Mm In Mediolateral Research Articles

Assessment of setup error in orthogonal megavoltage X-ray film for whole breast radiation with breast bracket immobilized

Objective To quantify the setup errors measured with orthogonal megavoltage X-ray film in breast cancer patients immobilized in breast bracket.To probe into the margins from clinical target volume (CTV) to planning target volume (PTV) in 3 directions.Methods Repeat orthogonal megavoltage X-ray films were acquired for routine of fine setup verification in 29 breast cancer patients after conserving surgery,17 received whole breast radiation and 12 received both whole breast and supraclavicular node radiation.All patients were immobilized in the supine position with both arms raised over their heads,using a personalized α-cradle (breast bracket).Registrations of the bony anatomy for megavoltage X-ray films to digitally reconstructed-radiographs from the planning CT were compared.Systematic and random setup errors were quantified,and the differences between groups with and without supraclavicular node radiation were compared by independent two-sample t-test.Results The mean set up deviation,systematic error and random error were (0.9±3.1) mm,(0.7±3.0) mm,(1.2±2.1) mmand3.1 mm,3.0 mm,2.1 mm and 2.7 mm,3.3 mm,3.5 mm in the mediolateral,superoinferior and anteroposterior dimensions.There is no difference of set up deviation between patients received supraclavicular node radiation and those did not (t =0.02,0.20,0.20,P =0.98,0.85,0.85).The margins from CTV to PTV were 9.6 mm,9.8 mm,7.7 mm in mediolateral,superoinferior and anteroposterior directions.Conclusion For whole breast irradiation patients immobilized with breast bracket,the margins from CTV to PTV were recommended as 9.6 mm,9.8mm,7.7 mm in mediolateral,superoinferior and anteroposterior directions. Key words: Breast bracket immobilized; Setup error; Megavoltage X-ray film; Whole breast intensity-modulated radiotherapy

Assessment of three-dimensional set-up errors in conventional head and neck radiotherapy using electronic portal imaging device

BackgroundSet-up errors are an inherent part of radiation treatment process. Coverage of target volume is a direct function of set-up margins, which should be optimized to prevent inadvertent irradiation of adjacent normal tissues. The aim of this study was to evaluate three-dimensional (3D) set-up errors and propose optimum margins for target volume coverage in head and neck radiotherapy.MethodsThe dataset consisted of 93 pairs of orthogonal simulator and corresponding portal images on which 558 point positions were measured to calculate translational displacement in 25 patients undergoing conventional head and neck radiotherapy with antero-lateral wedge pair technique. Mean displacements, population systematic (Σ) and random (σ) errors and 3D vector of displacement was calculated. Set-up margins were calculated using published margin recipes.ResultsThe mean displacement in antero-posterior (AP), medio-lateral (ML) and supero-inferior (SI) direction was -0.25 mm (-6.50 to +7.70 mm), -0.48 mm (-5.50 to +7.80 mm) and +0.45 mm (-7.30 to +7.40 mm) respectively. Ninety three percent of the displacements were within 5 mm in all three cardinal directions. Population systematic (Σ) and random errors (σ) were 0.96, 0.98 and 1.20 mm and 1.94, 1.97 and 2.48 mm in AP, ML and SI direction respectively. The mean 3D vector of displacement was 3.84 cm. Using van Herk's formula, the clinical target volume to planning target volume margins were 3.76, 3.83 and 4.74 mm in AP, ML and SI direction respectively.ConclusionThe present study report compares well with published set-up error data relevant to head and neck radiotherapy practice. The set-up margins were <5 mm in all directions. Caution is warranted against adopting generic margin recipes as different margin generating recipes lead to a different probability of target volume coverage.