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Original Article
Breast cancer Assessment of Eligibility and Utilization of Accelerated Partial Breast Irradiation in Korean Breast Cancer Patients (KROG 22-15)
Seok-Joo Chun1,a)orcid, Ji Hwan Jo2orcid, Yong Bae Kim3, Sangjoon Park3, Sung-Ja Ahn4, Su Ssan Kim2, Kyubo Kim5,orcid, Kyung Hwan Shin1,6,7,orcid
Cancer Research and Treatment : Official Journal of Korean Cancer Association 2024;56(2):549-556.
DOI: https://doi.org/10.4143/crt.2023.1109
Published online: December 8, 2023

1Department of Radiation Oncology, Seoul National University Hospital, Seoul, Korea

2Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea

3Department of Radiation Oncology, Yonsei University College of Medicine, Seoul, Korea

4Department of Radiation Oncology, Chonnam National University Hwasun Hospital, Chonnam National University Medical School, Hwasun, Korea

5Department of Radiation Oncology, Seoul National University Bundang Hospital, Seongnam, Korea

6Department of Radiation Oncology, Seoul National University College of Medicine, Seoul, Korea

7Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, Korea

Correspondence: Kyung Hwan Shin, Department of Radiation Oncology, Seoul National University College of Medicine, 101 Daehak-ro, Jongno-gu, Seoul 03080, Korea
Tel: 82-2-2072-2524 Fax: 82-2-742-2073 E-mail: radiat@snu.ac.kr
Co-correspondence: Kyubo Kim, Department of Radiation Oncology, Seoul National University Bundang Hospital, 82 Gumi-ro 173beon-gil, Bundang-gu, Seongnam 13620, Korea
Tel: 82-31-787-7657 Fax: 82-31-787-4019 E-mail: kyubokim.ro@gmail.com
*Seok-Joo Chun and Ji Hwan Jo contributed equally to this work.
a)Present address: Department of Radiation Oncology, Dongguk University Ilsan Hospital, Dongguk University College of Medicine, Goyang, Korea
• Received: October 7, 2023   • Accepted: December 7, 2023

