MammoSite Breast Brachytherapy Research Articles

Treatment Efficacy With Accelerated Partial Breast Irradiation (APBI): Final Analysis of the American Society of Breast Surgeons MammoSite Breast Brachytherapy Registry Trial

Treatment Efficacy With Accelerated Partial Breast Irradiation (APBI): Final Analysis of the American Society of Breast Surgeons MammoSite Breast Brachytherapy Registry Trial

Treatment Efficacy with Accelerated Partial Breast Irradiation (APBI): Final Analysis of the American Society of Breast Surgeons MammoSite® Breast Brachytherapy Registry Trial

The purpose of this study was to examine data on treatment efficacy, cosmesis and toxicities for the final analysis of the American Society of Breast Surgeons MammoSite(®) breast brachytherapy registry trial. A total of 1,449 cases of early-stage breast cancer underwent breast conserving therapy. The single-lumen MammoSite(®) device was used to deliver accelerated partial breast irradiation (APBI) (34 Gy in 3.4 Gy fractions). Of these, 1,255 cases (87 %) had invasive breast cancer (IBC) and 194 cases had DCIS. Median follow-up was 63.1 months with 45 % of all patients having follow-up of 6 years or longer. There were 41 cases (2.8 %) that developed an ipsilateral breast tumor recurrence (IBTR) for a 5-year actuarial rate of 3.8 % (3.7 % for IBC and 4.1 % for DCIS). Tumor size (odds ratio [OR] = 1.1, p = 0.03) and estrogen receptor negativity (OR = 3.0, p = 0.0009) were associated with IBTR, while a trend was noted for positive margins (OR = 2.0, p = 0.06) and cautionary/unsuitable status compared with suitable status (OR = 1.8, p = 0.07). The percentage of patients with excellent/good cosmetic results at 60, 72, and 84 months was 91.3, 90.5, and 90.6 %, respectively. The overall rates of fat necrosis and infections remained low at 2.5 and 9.6 % with few late toxicity events beyond 2 years. The overall symptomatic seroma rate was 13.4 and 0.6 % beyond 2 years. The final analysis of treatment efficacy, cosmesis, and toxicity from the American Society of Breast Surgeons MammoSite(®) breast brachytherapy registry trial confirms previously noted excellent results and compares favorably with other forms of APBI with similar follow-up and to outcomes seen in selected patients treated with whole breast irradiation.

Six-Year Analysis of Treatment-Related Toxicities in Patients Treated with Accelerated Partial Breast Irradiation on the American Society of Breast Surgeons MammoSite Breast Brachytherapy Registry Trial

The American Society of Breast Surgeons (ASBrS) enrolled women in a registry trial to prospectively study patients treated with the MammoSite RTS device. This report presents 6-year data on treatment-related toxicities from the trial. A total of 1449 primary early-stage breast cancers were treated with accelerated partial breast irradiation (APBI) using the MammoSite device (34 Gy in 10 fractions) in 1440 women. Of these, 1255 case (87%) had invasive breast cancer (IBC) (median size = 10 mm) and 194 cases (13%) had ductal carcinoma in situ (DCIS) (median size = 8 mm). Median follow-up was 59 months. Fisher exact test was performed to correlate categorical covariates with toxicity. Breast seromas were reported in 28% of cases (35.5% with open cavity and 21.7% with closed cavity placement). Also, 13% of all treated breasts developed symptomatic seromas, and 77% of these seromas developed during the 1st year after treatment. There were 172 cases (11.9%) that required drainage to correct. Use of chemotherapy and balloon fill >50 cc were associated with the development of symptomatic seromas. Also, 2.3% of patients developed fat necrosis (FN). The incidence of FN during years 1 and 2 were 0.9% and 0.8%, respectively. Seroma formation, use of hormonal therapy, breast infection, and A/B cup size were associated with fat necrosis. There were 138 infections (9.5%) recorded; 98% occurred during the 1st year after treatment. Chemotherapy and seroma formation were associated with the development of infections. Treatment-related toxicities 6 years after treatment with APBI using the MammoSite device are similar to those reported with other forms of APBI with similar follow-up.

