Preoperative Accelerated Partial Breast Irradiation for Early-Stage Breast Cancer: Preliminary Results of a Prospective, Phase 2 Trial

The Role of MRI in Breast Cancer and Breast Conservation Therapy

Contrast-enhanced breast MRI has an established role in aiding in the detection, evaluation, and management of breast cancer. This article discusses MRI sequences, the clinical utility of MRI, and how MRI has been evaluated for use in breast radiotherapy treatment planning. We highlight the contribution of MRI in the decision-making regarding selecting appropriate candidates for breast conservation therapy and review the emerging role of MRI-guided breast radiotherapy.

A narrative review for radiation oncologists to implement preoperative partial breast irradiation

The strategy to anticipate radiotherapy (RT) before surgery, for breast cancer (BC) treatment, has recently generated a renewed interest. Historically, preoperative RT has remained confined either to highly selected patients, in the context of personalized therapy, or to clinical research protocols. Nevertheless, in the recent years, thanks to technological advances and increased tumor biology understanding, RT has undergone great changes that have also impacted the preoperative settings, embracing the modern approach to breast cancer. In particular, the reappraisal of preoperative RT can be viewed within the broader view of personalized and tailored medicine. In fact, preoperative accelerated partial breast irradiation (APBI) allows a more precise target delineation, with less variability in contouring among radiation oncologists, and a smaller treatment volume, possibly leading to lower toxicity and to dose escalation programs. The aim of the present review, which represents a benchmark study for the AIRC IG-23118, is to report available data on different technical aspects of preoperative RT including dosimetric studies, patient's selection and set-up, constraints, target delineation and clinical results. These data, along with the ones that will become available from ongoing studies, may inform the design of the future trials and representing a step toward a tailored APBI approach with the potential to challenge the current treatment paradigm in early-stage BC.Trial registration: The study is registered at clinicaltrials.gov (NCT04679454).

Definitive ablative stereotactic partial breast irradiation in early stage inoperable breast cancer

PURPOSE

This case series and literature review aims to investigate the efficacy and safety of definitive ablative radiation therapy as a treatment modality for non-operable patients with early stage breast cancer. We present two cases demonstrating the potential of this approach to achieve durable responses.

METHODS

We assessed the long-term response of two non-operable patients diagnosed with Stage II (cT2N0M) and Stage IA (T1bN0M0) invasive ductal carcinoma (IDC), who were deemed unfit for surgery due to significant co-morbid conditions. Definitive ablative radiation therapy was administered using stereotactic partial breast irradiation with ablative doses delivered in either a single fraction or two fractions. Serial imaging was conducted to assess treatment response and monitor adverse events.

RESULTS

Both patients exhibited notable treatment responses following definitive ablative radiation therapy. The first patient, an 84-year-old woman, experienced a 69% reduction in tumor size over a follow-up period exceeding 2 years. The second patient, an 87-year-old woman, achieved complete resolution of disease on imaging, with no signs of progression even 26 month post-treatment. Both patients tolerated the treatment well, without significant treatment-related adverse events.

CONCLUSIONS

Our case series suggests that definitive ablative radiation therapy may serve as a safe and effective treatment option for non-operable patients with early stage breast cancer. The observed durable treatment responses and minimal toxicity support the potential of this approach. Furthermore, a longer interval between ablative radiation therapy and surgery may enhance treatment response, potentially leading to increased complete pathologic response rates.

Advances in Radiotherapy for Breast Cancer

Breast cancer is the most prevalent cancer in women, and the second leading cause of cancer death in women in the United States. Radiation therapy is an important component in the multimodal management of breast cancer, including early stage and locally advanced breast cancers, as well as metastatic cases. Breast cancer radiation therapy has seen significant advancements over the past 20 years. This article discusses the latest advances in the radiotherapeutic management of breast cancer, especially focusing on the technological advances in radiation treatment planning and techniques that have exploited the understanding of radiation biology.

Preoperative Partial Breast Irradiation in Patients with Low-Risk Breast Cancer: A Systematic Review of Literature

BACKGROUND

Preoperative instead of standard postoperative partial breast irradiation (PBI) after breast-conserving surgery (BCS) has the advantage of reducing the irradiated breast volume, toxicity, and number of radiotherapy sessions and can allow tumor downstaging. In this review, we assessed tumor response and clinical outcomes after preoperative PBI.

PATIENTS AND METHODS

We conducted a systematic review of studies on preoperative PBI in patients with low-risk breast cancer using the databases Ovid Medline, Embase.com, Web of Science (Core Collection), and Scopus (PROSPERO registration CRD42022301435). References of eligible manuscripts were checked for other relevant manuscripts. The primary outcome measure was pathologic complete response (pCR).

RESULTS

A total of eight prospective and one retrospective cohort study were identified (n = 359). In up to 42% of the patients, pCR was obtained and this increased after a longer interval between radiotherapy and BCS (0.5-8 months). After a maximum median follow-up of 5.0 years, three studies on external beam radiotherapy reported low local recurrence rates (0-3%) and overall survival of 97-100%. Acute toxicity consisted mainly of grade 1 skin toxicity (0-34%) and seroma (0-31%). Late toxicity was predominantly fibrosis grade 1 (46-100%) and grade 2 (10-11%). Cosmetic outcome was good to excellent in 78-100% of the patients.

CONCLUSIONS

Preoperative PBI showed a higher pCR rate after a longer interval between radiotherapy and BCS. Mild late toxicity and good oncological and cosmetic outcomes were reported. In the ongoing ABLATIVE-2 trial, BCS is performed at a longer interval of 12 months after preoperative PBI aiming to achieve a higher pCR rate.

Prediction of pathologic complete response after single-dose MR-guided partial breast irradiation in low-risk breast cancer patients: the ABLATIVE-2 trial-a study protocol

BACKGROUND

Partial breast irradiation (PBI) is standard of care in low-risk breast cancer patients after breast-conserving surgery (BCS). Pre-operative PBI can result in tumor downstaging and more precise target definition possibly resulting in less treatment-related toxicity. This study aims to assess the pathologic complete response (pCR) rate one year after MR-guided single-dose pre-operative PBI in low-risk breast cancer patients.

