The Piotron: II. Methods and initial results of dynamic pion therapy in phase II studies.

Negative pi-meson (pion) therapy employing dynamic scanning with a focused spot of convergent beams has been in use since 1981 at SIN. Three-dimensional conformation of the treatment volume to the target volume can thus be achieved. Following previously reported Phase I and Ib clinical trials, a Phase II trial was initiated with the goal of treating primary deep-seated tumors in a dose optimization schedule which included stepwise increase of total pion dose and of target volume. Patients with multicentric superficial bladder tumors who were cystectomy candidates were initially selected. Since then, more invasive cases have been treated. A graded scoring of acute tissue reactions was employed. Follow-up periods were from 10 to 20 months. The pion dose escalation ranged from 3000 rad (minimum) to 3600 rad (minimum) in 20 fractions over 5 weeks. The treatment volumes encompassed 190 cc for local to 1,820 cc for extended volume therapy. Treatment reactions ranged from a faint erythema and increase of bladder frequency to dry desquamation, mild nausea, moderate dysuria, and moderate proctitis or diarrhea with mucus. These reactions were closely related to treatment volume and site. One severe late cystitis has occurred in a patient treated with 2 courses of pions (4475 rad). Mild to moderate late proctitis has been seen in 4 patients. Ten of 13 bladder cancer patients had local control of disease while all 3 pancreas or biliary tract cancer patients had microscopic residual disease locally at time of death from metastasis. A total of 11 of 17 patients are thus clinically or pathologically free of local tumor to time of last observation.