Copyright © 2024 by the Korean Cancer Association

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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  • Purpose
    We investigated the proportions of patients eligible for accelerated partial breast irradiation (APBI) among those with pT1-2N0 breast cancer, based on the criteria set by the American Society for Radiation Oncology (ASTRO), the Groupe Européen de Curiethérapie and the European Society for Radiotherapy and Oncology (GEC-ESTRO), the American Brachytherapy Society (ABS), and the American Society of Breast Surgeons (ASBS). Additionally, we analyzed the rate of APBI utilization among eligible patients.
  • Materials and Methods
    Patients diagnosed with pT1-2N0 breast cancer in 2019 were accrued in four tertiary medical centers in Korea. All patients had undergone breast conserving surgery followed by radiotherapy, either whole breast irradiation or APBI. To determine which guideline best predicts the use of APBI in Korea, the F1 score and Matthews Correlation Coefficient (MCC) were determined for each guideline.
  • Results
    A total of 1,251 patients were analyzed, of whom 196 (15.7%) underwent APBI. The percentages of eligible patients identified by the ASTRO, GEC-ESTRO, ABS, and ASBS criteria were 13.7%, 21.0%, 50.5%, and 63.5%, respectively. APBI was used to treat 54.4%, 37.2%, 27.1%, and 23.7% of patients eligible by the ASTRO, GEC-ESTRO, ABS, and ASBS criteria, respectively. The ASTRO guideline exhibited the highest F1 score (0.76) and MCC (0.67), thus showing the best prediction of APBI utilization in Korea.
  • Conclusion
    The proportion of Korean breast cancer patients who are candidates for APBI is substantial. The actual rate of APBI utilization among eligible patients may suggest there is a room for risk-stratified optimization in offering radiation therapy.
  • Key words: Early breast cancer, Radiotherapy, Accelerated partial breast irradiation, APBI guidelines
The current standard treatment for early breast cancer is breast-conserving surgery (BCS) followed by breast radiotherapy [1,2]. Traditionally, whole breast irradiation (WBI) was administered over 25-28 fractions, taking 5-6 treatment weeks. Moderate hypofractionated regimen reduced the treatment duration to 3-4 weeks. In addition, accelerated partial breast irradiation (APBI) has been a subject of numerous trials to reduce overall treatment time further and the treatment volume as well. Many randomized phase 3 trials have demonstrated the non-inferiority of APBI to WBI in selected low-risk early breast cancer [3-6]. These findings support the adoption of APBI as an alternative treatment option, offering comparable local control and survival [1,2].
Several guidelines seek to determine patient eligibility for APBI [7-10], including those of the American Society for Radiation Oncology (ASTRO), the Groupe Européen de Curiethérapie and the European Society for Radiotherapy and Oncology (GEC-ESTRO), the American Brachytherapy Society (ABS), and the American Society of Breast Surgeons (ASBS). The guidelines vary in their specific criteria, but commonly considered factors include age (typically over 45-50 years), negative lymph nodes, negative resection margin, tumor size less than 2 or 3 cm, and no lymphovascular space invasion (LVSI).
The percentages of ‘suitable’ patients for APBI by the ASTRO guideline were 41.2% and 39.0% of early breast cancer in the studies using Surveillance Epidemiology and End Results (SEER) and National Cancer Database (NCDB), respectively [11,12]. However, Korean breast cancer patients are younger at diagnosis than are other breast cancer populations [13]. Furthermore, the small breast size of Korean patients can render APBI challenging and potentially unfeasible [14]. Given the clinical differences between Korean and Western patients, we investigated the proportion of patients eligible for APBI among Korean women with pT1-2N0 invasive breast cancer who underwent BCS, based on the ASTRO, GEC-ESTRO, ABS, and ASBS criteria. Additionally, we derived the rate of APBI utilization among eligible patients.
1. Patients
Patients diagnosed with pT1-2N0 breast cancers in 2019 were accrued from four institutions, three of which routinely administer APBI. All patients underwent BCS followed by radiotherapy, either WBI or APBI. Patients with a history of prior breast cancer, thoracic radiotherapy, neoadjuvant chemotherapy, bilateral breast cancer, or distant metastasis at diagnosis were excluded.
2. Guidelines
The ASTRO, GEC-ESTRO, ABS, and ASBS guidelines are summarized in Table 1. These guidelines consider clinicopathologic factors including age, histology, tumor size, resection margin status, LVSI, estrogen receptor status, human epidermal growth factor receptor 2 (HER2) expression, extensive intraductal component (EIC), focality and centricity of the tumor. We classified patients using the criteria shown in Table 1. Notably, EIC is considered only in ‘cautionary’ factors as an EIC ≤ 3 cm in ASTRO guideline. We considered a total tumor size ≤ 3 cm to be both ‘suitable’ and ‘cautionary’; an EIC was excluded from the ‘suitable’ group. Additionally, the ABS and ASBS guidelines allowed that patients with focal LVSI are eligible for APBI. However, given certain limitations in the pathological reports, LVSI classifications (focal or extensive) were not available. To ensure consistency and accuracy, we implemented strict criteria; no LVSI was permitted by the ABS and ASBS guidelines.
3. F1 score and Mathews correlation coefficient
To investigate which guideline best predicted APBI use, we derived F1 scores and Matthews correlation coefficients (MCCs) for all guidelines [15]. These metrics predict correlations between binary datasets. We defined the following terms for our analysis. True positive (TP): APBI was performed for patients recommended by the guidelines; True negative (TN): WBI was performed for patients not recommended for APBI; False positive (FP): WBI was performed for patients recommended for APBI; False negative (FN): APBI was performed for patients not recommended for APBI.