METHODS

The ABLATIVE-2 trial is a multicenter prospective single-arm trial using single-dose ablative PBI in low-risk breast cancer patients. Patients ≥ 50 years with non-lobular invasive breast cancer ≤ 2 cm, grade 1 or 2, estrogen receptor-positive, HER2-negative, and tumor-negative sentinel node procedure are eligible. A total of 100 patients will be enrolled. PBI treatment planning will be performed using a radiotherapy planning CT and -MRI in treatment position. The treatment delivery will take place on a conventional or MR-guided linear accelerator. The prescribed radiotherapy dose is a single dose of 20 Gy to the tumor, and 15 Gy to the 2 cm of breast tissue surrounding the tumor. Follow-up MRIs, scheduled at baseline, 2 weeks, 3, 6, 9, and 12 months after PBI, are combined with liquid biopsies to identify biomarkers for pCR prediction. BCS will be performed 12 months after radiotherapy or after 6 months, if MRI does not show a radiologic complete response. The primary endpoint is the pCR rate after PBI. Secondary endpoints are radiologic response, toxicity, quality of life, cosmetic outcome, patient distress, oncological outcomes, and the evaluation of biomarkers in liquid biopsies and tumor tissue. Patients will be followed up to 10 years after radiation therapy.

DISCUSSION

This trial will investigate the pathological tumor response after pre-operative single-dose PBI after 12 months in patients with low-risk breast cancer. In comparison with previous trial outcomes, a longer interval between PBI and BCS of 12 months is expected to increase the pCR rate of 42% after 6-8 months. In addition, response monitoring using MRI and biomarkers will help to predict pCR. Accurate pCR prediction will allow omission of surgery in future patients.

TRIAL REGISTRATION

The trial was registered prospectively on April 28th 2022 at clinicaltrials.gov (NCT05350722).

Special issue. De-escalation of loco-regional treatment in breast cancer: Time to find the balance? Partial breast irradiation

Breast cancer is the most common cancer in women worldwide. Over the past few decades, remarkable progress has been made in understanding the biology and pathology of breast cancer. A personalized conservative approach has been currently adopted addressing the patient's individual risk of relapse. After postoperative whole breast irradiation for early-stage breast cancer, a rate of recurrences outside the initial tumour bed lower than 4% was observed. Thus, the highest benefits of breast irradiation seem to result from the dose delivered to the tissue neighbouring the tumour bed. Nonetheless, reducing treatment morbidity while maintaining radiation therapy's ability to decrease local recurrences is an important challenge in treating patients with radiation therapy. In this regard, strategies such as partial-breast irradiation have been developed to reduce toxicity without compromising oncologic outcomes. According to the national and international published guidelines, clinical oncologists can refer to specific dose/fractionation schedules and eligible criteria. However, there are still some areas of open questions. Breast cancer represents a multidisciplinary paradigm; it should be considered a heterogeneous disease where a "one-treatment-fits-all" approach cannot be considered an appropriate option. This is a wide overview on the main partial breast irradiation advantages, risks, timings, techniques, and available recommendations. We aim to provide practical findings to support clinical decision-making, exploring future perspectives, towards a balance for optimisation of breast cancer.

Pathologic Response to Neoadjuvant Sequential Chemoradiation Therapy in Locally Advanced Breast Cancer: Preliminary, Translational Results from the French Neo-APBI-01 Trial

Background: Radiation therapy (RT), a novel approach to boost the anticancer immune response, has been progressively evaluated in the neoadjuvant setting in breast cancer (BC). Purpose: We aimed to evaluate immunity-related indicators of response to neoadjuvant chemoradiation therapy (NACRT) in BC for better treatment personalization. Patients and Methods: We analyzed data of the first 42 patients included in the randomized phase 2 Neo-APBI-01 trial comparing standard neoadjuvant chemotherapy (NACT) and NACRT regimen in locally advanced triple-negative (TN) and luminal B (LB) subtype BC. Clinicopathological parameters, blood counts and the derived parameters, total tumor-infiltrating lymphocytes (TILs) and their subpopulation, as well as TP53 mutation status, were assessed as predictors of response. Results: Twenty-one patients were equally assigned to each group. The pathologic complete response (pCR) was 33% and 38% in the NACT and NACRT groups, respectively, with a dose-response effect. Only one LB tumor reached pCR after NACRT. Numerous parameters associated with response were identified, which differed according to the assigned treatment. In the NACRT group, baseline hemoglobin of ≥13 g/dL and body mass index of <26 were strongly associated with pCR. Higher baseline neutrophils-to-lymphocytes ratio, total TILs, and T-effector cell counts were favorable for pCR. Conclusion: This preliminary analysis identified LB and low-TIL tumors as poor responders to the NACRT protocol, which delivered RT after several cycles of chemotherapy. These findings will allow for amending the selection of patients for the trial and help better design future trials of NACRT in BC.

Pilot/Phase II Trial of Hypofractionated Radiation Therapy to the Whole Breast Alone Before Breast Conserving Surgery

Purpose

Our purpose was to report the results of a phase II trial of patients with breast cancer treated with hypofractionated whole breast radiation therapy (RT) before breast-conserving surgery (BCS).

Methods and materials

Between 2019 and 2020, patients with cT0-T2, N0, M0 breast cancer were enrolled. Patients were treated with hypofractionated whole breast RT, 25 Gy in 5 fractions, 4 to 8 weeks before BCS. Pathologic assessment was performed using the residual cancer burden (RCB). Toxicities were assessed according to Common Terminology Criteria for Adverse Events (version 4). Quality of life was assessed with Patient-Reported Outcomes version of the Common Terminology Criteria for Adverse Events, The Breast Cancer Treatment Outcome Scale, Linear Analogue Self-Assessment, and Patient-Reported Outcomes Measurement Information System.

Results

Twenty-two patients were enrolled. Median follow-up was 7.6 months (range, 0.2-16.8). Seven (32%) and 2 (9%) patients experienced grade 2+ or 3 toxicities, respectively. Overall quality of life Linear Analogue Self-Assessment and Patient-Reported Outcomes Measurement Information System did not change significantly from baseline (P = .21 and P = .72, respectively). There was no clinically significant change (≥1 point) in any of The Breast Cancer Treatment Outcome Scale domains. Only 1 (5%) patient experienced a clinical deterioration that corresponded to a "fair" outcome on the Harvard Cosmesis Scale. At pathologic evaluation, 14 (64%) patients had RCB-0 or RCB-I, including 3 (14%) patients with a pathologic complete response (RCB-0). Eight patients (36%) had RCB-II. No local or distant recurrences have been observed.

Conclusions

Extremely hypofractionated whole breast RT before BCS is a feasible approach. There were low rates of toxicities and good cosmesis. Further investigation into this approach with RT before BCS is warranted.

