Author's reply to Paulides’ commentary on developing effective hyperthermia application for nasopharyngeal cancer

We thank Dr Paulides et al. [1] for their interest and their comments concerning our recent phase III clinical study about using hyperthermia to treat nasopharyngeal cancer [2].

Our hyperthermia applicator system was designed by Professor Li and obtained a national patent (P.R. China). It consists of a hot wire and two temperature probes. There are two ports at the bottom of the applicator, one port is used to transmit the temperature signal to the central controller, and then the output signal through another port adjusts the power of the hot wire to keep the temperature at a defined level.

Before this was used clinically, we conducted thermometry experiments in the nasopharynx of a beagle dog. We put seven thermometers in different locations to measure the temperature around the nasopharynx cavity during heating. Three thermometers were 2 cm deep to the nasopharynx mucosa, two thermometers were 3 cm deep to the mucosa, and two thermometers were 4 cm deep to the mucosa. The hyperthermia applicator was put to the nasopharynx cavity through a nostril. We found, when the applicator showed the temperature was 43–43.5°C, the two thermometers 3 cm deep to the nasopharynx mucosa measured 42.7°C, which was in the scope of the effective hyperthermia temperature. So we deduced the effective treatment space can cover the 3-3.5 cm deep to the mucosal surface.

According to the experimental data, we can infer that the paranasopharyngeal space was included in the effective hyperthermia scope. The treatment volume of nasopharyngeal cancer was very irregular, the space of 90% treatment volume was also irregular, so T90 was difficult to describe. In our paper, we define the T90 as the lowest temperature in paranasopharyngeal space. The hyperthermia applicator had only one temperature reading representing the nasopharynx surface, not the temperature of paranasopharyngeal space. The T90 was estimated from the experimental data, as described above.