Treatment of Achalasia: Botulinum Toxin Injection vs. Pneumatic Balloon Dilation. A Prospective Study with Long-Term Follow-Up - Allescher, H. D.; Storr, M.; Seige, M.; Gonzales-Donoso, R.; Ott, R.; Born, P.; Frimberger, E.; Weigert, N.; Stier, A.; Kurjak, M.; Rösch, T.; Classen, M. (Endoscopy, 2001)