Accelerated Partial Breast Irradiation: Florence Phase 3 Trial Experience and Future Perspectives

Accelerated partial breast irradiation Florence phase 3 trial is a single-center study comparing intensity-modulated based accelerated partial breast irradiation (PBI, 30 Gy in 5 fractions) and whole breast irradiation (50 Gy in 25 fractions) followed by a tumor bed boost (10 Gy in 5 fractions). This easy-to-deliver PBI approach showed excellent long-term disease control with favorable safety and cosmetic outcome profiles. A plateau has been probably reached concerning the reduction of the number of fractions in the postoperative PBI setting. A 5-fraction schedule is the standard regimen and probably the appropriate compromise in terms of efficacy, safety, and quality of life, also considering the negative results of most intraoperative single-fraction PBI trials. A new frontier is now open on the potential benefit of preoperative PBI delivery, although concerns remain on the optimal dose, fractionation, and technique. Hereby we report the accelerated PBI Florence phase 3 trial experience and future perspectives.

Preoperative Radio(Chemo)Therapy in Breast Cancer: Time to Switch the Perspective?

AIM

Radiation therapy represents, together with surgery and systemic treatment, the triad on which the current management of patients with breast cancer is based, achieving high control and survival rates. In recent years we have witnessed a (r)evolution in the conception of breast cancer treatment. The classic scheme of surgery followed by systemic treatment and radiotherapy is being subverted and it is becoming more and more frequent to propose the primary administration of systemic treatment before surgery, seeking to maximize its effect and favoring not only the performance of more conservative surgeries but also, in selected cases, increasing the rates of disease-free survival and overall survival. Radiotherapy is also evolving toward a change in perspective: considering preoperative primary administration of radiotherapy may be useful in selected groups. Advances in radiobiological knowledge, together with technological improvements that are constantly being incorporated into clinical practice, support the administration of increasingly reliable, precise, and effective radiotherapy, as well as its safe combination with antitumor drugs or immunotherapy in the primary preoperative context. In this paper, we present a narrative review of the usefulness of preoperative radiotherapy for breast cancer patients and the possibilities for its combination with other therapies.

Preoperative robotic radiosurgery for early breast cancer: Results of the phase II ROCK trial (NCT03520894)

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Preoperative partial breast irradiation treats well-defined target.

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Stereotactic body radiation therapy have been routinely implemented in clinical practice.

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No acute toxicity greater than grade 2 was recorded.

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A single 21 Gy dose preoperative robotic radiosurgery represents a feasible technique.

Background and purpose

Preoperative partial breast irradiation (PBI) has got the advantage of treating a well-defined target. We report the results of the phase II ROCK trial (NCT03520894), enrolling early breast cancer (BC) patients treated with preoperative robotic radiosurgery (prRS), in terms of acute and early late toxicity, disease control, and cosmesis.

Material and methods

The study recruited between 2018 and 2021 at our Radiation Oncology Unit. Eligible patients were 50 + years old BC, hormonal receptors positive/human epidermal growth factor receptor 2 negative (HR+/HER2-), sized up to 25 mm. The study aimed to prospectively assess the toxicity and feasibility of a robotic single 21 Gy-fraction prRS in preoperative setting.

Results

A total of 70 patients were recruited and 22 patients were successfully treated with pRS. Overall, three G1 adverse events (13.6 %) were recorded within 7 days from prRS. Three events (13.6 %) were recorded between 7 and 30 days, one G2 breast oedema and two G1 breast pain. No acute toxicity greater than G2 was recorded. Five patients experienced early late G1 toxicity. One patient reported G2 breast induration. No early late toxicity greater than G2 was observed. At a median follow up of 18 months (range 6–29.8), cosmetic results were scored excellent/good and fair in 14 and 5 patients, respectively, while 3 patients experienced a poor cosmetic outcome.

Conclusions

ROCK trial showed that a single 21 Gy dose prRS represents a feasible technique for selected patients affected by early BC, showing an acceptable preliminary toxicity profile.

Survival comparison between postoperative and preoperative radiotherapy for stage I-III non-inflammatory breast cancer

To compare the survival benefit between preoperative and postoperative radiotherapy for stage I-III non-inflammatory breast cancer patients, we conducted a retrospective cohort study using surveillance, epidemiology and end results databases. Our study recruited patients who had been diagnosed with stage I-III breast cancer and underwent surgery and radiotherapy. The overall survival was calculated by Kaplan-Meier method. Cox risk model was used to determine the impact of radiotherapy according to stage, molecular subtype and other risk factors. Propensity score matching was used to balance measurable confounding factors. Of all the 411,279 enrolled patients varying from 1975 to 2016, 1712 patients received preoperative radiotherapy, and 409,567 patients received postoperative radiotherapy. Compared with the postoperative radiotherapy group, the preoperative radiotherapy group showed significantly higher risks of overall mortality and breast cancer-specific mortality. Survival differences in treatment sequences were correlated with stage, molecular subtypes and other risk factors. According to the results of this study, preoperative radiotherapy did not show a survival advantage, and postoperative radiotherapy is still the primary treatment. However, preoperative radiotherapy also has some theoretical advantages, such as phase reduction and recurrence reduction. Therefore, it is still worthy of further exploration.

Intrafraction motion during radiotherapy of breast tumor, breast tumor bed, and individual axillary lymph nodes on cine magnetic resonance imaging

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Intrafraction motion of the breast and individual axillary lymph nodes was studied.

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Displacements were investigated using cine magnetic resonance imaging.

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Motion was separated into breathing and drift components.

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Medians of the maximum displacements were small, <3 mm for breast and lymph nodes.

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Intrafraction motion of the tumor (bed) was less in prone than in supine position.

Background and purpose

In (ultra-)hypofractionation, the contribution of intrafraction motion to treatment accuracy becomes increasingly important. Our purpose was to evaluate intrafraction motion and resulting geometric uncertainties for breast tumor (bed) and individual axillary lymph nodes, and to compare prone and supine position for the breast tumor (bed).

Materials and methods

During 1–3 min of free breathing, we acquired transverse/sagittal interleaved 1.5 T cine magnetic resonance imaging (MRI) of the breast tumor (bed) in prone and supine position and coronal/sagittal cine MRI of individual axillary lymph nodes in supine position. A total of 31 prone and 23 supine breast cine MRI (in 23 women) and 52 lymph node cine MRI (in 24 women) were included. Maximum displacement, breathing amplitude, and drift were analyzed using deformable image registration. Geometric uncertainties were calculated for all displacements and for breathing motion only.