The formulae for the F1 score and MCC are as follows:
F1 score=2*TP2*TP+FP+FNMCC=TP*TN–FP*FN(TP+FP)*(TP+FN)*(TN+FP)*(TN+FN)
The F1 score ranges from 0 to 1. A score of 0 indicates that the TP rate is 0, reflecting misclassification of all positive samples. Conversely, a score of 1 indicates FP and FN rates of 0, i.e., perfect classification. The MCC ranges from −1 to 1, where −1 indicates TP and TN rates of 0, i.e., perfect misclassification, and 1 indicates FP and FN values of 0, i.e., perfect classification. A value of 0 suggests randomness, akin to coin tossing. Higher values of both metrics indicate strong correlations between predictions and reality.
In this analysis, we excluded the ASTRO ‘cautionary’ group and the GEC-ESTRO ‘intermediate-risk’ group because F1 score and MCC are used to evaluate 2×2 datasets, and the ASTRO ‘cautionary’ and GEC-ESTRO ‘intermediate-risk’ groups lack explicit recommendations regarding the use of APBI. As one institution did not routinely offer APBI, this analysis employed only data from the other three institutions that routinely offer APBI.
A total of 1,251 patients were accrued, of whom 196 (15.7%) received APBI. The dose-fractionation schedules of the three institutions that routinely offer APBI differed: 30 Gy/5fx, 38.5 Gy/10fx, and 40 Gy/10fx. All three institutions employed external beam APBI: magnetic resonance-guided radiotherapy in one, intensity-modulated radiotherapy (IMRT) in another, and the CyberKnife system in the third. The median patient age was 53 years; 60.4% of patients were older than 50 years. The proportion of pT1 tumors was 77.8%; 3.5% of patients had invasive tumors of diameter > 3 cm. Age and tumor size were the principal factors used to choose between WBI and APBI. In addition, the resection margin, LVSI, estrogen receptor, HER2, adjuvant chemotherapy, and endocrine therapy statuses differed between the WBI and APBI patients. The patient characteristics are summarized in Table 2.
In terms of APBI eligibility, 13.7%, 21.0%, 50.5%, and 63.5% of patients were eligible according to the ASTRO, GEC-ESTRO, ABS, and ASBS guidelines, respectively. Of these patients, the proportions who underwent APBI were 54.4%, 37.2%, 27.1%, and 23.7%, respectively. Table 3 summarizes the percentages of eligible patients according to each guideline. APBI was delivered to 10.2% of patients in the ASTRO ‘cautionary’ group and to 2.1% in the ‘unsuitable’ group. For the GEC-ESTRO guideline, 8.6% of patients underwent APBI in the intermediate-risk group and 5.9% in the high-risk group. The risk factors for ‘unsuitable’ patients by the ASTRO guideline who received APBI were a total tumor size > 3 cm (n=3), a positive resection margin (n=1), and tumor multifocality (n=4).
Korean radiation oncologists prefer the ASTRO guideline to the others. The F1 score and MCC were higher for the ASTRO guideline (0.76 and 0.67, respectively) than for the GEC-ESTRO (0.56 and 0.38), ABS (0.54 and 0.37), and ASBS (0.50 and 0.34) guidelines (Fig. 1).
In this study, we evaluated the eligibility for APBI per international guidelines in Korean patients with early breast cancer. Although we have shown that substantial proportions are eligible for APBI, the actual utilization rate of APBI remains low, which implies the potential room for additional APBI.
Multiple phase 3 randomized trials have demonstrated the non-inferiority of APBI in terms of oncological outcomes [3-6]. In the RAPID trial, external beam APBI was delivered at 38.5 Gy/10fx twice daily [3]. Although the 8-year ipsilateral breast tumor recurrence (IBTR) rates of APBI and WBI were similar (3.0% and 2.8% respectively), adverse late events and poor cosmesis were observed more frequently in the APBI group, potentially attributable to the twice-daily treatment regimen. The largest randomized trial was the NSABP B-39/RTOG 0413 trial of 4,216 patients [4]; the absolute difference in the 10-year IBTR rates between APBI and WBI was 0.7%. Although that study failed to meet the non-inferiority criteria, the absolute difference was very small, and the adverse event rates were similar between the two groups. The GEC-ESTRO trial, which utilized multi-catheter brachytherapy for APBI, reported the difference in the 10-year local recurrence rates between APBI and WBI was 1.93%, which was statistically insignificant [5]. APBI patients reported significantly better subjective cosmetic outcomes. The Florence trial enrolled 520 patients treated at a single institution with external beam APBI at 30 Gy/5fx [6]. The difference in the 10-year IBTR rate was insignificant (1.2%), and less toxicity and better cosmesis were reported in the APBI arm. Together, the data show that APBI affords oncological outcomes that are not inferior to those of WBI in select patients with low-risk early breast cancer. The adverse events and cosmetic outcomes are similar, although the former vary by the treatment technique and the dose-fractionation regimen employed.
