breast - conserving therapy ( bct ) has traditionally included whole breast irradiation after tumor lumpectomy . this approach is based on the premise that irradiation will eliminate residual foci of tumor adjacent to the surgical bed , and will reduce the risk of recurrence from areas in situ or infiltrating carcinoma elsewhere in the breast . growing body of data provides compelling evidence that irradiation after lumpectomy is effective only at the site of initial involvement , and thus may safely be limited to tissues immediately surrounding the excision cavity , with an expected local control rate comparable to the rate achieved with whole - breast irradiation [ 14 ] . most studies of phases i and ii using this technique have demonstrated acceptable 5- and 10-year rates of local control , and good cosmetic effect in highly selected , low - risk patients [ 5 , 6 ] . the mammosite applicator ( hologic inc . , bedford , ma , usa ) was one of the first devices designed to address these issues . one of the major limitations with the use of the mammosite to deliver apbi , relates to its single lumen design , and the fixed relationship between the geometry of balloon placement and the dose delivered . , aliso viejo , ca , usa ) was designed to provide additional options to achieve more idealized dosimetric goals ( fig . 1 ) . through the use of four additional lumens that are offset from the single central catheter lumen , dose shaping is possible . published dosimetric data have demonstrated the device 's ability to significantly reduce skin and rib doses , and improve on other treatment restrictions ( as a result of insufficient skin spacing or suboptimal conformance [ 711 ] ) . basing on our own studies , we verified dose distribution parameters for contura ( senorx , inc . ) , and artificially created single - lumen balloon applicator used for the same patient , applying two optimization algorithms : inverse planning simulated annealing ( ipsa ) and dose point optimization with distance option . from november 2009 to march 2011 we have treated 24 patients using contura multi - lumen breast balloon ( senorx , inc . ) . patients were treated with total dose of 34 gy in 10 fraction , 2 fractions per day in 5 consecutive days , excluding weekends in accelerated partial breast irradiation ( apbi ) mode . treatment plans were prepared using computed tomography ( ct ) imaging with slice thickness of 1 mm . ptv_eval was the volume in which the dose was reported , and was limited to 5 mm from the skin . if the skin or pectoral muscle were overlapping the margin creating planning target volume ( ptv ) , the overlapping parts were subtracted ( fig . the balloon was subtracted as well , as the doses inside the balloon were unlimited . anatomy reconstruction in contura application before each fraction , the dressing covering the breast of the patient and the applicator was removed . the configuration of the orientation line on the applicator , in relation to the line drawn on skin of the patient was checked just before the ct planning . air and fluid was removed before each fraction to keep the condition from the time of planning . oncentra masterplan vs 3.2 ( nucletron , an elekta company , elekta ab , stockholm , sweden ) treatment planning system was used for planning . dose distribution for treatment was calculated using ipsa algorithm with individually adapted optimization parameters ( ml ipsa ) . there were three additional virtual plans prepared for each patient in order to compare dose distribution , using single and multi - lumen devices used for apbi . the first virtual plan was calculated for the same device using dose points optimization with distance option ( ml dp ) . next plan for single lumen applicator was prepared by deleting the radial lumens from the applicator in treatment planning system . the first plan for virtual applicator was optimized using ipsa algorithm ( sl ipsa ) . the last plan was prepared for single lumen applicator , and was optimized using dose points optimization ( sl dp ) . to compare the dose optimization algorithms , no manual optimization was performed , as physicist interference and dose modification would compromise the results of tps calculations . the same way , a plan using ipsa optimization for single lumen applicator was optimized . dose distribution visualization primary dosimetric goals to accept treatment plan were defined as : ( a ) d95 in ptv_eval > 95% ; ( b ) v150 < 50 cc ; ( c ) v200 < 10 