Results

Median maximum displacements (range over the three orthogonal orientations) were 1.1–1.5 mm for the breast tumor (bed) in prone and 1.8–3.0 mm in supine position, and 2.2–2.4 mm for lymph nodes. Maximum displacements were significantly smaller in prone than in supine position, mainly due to smaller breathing amplitude: 0.6–0.9 mm in prone vs. 0.9–1.4 mm in supine. Systematic and random uncertainties were 0.1–0.4 mm in prone position and 0.2–0.8 mm in supine position for the tumor (bed), and 0.4–0.6 mm for the lymph nodes.

Conclusion

Intrafraction motion of breast tumor (bed) and individual lymph nodes was small. Motion of the tumor (bed) was smaller in prone than in supine position.

Single fraction ablative preoperative radiation treatment for early-stage breast cancer: the CRYSTAL study – a phase I/II clinical trial protocol

Background

Breast-conserving surgery (BCS) and whole breast radiation therapy (WBRT) are the standard of care for early-stage breast cancer (BC). Based on the observation that most local recurrences occurred near the tumor bed, accelerated partial breast irradiation (APBI), consisting of a higher dose per fraction to the tumor bed over a reduced treatment time, has been gaining ground as an attractive alternative in selected patients with low-risk BC. Although more widely delivered in postoperative setting, preoperative APBI has also been investigated in a limited, though increasing, and number of studies. The aim of this study is to test the feasibility, safety and efficacy of preoperative radiotherapy (RT) in a single fraction for selected BC patients.

Methods

This is a phase I/II, single-arm and open-label single-center clinical trial using CyberKnife. The clinical investigation is supported by a preplanning section which addresses technical and dosimetric issues. The primary endpoint for the phase I study, covering the 1st and 2nd year of the research project, is the identification of the maximum tolerated dose (MTD) which meets a specific target toxicity level (no grade 3–4 toxicity). The primary endpoint for the phase II study (3rd to 5th year) is the evaluation of treatment efficacy measured in terms of pathological complete response rate.

Discussion

The study will investigate the response of BC to the preoperative APBI from different perspectives. While preoperative APBI represents a form of anticipated boost, followed by WBRT, different are the implications for the scientific community. The study may help to identify good responders for whom surgery could be omitted. It is especially appealing for patients unfit for surgery due to advanced age or severe co-morbidities, in addition to or instead of systemic therapies, to ensure long-term local control. Moreover, patients with oligometastatic disease synchronous with primary BC may benefit from APBI on the intact tumor in terms of tumor progression free survival. The study of response to RT can provide useful information about BC radiobiology, immunologic reactions, genomic expression, and radiomics features, to be tested on a larger scale.

Trial registration

The study was prospectively registered at clinicaltrials.gov (NCT04679454).

Prone vs. supine accelerated partial breast irradiation on an MR-Linac: A planning study

BACKGROUND AND PURPOSE

Accelerated partial breast irradiation (APBI) may benefit from the MR-Linac for target definition, patient setup, and motion monitoring. In this planning study, we investigated whether prone or supine position is dosimetrically beneficial for APBI on an MR-Linac and we evaluated patient comfort.

MATERIALS AND METHODS

Twenty-patients (9 postoperative, 11 preoperative) with a DCIS or breast tumor <3 cm underwent 1.5 T MRI in prone and supine position. The tumor or tumor bed was delineated as GTV and a 2 cm CTV-margin and 0.5 cm PTV-margin were added. 1.5 T MR-Linac treatment plans (5 × 5.2 Gy) with 11 beams were created for both positions in each patient. We evaluated the number of plans that achieved the planning constraints and performed a dosimetric comparison between prone and supine position using the Wilcoxon signed-rank test (p-value <0.01 for significance). Patient experience during scanning was evaluated with a questionnaire.

RESULTS

All 40 plans met the target coverage and OAR constraints, regardless of position. Heart D_mean was not significantly different (1.07 vs. 0.79 Gy, p-value: 0.027). V5Gy to the ipsilateral lung (4.4% vs. 9.8% median, p-value 0.009) and estimated delivery time (362 vs. 392 s, p-value: 0.003) were significantly lower for prone position. PTV coverage and dose to other OAR were comparable between positions. The majority of patients (13/20) preferred supine position.

CONCLUSION

APBI on the MR-Linac is dosimetrically feasible in prone and supine position. Mean heart dose was similar in both positions. Ipsilateral lung V5Gy was lower in prone position.

Modern radiation techniques in early stage breast cancer for the breast radiologist

Partial breast irradiation (PBI) and ultra-hypofractionated whole breast irradiation (uWBI) are contemporary alternatives to conventional and standard hypofractionated whole breast irradiation (WBI), which shorten treatment from 3 to 6 weeks to 1-2 weeks for select patients. PBI and accelerated PBI (APBI) can be delivered with external beam radiation (3D conformal radiation therapy (3D-CRT) or intensity modulated radiation therapy (IMRT)), intraoperative radiation (IORT), or brachytherapy. These new radiation techniques offer the advantage of convenience and lower cost, which ultimately improves access to care. Globally, the COVID 19 pandemic has accelerated APBI/PBI and ultra-hypofractionated regimens into routine practice for carefully selected patients. Recent long-term data from randomized controlled trials (RCTs) have demonstrated these techniques are safe and effective in suitable patients demonstrating equivalent or improved local recurrence, acute/late toxicity, and cosmesis. PBI and APBI should be limited to low risk unifocal invasive ductal carcinoma and ductal carcinoma in situ with tumor size < 2 cm, clear margins (≥2 mm), ER+, and negative nodes. Based on the results from UK Fast-Forward and UK FAST ultra-hypofractionated breast radiation can be safely employed for early stage node negative patients, but is not yet considered an international standard of care. In this review, authors will appraise recent data for these shorter course radiation treatment regimens, as well as, considerations for breast radiologists including surveillance imaging and radiographic findings.

