Radiation Pneumonitis After Breast Cancer Radiotherapy: CT Imaging Findings, Differential Diagnosis, Treatment, and Prognosis
Clinical Hook
A 55-year-old woman presents to the emergency department with persistent cough, fever, and dyspnea several weeks after treatment for breast cancer.
At first glance, the clinical presentation may suggest ordinary pneumonia.
But the chest CT tells a different story.
Instead of a random or bronchocentric pulmonary opacity, the abnormality is concentrated in the portion of the right lung corresponding to the radiation treatment field, with ground-glass opacity, interstitial change, architectural distortion, and localized volume loss.
This is the imaging pattern that should immediately raise the possibility of radiation pneumonitis.
The case provided for this review describes a 55-year-old woman with invasive ductal carcinoma of the right breast who underwent breast-conserving surgery, regional radiotherapy, and chemotherapy. Four weeks after treatment, she developed persistent cough, fever, and dyspnea. CT demonstrated abnormalities in the right upper lung corresponding to the irradiated region.
The key radiologic question is therefore not simply:
“Is there pneumonia?”
It is:
“Why is the lung abnormality located exactly here?”
That question is often more diagnostically useful than the presence of GGO or consolidation itself.
Learning Objectives
After reading this article, readers should be able to:
Recognize the clinical setting of radiation pneumonitis after breast cancer radiotherapy.
Identify the characteristic CT findings of radiation-induced lung injury.
Understand why radiation-field correlation is one of the most important diagnostic clues.
Distinguish radiation pneumonitis from infection, drug-induced pneumonitis, pulmonary embolism, lymphangitic carcinomatosis, and metastases.
Understand the relationship between radiation pneumonitis and later radiation fibrosis.
Interpret dose-volume parameters such as V5, V20, and mean lung dose.
Understand the role of CT, multiplanar reconstruction, and treatment-plan correlation.
Recognize atypical patterns such as organizing pneumonia and radiation recall pneumonitis.
Understand the principles of treatment and follow-up.
Consider how AI could assist future radiation-induced lung injury workflows.
Clinical Case
A 55-year-old woman with right breast invasive ductal carcinoma underwent breast-conserving surgery followed by localized radiation therapy and chemotherapy.
Four weeks after treatment, she presented with:
Persistent cough
Fever
Dyspnea
Chest examination did not reveal a striking abnormality.
However, chest CT demonstrated pulmonary abnormalities in the right upper lung corresponding to the radiation treatment region, including ground-glass and fibrotic changes with localized volume loss and architectural distortion.
The combination of:
recent radiotherapy + compatible timing + respiratory symptoms + field-conforming CT abnormality
makes radiation pneumonitis the leading consideration.
The original case identifies the final diagnosis as radiation pneumonitis.
What Is Radiation Pneumonitis?
Radiation pneumonitis is an inflammatory manifestation of radiation-induced lung injury (RILI) occurring after exposure of lung tissue to therapeutic radiation.
RILI is commonly conceptualized as a continuum:
Radiation exposure → inflammatory lung injury → radiation pneumonitis → radiation fibrosis
The acute/subacute inflammatory phase and chronic fibrotic phase overlap biologically, but their clinical and imaging manifestations differ.
A major practical point is that the lung does not necessarily become abnormal immediately after radiation therapy.
The timing matters.
The provided case describes symptoms approximately four weeks after radiotherapy, which is compatible with the early post-radiation clinical setting. Breast cancer series have also demonstrated that CT-detected radiation-related abnormalities can be considerably more frequent than symptomatic pneumonitis.
Why Does Radiation Pneumonitis Occur?
Ionizing radiation produces cellular and endothelial injury within the irradiated tissue.
The chronic phase involves profibrotic signaling, including pathways involving transforming growth factor-β, collagen deposition, and tissue remodeling.
This explains why the radiologic appearance can evolve from inflammatory GGO or consolidation toward volume loss, architectural distortion, traction bronchiectasis, and fibrosis.
Why the Radiation Field Matters So Much
This is perhaps the single most important imaging principle in this case.
Ordinary infectious pneumonia tends to follow recognizable anatomic or airway-related patterns.
Radiation-induced injury, in contrast, often reflects the geometry of the radiation treatment field.
Therefore, a radiologist should ask:
Does the pulmonary abnormality conform to the radiation field?
