Key points of information in the Kodak guidelines:
"X-ray equipment used to inspect carry-on baggage uses a very low level of x-radiation that will not cause noticeable damage to most films. (Films of ISO 400 and slower tolerate multiple passes)
"However, baggage that is checked (loaded on the planes as cargo) often goes through equipment with higher energy X rays.
"Fog caused by the new (higher energy X-ray) baggage scanners is usually more pronounced than fog caused by other means. Fog from the CAT scan type of scanner typically appears as soft-edged bands 1/4 to 3/8 inch (1 to 1.5 cm) wide. The orientation of the fog stripe depends on the orientation of the film relative to the X-ray beam. The banding may be linear or wavy and can run lengthwise or horizontally on the film. It can also undulate, depending on the combination of the angle of exposure and the multiple laps of film on the roll. (See images below.) However, the fog will usually lack the more subtle patterns produced by traditional types of X-ray equipment. Additionally, whether or not this stripe is seen in the photographic print may depend on scene content. Busy scenes with flowers, foliage, etc. may obscure or lessen the perception of X-ray effects.
"Lead-lined bags, available from photo retailers, will weaken the X-radiation on film and reduce potential harm. However, the effectiveness of any particular lead bag depends on the intensity and electric potential of the X-ray generator, the lead's thickness, and the film speed."
Hand inspection is better than running the film thru the low energy scanners at security checkpoints, even when using the lead bags. If you use the lead bags, they probably will delay you some more, to see what is inside! But many places outside the USA will ignore requests for hand inspection...the guys at London's Heathrow probably don't speak English but speak only Sanskrit, judging by their totally absent response over the past 30 years to my requests for hand inspection.