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    Caveats dominate

    Pencil beam scanning proton vs IMRT photon PMRT: capsular contracture risk

    ForSubpectoral implant reconstruction (TE/I or DTI) receiving PMRT

    TL;DRProton vs photon PMRT CC HR 1.76 (0.93-3.32, P=.083) on MVA; 2-yr CC 50% with protons plus DTI.

    Why it mattersRadiation oncology

    The proton excess persists within both reconstruction types (2-yr CC 23% vs 12% after TE/I, 50% vs 35% after DTI) even though the adjusted HR crossed 1. Dose, fractionation and superficial constraints are not reported in source, so the PBS planning lever behind it is unknown. It bears on proton selection for implant pts.

    Monday clinic

    In a pt planned for subpectoral DTI reconstruction who is being considered for PBS proton PMRT, this questions that pairing (2-yr CC 50%); it does not address autologous or prepectoral reconstruction.

    12 details
    Design

    Retrospective, IRB-approved cohort from 2 centers within a single institution, Jan 2017 to Dec 2023. Hypothesis stated a priori: proton cohort would have higher CC. Median follow-up 42 mo proton, 47 mo photon.

    Population & inclusion

    Subpectoral 2-stage TE/I or DTI reconstruction with PMRT; N=175 (89 proton, 86 photon). Median age 49 (range 24-78), 63% Hispanic. Groups balanced except laterality and reconstruction type (both P<.001).

    Radiotherapy

    Pencil beam scanning proton vs IMRT photon PMRT; the TE was irradiated in all TE/I pts. Dose, fractionation, bolus and superficial dose constraints are not reported in source.

    Endpoints

    Capsular contracture by Kaplan-Meier; associated factors by Cox proportional hazards, verified with binary logistic regression.

    Results

    Reconstruction type was the only factor that stayed associated on multivariable analysis; the proton effect did not reach significance after adjustment (see tables).

    ComparisonModelHR (95% CI)P
    Proton vs photonUnivariate2.3 (1.26-4.30).007
    Proton vs photonMultivariable1.76 (0.93-3.32).083
    DTI vs TE/IMultivariable3.0 (1.7-5.5)<.001
    ReconstructionProtonPhoton
    DTI50% (n=36)35% (n=15)
    TE/I23% (n=53)12% (n=71)
    vs leading data

    The source frames proton vs photon CC data as scarce and reports this as the largest PBS PMRT reconstruction cohort to date. RADCOMP compares proton vs photon breast RT on cardiac outcomes, not reconstruction complications, so it will not settle this question.

    Applies to
    subpectoral TE/I or DTI implant reconstruction receiving PBS proton or IMRT photon PMRT
    Does not represent autologous or prepectoral reconstruction.
    Limitations

    Photon DTI stratum is only n=15, so the within-DTI modality contrast is underpowered. CC grading scale and RT planning parameters are absent from the abstract, which blocks translation to a specific planning change.

    Discussion

    Adjusted proton HR 1.76 with an interval of 0.93-3.32 excludes neither no effect nor a large one; P=.083 is not reassurance. The consistent direction within both reconstruction types is the stronger signal, and PBS plus DTI is where the risk concentrates.

    Rationale

    Retrospective cohort with reconstruction type imbalanced between modalities (P<.001); proton effect lost significance on multivariable analysis, so the modality signal stays confounded.