cc ; ( d ) skin dmax < 125% ; ( e ) rib dmax < 125% . plans were recognized as acceptable , if suboptimal application conditions prevented as from achieving primary goals , and the restrictions had to be lowered to : ( a ) d90 in ptv_eval > 90% prescribed dose ; ( b ) skin dmax < 145% prescribed dose , with the remaining parameters unchanged . to verify these plans , dose distribution parameters representing doses in target volume and in organs at risk were compared . were the following : d95 , d90 , v150 , v200 , d10 , d50 , and doses to oars all the parameters that represented the doses were taken into account as percent of prescribed dose , except of v150 and v200,which were presented in cm . the dose distribution parameters from three virtual plan sets , with the original plans prepared to treat the patients were compared using student 's t - test (  < 0.05 ) . the mean values with the standard deviations of achieved dose distribution parameters are presented in table 1 and figure 4 . table 2 contains p value of student 's t - test for comparison of dose distribution obtained for realized plan versus values calculated for virtual plans . mean values and sd for doses deposited to target ( d95 , d50 , v150 ) and oar ( dmaxskin ) for plans prepared using different methods dose distribution parameters ( mean values and sd ) for real and virtual plans ipsa  inverse planning simulated annealing , dp  dose points optimization , d  dose ( dose that covers % of the target volume ) , dmax maximal dose received by skin or rib , v  volume ( v150 , that is the percentage of the target volume that has received 50% more than the prescribed dose , v200  100% more ) comparison of p values : real plan with virtual plans ipsa inverse planning simulated annealing , dp  dose points optimization , d  dose ( dose that covers % of the target volume ) , dmax maximal dose received by skin or rib , v  volume ( v150 , that is the percentage of the target volume that has received 50% more than the prescribed dose , v200  100% more ) the highest values of d95 was obtained for ipsa optimized plan for multi - lumen ( ml ipsa ) applicator ( 99.32  6.75% ) . this difference was statistically significant for all three virtual plans : multi - lumen dose point optimized ( ml dp ) , single - lumen ipsa optimized ( sl ipsa ) , single - lumen dose point optimized ( sl dp ) , p < 0.0001 , p = 0.0367 and p < 0.0001 , respectively . no statistical significant differences were found ( ml dp p = 0.0816 , sl ipsa p = 0.7131 , sl dp p = 0.8763 ) . sl ipsa plans were not significantly different from ml ipsa plans , taking into account mean values of d90 ( p = 0.544 ) , d50 ( p = 0.2245 ) and v150 ( p = 0.2369 ) . the values of the other two virtual planning results , provided outcomes statistically different from obtained using ml ipsa for these dvh parameters d90 ( p = 0.0145 , p = 0.0350 ) , d50 ( p < 0.0001 , p < 0.0001 ) , and v150 ( p < 0.0001 , p < 0.0001 ) for ml dp and sl dp , respectively . apbi using intracavitary breast balloons is a technique which gives as opportunity to treat patients in short period of time . the main advantage of this method is that intracavitary application and high dose gradient permit us to irradiate the target area with prescribed dose , while conserving the organs at risk . the cosmetic outcome of the treatment is also very important , so the lowest possible skin doses and calculation of the smallest high - dose volumes are crucial [ 1217 ] . the multi - lumen construction of the applicator gives us broader possibility to adjust the dose distribution in the treated area [ 12 , 1820 ] . optimization of dose distribution using multi - lumen device had more degrees of freedom , as more active source dwell positions are available . the plans calculated with ipsa algorithm characterized with significantly better dose coverage of the treated area while keeping doses to skin surface at similar level . in this analysis , compared with standard single - lumen , balloon - based brachytherapy , potential improvements in dosimetric capabilities ( i.e. , reduced skin dose , improved ptv_eval coverage , and normal tissue avoidance ) were realized . clearly , higher standards for radiation coverage of target tissue with apbi can now be routinely achieved , and previously encountered toxicities can more easily be reduced - in many cases they can be completely avoided [ 7 , 2123 ] . analyzed issue was recently described in two published papers . eyre et al . 
