A Broad Evaluation of Left Breast Radiotherapy

Radiation Oncology- 21st Century Oncology of California, USA

^*Corresponding Author

Aime M Gloi

21st Century Oncology of California

1316 Nelson Avenue, Modesto, CA 95350

USA

Phone:209-575-5870

Fax:209-575-5872

Email: agloi7288@gmail.com

Abstract

Background: The aim of this study was to evaluate radiobiological model parameters and the secondary cancer risk to patients undergoing hypofractionated or conventionally fractionated irradiation of the left breast. Materials and Methods: 17 conventional (50 Gy) and 13 hypofractionated (42.56 Gy) plans were randomly selected and both biologically equivalent dose (EQD2) and effective dose (BED) were assessed in addition to dose homogeneity index, equivalent uniform dose, normal tissue complication probability (NTCP), and tumor control probability (TCP). Secondary cancer risks were estimated through dose volume histogram (DVHs) by calculating organ equivalent doses (OED) and excess absolute risks (EAR) using linear, bell-shaped, and plateau models. Results: EQD2 and TCPs were steady throughout a spectrum of α/βratios. TCPs for conventional treatment are 84.36 ± 7.68, 99.30 ± 0.71, and 17.87 ± 6.92 for  α/β =4, α/β =2.5, and α/β =10 respectively. Likewise, the TCP values for the hypofractionated regimen are 91.04±11.43, 98.67±4.23, and 24.31±8.74 for α/β =4, α/β =2.5, α/β =10 respectively. NTCP based LKB model with the pericarditis endpoint yielded a 0% risk. Logistic regression and LKB model have similar mean lung dose and can be used interchangeably for lung pneumonitis. A combined heart-lung, cardiac failure, and logistic lung model, based on this study, discloses a higher probability of heart failure in conventional treatment and lung toxicity in hypofraction. Estimates of secondary cancer were higher for conventional plans compared to hypofraction for all models, for patients over 30 years old. Conclusions: This work reveals significant similarities and differences between the hypofractionated and conventional treatment of the left breast, via radiobiology.

Keywords: Equivalent uniform dose (EUD), Normal tissue complication probability (NTCP), Tumor control probability (TCP), Organ-equivalent dose (OED), Excess absolute risk (EAR)

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