Postmastectomy Intensity Modulated Proton Therapy: 5-Year Oncologic and Patient-Reported Outcomes

Protons Versus Photons Postmastectomy Radiation Therapy Effects on Breast Reconstruction Outcomes and Dosimetry Analysis

PURPOSE

To compare the impact of proton versus photon postmastectomy radiation therapy (PMRT) on implant-related complications.

METHODS AND MATERIALS

The records of patients with breast cancer treated with mastectomy and expander and/or implant reconstruction followed by PMRT at our institution between 2011 and 2022 were reviewed. Patients were divided into 2 groups by treatment modality: proton and photon groups. All identified patients in the proton group were treated using conventional fractionation, and radiobiological effectiveness (RBE) was scaled to 1.1. Recorded complications included infection/skin necrosis requiring operative debridement, capsular contracture necessitating capsulotomy, absolute reconstruction failure implying complete loss of reconstruction, and overall reconstruction failure defined as multiple revisions leading to replacement of the implant or salvage autologous reconstruction. Subgroup analysis for patients in the proton group explored the correlation between dosimetric parameters and complications. Logistic regression and Cox proportional hazards regression models were used.

RESULTS

A total of 203 patients with an overall median follow-up of 4.7 years were identified. Among those 203 patients, 50 patients (25%) received proton PMRT, while 153 patients (75%) received photon PMRT. The complication rates for proton versus photon therapies were infection/necrosis (20% vs 13%; OR, 1.6; P = .2), capsular contracture (30% vs 10%; OR, 3.9; P < .001), absolute reconstruction failure (16% vs 12%; OR, 1.4; P = .4), and overall reconstruction failure (56% vs 36%; OR, 2.2; P = .01). Sensitivity analyses and time-to-event models yielded similar results. The median (Dmean) for clinical target volume, implant, and skin was 50.6, 50.8, and 6.7 Gy (RBE), respectively. The median hot spot (D1cc) for clinical target volume, implant, and skin was 52.8, 52.7, and 49.8 Gy (RBE), respectively. None of these parameters were significantly correlated with complications. The 5-year local failure cumulative incidence was 0% versus 4% (P = .13) for proton and photon cohorts, respectively.

CONCLUSIONS

Proton PMRT was associated with higher rates of implant capsular contracture and reconstruction failures than photon PMRT with comparable local control. No dosimetric parameter correlated with reconstruction complications.

Study of linear energy transfer effect on rib fracture in breast cancer patients receiving pencil-beam-scanning proton therapy

BACKGROUND

In breast cancer patients treated with pencil-beam scanning proton therapy (PBS), the increased linear energy transfer (LET) near the end of the proton range can affect nearby ribs. This may associate with a higher risk of rib fractures.

PURPOSE

To study the effect of LET on rib fracture in breast cancer patients treated with PBS using a novel tool of dose-LET volume histogram (DLVH).

METHODS

From a prospective registry of patients treated with post-mastectomy proton therapy to the chest wall and regional lymph nodes for breast cancer between 2015 and 2020, we retrospectively identified rib fracture cases detected after completing treatment. Contemporaneously treated control patients who did not develop rib fracture were matched to patients 2:1 considering prescription dose, boost location, reconstruction status, laterality, chest wall thickness, and treatment year. The DLVH index, V(d, l), defined as volume(V) of the structure with at least dose(d) and dose-averaged LET (l) (LETd), was calculated. DLVH plots between the fracture and control group were compared. Conditional logistic regression (CLR) model was used to establish the relation of V(d, l) and the observed fracture at each combination of d and l. The p-value derived from CLR model shows the statistical difference between fracture patients and the matched control group. Using the 2D p-value map derived from CLR model, the DLVH features associated with the patient outcomes were extracted.