Reproducibility of a novel, vacuum-assisted immobilization for breast stereotactic radiotherapy

A novel, breast‐specific stereotactic radiotherapy device has been developed for delivery of highly conformal, accelerated partial breast irradiation. This device employs a unique, vacuum‐assisted, breast cup immobilization system that applies a gentle, negative pressure to the target breast with the patient in the prone position. A device‐specific patient loader is utilized for simulation scanning and device docking. Prior to clinical activation, a prospective protocol enrolled 25 patients who had been or were to be treated with breast conservation surgery and adjuvant radiotherapy for localized breast cancer. The patients underwent breast cup placement and two separate CT simulation scans. Surgical clips within the breast were mapped and positions measured against the device’s integrated stereotactic fiducial/coordinate system to confirm reproducible and durable immobilization during the simulation, treatment planning, and delivery process for the device. Of the enrolled 25 patients, 16 were deemed eligible for analysis. Seventy‐three clips (median, 4; mean, 4.6; range, 1–8 per patient) were mapped in these selected patients on both the first and second CT scans. X, Y, and Z coordinates were determined for the center point of each clip. Length of vector change in position was determined for each clip between the two scans. The mean displacement of implanted clips was 1.90 mm (median, 1.47 mm; range, 0.44–6.52 mm) (95% CI, 1.6–2.20 mm). Additional analyses stratified clips by position within the breast and depth into the immobilization cup. Overall, this effort validated the clinically utilized 3‐mm planning target volume margin for accurate, reliable, and precise employment of the device.

Evaluation of Early Response to Preoperative Accelerated Partial Breast Irradiation (PAPBI) by Histopathology, Magnetic Resonance Imaging, and 18F-fluorodexoyglucose Positron Emission Tomography/Computed Tomography (FDG PET/CT)

PURPOSE

This study aimed to find indicators for early response to radiation therapy in breast cancer. These would be of help in tailoring treatment for individual patients.

METHODS AND MATERIALS

We analyzed 66 patients with low-risk breast cancer (≥60 years; cT1-2pN0) treated within the Preoperative Accelerated Partial Breast Irradiation (PAPBI) trial. Patients received radiation therapy (RT; 10 x 4 Gray or 5 x 6 Gray), followed by a wide local excision after 6 weeks. Patients underwent magnetic resonance imaging (MRI) and 18F-fluorodexoyglucose (FDG) positron emission tomography/computed tomography (PET/CT) before RT and 5 weeks after RT, before surgery. We assessed the response to PAPBI using a histopathologic assessment and correlated this with responses on MRI and FDG PET/CT. We calculated the positive predictive values (PPVs) of MRI and PET/CT as the number of true positives (complete response on MRI/normalized at visual evaluation on PET/CT and pathologic complete response) divided by the number of patients with a complete response on MRI/normalized at visual evaluation on PET/CT. Similarly, the negative predictive values (NPVs) of MRI and PET/CT were calculated.

RESULTS

The pathologic response was (nearly) complete in 15 (23%) of the 66 patients and partially complete in 28 (42%). The remaining 23 patients (35%) were nonresponders. The PPV of MRI (Response evaluation criteria in solid tumors [RECIST]) was 87.5% and the NPV was 85%. The PPV and NPV of PET/CT were 25% and 92%, respectively.

CONCLUSIONS

The most accurate method to predict a response and residual disease after preoperative RT in low-risk breast cancer was MRI, using RECIST.

Tumor-Infiltrating Lymphocytes in Low-Risk Patients With Breast Cancer Treated With Single-Dose Preoperative Partial Breast Irradiation

PURPOSE

Preoperative partial breast irradiation (PBI) has the potential to induce tumor regression. We evaluated the differences in the numbers of preirradiation tumor infiltrating lymphocytes (TILs) between responders and nonresponders after preoperative PBI in low-risk patients with breast cancer. Furthermore, we evaluated the change in number of TILs before and after irradiation.

METHODS AND MATERIALS

In the prospective ABLATIVE study, low-risk patients with breast cancer underwent treatment with single-dose preoperative PBI (20 Gy) to the tumor and breast-conserving surgery after 6 or 8 months. In the preirradiation diagnostic biopsy and postirradiation resection specimen, numbers of TILs in 3 square regions of 450 × 450 μm were counted manually. TILs were visualized with CD3, CD4, and CD8 immunohistochemistry. Differences in numbers of preirradiation TILs between responders and nonresponders were tested using Mann-Whitney U test. Responders were defined as pathologic complete or near-complete response, and nonresponders were defined "as all other response." Changes in numbers of TILs after preoperative PBI was evaluated with the Wilcoxon signed rank test.

RESULTS

Preirradiation tissue was available from 28 patients, postirradiation tissue from 29 patients, resulting in 22 pairs of preirradiation and postirradiation tissue. In these 35 patients, 15 had pathologic complete response (43%), 11 had a near-complete response (31%), 7 had a partial response (20%), and 2 had stable disease (6%). The median numbers of CD3⁺ TILs, CD4⁺ TILs, and CD8⁺ TILs in the preirradiation tumor tissue were 49 (interquartile range [IQR], 36-80), 45 (IQR, 28-57), and 19 (IQR, 8-35), respectively. The number of preirradiation TILs did not differ significantly between responders and nonresponders. The median numbers of CD3⁺ TILs, CD4⁺ TILs, and CD8⁺ TILs in postirradiation tumor tissue were 17 (IQR, 13-31), 26 (IQR, 16-35), and 7 (IQR, 5-11), respectively.

CONCLUSIONS

After preoperative PBI in this limited cohort, the number of TILs in tumor tissue decreased. No differences in numbers of preirradiation TILs between responders and nonresponders were observed.

Mammographically guided noninvasive breast brachytherapy: Preoperative partial breast radiotherapy markedly improves targeting accuracy and decreases irradiated volume

PURPOSE

Mammographically based noninvasive image-guided breast brachytherapy (NIBB) partial breast irradiation (PBI) is ideally suited for preoperative treatment. We hypothesize that delivering NIBB PBI to the preoperative tumor volume compared with the postoperative lumpectomy bed would simplify target identification and allow for a reduction in irradiated volume along each orthogonal axis.

METHODS AND MATERIALS

Patients with invasive breast cancer treated with NIBB PBI at our institution were identified. Preoperative NIBB treatments were modeled along orthogonal craniocaudal and mediolateral axes with an applicator encompassing the gross lesion plus a 1 cm clinical target volume margin. Preoperative treatment volumes were calculated along each axis using the selected applicator surface area multiplied by the preoperative mammogram separation. The actual applicator size and breast separation from the first fraction of postoperative treatment was used to calculate the postoperative treatment volume. Paired -test was used to compare the preoperative and postoperative treatment separation, area, and volume for each patient.

