Final answer:
For treatment of the nasopharyngeal or oropharyngeal region, particles approximately 70 nm in size are found to be more effective for retention and penetration in tumor sites compared to larger particles. Nanoparticles must be small enough to pass through capillary gaps to reach tumor tissues and remain there to provide therapeutic effects.
Step-by-step explanation:
When considering what size the particle has to be to treat nasopharyngeal or oropharyngeal regions, it's important to understand that the efficacy of nanoparticles in drug delivery systems relies heavily on their size. In the context of nanocarrier-based treatments, such as those for cancers, the hydrodynamic radius of these nanocarriers is a pivotal factor for the therapeutic agent to reach and penetrate tumor tissues effectively. Studies have shown that nanocarriers sized around 70 nm demonstrate a greater retention in tumor sites than larger particles. For example, in the study conducted by Tseng, 70 nm sized magnetothermally-responsive doxorubicin loaded supramolecular magnetic nanoparticles (Dox-SMNPs) displayed a significantly higher accumulation in malignant tissue in comparison to larger particles sized at 100 and 160 nm.
The ability of nanoparticles to pass through capillary interendothelial gaps, which allows them to reach the tumor interstitial fluid, is influenced by their size. Nanoparticles that are too large are more likely to be removed by the reticuloendothelial system (RES) before reaching the tumor area. Additionally, smaller nanoparticles are known to diffuse through the tumor mass over time, while larger particles remain mostly within the blood vessels. Therefore, for treatments targeting the nasopharyngeal or oropharyngeal cancerous regions, smaller nanoparticles, perhaps in the range of 20-70 nm, would likely be more effective for penetration and retention within the tumor tissue.