RESULTS

Seven rib fracture patients were identified, and fourteen matched patients were selected for the control group. The median time from the completion of proton therapy to rib fracture diagnosis was 12 months (range 5-14 months). Two patients had grade 2 symptomatic rib fracture while the remaining 5 were grade 1 incidentally detected on imaging. The derived p-value map demonstrated larger V(0-36 Gy[RBE], 4.0-5.0 keV/µm) in patients experiencing fracture (p < 0.1). For example, the p-value for V(30 Gy[RBE], 4.0 keV/um) was 0.069.

CONCLUSION

In breast cancer patients receiving PBS, a larger volume of chest wall receiving moderate dose and high LETd may result in an increased risk of rib fracture.

Impact of Prepectoral Implant Placement and Radiation Modalities (Protons/Photons/Dosimetry) in Mastectomy Patients Undergoing Immediate Single Stage Direct-to-Implant Breast Reconstruction

PURPOSE

For patients with breast cancer receiving mastectomy with direct-to-implant (DTI) immediate breast reconstruction, placing the implant in the prepectoral or subpectoral plane remains debatable, especially in settings of postmastectomy radiation therapy (PMRT).

METHODS AND MATERIALS

We reviewed 3039 patients who underwent mastectomy and reconstruction at our institution between 2005 and 2020. Patients receiving DTI with and without PMRT were included. PMRT was delivered either with a photon (3-dimensional-conformal or volumetric arc therapy) or proton therapy, mainly with pencil-beam-scanning. All patients received conventional fractionation (50-50.4 Gy in 25-28 fractions). Primary endpoints were reconstruction complications defined as infection/necrosis requiring debridement; capsular contracture requiring capsulotomy; absolute reconstruction failure entailing permanent removal of the implant without replacement (ie, no salvage reconstruction); and overall reconstruction failure (removal of the implant for any complication with and without salvage reconstruction). Different subgroup analyses were done.

RESULTS

A total of 815 patients met inclusion criteria, with an overall median follow-up of 6.2 years. We found that there is no significant difference between prepectoral versus subpectoral for infection/necrosis (odds ratio [OR], 1.5; P = .3); capsular contracture (OR, 0.97; P = .9); absolute reconstruction failure (OR, 1.9; P = .12); and overall reconstruction failure (OR, 1.2; P = .5). Findings were confirmed using both logistic regression, time-to-event analysis, and multivariable analyses for the entire cohort and subgroups with and without PMRT. There was no significant difference between protons and photons in terms of infection/necrosis (OR, 1.6; P = .4) and absolute reconstruction failure (OR, 1.2; P = .7), but there were significantly higher risks for capsular contracture with protons (OR, 4.4; P < .001) and overall reconstruction failure compared with photons (OR, 2.0; P = .05). We did not find a significant correlation pattern between different dosimetry factors (the average dose, the maximum dose, and volume in cubic centimeter) in either the reconstructed chest wall target or the skin structure, about reconstruction complications, whether for proton or photon patients.

CONCLUSIONS

For patients receiving single-stage DTI reconstruction with and without PMRT, prepectoral implant placement had similar rates of complications and reconstruction failure compared with subpectoral reconstruction. Protons compared with photons did not increase the risk of infection/necrosis but significantly increased capsular contracture risks.

The Impact of Adjuvant Radiotherapy on Immediate Prepectoral Implant-Based Breast Reconstruction

BACKGROUND

Immediate prepectoral implant-based breast reconstruction (IBBR) rates have increased in recent years owing to improved cosmetic and psychological benefits. However, there is a lack of studies regarding complications rates following adjuvant radiotherapy (RT) among patients undergoing immediate prepectoral IBBR.

METHODS

We conducted a retrospective monocentric analysis of a cohort of consecutively treated patients who underwent NSM following immediate prepectoral IBBR at our institution between March 2017 and November 2021. Patient demographics, quality of life, complication rates, and oncological safety were evaluated in the RT and non-RT groups. Data analysis was performed using IBM SPSS Version 24 (IMB Corp., Armonk, NY, USA).