RESULTS

Forty-eight patients with Stage I-II breast cancer had imaging and treatment data available for review. Along the axis, the mean preoperative treatment volume was significantly less than the mean postoperative treatment volume (116 cm ³ vs. 204 cm ³, respectively; p < 0.0001). Similarly, along the mediolateral axis, the mean preoperative treatment volume was significantly less than the mean postoperative treatment volume (125 cm ³ vs. 216 cm ³, respectively; p < 0001).

CONCLUSIONS

Based on our retrospective comparison, PBI delivered using NIBB to the preoperative tumor may reduce the volume of healthy breast tissue receiving radiation as compared with NIBB to the postoperative tumor bed.

Consensus on Contouring Primary Breast Tumors on MRI in the Setting of Neoadjuvant Partial Breast Irradiation in Trials

PURPOSE

Our purpose was to present and evaluate expert consensus on contouring primary breast tumors on magnetic resonance imaging (MRI) in the setting of neoadjuvant partial breast irradiation in trials.

METHODS AND MATERIALS

Expert consensus on contouring guidelines for target definition of primary breast tumors on contrast-enhanced MRI in trials was developed by an international team of experienced breast radiation oncologists and a dedicated breast radiologist during 3 meetings. At the first meeting, draft guidelines were developed through discussing and contouring 2 cases. At the second meeting 6 breast radiation oncologists delineated gross tumor volume (GTV) in 10 patients with early-stage breast cancer (cT1N0) according to draft guidelines. GTV was expanded isotropically (20 mm) to generate clinical target volume (CTV), excluding skin and chest wall. Delineations were reviewed for disagreement and guidelines were clarified accordingly. At the third meeting 5 radiation oncologists redelineated 6 cases using consensus-based guidelines. Interobserver variation of GTV and CTV was assessed using generalized conformity index (CI). CI was calculated as the sum of volumes each pair of observers agreed upon, divided by the sum of encompassing volumes for each pair of observers.

RESULTS

For the 2 delineation sessions combined, mean GTV ranged between 0.19 and 2.44 cm3, CI for GTV ranged between 0.28 and 0.77, and CI for CTV between 0.77 and 0.94. The largest interobserver variation in GTV delineations was observed in cases with extended tumor spiculae, blood vessels near or markers within the tumor, or with increased enhancement of glandular breast tissue. Consensus-based guidelines stated to delineate all visible tumors on contrast enhanced-MRI scan 1 to 2 minutes after contrast injection and if a marker was inserted in the tumor to include this.

CONCLUSIONS

Expert-based consensus on contouring primary breast tumors on MRI in trials has been reached. This resulted in low interobserver variation for CTV in the context of a uniform 20 mm GTV to CTV expansion margin.

Accelerated Partial Breast Irradiation (APBI): Where Are We Now?

Purpose of Review

Accelerated partial breast irradiation (APBI) is an alternative approach to breast conserving therapy (BCT) where radiation (RT) is delivered over a shorter period of time compared with whole breast irradiation (WBI), resulting in improved patient convenience and cost savings. APBI can be delivered using brachytherapy, intraoperative RT, or conformal external beam radiation therapy (EBRT) techniques. In this review, the authors appraise the latest modern randomized controlled trials (RCTs) of APBI and discuss the application of the data to clinical practice.

Recent Findings

The OCOG-RAPID and NSABP B-39/RTOG 0413 trials recently reported long-term outcomes of APBI. The OCOG-RAPID trial delivered 38.5 Gy/10 fractions twice daily (at least 6 h apart using EBRT) or WBI and demonstrated non-inferiority of APBI compared with WBI (8-year cumulative rate of ipsilateral breast tumor recurrence (IBTR) was 3% after APBI or 2.8% after WBI, HR 1.27, 90%CI: 0.84–1.91). While acute toxicity was reduced, late toxicity and breast cosmesis were worse with APBI. The NSABP B-39 trial included higher risk patients and was unable to demonstrate equivalence between APBI (38.5 Gy/10 fractions delivered twice daily using EBRT or brachytherapy techniques) and WBI. However, 10-year IBTR rates were low: 4.6% vs. 3.9%, respectively, HR 1.22, 90%CI: 0.94–1.58. The University of Florence demonstrated low rates of local recurrence at 10 years and overall excellent breast cosmetic outcomes when APBI was delivered using EBRT to a dose of 30 Gy/5 fractions delivered on non-consecutive days.

Summary

Recent RCTs of APBI have shed light on important factors for the integration of APBI into clinical practice, including patient selection and treatment delivery. APBI should be limited to patients with low-risk ductal carcinoma in situ or early stage (T1) invasive ductal cancer with clear margins of excision, estrogen receptor positivity, and node negative disease. Ongoing research should focus on the optimal dose/fractionation for delivery of EBRT-based APBI.

[Adjuvant and neoadjuvant radiotherapy in breast cancer: A literaure review and update on the state of the evidence in 2020]

Radiation therapy has benefited from many developments over the past 20 years. These developments are mainly linked to the technology, imaging and informatics evolutions which allow better targets definitions, ensure better organs-at-risk sparing and excellent reproducibility of treatments, with a perfect control of patient positioning. In breast cancer radiotherapy, the evolution was marked by the possibility of reducing the duration of treatments from 6-7 to 3-4 weeks by using hypofractionated regimens, or by further reducing the irradiation to one week when treatment is solely focalised to the tumour bed. This concept of accelerated partial breast irradiation has challenged the paradigm of the obligation to irradiate the whole breast after conservative surgery in all patients. In addition, the technical mastery of accelerated partial breast irradiation and the development of stereotactic radiotherapy techniques are currently contributing to the development of research projects in neoadjuvant settings. Thus, numerous ongoing studies are evaluating the impact of high-dose preoperative tumour irradiation, alone or in combination with systemic treatments, on biological tumor changes, on anti-tumour immunity, and on the pathologic complete response, which is considered as predictive of better long-term survival in some molecular breast cancer subtypes. In this review, we discuss all these developments which allow breast radiation therapy to enter the era of personalisation of treatments in oncology.

Tumour response 3 months after neoadjuvant single-fraction radiotherapy for low-risk breast cancer

Introduction

Standard treatment for early-stage invasive breast cancer (bca) consists of breast-conserving surgery and several weeks of adjuvant radiotherapy (rt). Neoadjuvant single-fraction rt is a novel approach for early-stage bca. We sought to investigate the effect of delaying surgery after neoadjuvant rt with respect to the rate of pathologic response (pr).