Rebuttal to Dr. Cuttino

What has not been mentioned in the reference to treatment volume with the SAVI, published in the same papers, is that 5% of these patients had skin bridges of <3 mm and 27% <7 mm, and 7% had both chest wall and skin <7 mm. When normal tissues are that close, the PTV is trimmed (per B-39 guidelines, excluding pectoralis/chestwall and 5-mm margin from the skin) leading to smaller targets, or PTV-EVALs ( [1] Yashar C.M. Blair S. Wallace A. et al. Initial clinical experience with the Strut-Adjusted Volume Implant brachytherapy applicator for accelerated partial breast irradiation. Brachytherapy. 2009; 8: 367-372 Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar ). Again, published data demonstrate that based on device size without the need to spare normal tissues, the average-treated PTV-EVAL is equivalent for the 8-1 SAVI, the 10-1 SAVI, and the Contura and MammoSite balloons. Therefore, the argument that the balloon devices treat more tissue is just not based on the published data ( 1 Yashar C.M. Blair S. Wallace A. et al. Initial clinical experience with the Strut-Adjusted Volume Implant brachytherapy applicator for accelerated partial breast irradiation. Brachytherapy. 2009; 8: 367-372 Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar , 2 Dickler A. Kirk M. Choo J. et al. Treatment volume and dose optimization of MammoSite breast brachytherapy applicator. Int J Radiat Oncol Biol Phys. 2004; 59: 469-474 Abstract Full Text Full Text PDF PubMed Scopus (69) Google Scholar , 3 Arthur D.W. Vicini F.A. Todor D.A. et al. Improvements in critical dosimetric endpoints using the Contura multilumen balloon breast brachytherapy catheter to deliver accelerated partial breast irradiation: Preliminary dosimetric findings of a phase IV trial. Int J Radiat Oncol Biol Phys. 2011; 79: 26-33 Abstract Full Text Full Text PDF PubMed Scopus (32) Google Scholar ).

Six-year Analysis of Treatment-related Toxicities by the American Society of Breast Surgeons MammoSite Breast Brachytherapy Registry Trial in Patients Treated with Accelerated Partial Breast Irradiation

Six-year Analysis of Treatment-related Toxicities by the American Society of Breast Surgeons MammoSite Breast Brachytherapy Registry Trial in Patients Treated with Accelerated Partial Breast Irradiation

Factors Associated With Optimal Cosmetic Results at 60 Months in Patients Treated With Accelerated Partial Breast Irradiation on the American Society of Breast Surgeons MammoSite Breast Brachytherapy Registry Trial

Factors Associated With Optimal Cosmetic Results at 60 Months in Patients Treated With Accelerated Partial Breast Irradiation on the American Society of Breast Surgeons MammoSite Breast Brachytherapy Registry Trial

Ductal carcinoma in situ treated with breast‐conserving surgery and accelerated partial breast irradiation

The purpose of this study was to determine the ipsilateral breast tumor recurrence (IBTR) in ductal carcinoma in situ (DCIS) patients treated in the American Society of Breast Surgeons MammoSite Breast Brachytherapy Registry Trial who met the criteria for E5194 treated with local excision and adjuvant accelerated partial breast irradiation (APBI). A total of 194 patients with DCIS were treated between 2002 and 2004 in the Mammosite registry trial; of these, 70 patients met the enrollment criteria for E5194: 1) low to intermediate grade (LIG)-pathological size >0.3 but <2.5 cm and margins ≥3 mm (n = 41) or 2) high grade (HG)-pathological size <1 cm and margins ≥3 mm (n = 29). All patients were treated with lumpectomy followed by adjuvant APBI using MammoSite. Median follow-up was 52.7 months (range, 0-88.4). SAS (version 8.2) was used for statistical analysis. In the LIG cohort, the 5-year IBTR was 0%, compared with 6.1% at 5 years in E5194. In the HG cohort, the 5-year IBTR was 5.3%, compared with 15.3% at 5 years in E5194. The overall 5-year IBTR was 2%, and there were no cases of elsewhere or regional failures in the entire cohort. The 5-year contralateral breast event rate was 0% and 5.6% in LIG and HG patients, respectively (compared with 3.5% and 4.2%, respectively, in E5194). This study found that patients who met the criteria of E5194 treated with APBI had extremely low rates of recurrence (0% vs 6.1% in the LIG cohort and 5.3% vs 15.3% in the HG cohort).