If the answer is yes, the probability of radiation-induced injury increases substantially.
The 2021 British Journal of Radiology study specifically evaluated CT manifestations of acute radiation pneumonitis after breast cancer radiotherapy. In that study, CT-detected abnormalities were much more common than symptomatic pneumonitis, and GGO and consolidation constituted the principal CT patterns.
The original case similarly emphasizes the spatial relationship between the right lung abnormality and the radiation field.
CT Findings of Radiation Pneumonitis
1. Ground-Glass Opacity
GGO is one of the most important early CT manifestations.
Inflammatory injury increases pulmonary attenuation while allowing underlying vessels and bronchial structures to remain partially visible.
In breast cancer patients, CT-detected GGO may occur without severe clinical symptoms. Therefore:
GGO ≠ automatically severe radiation pneumonitis.
Clinical severity must be assessed separately.
2. Consolidation
More pronounced alveolar injury may produce consolidation.
However, the mere presence of consolidation is nonspecific.
The more important question is:
Where is the consolidation?
A consolidation conforming to the radiation field is much more suggestive of radiation-induced injury than an unrelated lobar consolidation elsewhere.
The supplied case emphasizes that radiation pneumonitis can produce GGO and consolidation with a geographic distribution corresponding to the treatment field.
3. Geographic Distribution
Radiation pneumonitis frequently demonstrates a geographic or field-conforming distribution.
This may appear unusual when compared with ordinary infectious pneumonia because the boundary may correspond to the geometry of radiation delivery rather than a conventional bronchopulmonary segment.
This is why reviewing the radiation treatment plan can be extremely valuable.
4. Volume Loss
Volume loss becomes increasingly important as radiation-induced injury evolves toward fibrosis.
In the present case, localized volume loss accompanies the pulmonary abnormality.
5. Architectural Distortion
Architectural distortion indicates alteration of normal pulmonary anatomy.
Associated findings may include:
Parenchymal bands
Traction bronchiectasis
Volume loss
Pleural/subpleural thickening
Fibrotic change
These findings are particularly useful when assessing chronic radiation-induced changes.
Figure 1. Axial CT
Figure 1. Axial lung-window CT demonstrating radiation-field-conforming pulmonary abnormality.
The supplied case describes linear and reticular interstitial abnormalities in the peripheral right upper lung corresponding spatially to the radiation treatment region.
Radiologic interpretation
The critical finding is not simply the presence of interstitial opacity.
It is the spatial concordance between the abnormal lung and the irradiated field.
Imaging Pearl
Radiation-field conformity can be more diagnostically informative than the specific CT morphology.
Figure 2. Coronal CT
Figure 2. Coronal reconstruction demonstrating the longitudinal extent of radiation-associated pulmonary abnormality.
Coronal reconstruction can make the relationship between the abnormal lung and the radiation field easier to appreciate than axial images alone. The supplied case specifically emphasizes the value of coronal and sagittal multiplanar reconstruction.
Why MPR Matters
Radiation treatment is inherently three-dimensional.
Therefore, evaluation should not be restricted to axial images.
A practical approach is:
Axial → Coronal → Sagittal → Radiation treatment plan
This can provide a more complete understanding of disease distribution.
Radiation Pneumonitis vs Radiation Fibrosis
One of the most important interpretive distinctions is whether the patient is predominantly in the inflammatory phase or the chronic fibrotic phase.
| Feature | Radiation Pneumonitis | Radiation Fibrosis |
|---|---|---|
| Phase | Acute/subacute | Late/chronic |
| GGO | Common | May persist |
| Consolidation | Common | May evolve into fibrosis |
| Volume loss | Variable | More characteristic |
| Architectural distortion | May develop | Common |
| Traction bronchiectasis | Possible | More common |
| Main process | Inflammation | Fibrotic remodeling |
| Steroid responsiveness | Potentially useful | Limited once established |
The supplied case appropriately stresses that radiation pneumonitis and established radiation fibrosis should not simply be labeled as the same process.
How Common Is It?
Modern radiation techniques have reduced clinically significant pulmonary toxicity.
Importantly, however:
Radiologic radiation change is more common than symptomatic radiation pneumonitis.
