Quinazolines/pharmacology; Radiation-Sensitizing Agents/pharmacology; Triazenes/pharmacology; Antineoplastic Agents/metabolism; Antineoplastic Agents/pharmacokinetics; Antineoplastic Agents/pharmacology; Antineoplastic Agents/radiation effects; Antineoplastic Agents, Alkylating/metabolism; Antineoplastic Agents, Alkylating/pharmacokinetics; Antineoplastic Agents, Alkylating/pharmacology; Antineoplastic Agents, Alkylating/radiation effects; Apoptosis/drug effects; Apoptosis/radiation effects; Cell Cycle/drug effects; Cell Cycle/radiation effects; Cell Line, Tumor; Cell Survival/drug effects; Cell Survival/radiation effects; DNA Damage/drug effects; DNA Damage/radiation effects; Dose-Response Relationship, Drug; Enzyme Inhibitors/metabolism; Enzyme Inhibitors/pharmacokinetics; Enzyme Inhibitors/pharmacology; Enzyme Inhibitors/radiation effects; ErbB Receptors/antagonists & inhibitors; Gefitinib; Humans; Microscopy, Fluorescence; Quinazolines/metabolism; Quinazolines/pharmacokinetics; Quinazolines/radiation effects; Radiation-Sensitizing Agents/metabolism; Radiation-Sensitizing Agents/pharmacokinetics; Radiation-Sensitizing Agents/radiation effects; Triazenes/metabolism; Triazenes/pharmacokinetics; Triazenes/radiation effects; Tumor Stem Cell Assay; X-Rays