the american college of surgeons oncology group ( acosog ) z0011 trial showed that patients with early breast cancer and limited sentinel node involvement receiving lumpectomy , whole breast radiotherapy ( rt ) , and adjuvant systemic treatment no longer require axillary lymph node dissection ( alnd ) [ 1 , 2 ] . considering that the regional recurrence rate after sentinel lymph node dissection ( slnd ) alone was < 1% , despite the fact that 27.3% of patients had additional disease in the undissected axillary nodes , not all axillary occult diseases manifest as failure . however , there was a nontrivial percentage of patients treated contrary to protocol requirements ; more than half of patients received rt coverage on not only the whole breast but also axillary lymph node ( aln ) . therefore , a value of aln coverage by tangential field for whole breast rt was still one of the most curious questions to physicians who treat a breast cancer . previous studies have explored aln coverage of the standard or high tangential field for whole breast rt [ 413 ] , and the axillary mean doses were 2050  gy for axilla level i and 347  gy for level ii [ 48 ] . dose depends on the somatotype , such as convexity of chest wall , axillary vein route , and fatness , as well as rt technique , such as standard tangential field , high tangential field , and/or field - in - field using multileaf collimator modification , according to physician preference [ 4 , 9 , 11 ] . however , discrepancies in aln coverage in same patient between institutions have not yet been explored . furthermore , there was only one study reporting axilla coverage in korean women . in this study , we evaluated the dose distribution and coverage of axilla levels i - ii using only the tangential field for whole breast rt with same patient simulation data at three institutions ( kyung hee university medical center , asan medical center , and korea university medical center ) in korea . we used computed tomography ( ct ) images of nine consecutive one to two sln - positive breast cancer patients who underwent breast conserving surgery ( bcs ) and whole breast rt without alnd for their clinical t1-t2n0 breast cancer at the kyung hee university medical center . all patients had a tumor 50  mm in greatest dimension with a median tumor diameter of 2.2  cm . four patients had a right - sided and 5 had a left - sided tumor . patients were placed supine with both arms up and both hands holding on to a support during ct simulation . ct scan images with 5 mm sections were obtained and the ct data were transferred to each of the three radiation oncologists at 3 different institutions ( kyung hee university medical center , asan medical center , and korea university medical center ) . the three radiation oncologists were randomly selected among radiation oncologists with more than 10 years of experience treating breast cancer patients at 3 institutions . each radiation oncologist made treatment plans for all nine patients using tangential field to whole breast . tangential fields were determined according to physician preference , and the superior borders of these fields intended to treat the breast only , without regard to nodal coverage . a dose of 50  gy was delivered in 25 fractions to the whole breast . one of the three radiation oncologists contoured all axillary nodal volumes and organs at risk using the danish guidelines . mean dose , dose delivered to 95% and 50% of the axillary levels ( d95% and d50% ) , percent volume of the axillary levels receiving 95% and 50% of the prescribed dose ( vd95% and vd50% ) , and percent volume of the ipsilateral lung receiving 20  gy , 10  gy , and 5  gy ( v20  gy , v10  gy , and v5  gy ) were calculated using dose - volume histograms . percent volume of the heart receiving 30  gy ( v30  gy ) and mean dose received by heart were calculated for the 5 patients with left - sided breast cancer . these values were compared between the three institutions by one - way analyses of variance with tukey 's post hoc tests . associations between the distance from the humeral head to the superior border of the tangential field ( dhs ) with dose - volume parameters were analyzed by univariate linear regression . a p  value < 0.05 was considered to be statistically significant . all statistical analyses were performed using the spss statistical package ( version 18.0 , spss inc . , chicago , il ) . all plans had adequate coverage to the breast , defined as 95% of the breast volume receiving at least 95% of the prescribed dose . the mean volumes of axillary levels i and ii were 56.0  cm ( range 24.096.3  cm ) and 27.7  cm ( range 12.545.0  cm ) , respectively . the mean doses delivered to levels i and ii were 31.9  gy ( range 9.947.9  gy ) and 22.3  gy ( 3.447.7  gy ) , respectively . ninety - five percent of levels i and ii received a mean dose of 11.8  gy ( range 0.443.0  gy ) and 3.0  gy ( 0.340.0  gy ) , respectively , and the percent volumes of levels i and ii covered by the 95% of prescribed dose were only 29.0% ( range 0.274.1% ) and 11.5% ( 0.070.1% ) , respectively . the dose and volume results are summarized in table 1 . the mean dhs was 2.4  cm . in 3 of the 27 treatment plans , the superior border of the tangential field was set above the humeral head . doses delivered to levels i and ii and volumes received by radiation were related to dhs . when the superior border of the tangential field was closer to the humeral head , the axillary coverage increased ( level i mean dose , p < 0.001 ; level i d95% , p < 0.001 ; level i d50% , p < 0.001 ; level i vd95% , p < 0.001 ; level i vd50% , p < 0.001 ; level ii mean dose , p < 0.001 ; level ii d95% , p = 0.024 ; level ii d50% , p < 0.001 ; level ii vd95% , p = 0.011 ; level ii vd50% , p < 0.001 ) . there was no significant difference in aln coverage between right- and left - sided tumors . in all parameters related to levels i and ii , except d95% to level ii , there were significant discrepancies between the three institutions ( table 2 ) . the aln coverage was lower in institutions a and b than in institution c. the mean dose delivered to aln in institution c was significantly higher than in institutions a and b ( level i , 44.8  gy versus 23.8  gy versus 27.0  gy ; level ii , 35.4  gy versus 12.9  gy versus 18.6  gy ) . the mean dhs in institutions a and b was 3.6  cm and 2.9  cm , respectively , but was 0.7  cm in institution c. there were two cases in institution c where the superior border of the tangential field was set above the humeral head . institution c used a high tangential field , which was defined with the superior border of the tangential field set < 2  cm below the humeral head in all plans . in contrast , institutions a and b used a high tangential field in two cases , respectively . the mean doses and the percentage volumes of ipsilateral lung receiving 5  gy ( v5  gy ) , 10  gy ( v10  gy ) were significantly higher in institution c than in institutions a and b. however , there was no significant statistical discrepancy between the three institutions for the mean heart dose and v30  gy . the acosog z0011 trial concluded that slnd without alnd can offer excellent regional control and equivalent survival , so it may be reasonable management for selected patients with early - stage breast cancer treated with bcs and adjuvant systemic therapy [ 1 , 2 ] . the trial also demonstrated that adverse surgical effects were reported in 70% of patients after slnd + alnd and in 25% after slnd alone . the use of slnd + alnd resulted in more wound infections , axillary seromas , and paresthesias than slnd alone . the eortc amaros trial , which enrolled patients with t1 - 2 primary breast cancer and no palpable lymphadenopathy ( 744 alnd group and 781 axillary rt group ) , was another important study showing equivalent regional control and survival of axillary rt without alnd . however , there was a significant difference in the incidence and severity of lymphedema in favor of the axillary rt group ( 5-year incidence of clinical signs of lymphedema in the ipsilateral arm , 23% versus 11% , p < 0.0001 ) . the practice pattern was changed after these studies which showed excellent axillary control and lower treatment related complications , and , in the treatment setting that omits alnd , the aln coverage of rt needed further investigation . in the present study , we evaluated the dose distribution and coverage of axillary levels i - ii using the tangential field for whole breast rt at three institutions in korea . the tangential field planned for the mean doses delivered to levels i and ii were 31.9  gy ( range 9.947.9  gy ) and 22.3  gy ( 3.447.7  gy ) , respectively . only 29.0% of level i and 11.5% of level ii were covered by the 95% prescription dose . results of the present study correspond with earlier studies , which reported insufficient axillary coverage of the tangential field [ 48 ] . we also found discrepancy in axillary coverage between the three institutions when we compared data from same ct image and axillary contour . institution c had greater axillary coverage than institutions a and b in all dose - volume parameters , except d95% to level ii . to the best of our knowledge , this is the first study that statistically evaluated discrepancies in axillary coverage with the same patient data between multiple institutions . aln coverage by the tangential field for whole breast rt had discrepancies according to a patient 's anatomical features and physician preference . previous studies reported a broad range of aln coverage by the tangential field [ 4 , 6 , 14 ] . .   