Evaluation of the Effects of Balloon Deformation and Position of the Source on Dosimetry in High-dose Rate Mammosite Breast Brachytherapy

Evaluation of the Effects of Balloon Deformation and Position of the Source on Dosimetry in High-dose Rate Mammosite Breast Brachytherapy

Five‐year outcome of patients classified using the American Society for Radiation Oncology consensus statement guidelines for the application of accelerated partial breast irradiation

The American Society for Radiation Oncology (ASTRO) consensus statement (CS) for the application of accelerated partial breast irradiation (APBI) was applied to patients who were treated with this technique on the American Society of Breast Surgeons MammoSite Registry Trial to determine potential differences in clinical outcome based on classification group. Patients were classified based on the CS groups of "suitable," "cautionary," and "unsuitable." Rates of ipsilateral breast tumor recurrence (IBTR), regional lymph node failure, distant metastases, disease-free survival, cause-specific survival, and overall survival were assessed. Of the 1449 cases who were treated, 1025 patients (71%) could be classified according to the CS groupings, including 419 patients (41%) who fit the "suitable" criteria, 430 patients (42%) who fit the "cautionary" criteria, and 176 patients (17%) who fit the "unsuitable" criteria. At a median follow-up of 53.5 months, the 5-year actuarial rates of IBTR for the "suitable," "cautionary," and "unsuitable" groups were 2.59%, 5.43%, and 5.28%, respectively (P = .1884). Univariate analysis of factors potentially associated with IBTR indicated that negative estrogen receptor status was the only variable associated with IBTR among patients with invasive breast cancer (odds ratio [OR], 4.01; P = .0003). Larger tumor size was associated with a greater risk of distant metastasis (OR, 3.05; P = .0001). Among patients with ductal carcinoma in situ, only age <50 years and close-positive margins were associated with IBTR (OR, 1.12 [P = .0079] and OR, 7.81 [P = .0131], respectively). The ASTRO CS groupings did not differentiate a subset of patients with a significantly worse rate of IBTR when they were treated with the MammoSite breast brachytherapy catheter to deliver APBI.

Five-Year Analysis of Treatment Efficacy and Cosmesis by the American Society of Breast Surgeons MammoSite Breast Brachytherapy Registry Trial in Patients Treated With Accelerated Partial Breast Irradiation

To present 5-year data on treatment efficacy, cosmetic results, and toxicities for patients enrolled on the American Society of Breast Surgeons MammoSite breast brachytherapy registry trial. A total of 1440 patients (1449 cases) with early-stage breast cancer receiving breast-conserving therapy were treated with the MammoSite device to deliver accelerated partial-breast irradiation (APBI) (34 Gy in 3.4-Gy fractions). Of 1449 cases, 1255 (87%) had invasive breast cancer (IBC) (median size, 10 mm) and 194 (13%) had ductal carcinoma in situ (DCIS) (median size, 8 mm). Median follow-up was 54 months. Thirty-seven cases (2.6%) developed an ipsilateral breast tumor recurrence (IBTR), for a 5-year actuarial rate of 3.80% (3.86% for IBC and 3.39% for DCIS). Negative estrogen receptor status (p=0.0011) was the only clinical, pathologic, or treatment-related variable associated with IBTR for patients with IBC and young age (<50 years; p=0.0096) and positive margin status (p=0.0126) in those with DCIS. The percentage of breasts with good/excellent cosmetic results at 60 months (n=371) was 90.6%. Symptomatic breast seromas were reported in 13.0% of cases, and 2.3% developed fat necrosis. A subset analysis of the first 400 consecutive cases enrolled was performed (352 with IBC, 48 DCIS). With a median follow-up of 60.5 months, the 5-year actuarial rate of IBTR was 3.04%. Treatment efficacy, cosmesis, and toxicity 5 years after treatment with APBI using the MammoSite device are good and similar to those reported with other forms of APBI with similar follow-up.

