Early Breast Cancer After Bct To Improve The Accuracy Of Tumor Bed Irradiation

Part I:Changes of tumor bed and whole breast volumes during breast irradiationPurpose:To observe the changes of whole breast and tumor bed volumes during the breast irradiation,and measure the transverse and longitudinal dimensions of surgical clips placed in the tumor bed.Material and methods:16 early-stage breast cancer patients underwent breast conservative surgery were consecutively scanned three times by simulated CT during the whole breast irradiation From 2008.7 to 2009.1 in our hospital the scanning times are before the start of radiation(CT1),during the radiation(CT2) and before the tumor bed boost(CT3) respectively.The tumor bed GTVs and whole breast PTVs were contoured in these CTs.The dimensions between medial and lateral clips,superior and inferior clips which represented the transverse and longitudinal dimensions were measured.Results:The average whole breast PTV volumes are 579.6cm3,575.7 cm3,566.1 cm3 (p=0.990),and the meantumor bed volumes are 49.5 cm3,25.6 cm3,22.2 cm3(p= 0.007).The changes between CT1 and CT2,CT3 are both statistically significant,but none between CT2 and CT3.The mean reduction of tumor bed volumes from CT1 to CT3 are 43.4%,14 of 16 patients declined by more than 20%,accounting for 87.5%,6 patients decreased over 50%,accounting for 37.5%.the average distance between the superior and inferior clips decreased by 0.89cm(p=0),and by 0.75cm(p=0.001) between the medial and lateral clips.Initial tumor bed volumes show a significant correlation with the percentage of changes between CT1 and CT3(r=0.57,p=0.021).The changes of breast volume between CT3 and CT1 are significantly associated with the decrease of tumor bed volumes(r=0.726,p=0.000).The decrease of tumor bed volumes are associated with the changes of distances between surgical clips in transverse and longitudal directions(r= 0.529 and 0.606,p= 0.035 and 0.013 respectively).Conclusions:During the whole breast irradiation,many patients have a significant reduction in the tumor bed volumes and distances within clips,the changes of tumor bed volumes are more prominent in early stage of breast radiation,and the decrease of the distances within clips are associated with the changes of tumor bed volumes. Part II:Evaluation of the accuracy of tumor bed boost using clips-based electron fields in early-stage breast cancer patients receiving breast conservative surgery.Purpose:To evaluate the accuracy of definition of breast tumor bed according to the clips in the lumpectomy cavity.Material and methods:Thirty consecutive patients with early-stage breast cancer underwent planning CT from July 2008 to January 2009 after breast-conservative surgery were evaluated for the accuracy of tumor bed boost using surgical clips.Lumpectomy cavities were marked by no less than 4 clips at the superior,inferior,medial and lateral margins respectively.For each patients,cavity visualization score(CVS) from 1 to 5 was evaluated,and none of the patients had a CVS below 3.Tumor bed GTV and PTV(GTV+2cm) were contoured by one radiation oncologist.Hypothetical clips-based electron boost fields were defined as perpendicular to the tumor bed GTV encompassing all clips with 2cm margins.Results:The median number of clips in the lumpectomy cavity was 4(4-6).The mean tumor bed GTV maximal depth was 3±0.7cm.The mean GTV margins extended beyond the clips by 0.4±0.7cm superiorly,0.3±0.4cm inferiorly,0.5±0.7cm medially and 0.3±0.6cm laterally.The maximal GTV margins beyond the clips at any direction in each patient is named Dmax.Dmax were≤0.5cm in 12 patients,0.5-1cm in 9 patients and >1 cm in 9 patients. The mean volume of GTV and PTV were 24.1±10.8cm~3 and 125.1±43.9cm~3 respectively. The mean GTV projection area on DRR was 26.4cm~2.Electron energy was chosen based on the maximal depth of GTV with 9MeV in 18 patients,12MeV in 9 patients and 15MeV in 3 patients.Clips-based simple electron boost field resulted in insufficient tumor bed coverage, with minimal dose received by 90%of the tumor bed PTV(D90) >90%in 46.7%of the patients,above 80%in 70%.Geographical miss(defined as having less than 50%of the prescribed dose within the PTV) was found in 36.7%of patients.Better PIV coverage is found in patients with smaller Dmax.In univariate analysis,Dmax above 0.5cm was associated with D90<90%(p=0.000) and Dmax above 1cm was associated with geographic miss (p=0.000).Conclusions:Our study suggests that clips-based simple electron boost does not provide sufficient tumor bed coverage and integrated CT planning with tumor bed boost is warranted.