Radiation therapy (RT) concurrent with chemotherapy improves local lung cancer control but may cause systemic toxicity. There is an unmet clinical need of treatments that can selectively sensitize cancer cells to RT. Herein, we explored a radiosensitizing strategy that combines doxorubicin (DOX)-encapsulated polyaspartamide nanoparticles and 5-aminolevulinic acid (5-ALA). The DOX-polyaspartamide nanoparticles were coupled with NTSmut, a ligand specific to neurotensin receptor type 1 (NTSR1), for lung cancer targeting. DOX was coupled to the polymer backbone through a pH-sensitive hydrazone linker, which allows for controlled release of the drug in an acidic tumor micromovement. Meanwhile, 5-ALA accumulates in the cancer cell's mitochondria, forming protoporphyrin (PpIX) that amplifies RT-induced oxidative stress. When tested in vitro in H1299 cells, DOX-encapsulated nanoparticles in conjugation with 5-ALA enhanced cancer cell killing owing to the complementary radiosensitizing effects of DOX and 5-ALA. In vivo studies confirmed that the combination improved tumor suppression relative to RT alone without causing toxicity to normal tissues. Overall, our study suggests an effective and selective radiosensitizing approach.