The proportions of patients eligible for APBI were reported using both population- and hospital-based databases from the United States [11,12]; the SEER and NCDB studies indicated that 74.6% and 72.5% of patients, respectively, were eligible using the ABS guideline. The proportion in our study (50.5%) was lower, reflecting the updated ABS risk factors such as unifocality and HER2 status. However, the proportions of patients eligible according to the ASTRO and GEC-ESTRO guidelines differed significantly. The proportions of ‘suitable’ patients according to the ASTRO guideline were 41.2% and 39.0% in the SEER and NCDB studies, respectively. The SEER and NCDB studies found that the proportions of low-risk patients according to the GEC-ESTRO guideline were 74.6% and 45.7%, respectively. These substantial differences between the SEER and NCDB studies can be attributed to variations in age criteria, resection margin status, and the prevalence of LVSI. Additionally, the corresponding figures were even lower, 13.7% for ASTRO ‘suitable’ and 21.0% for GEC-ESTRO ‘low-risk’ group in this study, reflecting both population differences (pT1-2N0 patients in the SEER study, pN0 patients > 40 years of age in the NCDB study, and pT1-2N0 patients in this study) and pathological features that were not evaluated in the SEER and NCDB studies. Additionally, the ASTRO and ABS guidelines were revised in 2016 and 2022, respectively. The updates in these guidelines involve changes in age criteria and LVSI, which could potentially account for differences in the proportion of eligible patients. In fact, adverse pathological findings such as EIC, LVSI, and close resection margins were evident in upto 40% of patients, resulting in a lower than expected proportion of ‘suitable’ patients according to the ASTRO criteria. As adverse features were substantial according to this study, comprehensive evaluation of pathological features should be done for determining eligibility of APBI.
The resection margin status critically affects the locoregional recurrence of breast cancer patients [16,17]. All APBI guidelines emphasize the importance of a negative resection margin; two guidelines recommend a safety margin ≥ 2 mm [7-10]. However, several studies reported that positive superficial or deep resection margins did not significantly impact the local recurrence rate [18-20]. The policies of our participating institutions in terms of surgical resection depth varied. Thus, the proportions of positive or close superficial/deep resection margins differed across the institutions (S1 Table). As the current APBI guidelines do not distinguish superficial/deep margins from parenchymal resection margins, the APBI eligibility rates also varied across the institutions. However, when assuming the superficial and deep resection margins were negligible, the institutional eligibility rates were comparable (S2 Table). As cosmetic outcomes become of more concern, it is likely that more patients will exhibit positive or close superficial/deep margins. Thus, future guidelines should address marginal status when defining eligibility.
As evidence on long-term treatment outcomes accumulates, APBI use is increasing. A recent survey of Korean radiation oncologists reported that 17% offered APBI to treat early breast cancer in 2022, higher than the 2017 figure of only 5% [21]. Additionally, they have reported that more than half of respondents (7 out of 12) followed ASTRO guideline. We found that F1 score and MCC were the highest in ASTRO guideline, implying that the actual practice of APBI has a strong correlation with ASTRO guideline, consistent with the survey data. Several Korean APBI studies have been published [22,23]. Lee et al. [22] compared APBI with hypofractionated WBI for patients who were ‘suitable’ according to the ASTRO guideline. Although no significant difference in the oncological outcome was apparent between the two arms, APBI reduced acute and late toxicities. In a prospective cohort study, Byun et al. [23] compared APBI and WBI for patients with early breast cancer; APBI was associated with significantly lower fibrosis of the uninvolved breast quadrant at both 6 and 12 months compared with WBI.
Although APBI utilization has increased, it remains low [24]. The possible explanations include the small breast size of Korean women and reimbursement issues. One prospective Korean study found that during APBI planning using a three-dimensional conformal technique, 57.1% of patients exhibited variations from the dose constraints of the RTOG 0319 protocol, primarily attributable to higher doses to the ipsilateral breast or organs at risk [14]. Additionally, half of ipsilateral breast had dose more than 50% of prescribed dose (V50) in 9.5% of patients and the median V50 for the ipsilateral breast was 41.9%. Another Korean study reported similar findings; the mean V50 for the ipsilateral breast was 50.3% after IMRT planning [25]. Another important factor contributing to the low utilization of APBI comes from the reimbursement issue. Korean facilities are typically reimbursed by the number of treatment fractions. Conventional radiotherapy is delivered in 25-28 fractions, moderate hypofractionated radiotherapy in 15-20 fractions, and APBI in 5-10 fractions. Consequently, facilities receive lower reimbursement for APBI due to the reduced number of treatment fractions. Thus, appropriate compensation for APBI treatment should be considered to reduce gap between the guidelines and the actual use of APBI.
One of the weaknesses of this study lies in the limited institutions which do not represent whole breast cancer patients in Korea. Additionally, some pathologic features such as LVSI and resection margin status were unavailable in some patients due to the retrospective nature of our study. Despite these limitations, we comprehensively investigated the clinicopathologic factors of all guidelines when categorizing our patients and reported APBI utilization according to each set of guidelines.
In conclusion, we report a substantial proportion of early breast cancer is eligible for APBI in Korea. However, current actual utilization of APBI is relatively low, suggesting a room for risk-stratified optimization in offering radiation therapy for breast cancer.
Supplementary materials are available at Cancer Research and Treatment website (https://www.e-crt.org).
crt-2023-1109-Supplementary-Table-S1.pdf
crt-2023-1109-Supplementary-Table-S2.pdf

Ethical Statement

The study was approved by the Institutional Review Board of Seoul National University Hospital (IRB No. 2301-164-1403), and the need for informed consent was waived.

Author Contributions

Conceived and designed the analysis: Kim K, Shin KH.

Collected the data: Chun SJ, Jo JH, Kim YB, Park S, Ahn SJ, Kim SS, Shin KH.

Contributed data or analysis tools: Chun SJ, Kim K, Shin KH.

Performed the analysis: Chun SJ, Kim K.

Wrote the paper: Chun SJ, Jo JH, Kim YB, Park S, Ahn SJ, Kim SS, Kim K, Shin KH.

Conflicts of Interest

Conflict of interest relevant to this article was not reported.

Fig. 1.
The F1 score and Matthew Correlation Coefficient to each guideline. ABS, American Brachytherapy Society; ASBS, American Society of Breast Surgeons; ASTRO, American Society for Radiation Oncology; GEC-ESTRO, Groupe Européen de Curiethérapie and the European Society for Radiotherapy and Oncology; MCC, Matthew correlation coefficient.
crt-2023-1109f1.jpg
Table 1.
Summary of clinical guidelines for accelerated partial breast irradiation
ABS ASBS ASTRO (‘suitable’) ASTRO (‘cautionary’) GEC-ESTRO (‘low-risk’) GEC-ESTRO (‘intermediate-risk’)
Age (yr) ≥ 45 ≥ 45 ≥ 50 ≥ 40 > 50 > 40, ≤ 50
Histology All invasive All invasive All invasive, but not ILC All invasive, including ILCa) IDC, mucinous, tubular, medullary, colloid IDC, ILC, mucinous, tubular, medullary, colloid
Tumor size (cm) ≤ 3 (total) ≤ 3 (total) ≤ 2 (tumor) 2-3 (tumor)a) ≤ 3 (tumor size) ≤ 3 (tumor size)
≤ 3 (total) ≤ 3 (total)
Lymph node pN0 pN0 pN0 pN0 pN0 pN0
Margin Negative Negative ≥ 2 mm Close (< 2 mm)a) ≥ 2 mm Close (< 2 mm)
LVSI No No No Yesa) No No
ER Any Any Positive Negativea) Any Any
HER2 Negative Any Any Any Any Any
EIC Any Any No ≤ 3 cma) No No
Focality Unifocal Any Unifocal Unifocalb) Unifocal Any

ABS, American Brachytherapy Society; ASBS, American Society of Breast Surgeons; ASTRO, American Society for Radiation Oncology; EIC, extensive intraductal component; ER, estrogen receptor; GEC-ESTRO, Groupe Européen de Curiethérapie and the European Society for Radiotherapy and Oncology; HER2, human epidermal growth factor receptor 2; IDC, invasive ductal carcinoma; ILC, invasive lobular carcinoma; LVSI, lymphovascular invasion.

a) At least one of these factors is required for the ASTRO ‘cautionary’ classification,

b) Clinically unifocal with a total size of 2.1-3.0 cm.