  published a study directly comparing four dosimetric techniques for balloon - based partial breast brachytherapy : single source , standard line source , and both forward planned and inverse planned multi - lumen ( ml ) . they presented a standard line source plan to be used in a single catheter or as a starting point for forward planned ml . twelve treatment plans of patients previously treated with a single lumen were a basis for preparing inverse plans , and used to create a standard line source plan . authors concluded that multiple sources in a single catheter improved coverage at catheter ends , whereas ml can further improve coverage and reduce dose to organs at risk . using a standard line source as a starting point for forward planning ml means increase in planning time is kept to a minimum , making it a practicable option for centers without inverse planning software . recently published a final dosimetric findings of a completed , multi - institutional , phase 4 registry trial using the contura multi - lumen balloon ( mlb ) breast brachytherapy catheter , to deliver apbi in patients with early - stage breast cancer . the idea was to compare 3 dosimetric plans with identical target coverage for each patient to compare : multi - lumen multi - dwell ( mlmd ) ; central - lumen multi - dwell ( clmd ) , and central - lumen single - dwell ( clsd ) loading of the contura catheter . the use of the contura mlb catheter produced statistically significant improvements in dosimetric capabilities between clsd and clmd treatments . this device approach demonstrates the ability not only to overcome the barriers of limited skin thickness and close rib proximity , but to consistently achieve a higher standard of dosimetric planning goals . in our observations , ipsa optimized single - lumen applications resulted in acceptable dose coverage  d90 and it was comparable with ml ipsa application . additionally , the skin doses were not differing , only the doses to ribs were higher , however acceptable for vast majority of plans . ipsa algorithm allowed to achieve better plans for single - lumen applicator than for ml dp application . the plans were calculated using dose point optimization with smaller high dose regions , but it was strictly related with underdosing of the treated area . this fact is not clinically crucial as such plans would be optimized manually before treatment of patient . aim of the study was to test tools implemented to treatment planning system , without physicist intervention . the significant advantage of intracavitary breast balloons is active source dwell positions localized inside the balloon , and separated from the treated tissue . this feature allows to achieve much smaller high dose regions in patient tissue , and decrease the maximum dose . appropriate construction of the applicator is the reason for the highest dose being absorbed by fluid inside the balloon , therefore the dose distribution is much more homogenous in the target area . dose distribution obtained using multi - lumen ipsa optimized application was characterized with the highest target coverage while preserving acceptable doses to organs at risk . optimization method was proven to be more important than the number of catheters in the applicator , however , overall outcome of multi - lumen application gives more possibilities of dose distribution adjustment .
purposethe aim of the study was to verify dose distribution parameters for multi - lumen , and artificially created single - lumen balloon applicator used for the same patient with two optimization algorithms : inverse planning simulated annealing ( ipsa ) and dose point optimization with distance option.material and methodsgroup of 24 patients with multi - lumen balloon applied were investigated . 
 each patient received 10 fractions of 3.4 gy ( 2 fractions daily ) . 
 for every patient , four treatment plans were prepared . 
 firstly , for five - lumen balloon optimized with ipsa algorithm and optimization parameters adjusted for each case . secondly , for the same applicator optimized with dose point optimization and distant option . 
 two other plans were prepared for single - lumen applicator , created by removing four peripheral lumens , optimized with both algorithms.resultsthe highest d95 parameter was obtained for plans optimized with ipsa algorithm , mean value 99.3 percent of prescribed dose , and it was significantly higher than plans optimized with dose point algorithm ( mean = 83.50% , p < 0.0001 ) , ipsa single - lumen balloon plan ( mean = 83.50% , p = 0.0037 ) and optimized to dose point single - lumen balloon ( mean = 85.51% , p < 0.0001 ) . 
 there were no statistically significant differences concerning maximum doses distributed to skin surface for neither application nor optimization method . 
 volumes receiving 200% of prescribed dose in ptv were higher for multi - lumen balloon dose point optimized plans ( mean = 8.78% ) , than for other plans ( ipsa multi - lumen balloon plan : mean = 7.37% , p < 0.0001 , single - lumen ipsa : mean = 7.20% , p < 0.0001 , single - lumen dose point : mean = 7.19% , p < 0.0001).conclusionsbasing on performed survey , better dose distribution parameters are obtained for patients with multi - lumen balloon applied and optimized using ipsa algorithm with individualized optimization parameters .