In a 61-patient breast cancer CT study, 37.7% had no CT evidence of acute RP, while 13.1% had Grade 1 changes, 44.3% had Grade 2 changes, and 4.9% had Grade 3 changes; only one patient developed symptomatic RP.
This distinction is clinically important.
A CT abnormality does not automatically mean that the patient has severe symptomatic radiation pneumonitis.
Radiation Dose: Why Dose Alone Is Not Enough
Radiation toxicity depends on more than total prescribed dose.
Important factors include:
Total dose
Dose per fraction
Irradiated lung volume
Mean lung dose
V5
V10
V20
V30
Treatment technique
Regional nodal irradiation
Baseline pulmonary status
Concomitant systemic therapy
The supplied case correctly emphasizes the importance of dose-volume relationships.
A useful conceptual equation is:
Toxicity risk ≠ total dose alone
Instead:
Toxicity risk ≈ dose + irradiated volume + patient susceptibility + treatment context
Dose-volume histogram analysis therefore provides information that cannot be obtained from the prescription dose alone.
What About V20 and Mean Lung Dose?
V20 represents the percentage of lung receiving at least 20 Gy.
Mean lung dose represents the average radiation dose delivered to the lung volume being analyzed.
These parameters are widely used in radiation oncology to characterize pulmonary exposure.
However, an important editorial correction is necessary:
A numerical threshold should not be interpreted as a universal diagnostic cutoff for an individual patient.
Different treatment techniques, fractionation schedules, contouring methods, and patient populations can produce different risk relationships.
Recent breast cancer imaging research has also demonstrated associations between chronic CT changes and multiple dose-volume parameters, including V5, V20, V30, and V40.
Differential Diagnosis
A post-radiotherapy patient with cough, fever, dyspnea, and GGO requires a structured differential diagnosis.
| Diagnosis | Typical Imaging Pattern | Key Clue |
|---|---|---|
| Radiation pneumonitis | GGO/consolidation | Radiation-field conformity |
| Bacterial pneumonia | Lobar/segmental consolidation | Airway/infectious distribution |
| Viral pneumonia | Multifocal/bilateral GGO | Often diffuse or bilateral |
| Drug-induced pneumonitis | GGO, OP, NSIP and other ILD patterns | Drug exposure + timing |
| Lymphangitic carcinomatosis | Septal thickening, nodularity | Tumor progression |
| Pulmonary metastases | Multiple nodules | Hematogenous spread |
| Pulmonary embolism | Usually nonspecific parenchymal findings | Vascular abnormality on CTPA |
| Cardiogenic edema | GGO, septal thickening, effusions | Cardiac/hemodynamic context |
The original case highlights these differential diagnoses and emphasizes that infection and tumor progression should not be overlooked.
Radiation Pneumonitis vs Drug-Induced Pneumonitis
This is one of the most important practical distinctions in modern breast cancer imaging.
Breast cancer treatment may involve:
Chemotherapy
HER2-targeted therapy
Endocrine therapy
Immunotherapy
Other systemic agents
Some of these therapies can cause drug-associated interstitial lung disease.
The key imaging distinction is often:
Radiation pneumonitis → localized and field-conforming
versus
Drug-induced pneumonitis → often more diffuse and non-field-conforming
But this is not absolute.
A patient may have both radiation-induced and drug-induced lung injury.
The 2024 Korean Journal of Radiology review specifically emphasizes this diagnostic overlap and also describes radiation recall pneumonitis and radiation-induced organizing pneumonia as important atypical patterns.
An Important Exception: Radiation Recall Pneumonitis
Not every radiation-related pneumonitis occurs immediately after radiotherapy.
Radiation recall pneumonitis is an inflammatory reaction that develops within a previously irradiated field after exposure to a triggering systemic agent.
This distinction matters because the timeline can be misleading.
A patient may have completed radiotherapy months earlier and subsequently develop a new field-conforming opacity after a drug exposure.
Therefore, when evaluating a new pulmonary abnormality, ask:
When was radiation delivered?
When did the pulmonary abnormality appear?
What systemic drugs were given?
Was there a recent medication change?
Does the abnormality conform to the previous radiation field?
Another Important Exception: Organizing Pneumonia
Radiation-associated organizing pneumonia can occur outside the radiation field.
This is an important reason not to use:
“Outside the field = impossible”
as a diagnostic rule.