Table 2.
Patient characteristics
Variable Total patients (n=1,251) WBI (n=1,055) APBI (n=196) p-value
Age (yr)
 < 45 218 (17.4) 216 (20.5) 2 (1.0) < 0.001
 45-50 277 (22.1) 248 (23.5) 29 (14.8)
 > 50 756 (60.4) 591 (56.0) 165 (84.2)
Laterality
 Left 621 (49.6) 525 (49.8) 96 (49.0) 0.902
 Right 630 (50.4) 530 (50.2) 100 (51.0)
Axillary surgery
 SLNBx 1,222 (97.7) 1,029 (97.5) 193 (98.5) 0.499
 ALND 25 (2.0) 23 (2.2) 2 (1.0)
 Not done 4 (0.3) 3 (0.3) 1 (0.5)
Histology
 IDC 1,155 (92.3) 982 (93.1) 173 (88.3) < 0.001
 ILC 44 (3.5) 40 (3.8) 4 (2.0)
 Others 52 (4.2) 33 (3.1) 19 (9.7)
Size (invasive tumor only) (cm)
 ≤ 2 973 (77.8) 794 (75.3) 179 (91.3) < 0.001
 > 2 and ≤ 3 234 (18.7) 218 (20.7) 16 (8.2)
 > 3 44 (3.5) 43 (4.1) 1 (0.5)
Size (including DCIS) (cm)
 ≤ 2 788 (63.0) 620 (58.8) 168 (85.7) < 0.001
 > 2 and ≤ 3 307 (24.5) 282 (26.7) 25 (12.8)
 > 3 156 (12.5) 153 (14.5) 3 (1.5)
EIC
 Positive 322 (25.7) 294 (27.9) 28 (14.3) < 0.001
 Negative 883 (70.6) 727 (68.9) 156 (79.6)
 N/A 46 (3.7) 34 (3.2) 12 (6.1)
Focality
 Unifocal 1,082 (86.5) 902 (85.5) 180 (91.8) 0.023
 Multifocal 169 (13.5) 153 (14.5) 16 (8.2)
Centricity
 Unicentric 1,245 (99.5) 1,049 (99.4) 196 (100) 0.620
 Multicentric 6 (0.5) 6 (0.6) 0
Resection margin
 Positive 74 (5.9) 73 (6.9) 1 (0.5) < 0.001
 Close (< 2 mm) 436 (34.9) 404 (38.3) 32 (16.3)
 Negative (≥ 2 mm) 615 (49.2) 495 (46.9) 120 (61.2)
 N/Aa) 126 (10.1) 83 (7.9) 43 (21.9)
LVSI
 Positive 129 (10.3) 127 (12.0) 2 (1.0) < 0.001
 Negative 1,122 (89.7) 928 (88.0) 194 (99.0)
ER status
 Positive 1,000 (79.9) 806 (76.4) 194 (99.0) < 0.001
 Negative 251 (20.1) 249 (23.6) 2 (1.0)
HER2 status
 Positive 153 (12.2) 151 (14.3) 2 (1.0) < 0.001
 Negative 1,097 (87.7) 903 (85.6) 194 (99.0)
 N/A 1 (0.1) 1 (0.1) 0
Ki-67 (%)
 < 20 803 (64.2) 622 (59.0) 181 (92.3) < 0.001
 ≥ 20 445 (35.6) 430 (40.8) 15 (7.7)
 N/A 3 (0.2) 3 (0.3) 0
Adjuvant chemotherapy
 Yes 426 (34.1) 409 (38.8) 17 (8.7) < 0.001
 No 825 (65.9) 646 (61.2) 179 (91.3)
Adjuvant endocrine therapy
 Yes (TMX) 535 (42.8) 481 (45.6) 54 (27.6) < 0.001
 Yes (AI) 421 (33.7) 311 (29.5) 110 (56.1)
 No 295 (23.6) 263 (24.9) 32 (16.3)

Values are presented as number (%). AI, aromatase inhibitor; ALND, axillary lymph node dissection; APBI, accelerated partial breast irradiation; DCIS, ductal carcinoma in situ; EIC, extensive intraductal component; ER, estrogen receptor; HER2, human epidermal growth factor receptor 2; IDC, invasive ductal carcinoma; ILC, invasive lobular carcinoma; LVSI, lymphovascular space invasion; N/A, not available; SLNBx, sentinel lymph node biopsy; TMX, tamoxifen; WBI, whole breast irradiation.

a) Resection margin status was negative, but safety margin width unknown.

Table 3.
Proportions of patients eligible for accelerated partial breast irradiation according to each guideline
Criteria Total patients (n=1,251) WBI (n=1,055) APBI (n=196) Actual APBI rates
ASTROa)
 Suitable 158 (13.7) 72 (7.2) 86 (55.1) 86/158 (54.4)
 Cautionary 610 (52.9) 548 (54.9) 62 (39.7) 62/610 (10.2)
 Unsuitable 386 (33.4) 378 (37.9) 8 (5.1) 8/386 (2.1)
GEC-ESTROa)
 Low-risk 242 (21.0) 152 (15.2) 90 (58.4) 90/242 (37.2)
 Intermediate-risk 385 (33.3) 352 (35.2) 33 (21.4) 33/385 (8.6)
 High-risk 527 (45.7) 496 (49.6) 31 (20.1) 31/527 (5.9)
ABS
 Acceptable 632 (50.5) 461 (43.7) 171 (87.2) 171/632 (27.1)
 Unacceptable 619 (49.5) 594 (56.3) 25 (12.8) 25/619 (4.0)
ASBS
 Recommended 794 (63.5) 606 (57.4) 188 (95.9) 188/794 (23.7)
 Not recommended 457 (36.5) 449 (42.6) 8 (4.1) 8/457 (1.8)

Values are presented as number (%). ABS, American Brachytherapy Society; APBI, accelerated partial breast irradiation; ASBS, American Society of Breast Surgeons; ASTRO, American Society for Radiation Oncology; GEC-ESTRO, Groupe Européen de Curiethérapie and the European Society for Radiotherapy and Oncology; WBI, whole breast irradiation.

a) Using only the available data.

