Breast cancer is the second most commonly diagnosed cancer (11.6%) in both sexes after lung, among females, breast cancer is the most commonly diagnosed cancer, and it is the leading cause of cancer death (Bray et al., 2018). Radiotherapy has major advantages in the treatment of breast cancer. It reduces the risk of locoregional recurrences and improves overall survival both for early-stage breast cancer after breast-conserving surgery and after mastectomy for locally advanced disease (Darby et al., 2011). Unfortunately, these advantages were accompanied by a number of adverse effects to the heart, lungs, and the opposite breast tissue (Jagsi et al., 2007). Radiation-induced lung injury (RILI) was originally described in 1925 and divided into an acute injury stage, radiation pneumonitis (RP), and chronic injury stage, radiation pulmonary fibrosis (RPF) (Bradley and Movsas, 2008). Radiation pneumonitis occurs within 6 months of therapy (mostly within 12 weeks), while RPF occurs > 1 year following therapy (Yarnold et al., 2010;Bernchou et al., 2013). Despite of most patients receiving thoracic irradiation are at risk for RILI, several factors may modify their risk. Patient-related factors as history of smoking, chronic obstructive pulmonary diseases, and interstitial

Liquid biopsy analysis represents a suitable alternative analysis procedure in several cases where no tumor tissue is available or in poor patient conditions. Amino acids can play a crucial role in aiding cancer diagnosis. Monitoring of tryptophan (Trp) catabolism can aid in tracking cancer progression. Therefore, a novel nanocomposite was fabricated using overoxidized polypyrrole film doped with nano-carbon dots (nano-CDs) on the pencil graphite electrode (PGE) surface for sensitive evaluation of Trp in human serum. Using square wave voltammetry (SWV), the overoxidized polypyrrole/carbon dots/pencil graphite electrode (Ov-Ox PPy/CDs/PGE) achieved excellent electrochemical catalytic activity for evaluating Trp. The modified electrode, known as Ov-Ox PPy/CDs/PGE, demonstrated superior electrochemical catalytic activity compared to bare PGE, CDs/PGE, PPy/PGE, and PPy/CDs/PGE for evaluation of Trp. The method’s excellent sensitivity was confirmed by the low limits of detection (LOD = 0.003 μmol L−1) and limit of quantitation (LOQ = 0.009 μmol L−1). The biosensor that was developed can measure tryptophan (Trp) levels in the serum of both healthy individuals and female breast cancer patients with high accuracy and sensitivity. The results indicate that there is a significant difference, as shown by the F-test, between healthy individuals and those with breast cancer. This suggests that Trp amino acid could be an essential biomarker for cancer diagnosis. Consequently, liquid biopsy analysis presents a valuable opportunity for early disease detection, particularly for cancer. Graphical abstract