Instead:
Field-conforming disease strongly supports classic radiation pneumonitis, but atypical radiation-related syndromes exist.
This distinction is particularly important in patients whose CT abnormalities migrate or appear in the contralateral lung.
Is MRI Useful?
MRI is not the routine first-line modality for evaluating pulmonary parenchymal radiation injury.
Chest CT remains the principal imaging modality.
Thin-section CT and multiplanar reconstruction provide excellent visualization of:
GGO
Consolidation
Fibrotic bands
Architectural distortion
Traction bronchiectasis
Volume loss
Pleural changes
The supplied case appropriately identifies CT as the primary modality and MRI as a secondary modality for selected problems rather than the routine test for radiation pneumonitis.
Treatment
Treatment depends primarily on clinical severity.
Asymptomatic or Mild Disease
Patients with limited radiologic changes and minimal symptoms may require:
Clinical observation
Follow-up imaging
Pulmonary function assessment when appropriate
Evaluation for alternative causes
Not every radiologic radiation change requires systemic corticosteroids.
Symptomatic Disease
Clinically significant radiation pneumonitis may be treated with corticosteroids after appropriate assessment for infection and other competing diagnoses.
The supplied case describes systemic corticosteroid treatment followed by gradual tapering.
The exact regimen should be individualized according to:
Severity
Oxygenation
Pulmonary function
Infection risk
Comorbidities
Response to treatment
Radiation-induced lung injury reviews similarly emphasize that treatment of acute pneumonitis depends on clinical severity and that corticosteroids are commonly effective in symptomatic disease.
Why Is Steroid Tapering Important?
Abrupt discontinuation after clinical improvement can be problematic in patients receiving prolonged corticosteroid therapy.
The original case emphasizes gradual tapering because symptoms can recur during dose reduction.
However, treatment should never be reduced to the simplistic formula:
“GGO = steroid.”
The correct sequence is:
Clinical severity → alternative diagnoses → infection assessment → treatment decision → response monitoring → individualized taper
Prognosis
Most mild cases have a favorable clinical course.
However, some patients develop persistent or chronic fibrotic abnormalities.
Potentially relevant factors include:
Irradiated lung volume
Mean lung dose
Dose-volume parameters
Baseline pulmonary function
Pre-existing interstitial lung disease
Smoking history
Systemic therapy
Radiation field
Clinical severity
The supplied case emphasizes these prognostic considerations.
The key distinction is:
Inflammation may improve. Established fibrosis may persist.
The Radiologist's Six Questions
When reading a chest CT in a patient who recently underwent breast radiotherapy, ask:
1. When was radiation therapy performed?
Timing establishes the clinical context.
2. Where is the abnormality?
Is it located within the irradiated lung?
3. Does the morphology fit?
Look for:
GGO
Consolidation
Interstitial opacity
Fibrotic bands
Architectural distortion
4. Does the distribution conform to the radiation field?
This is often the most useful question.
5. Could another disease explain it better?
Consider:
Infection
Drug-induced pneumonitis
PE
Tumor progression
Lymphangitic carcinomatosis
Cardiogenic edema
6. Is this inflammation or established fibrosis?
This determines the clinical interpretation and follow-up strategy.
AI Perspective: Where Could Artificial Intelligence Help?
Radiation pneumonitis is an interesting future application for medical AI because diagnosis requires more than recognizing an opacity.
The critical information is spatial and temporal.
Foundation Models
Medical foundation models may eventually support multimodal interpretation by integrating imaging with clinical and treatment information.
The key challenge is not simply detecting GGO.
It is understanding:
“Is this GGO located where radiation was delivered?”
Vision AI
Computer vision algorithms could potentially identify:
GGO
Consolidation
Fibrotic bands
Volume loss
Traction bronchiectasis
Pleural changes
Automated segmentation could then quantify abnormal lung volume.
Dose-Image Registration
A particularly valuable future application would be registration of:
radiation dose map ↔ CT anatomy
This could allow AI to quantify the relationship between dose distribution and observed pulmonary injury.
Rather than reporting only:
“Right upper-lobe GGO.”
an AI system could potentially report:
“Pulmonary opacity spatially overlaps the high-dose region and demonstrates interval evolution compatible with radiation-associated injury.”
Such an output would be much closer to clinical reasoning.
