Manslaughter charges arises from radiation overdoses given to nearly 450 cancer patients in a French hospital, for which two doctors and a radio physicist were due to go on a trial.
At least seven people died as a result of overdoses administered to patients at the Jean Monnet hospital in Epinal in northeastern France between 2001 and 2006.
At least 24 people treated between May 2004 and August 2005 received 20 percent more radiation than they should have due to a calibration error.
Scores of victims are due to testify from Monday until October 31, some of them by video-link because they are too ill to attend court.
The two doctors, Jean-Francois Sztermer, 64, Michel Aubertel, 62, and radio physicist Joshua Anah, 54, are accused of involuntary homicide, not helping people in danger and destroying evidence.
Three health executives are also in the dock on charges of not helping people in danger.
The errors occurred when the radiation machines were being upgraded with new ones acquired in 2004 and also due to doses being miscalculated.
Michel Noel, 63, said he wanted justice.
"My state of mind before the start of the trial is not good," said Noel, who underwent treatment at the general hospital for prostrate cancer at the end of 2005.
"All that I hope for is that the officials accept their errors and are sentenced," he told AFP.
"I live with a pouch (that collects urine) and I cannot have sex," he said. "It's very difficult."