Status of Accelerated Partial Breast Irradiation

Breast-conserving therapy is accepted as a standard of care option for patients with early-stage breast cancer. However, studies examining patterns of failure after treatment suggest that a lengthy course of adjuvant whole breast irradiation delivered as a component of breast-conserving therapy may not always be necessary; indeed, in appropriately selected patients, radiation therapy delivered only to the tumor bed may be acceptable. Several modalities of delivering accelerated partial breast irradiation (APBI) have been developed, the most prevalent being multi-catheter interstitial brachytherapy, the MammoSite breast brachytherapy catheter (Hologic Corporation, Bedford, MA) and three-dimensional conformal external-beam radiation therapy. The purpose of this article is to review the published experiences on the most common modalities of delivering APBI and to outline the current open national phase 3 trial. To date, phase 1/2 studies have demonstrated excellent local control and cosmetic outcomes in early-stage breast cancer patients treated with APBI. As increasing knowledge is accumulated regarding the efficacy and safety of APBI, a consensus will emerge regarding its potential replacement of whole breast irradiation in selected early-stage breast cancer patients.

A Comparison of Skin and Chest Wall Dose Delivered With Multicatheter, Contura Multilumen Balloon, and MammoSite Breast Brachytherapy

Skin and chest wall doses have been correlated with toxicity in patients treated with breast brachytherapy . This investigation compared the ability to control skin and chest wall doses between patients treated with multicatheter (MC), Contura multilumen balloon (CMLB), and MammoSite (MS) brachytherapy. 43 patients treated with the MC technique, 45 patients treated with the CMLB, and 83 patients treated with the MS were reviewed. The maximum doses delivered to the skin and chest wall were calculated for all patients. The mean maximum skin doses for the MC, CMLB, and MS were 2.3 Gy (67% of prescription dose), 2.8 Gy (82% of prescription dose), and 3.2 Gy per fraction (94% of prescription dose), respectively. Although the skin distances were similar (p = 0.23) for the two balloon techniques, the mean skin dose with the CMLB was significantly lower than with the MS (p = 0.05). The mean maximum rib doses for the MC, CMLB, and MS were 2.3 Gy (67% of prescription dose), 2.8 Gy (82% of prescription dose), and 3.6 Gy per fraction (105% of prescription dose), respectively. Again, the mean rib dose with the CMLB was significantly lower than with the MS (p = 0.002). The MC and CMLB techniques are associated with significantly lower mean skin and rib doses than is the MS. Treatment with the MS was associated with significantly more patients receiving doses to the skin or rib in excess of 125% of the prescription. Treatment with the CMLB may prove to yield less normal tissue toxicity than treatment with the MS.

Partial Breast Irradiation as an Alternative to Whole Breast Radiation

Accelerated partial breast irradiation (APBI) is a novel method of post-operative radiotherapy that consists of irradiation of a limited volume of mammary gland immediately surrounding the tumour bed over a shorter time than whole breast irradiation. Several modalities are currently being explored as a means to deliver APBI, including multicatheter interstitial brachytherapy, the MammoSite breast brachytherapy catheter (Cytyc Corporation, Marlborough, MA), intraoperative radiation therapy and 3D conformal external-beam radiation therapy. To date, although still limited, randomised evidence is encouraging about the future role of APBI since it does not seem to jeopardise overall survival in patients with early breast cancer. Additional phase III studies are under way to determine the subgroups of patients who will really benefit from APBI.