showed that mean doses ranged from 1 to 57  gy ( median 22  gy ) to level i and 046  gy ( median 4  gy ) to level ii . in a study by alo et al . , the ranges of mean doses delivered to levels i and ii were 16.750.4  gy and 4.550.27  gy , respectively . because each whole breast rt was planned with consideration of patient 's chest wall convexity and breast contour rather than the axillary vein route , these results , which showed a broad range of axillary coverage by the tangential field , were natural . furthermore , dhs was one of the most important factors affecting the discrepancy of axillary coverage . demonstrated that when high tangents are applied , the coverage improved significantly . in the present study , although we evaluated axillary coverage using the same ct image for planning in each institution , dhs was significantly different between the institutions . institution c had higher superior borders of the tangential field than did institutions a and b. these results suggested that the tangential field for breast cancer , especially the superior border of the field , could vary significantly between physicians . these differences in rt field also appeared in the z0011 trial , which was conducted with a well - designed protocol . the study of rt field design in the z0011 trial demonstrated that , of the 228 patients with detailed rt records , 18.9% received directed regional nodal rt using at least three fields and 51% received high tangential field rt . advanced rt technique such as high tangential field and/or field - in - field using multileaf collimator modification improved aln coverage [ 4 , 9 , 11 ] . from the adequate aln coverage view , the use of direct fields like in the amaros trial could be considered . however , whether such treatment might benefit patients with minimal axillary disease detected on slnd remains unknown , as we currently lack the data to draw conclusions about the relationship between aln coverage and axillary tumor control . indeed , not all aln metastases develop into clinically detectable disease . in the z0011 trial , based on the finding that 27% of patients in the alnd arm had additional nodal metastases , patients randomized to the slnd alone arm were likely to have residual non - sn metastasis that was not removed by operation . therefore , further study to define the optimal field and to reveal the relationship between aln coverage and axillary tumor control should be conducted . another limitation is that our study was performed using only three radiation oncologists with experience in the treatment of breast cancer in 3 institutions . despite these limitations , the present results provide valuable information about aln coverage of the tangential field and the discrepancies between institutions , which could serve to motivate further research on standard rt field with a nationwide scale .
introduction . to evaluate the dose distribution and coverage of axilla using only tangential field for whole breast radiotherapy ( rt ) at three institutions in korea . methods . 
 we used computed tomography ( ct ) images of nine consecutive 1 - 2 sentinel lymph node - positive patients who underwent breast conserving surgery and whole breast rt without axillary lymph node ( aln ) dissection for clinical t1 - 2n0 breast cancer . 
 the ct data were transferred to three radiation oncologists in 3 institutions and each radiation oncologist created treatment plans for all nine patients ; a total of 27 treatment plans were analyzed . 
 results . 
 the mean doses delivered to levels i and ii were 31.9  gy ( 9.947.9  gy ) and 22.3  gy ( 3.447.7  gy ) . 
 ninety - five percent of levels i and ii received a mean dose of 11.8  gy ( 0.443.0  gy ) and 3.0  gy ( 0.340.0  gy ) . the percent volumes of levels i and ii covered by 95% of the prescribed dose were only 29.0% ( 0.274.1% ) and 11.5% ( 0.070.1% ) . 
 the dose distribution and coverage of axilla were significantly different between three institutions ( p = 0.001 ) . 
 conclusion . 
 there were discrepancies in aln coverage between three institutions . 
 a standardization of whole breast rt technique through further research with a nationwide scale is needed .