Tumor Control Probability (TCP) and Normal Tissue Complication Probability (NTCP) in Mono and Dual-isocentric Techniques of Breast Cancer Radiation Therapy

Background: Nowadays, radiation therapy plays an important role in thetreatment of breast cancer. The important point is the optimal control of the tumoralong with the protection of organs at risk. This study aims to investigate andcompare the radiobiological factors of the tumor and organs at risk in two differentradiation therapy techniques of breast cancer.Methods: Ten left-sided breast cancer patients with breast-conservative surgerywere selected for this study. Three-dimensional treatment planning was performedusing CT scan images of the patients using PCRT ۳D software. Two differenttangential external beam techniques were compared: first, dual-isocentric technique(DIT) with two isocentre, one on the breast tissue, and the other one on thesupraclavicular lymph nodes and second, a mono-isocentric technique (MIT) withone isocentre at the intersection of the tangential and the supraclavicular field. Thetotal prescribed dose was ۵۰۰۰ cGy per ۲۵ fractions. Dose-volume histograms(DVHs), Tumor control probability (TCP), and normal tissue complicationprobability (NTCP) curves were used to compare the dosimetric and radiobiologicalparameters of the tissues in the prementioned techniques.Results: The results showed that the maximum doses in planning target volume(PTV) with mean values of ۱۰۹% and ۱۱۰% in the SI and DIT were not significantlydifferent in both techniques and that they were indeed at the optimum level based onthe RTOG ۱۰۰۵ protocol. The dose homogeneity index in MMIT was more thanthat in DIT, while the conformity index and the mean TCP did not show a significantdifference in the two techniques. Furthermore, minimum, mean, and maximumdose in the lung and the probability of pneumonitis decreased in MIT. On the otherhand, the maximum dose, the dose of ۳۳%, ۶۶%, and ۱۰۰% of the heart, and theprobability of pericarditis in MIT were lower than the figure in DIT.Conclusion: Due to the absence of hot spots at the intersection of tangential andsupraclavicular fields and the reduction of mechanical movements of the coachand collimator in MIT, the superiority of this method was confirmed.