Wensha Yang, an instructor in radiation oncology, and colleagues are exploiting the light-emitting properties of quantum dots - specifically, their light emission upon exposure to the MV X-ray beams used in radiation therapy.

When hit with high doses of radiation, the dots become luminescent; that light then triggers the cancer-killing activity of a PDT photosensitizer called Photofrin (a drug that's absorbed selectively by cancer cells).

Photofrin is currently used for PDT treatments of certain classes of shallowly located tumours. However, Yang and his co-workers reckon that their multimodal approach, which so far has only been studied in cancer cells grown in culture, could work on tumours located deep within the body.

To prevent normal tissues from being affected by the treatment, the quantum dot-Photofrin conjugate only becomes cytotoxic upon irradiation by the MV X-ray source. What's more, says Wang, conformal delivery of the radiation ensures that "the toxicity of the drug is substantially lower in the lower-radiation-dose area" outside the boundaries of the tumour.

In tests on human-lung carcinoma cells, the process resulted in a 2-6 times lower tumour-cell survival compared to radiation alone. The researchers report minimal toxicity to nearby cells.

Yang presented the results at the 50th annual meeting of the American Association of Physicists in Medicine (AAPM) in Houston, TX.