New Techniques for Irradiating Early Stage Breast Cancer: Stereotactic Partial Breast Irradiation

Effectiveness and toxicity of five-fraction prone accelerated partial breast irradiation

PURPOSE

Our institution was an early adopter of 5-fraction accelerated partial breast irradiation (ABPI) to treat women with early-stage breast cancer. This study reports long-term oncologic and cosmetic outcomes.

METHODS

We included patients receiving APBI 600 cGy × 5 fx delivered every other day or every day between 2010 and 2022. Logistic regression models were used to identify factors associated with development of late toxicities, clinician, and patient-rated cosmesis. Kaplan-Meier methodology was used to calculate overall survival (OS), disease-free survival (DFS), and locoregional recurrence-free survival (LR-RFS).

RESULTS

442 patients received APBI either daily (56%) or every other day (44%) in the prone position (92%). At a median follow-up of 48 months (range: 5.96-155 months), 12 (2.7%) patients developed a local recurrence (LR). Out of 258 patients with > 3-month toxicity data available, the most common late grade ≥ 2 adverse event was breast fibrosis (6.2%). On multivariate analysis, daily APBI treatment (vs every other day) did not correlate with an increased risk of any late grade ≥ 2 toxicity though it did correlate with a lower risk of any late grade ≥ 2 fibrosis. Overall, at a median follow-up of 80 months, the rates of good-excellent physician and patient-rated cosmesis were 95% and 85%, respectively, with no difference between patients treated on consecutive vs. every other day. On multivariate analysis, patients who did not receive any adjuvant therapy were at increased risk of developing a LR. Five-year OS, LRFS, and DFS were 97.2%, 97.7%, and 89.5%, respectively.

CONCLUSIONS

Five-fraction APBI delivered primarily in the prone position either daily or every other day was effective with low rates of local recurrence, minimal toxicity, and excellent cosmesis at long-term follow-up.

Large institutional experience of early outcomes and dosimetric findings with postoperative stereotactic partial breast irradiation in breast cancer

PURPOSE

To analyze the dosimetric and toxicity outcomes of patients treated with postoperative stereotactic partial breast irradiation (S-PBI).

METHODS

We identified 799 women who underwent S-PBI at our institution between January 2016 and December 2022. The most commonly used dose-fraction and technique were 30 Gy in 5 fractions (91.7 %) and a robotic stereotactic radiation system with real-time tracking (83.7 %). The primary endpoints were dosimetric parameters and radiation-related toxicities. For comparison, a control group undergoing ultra-hypofractionated whole breast irradiation (UF-WBI, n = 468) at the same institution was selected.

RESULTS

A total of 815 breasts from 799 patients, with a median planning target volume (PTV) volume of 89.6 cm3, were treated with S-PBI. Treatment plans showed that the mean and maximum doses received by the PTV were 96.2 % and 104.8 % of the prescription dose, respectively. The volume of the ipsilateral breast that received 50 % of the prescription dose was 32.3 ± 8.9 %. The mean doses for the ipsilateral lung and heart were 2.5 ± 0.9 Gy and 0.65 ± 0.39 Gy, respectively. Acute toxicity occurred in 175 patients (21.5 %), predominantly of grade 1. Overall rate of late toxicity was 4 % with a median follow-up of 31.6 months. Compared to the UF-WBI group, the S-PBI group had comparably low acute toxicity (21.5 % vs. 25.2 %, p = 0.12) but significantly lower dosimetric parameters for all organs-at-risks (all p < 0.05).

CONCLUSION

In this large cohort, S-PBI demonstrated favorable dosimetric and toxicity profiles. Considering the reduced radiation exposure to surrounding tissues, external beam PBI with advanced techniques should at least be considered over traditional WBI-based approaches for PBI candidates.

Cosmetic Outcome and Toxicity After Stereotactic Accelerated Partial Breast Irradiation in Early Breast Cancer: A Prospective Observational Cohort Study

PURPOSE

The aim of this work was to prospectively evaluate the toxicity and cosmetic outcomes of 5-fraction, stereotactic, accelerated partial breast irradiation (APBI).

METHODS AND MATERIALS

This prospective observational cohort study enrolled women who underwent APBI for invasive carcinoma or carcinoma in situ of the breast. APBI was delivered using a CyberKnife M6 robotic radiosurgery system at 30 Gy in 5 nonconsecutive, once-daily fractions. Women undergoing whole breast irradiation (WBI) were also enrolled for comparison. Patient-reported and physician-assessed adverse events were recorded. Breast fibrosis was measured using a tissue compliance meter, and breast cosmesis was assessed using BCCT.core (an automatic, computer-based software). Outcomes were collected until 24 months posttreatment according to the study protocol.

