The guitarist received the treatment for lymphoma, after he was diagnosed with the cancer back in January.
The illness came after Black Sabbath announced plans for a reunion tour and new album in November, and so Iommi insisted he carry on working on the project with bandmates Ozzy Osbourne and Geezer Butler.
"Me and Ozzy came to England to work at Tony's studio," Butler told Kerrang!. "He was going to the hospital one day, and we'd go into the studio the next depending on how the chemo was affecting him."
Asked if he really recorded the album in between his chemotherapy sessions, Iommi replied: "Yeah, well, I get bored doing nothing.
"It was good for me to do that. I did feel tired and sick - and it does make you sick, you start throwing up. But on the days when I felt I could do it, we were all there working."
The band revealed that they have recorded 15 new tracks in total and are expecting to write a further two for the new album.
"The stuff we've written is f**king killer, man," Osbourne said. "When we first started playing together again, we were just feeling to see if we bounced off each other. But it's f**king killer!"
Iommi announced that he had completed his course of chemotherapy back in March.
Black Sabbath will headline Download festival this weekend (June 8 to June 10) at Donington Park.
Watch Black Sabbath perform 'Iron Man' back in 2005 below: