New Dai Henwood series: 'Optimism won't cure me, but pessimism will kill me'

Spoilers: This story contains details about the three-part series Live and Let Dai.

Preview: Dai Henwood likens the brutal regime of chemotherapy he has undergone to "keeping a classic car on the road" until further treatments emerge.

Henwood was diagnosed with incurable bowel cancer three years ago. It had spread to his liver and cancer was also detected in his lungs.

Over three episodes, Live and Let Dai, which drops on Three on Monday night, documents the popular TV host's courageous and determined battle to keep going with positivity.

"Optimism won't cure me, but pessimism will kill me," he says.

Henwood, who has hosted shows like Dancing with the Stars, 7 Days, Family Feud and Lego Masters, has undergone major surgeries and numerous bouts of chemotherapy. The chemo is tough on body and soul, he says.

"Imagine the worst hangover you've ever had, make that hangover last for four to five days, and you don't even have that small period of good times."

We see Henwood recovering in West Auckland's Piha, after day one of a chemo session.

"I feel sad, I feel broken, I feel so sick."

Things look better on day two, however.

"I've smashed a pie and had a coffee."

Piha is his spiritual home, and the family have a place there. It is where he heals and works on his comedy.

In between bouts of gruelling treatment, Henwood continues to work, telling a crowd in Devonport: "Cancer doesn't all have downsides, I've never been given so much weed in my life."

Much unsolicited medical advice comes his way, he says - little of it based in evidence.

"Turmeric up your bum won't cure anything, it's strictly recreational."

Henwood has had a decades-long love affair with Japan and has practised mediation for years. It forms an important part of his healing.

He meditates on death every day, he says.

"Mediation slows and calms the waters of my brain."

He explains how living with cancer occupies his thoughts constantly.

"I think so often, 'what did I think about before I had cancer?'"

Among the most moving moments in the doco are Henwood's distress that he might not be there for his family. He feels guilt for bringing a heaviness to family life.

"I feel like I need to apologise for having cancer."

While chemo is holding the cancer at bay, there will come a time where he develops resistance, he said.

The "hail Mary" is a drug trial. Progress is being made with immunotherapy for various cancers and Henwood visits an institute in Melbourne which is researching CAR T-cell therapy in solid tumours.

"What was happening as a potential cure for me was happening on our doorstep."

It is a cause for optimism, but tempered with the reality that treatment in a clinical setting is years away.

After 18 rounds of chemo, Henwood takes a break to visit Japan. There, in a monastery, we see him write a letter, tears streaming down his face.

"You don't deserve to be where you are," he writes.

It is part of a Tabidachi or 'departure ceremony'. Henwood must write down, under the watchful eye of a monk, the three most important objects, spiritual practices and people in his life and one by one let them go.

The process leaves Henwood bruised but lighter, he said, he had never "cried so much".

"You have become the wind, you have departed", the monk says, "Get up and feel the joy of living."

"It was almost as if my soul was a chicken, and I was plucking feathers off it 'til it was raw." Henwood says.

Nevertheless, it was a cathartic experience for him.

"Because the fear of death is gone, the joy of living is all that remains."

We also see Henwood where he is most at home, bringing the roof down at the Opera House in Wellington for his Dai Hard one-man show.

"Laughter is now crucial for me to survive," he says.

The documentary is equal parts heavy and light. Henwood says: "I am also confident it is the funniest cancer documentary ever made."