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    • Impact of the ASTRO 2024 Guideline on Partial Breast Irradiation Eligibility in Breast Cancer Patients (KROG 24-01)
      Seok-Joo Chun, Sangjoon Park, Yong Bae Kim, Sung-Ja Ahn, Kyubo Kim, Kyung Hwan Shin
      Practical Radiation Oncology.2024;[Epub]     CrossRef

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      Assessment of Eligibility and Utilization of Accelerated Partial Breast Irradiation in Korean Breast Cancer Patients (KROG 22-15)
      Cancer Res Treat. 2024;56(2):549-556.   Published online December 8, 2023
      DOI: https://doi.org/10.4143/crt.2023.1109
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    Assessment of Eligibility and Utilization of Accelerated Partial Breast Irradiation in Korean Breast Cancer Patients (KROG 22-15)
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    Fig. 1. The F1 score and Matthew Correlation Coefficient to each guideline. ABS, American Brachytherapy Society; ASBS, American Society of Breast Surgeons; ASTRO, American Society for Radiation Oncology; GEC-ESTRO, Groupe Européen de Curiethérapie and the European Society for Radiotherapy and Oncology; MCC, Matthew correlation coefficient.

    Fig. 1.

    Assessment of Eligibility and Utilization of Accelerated Partial Breast Irradiation in Korean Breast Cancer Patients (KROG 22-15)
    ABS ASBS ASTRO (‘suitable’) ASTRO (‘cautionary’) GEC-ESTRO (‘low-risk’) GEC-ESTRO (‘intermediate-risk’)
    Age (yr) ≥ 45 ≥ 45 ≥ 50 ≥ 40 > 50 > 40, ≤ 50
    Histology All invasive All invasive All invasive, but not ILC All invasive, including ILCa) IDC, mucinous, tubular, medullary, colloid IDC, ILC, mucinous, tubular, medullary, colloid
    Tumor size (cm) ≤ 3 (total) ≤ 3 (total) ≤ 2 (tumor) 2-3 (tumor)a) ≤ 3 (tumor size) ≤ 3 (tumor size)
    ≤ 3 (total) ≤ 3 (total)
    Lymph node pN0 pN0 pN0 pN0 pN0 pN0
    Margin Negative Negative ≥ 2 mm Close (< 2 mm)a) ≥ 2 mm Close (< 2 mm)
    LVSI No No No Yesa) No No
    ER Any Any Positive Negativea) Any Any
    HER2 Negative Any Any Any Any Any
    EIC Any Any No ≤ 3 cma) No No
    Focality Unifocal Any Unifocal Unifocalb) Unifocal Any
    Variable Total patients (n=1,251) WBI (n=1,055) APBI (n=196) p-value
    Age (yr)
     < 45 218 (17.4) 216 (20.5) 2 (1.0) < 0.001
     45-50 277 (22.1) 248 (23.5) 29 (14.8)
     > 50 756 (60.4) 591 (56.0) 165 (84.2)
    Laterality
     Left 621 (49.6) 525 (49.8) 96 (49.0) 0.902
     Right 630 (50.4) 530 (50.2) 100 (51.0)
    Axillary surgery
     SLNBx 1,222 (97.7) 1,029 (97.5) 193 (98.5) 0.499
     ALND 25 (2.0) 23 (2.2) 2 (1.0)
     Not done 4 (0.3) 3 (0.3) 1 (0.5)
    Histology
     IDC 1,155 (92.3) 982 (93.1) 173 (88.3) < 0.001
     ILC 44 (3.5) 40 (3.8) 4 (2.0)
     Others 52 (4.2) 33 (3.1) 19 (9.7)
    Size (invasive tumor only) (cm)
     ≤ 2 973 (77.8) 794 (75.3) 179 (91.3) < 0.001
     > 2 and ≤ 3 234 (18.7) 218 (20.7) 16 (8.2)
     > 3 44 (3.5) 43 (4.1) 1 (0.5)
    Size (including DCIS) (cm)
     ≤ 2 788 (63.0) 620 (58.8) 168 (85.7) < 0.001
     > 2 and ≤ 3 307 (24.5) 282 (26.7) 25 (12.8)
     > 3 156 (12.5) 153 (14.5) 3 (1.5)
    EIC
     Positive 322 (25.7) 294 (27.9) 28 (14.3) < 0.001
     Negative 883 (70.6) 727 (68.9) 156 (79.6)
     N/A 46 (3.7) 34 (3.2) 12 (6.1)
    Focality
     Unifocal 1,082 (86.5) 902 (85.5) 180 (91.8) 0.023
     Multifocal 169 (13.5) 153 (14.5) 16 (8.2)
    Centricity
     Unicentric 1,245 (99.5) 1,049 (99.4) 196 (100) 0.620
     Multicentric 6 (0.5) 6 (0.6) 0
    Resection margin
     Positive 74 (5.9) 73 (6.9) 1 (0.5) < 0.001
     Close (< 2 mm) 436 (34.9) 404 (38.3) 32 (16.3)
     Negative (≥ 2 mm) 615 (49.2) 495 (46.9) 120 (61.2)
     N/Aa) 126 (10.1) 83 (7.9) 43 (21.9)
    LVSI
     Positive 129 (10.3) 127 (12.0) 2 (1.0) < 0.001
     Negative 1,122 (89.7) 928 (88.0) 194 (99.0)
    ER status
     Positive 1,000 (79.9) 806 (76.4) 194 (99.0) < 0.001
     Negative 251 (20.1) 249 (23.6) 2 (1.0)
    HER2 status
     Positive 153 (12.2) 151 (14.3) 2 (1.0) < 0.001
     Negative 1,097 (87.7) 903 (85.6) 194 (99.0)
     N/A 1 (0.1) 1 (0.1) 0
    Ki-67 (%)
     < 20 803 (64.2) 622 (59.0) 181 (92.3) < 0.001
     ≥ 20 445 (35.6) 430 (40.8) 15 (7.7)
     N/A 3 (0.2) 3 (0.3) 0
    Adjuvant chemotherapy
     Yes 426 (34.1) 409 (38.8) 17 (8.7) < 0.001
     No 825 (65.9) 646 (61.2) 179 (91.3)
    Adjuvant endocrine therapy
     Yes (TMX) 535 (42.8) 481 (45.6) 54 (27.6) < 0.001
     Yes (AI) 421 (33.7) 311 (29.5) 110 (56.1)
     No 295 (23.6) 263 (24.9) 32 (16.3)
    Criteria Total patients (n=1,251) WBI (n=1,055) APBI (n=196) Actual APBI rates
    ASTROa)
     Suitable 158 (13.7) 72 (7.2) 86 (55.1) 86/158 (54.4)
     Cautionary 610 (52.9) 548 (54.9) 62 (39.7) 62/610 (10.2)
     Unsuitable 386 (33.4) 378 (37.9) 8 (5.1) 8/386 (2.1)
    GEC-ESTROa)
     Low-risk 242 (21.0) 152 (15.2) 90 (58.4) 90/242 (37.2)
     Intermediate-risk 385 (33.3) 352 (35.2) 33 (21.4) 33/385 (8.6)
     High-risk 527 (45.7) 496 (49.6) 31 (20.1) 31/527 (5.9)
    ABS
     Acceptable 632 (50.5) 461 (43.7) 171 (87.2) 171/632 (27.1)
     Unacceptable 619 (49.5) 594 (56.3) 25 (12.8) 25/619 (4.0)
    ASBS
     Recommended 794 (63.5) 606 (57.4) 188 (95.9) 188/794 (23.7)
     Not recommended 457 (36.5) 449 (42.6) 8 (4.1) 8/457 (1.8)
    Table 1. Summary of clinical guidelines for accelerated partial breast irradiation

