The only program that is capable of working or reliably creating .ptg projects, is ArtRage. The software should support import of all kind of graphics, including Photoshop PSD files and so is technically capable of psd to ptg conversion. However, it is not exactly a conversion, more like a working process in the program.
Convert Adobe Photoshop graphics file to ArtRage project.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert psd to ptg on Windows
A stylish painting package
Convert from psd file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.