Methods

Women 65 years of age or older with a new diagnosis of stage i luminal A bca were eligible for inclusion. A single 20 Gy dose to the primary breast tumour was given, followed by breast-conserving surgery 3 months later. The primary endpoint was the pr rate assessed by microscopic evaluation using the Miller-Payne system.

Results

To date, 10 patients have been successfully treated. Median age of the patients was 72 years (range: 65-84 years). In 8 patients, neoadjuvant rt resulted in a tumour pr with median residual cellularity of 3%. No immediate rt complications other than mild dermatitis were noted.

Conclusions

This study demonstrates a method for delivering single-fraction rt that can lead to a high level of pr in most patients. Continued accrual to this study and subsequent trials are needed to determine the feasibility, safety, and role of this novel technique in the management of early-stage bca.

Update on Partial Breast Irradiation

For early-stage breast cancer, partial breast irradiation (PBI) allows for reduction in the irradiated volume of normal tissues by confining the radiation target to the area surrounding the lumpectomy cavity after breast-conserving surgery. This approach has been supported by phase 2 data. However, widespread adoption of PBI has awaited the results of randomized controlled trials. This review discusses the results of randomized controlled trials comparing whole breast irradiation to PBI, including the recently published National Surgical Adjuvant Breast and Bowel Project (NSABP) B39/Radiotherapy Oncology Group (RTOG) 0413, and the Canadian RAPID trials. PBI techniques, dose/fractionation schedules, and patient selection are also reviewed.

DCE-MRI assessment of response to neoadjuvant SABR in early stage breast cancer: Comparisons of single versus three fraction schemes and two different imaging time delays post-SABR

PURPOSE

To determine the effect of dose fractionation and time delay post-neoadjuvant stereotactic ablative radiotherapy (SABR) on dynamic contrast-enhanced (DCE)-MRI parameters in early stage breast cancer patients.

MATERIALS AND METHODS

DCE-MRI was acquired in 17 patients pre- and post-SABR. Five patients were imaged 6-7 days post-21 Gy/1fraction (group 1), six 16-19 days post-21 Gy/1fraction (group 2), and six 16-18 days post-30 Gy/3 fractions every other day (group 3). DCE-MRI scans were performed using half the clinical dose of contrast agent. Changes in the surrounding tissue were quantified using a signal-enhancement threshold metric that characterizes changes in signal-enhancement volume (SEV). Tumour response was quantified using Ktrans and ve (Tofts model) pre- and post-SABR. Significance was assessed using a Wilcoxin signed-rank test.

RESULTS

All group 1 and 4/6 group 2 patients' SEV increased post-SABR. All group 3 patients' SEV decreased. The mean Ktrans increased for group 1 by 76% (p = 0.043) while group 2 and 3 decreased 15% (p = 0.028) and 34% (p = 0.028), respectively. For ve, there was no significant change in Group 1 (p = 0.35). Groups 2 showed an increase of 24% (p = 0.043), and Group 3 trended toward an increase (23%, p = 0.08).

CONCLUSION

Kinetic parameters measured 2.5 weeks post-SABR in both single fraction and three fraction groups were indicative of response but only the single fraction protocol led to enhancement in the surrounding tissue. Our results also suggest that DCE-MRI one-week post-SABR may be too early for response assessment, at least for single fraction SABR, whereas 2.5 weeks appears sufficiently long to minimize confounding acute effects.

Five-Year Results of the Preoperative Accelerated Partial Breast Irradiation (PAPBI) Trial

PURPOSE

In this multicenter phase 2 feasibility study, we investigated the impact of preoperative accelerated partial breast irradiation (PAPBI) on local control, breast fibrosis, and cosmetic outcome.

METHODS AND MATERIALS

Women aged >60 years with an invasive, unifocal (mammography and magnetic resonance imaging), nonlobular adenocarcinoma of the breast were treated with PAPBI. Six weeks after radiation therapy, a wide local excision was performed. Radiation therapy consisted of 10 × 4 Gy (2010-2013) or 5 × 6 Gy (after 2013) to the tumor (gross target volume) with a 25 mm margin (20 mm from gross target volume to clinical target volume, 5 mm planning target volume).

RESULTS

One hundred thirty-three patients treated between 2010 and 2016 were analyzed with a median follow-up of 5.0 years (0.9-8.8 years). Seventy-eight (59%) patients were treated with 10 × 4 Gy in 2 weeks and 55 (41%) patients with 5 × 6 Gy in 1 week. Eighteen postoperative complications (14%) occurred in 15 patients (11%). The proportion of patients with no to mild fibrosis in the treated part of the breast at 2 years and later time points was around 90%. Cosmesis improved over time in several patients: excellent to good cosmetic score as rated by the physician was 68% at 6 months and 92% at 5 years. Seventy-seven percent (6 months) to 82% (5 years) of patients were "satisfied" or "very satisfied" with their cosmetic outcome. Three recurrences were detected in the biopsy track and 1 recurrence in the ipsilateral breast.

CONCLUSIONS

PAPBI is a feasible method with a low postoperative complication rate, limited fibrosis, and good to excellent cosmetic outcome. The local recurrence rate was 3% at 5 years; however, no local recurrences were observed since removal of the needle biopsy track.

Use of Preoperative Radiation Therapy in Early-stage and Locally Advanced Breast Cancer

Purpose

There is growing interest in delivering radiation preoperatively (preopRT) rather than postoperatively (postopRT) for breast cancer. Using the National Cancer Database, we evaluated the use and outcomes of preopRT in breast cancer.

Methods

We identified adult females diagnosed with non-metastatic breast cancer treated with definitive surgery and radiation between 2004 and 2014. Logistic regression models evaluated factors associated with use of preopRT in early-stage (clinical T1-3/N0-1) and locally advanced (clinical T4/N2-3) disease. Rates of breast-conserving surgery, breast reconstruction, positive surgical margins, and 30-day surgical readmissions were compared between patients receiving preopRT and postopRT.

Results

Of 373,595 patients who met our inclusion criteria, 1,245 (0.3%) patients received preopRT. Patients receiving preopRT were more likely to be of lower socioeconomic status and have tumors with higher T stage. Younger age and N1 (vs N0) disease predicted for use of preopRT in early-stage disease, while older age and N0 disease predicted for use of preopRT in the locally advanced setting. PreopRT patients were less likely to undergo breast-conserving surgery and more likely to have positive surgical margins. Rates of unplanned readmissions within 30 days of surgery were similar among patients treated with preopRT and postopRT.