Five-year Analysis of Treatment Efficacy and Cosmesis by the American Society of Breast Surgeons MammoSite Breast Brachytherapy Registry Trial in Patients Treated with Accelerated Partial Breast Irradiation (APBI)

Five-year Analysis of Treatment Efficacy and Cosmesis by the American Society of Breast Surgeons MammoSite Breast Brachytherapy Registry Trial in Patients Treated with Accelerated Partial Breast Irradiation (APBI)

A dosimetric analysis comparing electron beam with the MammoSite brachytherapy applicator for intact breast boost

Introduction Electron beam radiation is the modality most often used to deliver an operative bed boost to breast cancer patients after completing whole breast radiation. However, electrons can potentially provide inadequate coverage. The MammoSite breast brachytherapy applicator may provide dosimetric advantages in the delivery of an operative bed boost and its role in this setting is not yet defined. Materials and methods The study population consisted of 15 patients with early stage breast cancer treated with partial breast irradiation (PBI) using the MammoSite device. For each patient, a theoretical boost plan using electrons and a second theoretical boost plan using the MammoSite applicator were created. To assess the adequacy of each boost plan, the PTV V90, PTV V95, and PTV V100 were calculated. To assess dose to normal tissues, the ipsilateral breast V50, ipsilateral lung V30, and heart V20 were calculated. Results The mean PTV V100 for the MammoSite boost was 95.5%, compared to 77.4% for the electron boost ( p < 0.001). The mean PTV V95 was 97.8%, compared to 93.3% for the electron boost ( p = 0.02). The mean PTV V90, mean breast V50, mean lung V30, and mean heart V20 were not statistically different for MammoSite compared to electrons. Conclusions A tumor bed boost using the MammoSite breast brachytherapy applicator provides superior target coverage and delivers similar doses to the ipsilateral breast and lung compared to a boost delivered with electrons. More investigation into the role of balloon brachytherapy in the delivery of a breast boost is warranted.

Factors Associated with Optimal Cosmetic Results at 36 Months in Patients Treated with Accelerated Partial Breast Irradiation (APBI) on the American Society of Breast Surgeons (ASBrS) MammoSite® Breast Brachytherapy Registry Trial

To evaluate factors associated with optimal cosmetic results at 36 months for early-stage breast cancer patients enrolled on the American Society of Breast Surgeons (ASBrS) MammoSite Breast Brachytherapy registry trial. 1,440 patients (1,449 cases) with early-stage breast cancer undergoing breast-conserving therapy were treated with the MammoSite radiation therapy system (RTS) brachytherapy catheter to deliver adjuvant accelerated partial breast irradiation (APBI) (34 Gy in 3.4-Gy fractions). Cosmetic outcome was evaluated at each follow-up visit and dichotomized as excellent/good or fair/poor. Median follow-up for surviving patients was 43.0 months (range 0-73.0 months). The percentage of patients with good/excellent cosmetic results at 12, 24, 36, and 48 months were as follows: 94.5% (n = 950/1,005), 93.8% (n = 781/833), 93.1% (n = 683/734), and 90.4% (n = 520/575), respectively. Three-year absolute rates of good/excellent cosmesis were as follows: breast-related wound infection (BWI) (83.3%) versus no BWI (94%), <7 mm skin spacing (87.5%) versus >or=7 mm skin spacing (93.6%). Using multiple regression analysis, factors predictive of worse cosmetic outcome at 36 months included smaller skin spacing [odds ratio (OR) 1.06, confidence interval (CI) 1.01-1.12] and BWI (OR 0.33, CI 0.16-0.70). A predictive model developed showed that presence of a BWI, use of chemotherapy, and skin spacing had the most effect on cosmetic outcomes. However, in patients that did not develop a breast infection, skin spacing and use of chemotherapy had the most effect on cosmesis. APBI delivered by MammoSite brachytherapy lead to good/excellent cosmesis in 93% of patients with 3-year follow-up. Breast wound infection, use of chemotherapy, and skin spacing were found to be the three most important predictors of cosmesis at 36 months in our cohort of patients.