RESULTS

A total of 98 patients were examined: 70 were assigned to have prepectoral IBBR without RT and 28 to the group who had prepectoral IBBR with RT. There was a statistically significant difference in overall capsular contracture rate between the RT and non-RT group (18% vs. 4.3%, p=0.04). The total implant loss in the cohort was 4% (10.7% vs. 1.4%, p=0.05). We obtained a high percentages of all BREAST-Q categories in both groups; however, satisfaction with the breast and sexual well-being was higher in the non-RT group. The three-year overall survivals were 97.4% in the RT group and 98.5% in the non-RT group.

CONCLUSION

Our findings showed that patients in the RT group had a higher rate of capsular contracture and implant loss than those in the non-RT group. However, complication rates were within acceptable range and with accurate preoperative information patients have more benefits from immediate reconstruction showing excellent overall quality of life irrespectively of radiation.

LEVEL OF EVIDENCE III

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Dosimetric Correlation of Acute Radiation Dermatitis in Patients With Breast Cancer Undergoing Hypofractionated Proton Beam Therapy Using Pencil Beam Scanning

PURPOSE

Pencil-beam scanning (PBS) is a modern delivery technique used in proton beam therapy (PBT) to reduce normal tissue reactions. No dosimetric correlation between dermatitis and PBS has been reported for breast cancer. The current study aimed to investigate the factors associated with grade 2 or higher dermatitis in patients with breast cancer undergoing PBT using PBS.

METHODS

The medical data of 42 patients with breast cancer who underwent adjuvant radiotherapy between December 2019 and September 2023 were reviewed. All patients received hypofractionated radiotherapy (HFRT), either 26 Gy (relative biological effectiveness [RBE])/five fractions or 40.05 or 43.5 Gy (RBE)/15 fractions, for the whole breast/chest wall with or without nodal irradiation. The duration of acute radiation dermatitis was defined as within 90 days from the start of radiotherapy. The Kaplan-Meier method and Cox proportional hazards model were used for univariate and multivariate analyses of the actuarial rates of grade 2-3 dermatitis.

RESULTS

Twenty-two (52.4%) and 20 (47.6%) patients were diagnosed with grade 1 and 2 dermatitis, respectively. Multivariate analysis revealed a clinical target volume (CTV) ≥ of 320 cc (p = 0.035) and a skin dose of D10cc ≥ 38.3 Gy (RBE) (p = 0.009) as independent factors of grade 2 dermatitis. The 10-week cumulative grade 2 dermatitis rates were 88.2%, 39.4%, and 8.3% (p < 0.001) for patients with both high, either high, and neither high CTV and D10cc, respectively.

CONCLUSION

To the best of our knowledge, this is the first study on dosimetric correlations for dermatitis in patients with breast cancer who underwent hypofractionated PBT using PBS. In the era of HFRT, skin dose modulation using PBS may reduce the incidence of dermatitis.

Exploring Helium Ions' Potential for Post-Mastectomy Left-Sided Breast Cancer Radiotherapy

Proton therapy presents a promising modality for treating left-sided breast cancer due to its unique dose distribution. Helium ions provide increased conformality thanks to a reduced lateral scattering. Consequently, the potential clinical benefit of both techniques was explored. An explorative treatment planning study involving ten patients, previously treated with VMAT (Volumetric Modulated Arc Therapy) for 50 Gy in 25 fractions for locally advanced, node-positive breast cancer, was carried out using proton pencil beam therapy with a fixed relative biological effectiveness (RBE) of 1.1 and helium therapy with a variable RBE described by the mMKM (modified microdosimetric kinetic model). Results indicated that target coverage was improved with particle therapy for both the clinical target volume and especially the internal mammary lymph nodes compared to VMAT. Median dose value analysis revealed that proton and helium plans provided lower dose on the left anterior descending artery (LAD), heart, lungs and right breast than VMAT. Notably, helium therapy exhibited improved ipsilateral lung sparing over protons. Employing NTCP models as available in the literature, helium therapy showed a lower probability of grade ≤ 2 radiation pneumonitis (22% for photons, 5% for protons and 2% for helium ions), while both proton and helium ions reduce the probability of major coronary events with respect to VMAT.