RESULTS

In total, 204 patients (APBI, n = 103; WBI, n = 101) were enrolled. Regarding patient-reported outcomes, the APBI group reported significantly less skin dryness (6.9% vs 18.3%; P = .015), radiation skin reaction (9.9% vs 23.5%; P = .010), and breast hardness (8.0% vs 20.4%; P = .011) at 6 months than the WBI group. On physician assessment, the APBI group had significantly less dermatitis at 12 months (1.0% vs 7.2%; P = .027) than the WBI group. Any severe toxicities after APBI were rare in patient-reported outcomes (score ≥3, 3.0%) and physician assessments (grade ≥3, 2.0%). In the uninvolved quadrants, measured fibrosis in the APBI group was significantly lower than that in the WBI group at 6 (P = .001) and 12 (P = .029) months but not at 24 months. In the involved quadrant, measured fibrosis in the APBI group was not significantly different from that in the WBI group at any time. Cosmetic outcomes in the APBI group were mostly excellent or good (77.6%) at 24 months, and there was no significant cosmetic detriment from the baseline.

CONCLUSIONS

Stereotactic APBI was associated with less fibrosis in the uninvolved breast quadrants than WBI. Patients showed minimal toxicity and no detrimental effects on cosmesis after APBI.

Towards precision radiation oncology: endocrine therapy response as a biomarker for personalization of breast radiotherapy

Targeted therapies, such as endocrine therapies (ET), can exert selective pressure on cancer cells and promote adaptations that confer treatment resistance. In this study, we show that ET resistance in breast cancer drives radiation resistance through reprogramming of DNA repair pathways. We also show that pharmacological bromodomain and extraterminal domain inhibition reverses pathological DNA repair reprogramming in ET-resistant breast tumors and overcomes resistance to radiation therapy.

Stereotactic Partial Breast Irradiation: What Does the Future Hold?

Breast irradiation has evolved significantly over the last several decades. Accelerated partial breast and stereotactic breast irradiation have evolved as strategies to reduce irradiated volumes, preserve appropriate oncologic control, and improve cosmetic outcome. The sequencing and/or combination of stereotactic partial breast irradiation with novel systemic agents is of great interest to the oncologic community. Here we explore the landscape of modern trials and opine on the future of partial breast irradiation.

Accelerated Partial Breast Irradiation: Technological Advances and Current Challenges

Accelerated partial breast irradiation is a mature, standard-of-care treatment option for many women with early-stage breast cancer. In this paper, we discuss technological challenges and advances in the delivery of accurate and reproducible accelerated partial breast irradiation.

Stereotactic partial breast irradiation in primary breast cancer: A comprehensive review of the current status and future directions

In selected low-risk breast cancer patients, accelerated partial breast irradiation (APBI) may represent an alternative option to the whole breast irradiation to reduce the volume of irradiated breast and total treatment duration. In the last few years, preliminary data from clinical trials showed that stereotactic partial breast radiotherapy may have the advantage to be less invasive compared to other APBI techniques, with preliminary good results in terms of local toxicity and cosmesis: the use of magnetic resonance, fiducial markers in the tumor bed, and new breast devices support both a precise definition of the target and radiation planning.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021257856, identifier CRD42021257856.

Intrafraction motion monitoring to determine PTV margins in early stage breast cancer patients receiving neoadjuvant partial breast SABR

BACKGROUND AND PURPOSE

To quantify intra-fraction tumor motion using imageguidance and implanted fiducial markers to determine if a 5 mm planning-target-volume (PTV) margin is sufficient for early stage breast cancer patients receiving neoadjuvant stereotactic ablative radiotherapy (SABR).

MATERIALS AND METHODS

A HydroMark© (Mammotome) fiducial was implanted at the time of biopsy adjacent to the tumor. Sixty-one patients with 62 tumours were treated prone using a 5 mm PTV margin. Motion was quantified using two methods (separate patient groups): 1) difference in 3D fiducial position pre- and post-treatment cone-beam CTs (CBCTs) in 18 patients receiving 21 Gy/1fraction (fx); 2) acquiring 2D triggered-kVimages to quantify 3D intra-fraction motion using a 2D-to-3D estimation method for 44 tumours receiving 21 Gy/1fx (n = 22) or 30 Gy/3fx (n = 22). For 2), motion was quantified by calculating the magnitude of intra-fraction positional deviation from the pretreatment CBCT. PTV margins were derived using van Herkian analysis.

RESULTS

The average ± standard deviation magnitude of motion across patients was 1.3 ± 1.15 mm Left/Right (L/R), 1.0 ± 0.9 mm Inferiorly/Superiorly (I/S), and 1.8 ± 1.5 mm Anteriorly/Posteriorly (A/P). 85/105 (81%) treatment fractions had dominant anterior motion. 6/62patients (9.7%) had mean intra-fraction motion during any fraction > 5 mm in any direction, with 4 in the anterior direction. Estimated PTV margins for single and three-fx patients in the L/R, I/S, and A/P directions were 6.0x4.1x5.9 mm and 4.5x2.9x4.3 mm, respectively.

