Iain Banks, who announced his diagnosis with gall bladder cancer in April, has posted another update to fans, in which he ruminates on everything from his new car to the possibility of chemotherapy.

The bestselling Scottish novelist has been the recipient of an outpouring of goodwill and support from his readers since he told them in early April that he was "officially very poorly". In a new message to fans, posted online yesterday, he said that his bilirubin level is continuing to fall, and that he has an appointment for a CT scan at the end of the month.

"If my bilirubin is below 50 – and if the tumours have behaved themselves – then chemotherapy will be an option, with these new CT results forming the base line for measuring the improvements chemo might provide," wrote Banks. "If the scan shows the tumours have been over-enthusiastic during the last couple of months, then – as I understand it – chemo would be pointless. Assuming it is an option I'll probably try chemo and see how I react, but if it wipes me out each time I shan't be persevering."

In the meantime, as well as fitting in a holiday on "(mostly) sunny" Barra, Banks has been letting other writers and artists know what they mean to him, with "what was basically a fan letter" sent to Alasdair Gray, "telling him how much his work has meant to me", and "something very similar" conveyed to M John Harrison.

He has also – after six years car-free to reduce his "carbon hoof-print" – bought a six-year-old BMW M5, "so I am back to scudding round the Highland roads again with a big grin on my fizzog (well, when I can grin, and the acceleration/braking force isn't distorting my face like somebody taking part in an early Nasa rocket sled experiment)".

And he is continuing to read the posts left for him by fans on the site, and is "still knocked out by the love and the depth of feeling coming from so many people". "Thank you, all of you," he said. "A few posts with unlikely-sounding cures get skimmed and an even smaller number skipped, following mention of one or more religious Arooga! terms, but together they account for less than one percent of the total."

Banks said he wished he could reply to everyone individually, but he doesn't have the time, so will only comment if there is something factually wrong mentioned. "So far the only point I can remember is one where an ex-neighbour of ours recalled (in an otherwise entirely kind and welcome comment) me telling him, years ago, that my SF novels effectively subsidised the mainstream works. I think he's just misremembered, as this has never been the case," wrote Banks.

"Until the last few years or so, when the SF novels started to achieve something approaching parity in sales, the mainstream always out-sold the SF – on average, if my memory isn't letting me down, by a ratio of about three or four to one. I think a lot of people have assumed that the SF was the trashy but high-selling stuff I had to churn out in order to keep a roof over my head while I wrote the important, serious, non-genre literary novels. Never been the case, and I can't imagine that I'd have lied about this sort of thing, least of all as some sort of joke. The SF novels have always mattered deeply to me – the Culture series in particular – and while it might not be what people want to hear (academics especially), the mainstream subsidised the SF, not the other way round. And … rant over."

The author's new novel, The Quarry, is out on 20 June and is, according to its publisher, "a virtuoso performance whose soaring riffs on the inexhaustible marvel of human perception and rage against the dying of the light will stand among Iain Banks's greatest work".