Proton Reirradiation for High-Risk Recurrent or New Primary Breast Cancer

Radiotherapy is an integral component of multidisciplinary breast cancer care. Given how commonly radiotherapy is used in the treatment of breast cancer, many patients with recurrences have received previous radiotherapy. Patients with new primary breast cancer may also have received previous radiotherapy to the thoracic region. Curative doses and comprehensive field photon reirradiation (reRT) have often been avoided in these patients due to concerns for severe toxicities to organs-at-risk (OARs), such as the heart, lungs, brachial plexus, and soft tissue. However, many patients may benefit from definitive-intent reRT, such as patients with high-risk disease features such as lymph node involvement and dermal/epidermal invasion. Proton therapy is a potentially advantageous treatment option for delivery of reRT due to its lack of exit dose and greater conformality that allow for enhanced non-target tissue sparing of previously irradiated tissues. In this review, we discuss the clinical applications of proton therapy for patients with breast cancer requiring reRT, the currently available literature and how it compares to historical photon reRT outcomes, treatment planning considerations, and questions in this area warranting further study. Given the dosimetric advantages of protons and the data reported to date, proton therapy is a promising option for patients who would benefit from the added locoregional disease control provided by reRT for recurrent or new primary breast cancer.

Detection of Early Myocardial Dysfunction by Imaging Biomarkers in Cancer Patients Undergoing Photon Beam vs. Proton Beam Radiotherapy: A Prospective Study

1. Background: We sought to determine acute and subacute changes in cardiac function after proton beam (PBT) and photon beam (PhT) radiotherapy (RT) using conventional and two-dimensional speckle tracking echocardiography (2D-STE) in patients with malignant breast and thoracic tumors. 2. Methods: Between March 2016 and March 2017, 70 patients with breast or thoracic cancer were prospectively enrolled and underwent transthoracic echocardiography with comprehensive strain analysis at pretreatment, mid-treatment, end of treatment, and 3 months after RT. 3. Results: PBT was used to treat 44 patients; PhT 26 patients. Mean ± SD age was 55 ± 12 years; most patients (93%) were women. The median (interquartile range) of the mean heart dose was lower in the PBT than the PhT group (47 [27-79] vs. 217 [120-596] cGy, respectively; p < 0.001). Ejection fraction did not change in either group. Only the PhT group had reduced systolic tissue Doppler velocities at 3 months. 2D-STE showed changes in endocardial and epicardial longitudinal, radial, and circumferential early diastolic strain rate (SRe) in patients undergoing PhT (global longitudinal SRe, pretreatment vs. end of treatment (p = 0.04); global circumferential SRe, pretreatment vs. at 3-month follow-up (p = 0.003); global radial SRe, pretreatment vs. at 3-month follow-up (p = 0.02) for endocardial values). Epicardial strain values decreased significantly only in patients treated with PhT. Patients in the PhT group had a significant decrease in epicardial global longitudinal systolic strain rate (GLSRs) (epicardial GLSRs, at baseline vs. at end of treatment [p = 0.009]) and in GCSRe and GRSRe (epicardial GCSRe, at baseline vs. at 3-month follow-up (p = 0.02); epicardial GRSRe, at baseline vs. at 3-month follow-up (p = 0.03)) during treatment and follow-up. No changes on 2D-STE were detected in the PBT group. 4. Conclusions: Patients who underwent PhT but not PBT had reduced tissue Doppler velocities and SRe values during follow-up, suggesting early myocardial relaxation abnormalities. PBT shows promise as a cardiac-sparing RT technology.