CONCLUSION

Our results suggest that a 5 mm PTV margin is sufficient for the I/S and A/P directions if a lateral kV image is acquired immediately before treatment. For the L/R direction, either further immobilization or a larger margin is required.

Improved Ipsilateral Breast and Chest Wall Sparing With MR-Guided 3-fraction Accelerated Partial Breast Irradiation: A Dosimetric Study Comparing MR-Linac and CT-Linac Plans

Purpose

External beam accelerated partial breast irradiation (APBI) is subject to treatment uncertainties that must be accounted for through planning target volume (PTV) margin. We hypothesize that magnetic resonance–guided radiation therapy with reduced PTV margins enabled by real-time cine magnetic resonance image (MRI) target monitoring results in better normal tissue sparing compared with computed tomography (CT)-guided radiation therapy with commonly used clinical PTV margins. In this study, we compare the plan quality of ViewRay MRIdian Linac forward planned intensity modulated radiation therapy and TrueBeam volumetric modulated arc therapy for a novel 3-fraction APBI schedule.

Methods and Materials

Targets and organs at risk (OARs) were segmented for 10 patients with breast cancer according to NSABP B39/RTOG 0413 protocol. A 3 mm margin was used to generate MR PTV_3mm and CT PTV_3mm plans, and a 10 mm margin was used for CT PTV_10mm. An APBI schedule delivering 24.6 Gy to the clinical target volume and 23.4 Gy to the PTV in 3 fractions was used. OAR dose constraints were scaled down from existing 5-fraction APBI protocols. Target and OAR dose-volume metrics for the following data sets were analyzed using Wilcoxon matched-pairs signed-rank test: (1) MR PTV_3mm versus CT PTV_3mm plans and (2) MR PTV_3mm versus CT PTV_10mm.

Results

Average PTVs were 84.3 ± 51.9 cm³ and 82.6 ± 55 cm³ (P = .5) for MR PTV_3mm and CT PTV_3mm plans, respectively. PTV V23.4Gy, dose homogeneity index, conformity index (CI), and R50 were similar. There was no meaningful difference in OAR metrics, despite MR PTV_3mm being larger than the CT PTV_3mm in 70% of the patients. Average PTVs for MR PTV_3mm and CT PTV_10mm plans were 84.3 ± 51.9 cm³ and 131.7 ± 74.4 cm³, respectively (P = .002). PTV V23.4Gy was 99% ± 0.9% versus 97.6% ± 1.4% (P = .03) for MR PTV_3mm and CT PTV_10mm, respectively. Dose homogeneity index, CI, and R50 were similar. MR PTV_3mm plans had better ipsilateral breast (V12.3Gy, 34.8% ± 12.7% vs 44.4% ± 10.9%, P = .002) and chest wall sparing (V24Gy, 8.5 ± 5.5 cm³ vs 21.8 ± 14.9 cm³, P = .004).

Conclusions

MR- and CT-based planning systems produced comparable plans when a 3 mm PTV margin was used for both plans. As expected, MR PTV_3mm plans produced better ipsilateral breast and chest wall sparing compared with CT PTV_10mm. The clinical relevance of these differences in dosimetric parameters is not known.

Definitive single fraction stereotactic ablative radiotherapy for inoperable early-stage breast cancer: A case report

We review a case of inoperable early stage breast cancer treated definitively with the use of stereotactic ablative radiotherapy (SABR). A 57-year-old female with a history of decompensated cirrhosis with early stage breast cancer was treated with 25 Gy in one fraction. At her 7-month follow up visit, there was a complete resolution of disease on imaging. This case represents a novel approach for the treatment of breast cancer with SABR when surgery is contraindicated.

X-ray-induced acoustic computed tomography for guiding prone stereotactic partial breast irradiation: a simulation study

PURPOSE

The aim of this study is to investigate the feasibility of x-ray-induced acoustic computed tomography (XACT) as an image guidance tool for tracking x-ray beam location and monitoring radiation dose delivered to the patient during stereotactic partial breast irradiation (SPBI).

