Asian Pacific Journal of Cancer Prevention

Asian Pacific Journal of Cancer Prevention (아시아태평양암예방학회)
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Breast Radiotherapy with Mixed Energy Photons; a Model for Optimal Beam Weighting

  • Birgani, Mohammadjavad Tahmasebi (Department of Medical Physics, Faculty of Medicine, Ahvaz Jundishapur University of Medical Sciences) ;
  • Fatahiasl, Jafar (Department of Medical Physics, Faculty of Medicine, Ahvaz Jundishapur University of Medical Sciences) ;
  • Hosseini, Seyed Mohammad (Departments of Clinical Oncology, Golestan Hospital, Ahvaz Jundishapur University of Medical Sciences) ;
  • Bagheri, Ali (Departments of Clinical Oncology, Golestan Hospital, Ahvaz Jundishapur University of Medical Sciences) ;
  • Behrooz, Mohammad Ali (Department of Medical Physics, Faculty of Medicine, Ahvaz Jundishapur University of Medical Sciences) ;
  • Zabiehzadeh, Mansour (Department of Medical Physics, Faculty of Medicine, Ahvaz Jundishapur University of Medical Sciences) ;
  • meskani, Reza (Department of Medical Physics, Faculty of Medicine, Ahvaz Jundishapur University of Medical Sciences) ;
  • Gomari, Maryam Talaei (Department of Medical Physics, Faculty of Medicine, Ahvaz Jundishapur University of Medical Sciences)
  • Published : 2015.12.03
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Abstract

Utilization of high energy photons (>10MV) with an optimal weight using a mixed energy technique is a practical way to generate a homogenous dose distribution while maintaining adequate target coverage in intact breast radiotherapy. This study represents a model for estimation of this optimal weight for day to day clinical usage. For this purpose, treatment planning computed tomography scans of thirty-three consecutive early stage breast cancer patients following breast conservation surgery were analyzed. After delineation of the breast clinical target volume (CTV) and placing opposed wedge paired isocenteric tangential portals, dosimeteric calculations were conducted and dose volume histograms (DVHs) were generated, first with pure 6MV photons and then these calculations were repeated ten times with incorporating 18MV photons (ten percent increase in weight per step) in each individual patient. For each calculation two indexes including maximum dose in the breast CTV ($D_{max}$) and the volume of CTV which covered with 95% Isodose line ($V_{CTV,95%IDL}$) were measured according to the DVH data and then normalized values were plotted in a graph. The optimal weight of 18MV photons was defined as the intersection point of $D_{max}$ and $V_{CTV,95%IDL}$ graphs. For creating a model to predict this optimal weight multiple linear regression analysis was used based on some of the breast and tangential field parameters. The best fitting model for prediction of 18MV photons optimal weight in breast radiotherapy using mixed energy technique, incorporated chest wall separation plus central lung distance (Adjusted R2=0.776). In conclusion, this study represents a model for the estimation of optimal beam weighting in breast radiotherapy using mixed photon energy technique for routine day to day clinical usage.

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References

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