    ABS, American Brachytherapy Society; ASBS, American Society of Breast Surgeons; ASTRO, American Society for Radiation Oncology; EIC, extensive intraductal component; ER, estrogen receptor; GEC-ESTRO, Groupe Européen de Curiethérapie and the European Society for Radiotherapy and Oncology; HER2, human epidermal growth factor receptor 2; IDC, invasive ductal carcinoma; ILC, invasive lobular carcinoma; LVSI, lymphovascular invasion.

    At least one of these factors is required for the ASTRO ‘cautionary’ classification,

    Clinically unifocal with a total size of 2.1-3.0 cm.

    Table 2. Patient characteristics

    Values are presented as number (%). AI, aromatase inhibitor; ALND, axillary lymph node dissection; APBI, accelerated partial breast irradiation; DCIS, ductal carcinoma in situ; EIC, extensive intraductal component; ER, estrogen receptor; HER2, human epidermal growth factor receptor 2; IDC, invasive ductal carcinoma; ILC, invasive lobular carcinoma; LVSI, lymphovascular space invasion; N/A, not available; SLNBx, sentinel lymph node biopsy; TMX, tamoxifen; WBI, whole breast irradiation.

    Resection margin status was negative, but safety margin width unknown.

    Table 3. Proportions of patients eligible for accelerated partial breast irradiation according to each guideline

    Values are presented as number (%). ABS, American Brachytherapy Society; APBI, accelerated partial breast irradiation; ASBS, American Society of Breast Surgeons; ASTRO, American Society for Radiation Oncology; GEC-ESTRO, Groupe Européen de Curiethérapie and the European Society for Radiotherapy and Oncology; WBI, whole breast irradiation.

    Using only the available data.

    Table 1.

    Table 2.

    Table 3.

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