Purpose: To update the incidence of late toxicity of RTOG 9406, a three-dimensional conformal radiation therapy (3DCRT) dose escalation trial for prostate cancer.
Methods and Materials: A total of 1,084 men were registered to this Phase I/II trial of 3DCRT (eligible patients, 1,055). The dose for level I was 68.4Gy; 73.8Gy for level II; 79.2Gy for level III; 74Gy for level IV; and 78Gy for level V. Patients in levels I to III received 1.8Gy/fraction, and those in levels IV to V received 2.0Gy/fraction. Disease group I patients were treated at the prostate only, group 2 patients were treated at the prostate and at the seminal vesicles with a prostate boost, and group 3 patients were treated at the prostate and seminal vesicles. The median follow-up period for surviving patients was 6.1y (level V) to 12.1y (level I).
Results: The incidence rates of RTOG grade 3 or less gastrointestinal or genitourinary toxicity were 3%, 4%, 6%, 7%, and 9% in group 1 and 6%, 2%, 6%, 9%, and 12% in group 2 at dose levels of I, II, III, IV, and V, respectively. In group 1, level V patients had a higher probability of grade 2 late or greater gastrointestinal or genitourinary toxicity than those in levels I, II, and III (hazard ratio [HR]=1.93, p=0.0101; HR=2.29, p=0.0007; HR=2.52, p=0.0002, respectively). In group 2, dose level V patients had a higher probability of grade 2 or greater late gastrointestinal or genitourinary toxicity than those in dose levels II, III, and IV (HR=2.61, p=0.0002; HR=2.22, p=0.0051; HR=1.60, p=0.0276, respectively).
Conclusions: Tolerance to high-dose 3DCRT remains excellent. There is significantly more grade 2 or greater toxicity with a dose of 78Gy at 2Gy/fraction than with 68.4Gy to 79.2Gy at 1.8Gy/fraction and with 74Gy at 2Gy/fraction.