Study Of Delineation And Dosimetry Of Supraclavicular Lymph Nodes Target In Postoperative Radiotherapy For Breast Cancer Patients

Part Ⅰ:Optimized definition and delineation of supraclavicular lymph nodes target inpostmastectomy radiotherapy for breast cancer patientsObjective: To explore the optimized methods to define and delineate supraclavicular lymphnodes(SCLN) target in postmastectomy radiotherapy for breast cancer patients.Methods: From September2012to August2013, ten breast cancer patients in Sun Yan-senUniversity Cancer Center was selected for this study, who underwent mastectomy andwould be performed postoperative radiotherapy. Two-dimensional SCLN targets weredefined according to bony landmarks in digital reconstructed radiograph after patientsunderwent CT simulation. At the same time, clinical target volume(CTV) of every patientwas delineated on CT-slices by6radiation oncologists. Then the distance between CTVmargins and bony landmarks was measured. Not only the coverage discrepancy betweenCTV and two dimensional target, but also that between different lymphatic nodes regions inCTV by oncologists was analyzed.Results: The average distance between inner margin and inside of stemoclavicular joint/central line of body, exterior margin and inside of the head of humerus, superior margin andunderside of cricoid cartilage was (1.39±0.54cm)/(-0.44±0.59cm),(0.12±0.45cm),(0.59±0.25cm), respectively. The percentage of the volume of Surgery–axilla region receivingradiation in two-dimensional target was16.71%±12.93%. None of intraclavicular-LNregion was covered in two-dimensional target with inside of stemoclavicular joint as inner margin.The average volume of CTV was109.51±28.06cm3. All SLN, neck-Ⅳ and axillaⅢ regions were covered in CTV, none of axillaⅠregion. The covergy rates ofnonsurgery-axillaⅡ, Rotter-LN, intraclavicular-LN, neck-Ⅴb, scalenus gap, neck-Ⅲ andsurgery-axilla Ⅱregions was75%,85%,73%,88%,68%,10%,17%respectively.Conclusion: SCLN-CTV delineated on CT-slices was more accurate than the twodimensional target in postmastectomy radiotherapy. SCLN, neck-Ⅳ and axilla Ⅲ regionsshould be covered according to consensus. However, the opinions of nonsurgery-axillaⅡ,Rotter-LN, intraclavicular-LN, neck-Ⅴb, scalenus gap, neck-Ⅲ and surgery–axilla Ⅱremain divisive. Part Ⅱ:Dosimetry study of supraclavicular lymph nodes target in postoperative radiotherapy forbreast cancer patientsObjective: To compare the dose difference of three-dimensional conformal radiationtherapy(3D-CRT) and intensity-modulated radiotherapy(IMRT) in supraclavicular lymphnodestarget in postmastectomy radiotherapy for breast cancer patients.Methods: From September2012to August2013, twenty-four breast cancer patients in SunYan-sen University Cancer Center was selected for this study, twelve of who underwentmastectomy and twelve of who underwent breast conservation surgery and would beperformed postoperative radiotherapy. Design three-dimensional conformal radiationtherapy in Pinnacle8.0planning system. Design static intensity-modulatedradiotherapy(sIMRT）including3-field intensity modulated radiotherapy(3F-IMRT),4-fieldintensity modulated radiotherapy(4F-IMRT),5-field intensity modulated radiotherapy(5F-IMRT) and Volumetric modulated arc therapy(VMAT) including single arc VMAT anddouble arc VMAT in Monaco planning system. Number of segments and total monitorunits(MU)were used to evaluate the efficady of each plans. At the same time, plans werecompared using multiple dose distributions and dose volume histograms(DVH) forplanning target volume(PTV) and OARs, including surgery–axilla, ipsilateral lung, bothlung, throat, esophagus, thyroid, brachial plexus, trachea, shoulder joint.Results: The95%prescribed dose can not cover95%of PTV of3D-CRT plan.180°doublearc VMAT and240°double arc VMAT have the best dose coverage. The conformity indexof5F-IMRT plan is the worst, and180°single arc VMAT is the best. The inhomogeneityindex of each plans has no difference. Surgery–Axilla has lower dose absorption in IMRTplans, in which240°single arc VMAT has the lowest V40. Ipisilateral lung has highestdose absorption in3D-CRT plans, then is5F-IMRT plan, with no difference among eachplans of the low dose absorption. The low dose absorption of throat, esophagus, thyroid,trachea, spinal cord have the lowest dose absorption in3D-CRT plans, sIMRT plans ishigher then VMAT plans. Thyroid and trachea have highest dose absorption in3F-IMRTplans. The MU of3D-CRT plan is more than IMRT plans and the MU of VMAT plans are more than sIMRT plans.Conclusion: IMRT plans have better dose coverage than3D-CRT plans. At the same time,surgery–axilla and lung have lower dose absorption in IMRT plans.180°arc VMAT,240°arc VMAT and4F-IMRT plan are worth to be recommend.