Medical Brainteaser

According to Jonah Lehrer, in his book: Imagine: How Creativity Works, 97% of the people asked could not come up with a solution to this problem.

You are a doctor faced with a patient who
has a malignant tumor in his stomach. It is
impossible to operate on the patient, but unless
the tumor is destroyed, the patient will
die. There is a kind of ray machine that can
be used to shoot at and destroy the tumor. If
the rays reach the tumor all at once at a
sufficiently high intensity, the tumor will be

109/568 destroyed. Unfortunately, at this intensity,
the healthy tissue that the rays pass through
on the way to the tumor will also be destroyed.
At lower intensities the rays are
harmless to healthy tissue, but they will not
affect the tumor either. What type of procedure
might be used to destroy the tumor
with the rays, and at the same time avoid
destroying the healthy tissue?

See if you can figure this one out... post your answer in the comments.