METHODS

An in-house simulation workflow was developed to assess the ability of XACT to act as an in vivo dosimetry tool for SPBI. To evaluate this simulation workflow, a three-dimensional (3D) digital breast phantom was created by a series of two-dimensional (2D) breast CT slices from a patient. Three different tissue types (skin, adipose tissue, and glandular tissue) were segmented and the postlumpectomy seroma was simulated inside the digital breast phantom. A treatment plan was made with three beam angles to deliver radiation dose to the seroma in breast to simulate SPBI. The three beam angles for 2D simulations were 17°, 90° and 159° (couch angles were 0 degrees) while the angles were 90 degrees (couch angles were 0°, 27°, 90°) in 3D simulation. A multi-step simulation platform capable of modelling XACT was developed. First, the dose distribution was converted to an initial pressure distribution. The propagation of this pressure disturbance in the form of induced acoustic waves was then modeled using the k-wave MATLAB toolbox. The waves were then detected by a hemispherical-shaped ultrasound transducer array (6320 transducer locations distributed on the surface of the breast). Finally, the time-varying pressure signals detected at each transducer location were used to reconstruct an image of the initial pressure distribution using a 3D time-reversal reconstruction algorithm. Finally, the reconstructed XACT images of the radiation beams were overlaid onto the structure breast CT.

RESULTS

It was found that XACT was able to reconstruct the dose distribution of SPBI in 3D. In the reconstructed 3D volumetric dose distribution, the average doses in the GTV (Gross Target Volume) and PTV (Planning Target Volume) were 86.15% and 80.89%, respectively. When compared to the treatment plan, the XACT reconstructed dose distribution in the GTV and PTV had a RMSE (root mean square error) of 2.408 % and 2.299 % over all pixels. The 3D breast XACT imaging reconstruction with time-reversal reconstruction algorithm can be finished within several minutes.

CONCLUSIONS

This work explores the feasibility of using the novel imaging modality of XACT as an in vivo dosimeter for SPBI radiotherapy. It shows that XACT imaging can provide the x-ray beam location and dose information in deep tissue during the treatment in real time in 3D. This study lays the groundwork for a variety of future studies related to the use of XACT as a dosimeter at different cancer sites.

Accelerated partial breast irradiation-Redefining the treatment target for women with early stage breast cancer

Following breast conserving surgery, the standard of care has been to deliver adjuvant radiation therapy directed to the whole breast (WBI) over a period of 3-7 weeks. Over the past decade, increasing data have supported the concept that treatment to the whole breast may not be required in selected patients, allowing for the emergence of partial breast irradiation (PBI). Multiple randomized trials with 5-10 years of follow-up have been published documenting the safety and efficacy associated with PBI using multiple techniques. Questions that remain to be answered include (a) what is the optimal PBI technique for each clinical scenario, (b) are there additional patients that can be effectively managed with PBI approaches, and (c) are there different techniques/dose schedules that allow for further reduction in treatment duration and/or toxicities? Partial breast irradiation represents a standard approach for appropriately selected patients. PBI provides comparable clinical outcomes to WBI while allowing for a reduction in the duration treatment and the potential for reduced toxicities. Future studies may also help to better define which patients require no radiation, PBI, hypofractionated WBI or conventional WBI, based upon patient, clinical, pathologic features as well as potentially using tumor genetics.

Robotic Stereotactic Boost in Early Breast Cancer, a Phase 2 Trial

PURPOSE

To evaluate the feasibility and toxicity of a single-fraction 8-Gy stereotactic boost after whole-breast irradiation in early breast cancer. The primary aim of this phase 2 study was to evaluate cutaneous breast toxicity using National Cancer Institute Common Terminology Criteria for Adverse Events (version 4) 3 months after the boost. Secondary objectives were local control, survival, and patient-reported quality of life using the European Organisation for Research and Treatment of Cancer QLQ-C30 and breast-specific European Organisation for Research and Treatment of Cancer QLQ-BR 23 questionnaires.

METHODS AND MATERIALS

Patients with invasive ductal or lobular pT1-2 breast cancer treated with lumpectomy with clear margins and pN0 were included. Patients requiring chemotherapy were excluded.

RESULTS

Twenty-eight eligible patients received the planned boost, and 26 had hormonal therapy. The procedure was technically successful without procedural complications. A median of 3 fiducials were tracked, and 115 beams were used. There were 22 acute grade 1 breast skin toxicities, including fibrosis, pain, erythema, or pigmentation. There were 2 acute grade 2 erythemas. Median skin boost dose was inversely correlated with acute skin toxicity (P = .028). QLQ-C30 scores revealed acute dyspnea and arm symptoms without correlation to the boost dose. Breast symptom QLQ-BR23 scores did not deteriorate, although upset with hair loss and systemic side effects of hormonal therapy were observed. After a median follow-up of 38 months, 1 patient had in-boost-field relapse, and there were 5 late grade 1 and 1 grade 2 skin toxicities.

CONCLUSIONS

Single-fraction stereotactic boost after conventional whole-breast irradiation in early breast cancer is feasible with minor toxicities. Quality of life and specific breast items showed excellent patient acceptance.