    Open questions
    • Does proton CC excess persist after matching on reconstruction type?
    • Which PBS superficial dose parameters drive capsular contracture?
    • Does prepectoral or autologous reconstruction change proton vs photon risk?
    📚 Sources · 📄 2 papers
    📄 PAPER Zerey; Gal; Feenstra et al. · International journal of radiation oncology, biology, physics (2026-04)
    Does Pencil Beam Scanning Proton Therapy Impart a Higher Risk of Capsular Contracture Compared With Intensity Modulated Photon Radiation Therapy in the Postmastectomy Reconstruction Setting?
    PMID 42009110 → doi
    Abstract
    BACKGROUND: Postmastectomy radiation therapy (PMRT) may cause adverse events in the reconstruction setting. Proton-based PMRT is increasingly used and has been shown to improve cardiac and pulmonary dosimetry. Data on the risk of capsular contracture (CC) with proton versus photon PMRT remain scarce. We compared the CC rate of the largest cohort of patients undergoing reconstruction after pencil beam scanning proton PMRT reported to date with an intensity modulated radiation therapy photon cohort, hypothesizing that the proton cohort would have a higher rate of CC.<br/><br/>METHODS AND MATERIALS: An institutional review board -approved retrospective study was conducted on patients with breast cancer who underwent subpectoral 2-stage tissue expander/implant (TE/I) or direct-to-implant (DTI) breast reconstruction and received either pencil beam scanning proton or intensity modulated radiation therapy photon PMRT between January 2017 and December 2023 at 2 centers within a single institution. All patients undergoing TE/I had the TE irradiated. CC rates were estimated using the Kaplan-Meier method. Cox proportional hazards analysis, denoted as hazard ratios (HRs) with 95% CIs, was used to assess variables potentially associated with the outcome, and a binary logistic regression model was used to verify the results.<br/><br/>RESULTS: The study cohort comprised 175 patients (89 proton; 86 photon). The median age was 49 years (range, 24-78), 63% were Hispanic. Patient demographics were well balanced between the groups, except in tumor laterality (P < .001) and reconstruction type (TE/I vs DTI; P < .001). The median follow-up was 42 and 47 months for the proton and photon groups, respectively. In a multivariable analysis, DTI patients had a significantly higher risk of CC compared with TE/I patients (HR, 3.0; 95% CI, 1.7-5.5; P < .001). Proton patients had a higher risk of developing CC compared with the photon group in univariate analysis (HR, 2.3; 95% CI, 1.26-4.30; P = .007), although this effect did not reach statistical significance in the multivariable model (HR, 1.76; 95% CI, 0.93-3.32; P = .083). The 2-year CC rate for patients treated with protons and DTI (n = 36), photons and DTI (n = 15), protons and TE/I (n = 53), and photons and TE/I (n = 71) was 50%, 35%, 23%, 12%, respectively (P < .001). No other factors were significantly associated with CC development.<br/><br/>CONCLUSION: In this contemporary large proton versus photon PMRT cohort, patients treated with proton showed a trend toward an increased risk of CC. Patients undergoing DTI who were treated with protons had the highest risk of CC (50%). Careful consideration of reconstruction and radiation therapy modalities, assessing CC risk, and also involving patient input, is important for treatment selection.
    📄 PAPER Zerey, M.M.; Gal, O.; Feenstra, N. et al. · International Journal of Radiation Oncology*Biology*Physics (2025-09)
    Does Pencil Beam Scanning Proton Therapy Impart a Higher Risk of Capsular Contracture when Compared with Intensity Modulated Photon Radiotherapy in the Post-Mastectomy Reconstruction Setting?
    doi
    📝 https://doi.org/10.1016/j.ijrobp.2025.07.1298

    Radiation Curative Retrospective Caveats dominate

    The longer read

    The takeaway most readers will carry, that protons raise capsular contracture risk, is weaker than the abstract's conclusion suggests. The univariate proton HR of 2.3 (1.26-4.30) falls to 1.76 (0.93-3.32) once covariates enter the model, and the only factor that kept a strong association was direct-to-implant reconstruction, HR 3.0 (1.7-5.5). That attenuation is the central methodological fact. Reconstruction type was unevenly distributed between cohorts (P<.001): 36 of the 89 proton pts had DTI against 15 of the 86 photon pts. An unadjusted modality comparison is therefore partly a comparison of reconstruction strategies.

    The confidence interval tells a reader how to hold the adjusted result. An interval running from 0.93 to 3.32 rules out neither no effect nor a clinically large one, and with only 15 photon DTI pts the study cannot separate a modality effect within DTI from noise. Reading P=.083 as evidence that protons are safe with implants would be as wrong as reading the univariate HR as proof of harm. The stratified 2-yr rates are more persuasive than either model: the proton rate is higher within DTI (50% vs 35%) and within TE/I (23% vs 12%). Those are still unadjusted Kaplan-Meier estimates, and the overall P<.001 cannot by itself apportion the spread between modality and reconstruction type.

    The abstract does not say why a proton excess would exist, and that limits what a radiation oncologist can do with it. A plausible mechanism would involve how PBS handles superficial dose around the implant and chest wall, but the source reports no dose, fractionation, bolus, skin constraint or planning technique. Without those, the finding cannot become a planning change, and a center with different superficial dose handling may or may not reproduce it. The laterality imbalance (P<.001) adds another layer. It plausibly reflects which pts were referred for protons, and referral patterns can carry confounders the model did not capture.

    The source frames the case for proton PMRT around better cardiac and pulmonary dosimetry, and RADCOMP is testing that case on cardiac outcomes. This cohort offers a counterweight specific to implant reconstruction. It does not argue against protons in general. It argues that the reconstruction plan belongs in the modality decision, and that PBS combined with DTI is where the signal concentrates. Median follow-up of 42 and 47 months is not the weak point; confounding is. The finding would be wrong if the proton excess reflects referral pattern, surgical practice or era rather than dose. A cohort matched or stratified on reconstruction type, with superficial dose metrics reported, is what would settle it.