Conclusions

PreopRT is a new treatment strategy for patients with breast cancer with different clinical and sociodemographic drivers of its use in the early-stage and locally advanced settings. We await the results of clinical trials studying the efficacy of this approach.

Preoperative radiotherapy: A paradigm shift in the treatment of breast cancer? A review of literature

The standard of care for early-stage breast cancer (BC) consists of breast-conserving surgery followed by postoperative irradiation. Recently, the concept of changing the usual sequence of treatment components in BC RT has been investigated. Potential advantages of preoperative RT in BC include a possible tumor downstaging with improved surgical cosmetic outcomes, accurate tumor site identification and better target volume delineation. Furthermore, preoperative RT could serve as a tool for treatment stratification for de-escalation of treatments in the event of pathological complete response. The present literature review analyzed the available clinical data regarding the potential impact of preoperative RT. Overall, available clinical evidence of preoperative RT in BC remains limited, deriving mostly from retrospective case series. Nevertheless, the experiences prove the feasibility of the preoperative RT approach and confirm the efficacy in almost all analyzed studies, including experiences using higher prescription RT doses or RT in combination with systemic therapy.

MR-guidance in clinical reality: current treatment challenges and future perspectives

Magnetic Resonance-guided radiotherapy (MRgRT) marks the beginning of a new era. MR is a versatile and suitable imaging modality for radiotherapy, as it enables direct visualization of the tumor and the surrounding organs at risk. Moreover, MRgRT provides real-time imaging to characterize and eventually track anatomical motion. Nevertheless, the successful translation of new technologies into clinical practice remains challenging. To date, the initial availability of next-generation hybrid MR-linac (MRL) systems is still limited and therefore, the focus of the present preview was on the initial applicability in current clinical practice and on future perspectives of this new technology for different treatment sites.MRgRT can be considered a groundbreaking new technology that is capable of creating new perspectives towards an individualized, patient-oriented planning and treatment approach, especially due to the ability to use daily online adaptation strategies. Furthermore, MRL systems overcome the limitations of conventional image-guided radiotherapy, especially in soft tissue, where target and organs at risk need accurate definition. Nevertheless, some concerns remain regarding the additional time needed to re-optimize dose distributions online, the reliability of the gating and tracking procedures and the interpretation of functional MR imaging markers and their potential changes during the course of treatment. Due to its continuous technological improvement and rapid clinical large-scale application in several anatomical settings, further studies may confirm the potential disruptive role of MRgRT in the evolving oncological environment.

Findings on Surveillance Imaging After Preoperative Partial Breast Irradiation for Early Stage Breast Cancer

PURPOSE

To evaluate the mammographic sequelae of preoperative accelerated partial breast irradiation (APBI) delivered via either stereotactic radiosurgery or a conventionally fractionated regimen.

METHODS AND MATERIALS

This multicenter, retrospective study evaluated surveillance mammograms from patients enrolled in 2 prospective, preoperative APBI clinical trials. At 1 site, 31 patients with cT1N0 invasive carcinomas or low- or intermediate-grade ductal carcinoma in situ (<2 cm) received preoperative stereotactic radiosurgery and had a total of 186 mammograms available for review. At the second site, 180 mammograms from 25 patients with cT1-2 (<3 cm) unifocal invasive carcinomas treated with conventionally fractionated, preoperative APBI were reviewed. Findings were compared with those of 26 early stage breast cancers treated with conventional postoperative whole breast radiation therapy.

RESULTS

At a median follow-up of 61 months, 17 patients (55%) treated with single-dose APBI exhibited exuberant fat necrosis at the lumpectomy site. Fat necrosis was believed to be clinically palpable in 5 (16%) of these patients within the first 3 years of follow-up. Exuberant fat necrosis developed in 5 patients (20%) treated with fractionated APBI over a median 68-month follow-up period but only 2 of those patients (8%) who underwent conventional whole breast radiation therapy.

CONCLUSIONS

In situ tumor targeting in the preoperative setting allows relative sparing of normal tissue but results in a larger and more vigorous area of change on surveillance imaging, potentially reflecting the interaction of surgical resection with an irradiated tissue bed. High-dose stereotactic radiosurgery in particular increases the risk of developing a uniquely robust and well-demarcated pattern of fat necrosis on mammogram that may also present clinically. With many ongoing studies evaluating the preoperative treatment approach, defining the landscape of expected imaging sequelae will provide useful anticipatory guidance for clinicians and patients.

Breast Cancer Biology: Clinical Implications for Breast Radiation Therapy

Historically, prognosis and treatment decision making for breast cancer patients have been dictated by the anatomic extent of tumor spread. However, in recent years, "breast cancer" has proven to be a collection of unique phenotypes with distinct prognoses, patterns of failure, and treatment responses. Recent advances in biologically based assays and targeted therapies designed to exploit these unique phenotypes have profoundly altered systemic therapy practice patterns and treatment outcomes. Data associating locoregional outcomes with tumor biology are emerging. However, the likelihood of obtaining level I evidence for fundamental radiation therapy questions within each of the specific subtypes in the immediate future is low. As such, this review aims to summarize the existing data and provide practical context for the incorporation of breast tumor biology into clinical practice.

Treatment constraints for single dose external beam preoperative partial breast irradiation in early-stage breast cancer

Background

Following breast-conserving surgery and post-operative 3D-conformal accelerated partial breast irradiation (APBI), suboptimal cosmetic results have been reported. Preoperative radiation delivery to the intact tumor enables better target visualization and treatment volume reduction. Single dose preoperative APBI has the potential to improve toxicity profiles, reduce treatment burden and enable in vivo exploration of breast cancer radiogenomics.

Purpose

Develop practical guidelines for single dose external beam preoperative APBI.

Methods

Recommended dose constraints were derived from pooled dosimetry estimates from 2 clinical trials. In an American dose escalation trial, a uniform 15, 18 or 21 Gy dose has previously been evaluated for non-lobular cT1N0 or low/intermediate grade DCIS <2 cm in prone position (n = 32). In the Netherlands, the feasibility of ablative APBI (20 Gy to GTV, 15 Gy to CTV) to non-lobular cT1N0 in supine position, is currently being explored (n = 15). The dosimetric adherence to the developed constraints was evaluated in new APBI plans with a 21 Gy uniform dose but an extended CTV margin (n = 32).

Results

Dosimetric data pooling enabled the development of practical guidelines for single dose preoperative APBI.

Conclusion

The developed guidelines will allow further explorations in the promising field of single dose preoperative external beam APBI for breast cancer treatment.