Future AI Workflow
This is a more realistic clinical AI direction than attempting to replace the radiologist with a single image classifier.
Clinical Pearls
Radiation-field conformity is one of the strongest imaging clues.
GGO is a common CT manifestation of acute radiation-induced injury.
Consolidation can occur and should be interpreted according to its distribution.
CT abnormalities can be much more common than symptomatic radiation pneumonitis.
Radiation pneumonitis and radiation fibrosis represent different phases of radiation-induced lung injury.
Drug-induced pneumonitis must be considered in breast cancer patients receiving systemic therapy.
Radiation recall pneumonitis can occur after a delayed triggering exposure.
Organizing pneumonia may occur outside the radiation field.
Dose-volume parameters provide more information than total prescribed dose alone.
Follow-up CT is particularly useful when distinguishing resolving inflammation from persistent fibrotic remodeling.
The Most Important Imaging Algorithm
When Should the Patient Be Evaluated Urgently?
New or worsening respiratory symptoms after cancer treatment should not automatically be attributed to radiation pneumonitis.
Particularly important warning signs include:
Progressive dyspnea
Resting hypoxemia
Rapid respiratory deterioration
Persistent or recurrent fever
New extensive bilateral pulmonary abnormalities
Hemodynamic instability
Suspicion of pulmonary embolism
Significant decline in exercise tolerance
The supplied case appropriately emphasizes that worsening dyspnea or hypoxemia should prompt active evaluation rather than simple observation.
Conclusion
Radiation pneumonitis is not simply “pneumonia after radiation therapy.”
It is a clinical-radiologic diagnosis that emerges from the relationship between:
history + timing + CT morphology + spatial distribution + radiation field + exclusion of competing diagnoses.
In breast cancer patients, the most valuable CT clue is often the geographic, radiation-field-conforming distribution of GGO or consolidation.
But expert interpretation goes further.
The radiologist must determine:
Where is the abnormality?
When did it appear?
Does it correspond to the treatment field?
Is it inflammatory or fibrotic?
Could a drug, infection, embolism, or recurrent cancer explain it better?
The supplied case demonstrates why these questions matter. The patient's persistent cough, fever, and dyspnea could initially suggest infection, but the combination of recent radiotherapy and field-conforming right-lung abnormalities strongly supports radiation-induced lung injury.
Ultimately, the most useful radiologic principle is simple:
Do not interpret the opacity alone. Interpret the opacity in the context of the radiation field and the patient's treatment timeline.
That is the difference between recognizing a pulmonary opacity and recognizing radiation pneumonitis.
QUIZ
What is the most likely diagnosis?
A. Lymphangitic carcinomatosis
B. Viral pneumonia
C. Drug-induced pneumonitis
D. Radiation pneumonitis
E. Idiopathic pulmonary fibrosis
Answer: D. Radiation pneumonitis. Key reasoning: The combination of compatible timing and radiation-field-conforming abnormality is the strongest clue.
2. Which CT feature is most diagnostically useful for classic radiation pneumonitis?
A. Bilateral honeycombing
B. Multiple cavitary nodules
C. Radiation-field-conforming GGO or consolidation
D. Diffuse pleural effusion
E. Random pulmonary metastases
Answer: C
3. Which statement about radiation dose is most accurate?
A. Total prescribed dose alone determines pneumonitis risk.
B. V20 is irrelevant after breast radiotherapy.
C. Dose-volume parameters and irradiated lung volume should be considered.
D. CT findings cannot be related to radiation dose.
E. Mean lung dose has no clinical relevance.
Answer: C
FAQ
What is radiation pneumonitis?
Radiation pneumonitis is an inflammatory form of radiation-induced lung injury occurring after therapeutic radiation exposure.
What are the most common symptoms?
Dry cough, dyspnea, fever, fatigue, and reduced exercise tolerance are common clinical manifestations.
When does radiation pneumonitis occur after breast radiotherapy?
It commonly appears during the early-to-intermediate period after radiotherapy, although the exact timing varies among patients and treatment regimens.
What is the most important CT finding?
A GGO or consolidation that conforms geographically to the irradiated lung field is a key clue.
Is every GGO after radiotherapy radiation pneumonitis?
No. Infection, drug-induced pneumonitis, edema, tumor progression, pulmonary embolism, and other interstitial lung diseases must be considered.
