New Jersey Radiation Underdose

It may seem odd that radiation underdoses (>20%) are reportable to the U.S. NRC.  Here's a recent report:

"At 11:30 a.m. [EDT] on July 16, 2013, a patient was being treated for three lesions with an Elekta Leksell Gamma Knife Perfexion unit, serial number 6016, at Cooper Health System in Camden, New Jersey. The prescribed total dose for all three lesions was 58 Gray.

"The first two lesions were treated as planned without incident.

"During treatment of the third lesion, treatment was interrupted because of mechanical failure. A 'Sensor Failure' error occurred, which caused the patient couch to retract and the shielding doors to close. An Elekta service engineer was called and no other treatments were attempted after the 'Sensor Failure'. Treatment of the third lesion was to be re-scheduled.

"It is estimated that only 44.8 Gray out of the prescribed dose of 58 Gray was actually delivered, which is an underdose of greater than 20%."

Why should the U.S. NRC care if someone received LESS radiation than he/she was supposed to?

Shouldn't they only be concerned with radiation overdoses?

The reason underdoses are reported is because:

1.  It shows something is wrong and whatever it is, it could lead to an overdose in different circumstances.

2.  The prescribed dose was intended to cause an effect.  An underdose may not result in the intended effect, and another treatment may be required.  Overall, this leads to an overdose.

Over and underdoses happen frequently around the country, but those who are vocally against nuclear power due to radiation concerns are generally silent on the issue.

It makes me wonder why that is.