomized TrialsDose/Target VolumesDurationInterstitial BrachytherapyNational Institute of Oncology (Hungary);GEC-ESTRO;NSABP B-39/RTOG 041336.4 Gy/7 fx BID;32 Gy/8 fx BID, 30.3 Gy/7 fx BID, 50 Gy PDR; 34 Gy/10 fx BID15-20 mm expansion (limit skin, chest wall);20 mm minimum (sum of pathologic margin + radiation margin) CTV; Cavity + 15 mm (5 mm from skin, posterior breast)4-5 treatment days;4-5 treatment days; 5 treatment daysApplicator Based BrachytherapyNSABP B-39/RTOG 041334 Gy/10 fx BID10 mm from surface/device (5 mm from skin and posterior breast)5 treatment days3D-CRTNSABP B-39/RTOG 0413; RAPID38.5 Gy/10 fx BID; 38.5 Gy/10 fx BID15 mm CTV (5 mm from skin and posterior breast), 10 mm PTV, PTV-EVAL (5 mm from skin, posterior breast); 10 mm CTV inside breast, 10 mm PTV5 treatment days; 5 treatment daysIMRTUniversity of Florence; IMPORT LOW30 Gy/5 fx QOD; 40 Gy/15 fx10 mm CTV (3 mm from skin), 10 mm PTV ( 4 mm into lung, 3 mm from skin); 15 mm CTV (5 mm from skin, pec fascia)/10 mm PTV (5 mm from skin)5 treatment days over 2 weeks; 3 weeks (15 treatments) Conclusions: Partial breast irradiation represents a standard of care strategy for appropriately selected patients. Citation Format: Vicini F. Techniques and technical considerations [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr ES4-3.