multiple randomized trials over the last four decades have established the equivalence of mastectomy and breast - conserving therapy ( bct ) in early stage breast cancer . more recently , accelerated partial breast irradiation ( apbi ) has become an acceptable means of delivering adjuvant radiation in early stage breast cancer patients who meet certain favorable criteria [ 2 , 3 ] . the benefits of apbi include shorter treatment times , sparing of a larger amount of normal tissue , and focal irradiation of the area highest at risk of recurrence around the tumor bed . initially , apbi consisted of interstitial catheter placement either via a template based approach or ultrasound guided free - hand approach   but these both required extensive expertise in their placement . after approval of mammosite ( hologic inc , bedford , ma , usa ) in 2002 and creation of newer multi - lumen devices such as contura ( hologic inc , bedford , ma , usa ) and savi ( cianna medical , aliso viejo , ca , usa ) , the rates of utilization of brachytherapy - based apbi ( b - apbi ) have continued to rise and now approach 11% in patients older than 50 years old who have undergone bct . multiple consensus guidelines have been developed to specify the appropriate candidates for b - apbi [ 7 , 8 , 9 , 10 ] . however , none of these address the role or feasibility of b - apbi in patients with existing breast implants who wish to undergo bct . given that now nearly 286,000 women undergo breast augmentation annually , an increase of 35% from 2000 to 2012 , the rates of patients with pre - existing implants who will be diagnosed with breast cancer will continue to rise . therefore , it is imperative to understand the clinical implications of b - apbi in this patient population . the reported experience with b - apbi in the setting of breast augmentation is limited [ 12 , 13 ] , with no known specific dose - constraints for breast implants to date . we had also previously reported the long - term outcome and dosimetric considerations in a patient with pre - existing breast implants who was treated with b - apbi . the present study expands on our work by examining the outcome and dosimetric evaluation of all the patients with breast augmentation who have been treated in our institution with b - apbi . to our knowledge , this is the first such reported series with early clinical outcomes in this patient population and detailed examination of the dosimetric parameters of breast implants in b - apbi . after obtaining appropriate institutional review board approval , we examined the database of patients who had undergone b - apbi at our institution from 2007 to 2013 and identified seven patients with existing breast implants at the time of surgery and throughout treatment . all patients had undergone lumpectomy prior to radiation treatment . due to the complexity of device placement adjacent to the breast implants , the breast surgeons placed the devices . each patient was treated using either a contura or savi device , and all of the devices were placed via a closed cavity approach . the planning computed tomography ( ct ) simulation was performed 48 - 72 hours following device placement in our department ( brilliance big bore , philips healthcare , andover , ma ) . all patients were simulated in the supine position , with the arm on the affected side raised over their head . a small amount of contrast ( 0.5 cc ) was added to the saline mixture filling the balloon for contura patients to improve visualization of the balloon on ct . given the variations in multi - lumen or catheter based brachytherapy , the integrity , orientation and size of the device , as well as distance to skin and rib were all verified prior to treatment planning before each treatment . treatment planning was completed using brachyvision treatment planning system ( varian , palo alto , ca , usa ) . the planning target volume for evaluation ( ptv_eval ) consisted of 1 cm of tissue surrounding the device but limited to a distance of 5 mm from the skin for the contura patients , 3 mm for the savi patients , and excluding the chest wall . we also attempted to minimize the v150 of normal breast tissue ( volume receiving 150% of prescribed dose ) to < 50 cc and v200 < 10 cc . the volume of air and seroma within the ptv_eval was less than 10% and this was also verified prior to each treatment . at the time of treatment planning , since no dose constraints were known for breast implants , no special considerations were made to exclude dose or ptv_eval from the implants . a total dose of 34 gy was prescribed to ptv_eval in 3.4 gy twice daily treatments using a high - dose - rate ir source . prior to each treatment , ct - based image guidance was used to verify the device size , position , and distance to skin . the volume of the breast implants was contoured retrospectively and dosimetric analysis were conducted based on the initial treatment plan on brachyvision . at the time of follow - up , harvard breast cosmesis scale was used to evaluate cosmetic outcome , which rates the outcome from excellent to poor depending on the difference compared to the untreated breast . follow - up pictures were obtained for visual comparison to the contralateral breast and the shape of the treated breast prior to treatment . all of the patients had undergone lumpectomy with the final pathology revealing invasive ductal carcinoma ( idc ) , ductal carcinoma in situ ( dcis ) , or both . the clinical stages ranged from tisn0m0 to t1cn0m0 and all patients with invasive disease had undergone sentinel lymph node biopsy . clinical characteristics and outcomes of the seven patients treated with brachytherapy - based accelerated partial breast irradiation ( b - apbi ) with existing breast implants idc  invasive ductal carcinoma , dcis  ductal carcinoma in situ , ajcc  american joint committee on cancer , 7 edition . cosmesis : based on the harvard / nsabp / rtog cosmesis grading scale ; late toxicity based on rtog late morbidity scoring schema ; tac  docetaxel , doxorubicin , cyclophosphamide at the time of last follow - up , all patients remained free of recurrence . figure 1 shows an axial image of each patient 's isodose lines along with their corresponding cosmetic outcome . five patients had a harvard breast cosmesis score of 1 or excellent , one patient had a score of 2 or good for difference in shape or size , and one had a score of 3 or fair for obvious difference in the size and shape of the treated breast . based on the rtog late radiation morbidity schema , three patients had a score of 0 , three had a score of 1 for presence of telangiectasia , hyperpigmentation or erythema , and one had a score of 2 for tender and bright erythema with moderate edema . left column shows a representative cross - section of their respective isodose lines along with the device location . red line represents 340 cgy ( 100% ) , white line 323 cgy ( 95% ) , green line 306 cgy ( 90% ) , blue line 272 cgy ( 80% ) . images do not necessarily correlate with the last follow - up date but represent the latest available images from each patient one of the patients had to undergo replacement of bilateral breast implants due to age - related leakage in bilateral breasts . another patient with cosmetic outcome of 3 experienced intra and extracapsular rupture of the treated implant almost 1.5 years after completion of apbi as evidenced by breast mri . an ultrasound of the breasts about 6 months after completion of her treatment had previously shown intact implants , therefore ruling out implant rupture due to apbi device placement . she also developed a cystic fluid collection close to her implant , which was aspirated and found to be benign . the remainder of the implants remained intact through the duration of the study . at last follow - up , all patients expressed satisfaction with their cosmetic outcomes and graded the overall appearance of the treated breast as excellent or good . the average device to breast implant surface in our population was 1.2 mm and the average device to skin surface was 4.4 mm ( range 2 - 7.6 mm ) . the mean volume of the ptv_eval amongst our patients was 55.9 cc and an air / seroma volume of 2.9 cc . the mean percentage of the ptv_eval volume receiving 90% , 95% , and 100% of the prescribed dose ( v90 , v95 , v100 ) was 97.7% , 95.9% , and 93.1% , respectively . the maximum skin dose ranged from 95.6% to 119% and the maximum rib dose 14.2% to 113.4% of the prescribed dose . the average volume of the normal breast tissue receiving 150% of the prescribed dose ( v150 ) and v200 was 20.1 cc and 9.4 cc , respectively . the average total breast implant volume was 279.3 cc and received an average mean dose of 12.1 gy , minimum dose of 1.9 gy , and a maximum dose of 234.1 gy . the percentage of breast implant volumes receiving 50% , 75% , 100% , 150% , and 200% of the prescribed dose ( implant v50 , v75 , v100 , v150 , v200 ) was 15.6% , 7.03% , 4.6% , 1.58% , and 0.46% , respectively . dosimetric characteristics of the seven patients treated with brachytherapy - based accelerated partial breast irradiation ( b - apbi ) with existing breast implants v50 , v75 , v100 , v150 , v200 represent the percentage of breast implant volumes receiving 50% , 75% , 100% , 150% , and 200% of the prescribed dose . all maximum doses were point doses to less than 1 cc of breast implant volume 
 table 3 shows the relative dose to the breast implant along with absolute volume of the implant receiving the same dose represented as v50 , etc . the two patients who did not have an excellent cosmetic outcome ( # 2 and # 7 ) also had the highest absolute volume of their implants receiving 50% of the prescribed dose as seen in figure 2 ( v50 to 72.9 and 111.9 cc , respectively ) . the higher treated volume was also apparent across the increasing dose ranges , although not as pronounced . patient # 7 , who has now experienced implant rupture , also had the highest maximum dose to the implant ( 535.1 gy ) and the highest mean dose ( 23.1 gy ) . however , patient # 2 's mean and maximum dose to the implant was closer to the average of the population ( 15.4 gy and 72.8 gy , respectively ) . outcomes based on the harvard scale , 1  excellent , 2  good , 3 v50 ( cc ) represents the absolute volume of breast implant that received 50% of the prescribed dose . all patients with excellent cosmetic outcome had v50 ( cc ) of less than 50 correlation of absolute and relative dose to existing breast implants and correlation with cosmetic outcome v50 , v75 , v100 , v150 , v200 represent the percentage of breast implant volumes receiving 50% , 75% , 100% , 150% , and 200% of the prescribed dose . v50 , v75 , v100 , v150 , and v200 represent the absolute volume of the breast implant receiving 50% , 75% , 100% , 150% , and 200% of the prescribed dose , respectively with the advent of b - apbi and its shorter treatment duration , an increasing number of women with breast cancer have access to adjuvant radiation therapy . per multiple national and international guidelines , b - apbi is now considered a standard of care option in women with early stage breast cancer [ 2 , 3 , 7 , 8 , 9 , 10 ] . although there are an increasing number of reports about the safety and efficacy of b - apbi , the appropriate patient population remains a contentious issue since only one randomized study has compared whole breast irradiation to b - apbi [ 16 , 17 ] . furthermore , data regarding treatment of patients with existing breast implants using b - apbi is limited . were the first to report on utilization of b - apbi in the setting of breast augmentation in the abstract form . even though they had a median follow - up of 36 months and observed an excellent or good cosmetic outcome in 97% of the patients , the majority were treated with interstitial implants . also recently published his interstitial technique in the presence of breast implants but no dosimetric data were reported . were the first to report on dosimetric parameters in a case report of a patient who had undergone treatment with b - apbi with existing breast implants but their follow - up was only 6 months post - treatment . comparison of studies reporting treatment with accelerated partial breast irradiation ( apbi ) in the setting of breast implants we had previously reported the longest follow - up to our knowledge at nearly 5 years post - treatment and suggested several dosimetric parameters relating to breast implants that could be of significance . we have now expanded on our original report by including all of our treated patients , with the longest reported follow - up in this patient population , and moreover adds several dosimetric parameters that can be useful while treating apbi with pre - existing breast implants . all of our patients have been free of disease to this date , even patients # 1 and # 4 who had focally positive margins . it is important to note that their margin status could be somewhat misleading since it was adjacent to the breast implant and a negative margin would have been nearly impossible to obtain , since there were no remaining tissue except the implant itself . b - apbi in those cases allowed those patients to maintain their existing breast implants with excellent cosmetic outcomes . the majority of the other patients also had excellent or good cosmetic outcome , except patient # 7 , who had a sizeable difference between her breasts even prior to start of her b - apbi and also has now experienced rupture of her implant on the treated side . importantly , all other women were able to maintain their breast implants except patient # 5 who had to undergo replacement of her implants bilaterally due to age - related leakage . there were no grade 3 or 4 late toxicities and all patients tolerated the treatments well . in terms of dose received by the breast implants , our values of mean dose of 12.1 gy , v50 of 15.6% , v75 of 7% , v100 of 4.6% , v150 of 1.58% , and v200 of 0.46% may represent benchmarks to be used for future treatment planning in patients with breast implants . overall , the lower the dose to the implant and the smaller the absolute implant volume treated , the more beneficial this appears to be in terms of late cosmetic outcome . as a result , b - apbi might be a better option compared to external beam radiation as well in patients who wish to maintain their implants since a smaller overall volume is treated . the correlation between volume of implant treated and cosmesis was apparent in our two patients who had the highest v50 along with the worst cosmetic outcomes . additionally , patient # 7 who had the highest mean , maximum , and absolute and relative dose to the implant went on to experience intra and extracapsular rupture of her implant , raising the possibility that there might exist an absolute implant dose tolerance . all of the patients with v50 of less than 50 cc had an excellent cosmetic outcome ( figure 2 ) , although this could potentially be a marker for overall lower dose to the implant . our patient with the worst cosmetic outcome also had the highest maximum and mean dose to the breast implant . furthermore , the distance from the device to the implant did not appear to have a significant impact on the cosmetic outcome as most devices were within 1 - 2 mm of the breast implants . we acknowledge that a larger population with longer follow - up is needed to confirm these findings . although the small number of patients in our series along with our limited follow - up limits our findings , we have nevertheless shown that b - apbi in patients with adjacent pre - existing breast implants is both safe and efficacious with good to excellent cosmetic outcomes in early clinical follow - up . ideally , the dose to the breast implants should be lowered as much as possible during the treatment planning process . based on the above results , unnecessary dose raises the possibility of future poorer cosmetic outcome and other complications like implant rupture . therefore , we believe that there is no need to expand the ptv_eval uniformly into the breast implant , since it contains no actual breast tissue and that ptv_eval can be pulled back as long as all of the necessary breast tissue is treated . additionally , the v50 can be used as a marker of appropriate amount of dose to the implant , with 50 cc or less receiving 50% of prescribed dose representing a reasonable marker . our other reported values of mean dose and the v50 , v75 , v100 , v150 , and v200 may be used as benchmarks to decrease the dose and any risks of possible complications . these parameters will need to be confirmed in a larger series with long - term follow - up . in the meantime , our dosimetric parameters have the added benefit of theoretically reducing the chances of capsular contracture , which is the most feared cosmetic complication in women with augmented breasts who undergo external beam whole breast irradiation . additionally , we have shown much better cosmetic outcomes compared to previously reported cases of whole breast irradiation in patients with existing breast implants , in which all twenty one patients were reported to have fair or poor cosmetic results . therefore , we conclude that with careful consideration during treatment planning and attention to tolerance of breast implants , b - apbi can be an excellent option for early stage breast cancer patients with augmented breasts who need to undergo adjuvant radiation therapy .