Can radiation pneumonitis cause consolidation?
Yes. Consolidation may occur as part of the acute inflammatory response.
What is radiation fibrosis?
Radiation fibrosis represents later structural remodeling after radiation-induced lung injury and may include volume loss, architectural distortion, traction bronchiectasis, and fibrotic bands.
Can radiation pneumonitis occur outside the radiation field?
Classic radiation pneumonitis is usually field-related, but radiation-associated organizing pneumonia and radiation recall pneumonitis can produce atypical distributions.
Is MRI routinely used?
No. Chest CT is the principal imaging modality for evaluating pulmonary radiation injury.
Does radiation pneumonitis require steroids?
Not always. Treatment depends on symptoms and severity. Clinically significant disease may require corticosteroid therapy.
Can radiation pneumonitis recur?
Symptoms may recur during corticosteroid tapering, and delayed radiation-related phenomena such as radiation recall can also occur.
Is radiation pneumonitis dangerous?
Many cases are mild and resolve, but clinically significant disease can cause respiratory impairment and, in some patients, persistent fibrotic changes.
What radiation parameters are important?
Mean lung dose and dose-volume parameters such as V5 and V20 are commonly considered in radiation planning and toxicity assessment.
Can AI diagnose radiation pneumonitis?
AI may assist with detection, segmentation, longitudinal comparison, and dose-image analysis, but clinical diagnosis currently requires integration of imaging, treatment history, symptoms, and competing diagnoses.
REFERENCES
The uploaded case already contains eight references. I additionally verified the key DOI/metadata for the major references against PubMed.
- A. Yi, H. H. Kim, H. J. Shin, M. O. Huh, S. D. Ahn, and B. K. Seo, “Radiation-induced complications after breast cancer radiation therapy: A pictorial review of multimodality imaging findings,” Korean J. Radiol., vol. 10, no. 5, pp. 496–507, 2009, doi: 10.3348/kjr.2009.10.5.496.
- W. Jung, S. S. Shim, and K. Kim, “CT findings of acute radiation-induced pneumonitis in breast cancer,” Br. J. Radiol., vol. 94, no. 1124, 2021, Art. no. 20200997, doi: 10.1259/bjr.20200997.
- A. N. Hanania et al., “Radiation-induced lung injury: Assessment and management,” Chest, vol. 156, no. 1, pp. 150–162, 2019, doi: 10.1016/j.chest.2019.03.033.
- T. J. Bledsoe, S. K. Nath, and R. H. Decker, “Radiation pneumonitis,” Clin. Chest Med., vol. 38, no. 2, pp. 201–208, 2017, doi: 10.1016/j.ccm.2016.12.004.
- L. Giuranno, J. Ient, D. De Ruysscher, and M. A. Vooijs, “Radiation-induced lung injury (RILI),” Front. Oncol., vol. 9, 2019, Art. no. 877, doi: 10.3389/fonc.2019.00877.
- R. De Ruysscher et al., “Radiotherapy toxicity,” Nat. Rev. Dis. Primers, vol. 5, 2019, Art. no. 13, doi: 10.1038/s41572-019-0064-5.
- A. Palma et al., “Meta-analysis of incidence of early lung toxicity in 3-dimensional conformal irradiation of breast carcinomas,” Radiat. Oncol., vol. 8, 2013, Art. no. 268, doi: 10.1186/1748-717X-8-268.
- A. B. Ozgen et al., “Radiation pneumonitis in relation to pulmonary function, dosimetric factors, TGFβ1 expression, and quality of life in breast cancer patients receiving post-operative radiotherapy,” 2022/2023.
- “Imaging features of radiation-induced lung disease and its relationship with clinical and dosimetric factors in breast cancer patients,” Radiation Oncology/related indexed literature, 2023. The study reported associations between chronic CT changes and dose-volume parameters including V5, V20, V30, and V40.
- R. Egashira et al., “CT findings of lung injury during breast cancer treatment,” Korean J. Radiol., vol. 25, no. 9, pp. 843–850, 2024.
- S. F. Lee et al., “Randomised controlled trials on radiation dose fractionation in breast cancer: systematic review and meta-analysis with emphasis on side effects and cosmesis,” BMJ, vol. 386, 2024, Art. no. e079089, doi: 10.1136/bmj-2023-079089.
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