For prosperity and if anyone else finds a need for it. I found
https://github.com/sammiq/dec-decode
This works on Windows XP but needs to be compiled.
Steps
1. Install Go Language for your operating system.
2. Download files from above link.
If using older version. Open command prompt and type the flags file line from above link. If errors (mine did) download flags zip of code manually and extract into folder says can't download software to shown in command prompt and extract into the folder. Open this folder in command prompt and type install.
3. Open folder where you extracted the zip file in the command prompt.
Type in command prompt window.
Build -- filename.exe
Once this has compiled move the exe to the folder goto the folder where your dot.dec files are and drag and drop the iso.dec files on to the exe file and it will start converting.
Happy to assist where I can.