Four-year clinical update from the American Society of Breast Surgeons MammoSite brachytherapy trial

Background We present a 4-year update on the efficacy, cosmetic results, and complications of MammoSite breast brachytherapy in patients enrolled in the American Society of Breast Surgeons registry trial. Methods A total of 1,449 breasts in 1,440 patients with early stage breast cancer undergoing breast-conserving therapy were treated with adjuvant, accelerated partial breast irradiation (APBI) (34 Gy in 3.4-Gy fractions) delivered with the MammoSite device. The median follow-up period for the entire group was 36.1 months. Results The 3-year actuarial rate of ipsilateral breast tumor recurrence was 2.15%. The 3-year actuarial rate of axillary recurrence was .36%. Complication rates were as follows: infection, 9.5%; seroma, 26.8% (symptomatic seroma, 12.7%); and fat necrosis, 2.0%. The percentages of breasts with good or excellent cosmetic results were as follows: 12 months, 95%; 24 months, 94%; 36 months, 94%; and 48 months, 91%. Conclusions Locoregional control, complications, and cosmetic outcomes from MammoSite APBI at the 4-year update are acceptable and similar to results seen with other forms of APBI.

Skin and chest wall dose with multi-catheter and MammoSite breast brachytherapy: Implications for late toxicity

PurposeAccelerated partial breast irradiation (APBI) continues to increase in popularity. Up to 14% of patients treated with the MammoSite (MS) report some degree of chronic pain, which may be related to chest wall toxicity. Reports from several institutions using the multicatheter (MC) technique have not shown associated elevated chest wall toxicity. Additionally, a recent investigation has suggested that increased toxicity may occur with the MS when the dose to the chest wall exceeds 125% of the prescribed dose. This investigation compares the skin and chest wall doses of a cohort of patients treated with the MC technique to a group treated with the MS. Methods and materialsThe dosimetric data for 43 patients treated with the MC technique and 83 patients treated with the MS at Virginia Commonwealth University were reviewed. This cohort represents consecutively treated patients from our most recent experience to minimize any learning curve effect on dosimetry. Plans were generated using 3D software (Brachyvision, Varian Medical Systems, Inc., Palo Alto, CA). Multiple dwell positions were used for all MS patients to optimize dose delivery. The minimum distances from the planning target volume to the skin and chest wall were calculated, as well as the maximum doses delivered to the skin and chest wall. ResultsThe mean skin distances for patients treated with the MC technique and the MS were 0.5 and 0.9cm, respectively (p<0.002). Despite the significantly smaller mean skin distance, the mean skin dose for the MC technique was only 2.3Gy per fraction (67% of prescription dose). The mean skin dose for the MS was 3.2Gy per fraction (94% of prescription dose, p<0.001). The mean chest wall distance was 0.9cm for the MC technique and 1.0cm for the MS (p=0.55). Again, the mean chest wall dose for the MC technique was only 2.3Gy per fraction (67% of prescription dose). The mean skin dose for the MS was 3.6Gy per fraction (105% of prescription dose, p<0.001). The percentage of patients receiving skin doses in excess of 125% for the MC and MS were 0% and 9.6%, respectively. The percentage of patients receiving chest wall doses in excess of 125% for the MC and MS were 0% and 38.6%, respectively. ConclusionThe MC technique results in more conformal dose delivery, with significantly lower mean skin and chest wall doses. Treatment with the MS was associated with significantly more patients receiving doses to the skin or chest wall in excess of 125% of the prescription. Given the limited followup available for the MS, and the significant dose delivered to the chest wall, the use of this device may be associated with a higher incidence of late chest wall toxicity than previously expected.

