We analyze the formation of three-dimensional spatiotemporal solitons in
waveguides with a parabolic refractive index profile and pure quartic chromatic
dispersion. We show, by applying both variational approaches and full
three-dimensional numerical simulations, that fourth-order dispersion has a
positive impact on soliton stabilization against spatiotemporal wave collapse.
Specifically, pure quartic spatiotemporal solitons remain stable within a
significantly larger energy range with respect to their second-order dispersion
counterparts