Photon activation therapy and brachytherapy

In photon activation therapy (PAT), energy deposition at critical sites within a tumor can be increased by complexing the DNA with higher Z atoms, and provoking the emission of Auger electrons after inducing a photoelectric effect. This in vivo study evaluates the hypothesis using X-rays from palladium-103 seeds to excite the L-edge of platinum (Pt) atoms bound to the DNA of cancerous cells.

Pt (II) tetrakis(N-methyl-4-pyridyl) porphyrin chloride was used to locate Pt atoms adjacent to the DNA of the KHJJ murine mammary carcinoma; a 2.3-mCi palladium-103 seed was implanted in the tumor.

The tumor periphery received subtherapeutic doses. The rate of tumor growth in mice treated with PAT was slower than in mice treated with brachytherapy only.

The tumor growth delay for PAT-treated mice is attributed to Auger emission from Pt atoms that produced substantial local damage. However, other co-existing mechanisms cannot be ruled out.