Dose volume histogram analysis of normal structures associated with accelerated partial breast irradiation delivered by high dose rate brachytherapy and comparison with whole breast external beam radiotherapy fields

PurposeTo assess the radiation dose delivered to the heart and ipsilateral lung during accelerated partial breast brachytherapy using a MammoSite™ applicator and compare to those produced by whole breast external beam radiotherapy (WBRT).Materials and methodsDosimetric analysis was conducted on patients receiving MammoSite breast brachytherapy following conservative surgery for invasive ductal carcinoma. Cardiac dose was evaluated for patients with left breast tumors with a CT scan encompassing the entire heart. Lung dose was evaluated for patients in whom the entire lung was scanned. The prescription dose of 3400 cGy was 1 cm from the balloon surface. MammoSite dosimetry was compared to simulated WBRT fields with and without radiobiological correction for the effects of dose and fractionation. Dose parameters such as the volume of the structure receiving 10 Gy or more (V10) and the dose received by 20 cc of the structure (D20), were calculated as well as the maximum and mean doses received.ResultsFifteen patients were studied, five had complete lung data and six had left-sided tumors with complete cardiac data. Ipsilateral lung volumes ranged from 925–1380 cc. Cardiac volumes ranged from 337–551 cc. MammoSite resulted in a significantly lower percentage lung V30 and lung and cardiac V20 than the WBRT fields, with and without radiobiological correction.ConclusionThis study gives low values for incidental radiation received by the heart and ipsilateral lung using the MammoSite applicator. The volume of heart and lung irradiated to clinically significant levels was significantly lower with the MammoSite applicator than using simulated WBRT fields of the same CT data sets.Trial registrationDana Farber Trial Registry number 03-179

Late chest wall toxicity after MammoSite ® breast brachytherapy

Purpose Accelerated partial breast irradiation (APBI) with the MammoSite ® breast brachytherapy (MBB) system is being investigated as an alternative to whole breast radiation in breast conservation therapy (BCT) at multiple centers worldwide. The newness of MBB means a complete understanding of long-term toxicity, particularly involving the chest wall, has yet to be completely articulated. We report the first pathologic rib fractures associated with MBB and dosimetric analysis of the original treatment plans. Methods and Materials As part of ongoing quality assurance, we reviewed the records of 129 sequential patients who underwent MBB for breast cancer and identified those who subsequently had clinically significant and radiographically documented rib fracture(s) involving the ipsilateral chest wall. Equivalent tolerance doses yielding a 5% and 50% risk of rib toxicity within 5 years from treatment with 10 fractions (as with MBB) were previously calculated using the linear quadratic equation based on 2 Gy per fraction treatments delivered to one-third of the rib volume (TD5/5 = 37 Gy; TD50/5 = 44 Gy). The original radiation therapy plans were evaluated vis-à-vis the plane films or PET/CT images documenting the osseous abnormalities and presenting complaints to find the specific fractured ribs. The specific effected ribs were contoured on the planning CT in “bone windows” using the Nucletron MicroSelectron-classic V2 (Nucletron B.V., Veenendaal, The Netherlands) for this analysis and the original patient treatments. With these datasets, we determined the dose–volume characteristics of the effected ribs including maximal dose encompassing the entire rib on one CT slice, V 20Gy, V 30Gy, V 37Gy, V 44Gy , D 50, D 25, and D 5 (the mean dose to 50%, 25%, and 5% of the rib). Results Between May 2002 and August 2007, three of 105 patients with a minimum of 6-months follow-up who underwent adjuvant APBI by MBB were found to have a total of five treatment-related rib fractures. The average dose–volume characteristics from the original plans were as follows: D 50 = 22.1 Gy, D 25 = 32.2 Gy, D 5 = 41.6 Gy, max dose to 1 cc = 34.8, D max (to 0.1 cc) = 45.6 Gy, V 20 Gy = 57.4%, V 30 Gy = 30.8%, V 37 Gy = 15.9%, V 44 Gy = 6.6%, and max dose through rib = 35.8 Gy. Two patients sustained two rib fractures and 1 patient had a single rib fracture. Four of five fractures occurred in postmenopausal patients and two of five fractures occurred in a patient with a history of osteoporosis and exposure to adjuvant chemotherapy. Conclusions Fractures occurred in ribs with V 37 Gy and V 44 Gy each well below 33%. As long-term toxicity data accrue from APBI series, the traditional models for estimating the biologic equivalent dose may benefit from refinements that specifically address the unique radiobiologic and physical properties intrinsic to high-dose-rate brachytherapy for breast conservation therapy.