GCR /alone/, maybe, but it’s, um, strange to pretend the substantial trapped radiation dose on ISS doesn’t exist, as you’re doing here (Table 2 in your linked paper shows the trapped dose at ISS is about equal to the GCR dose at ISS, so ignoring trapped dose makes your estimate off by approximately a factor of 2). It is the total effective dose (including quality factor) which matters, not cherry picking one particular source.