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Modified PSA Guidelines For Bone Scanning
(October 2006)
There is
general consensus that at the initial diagnosis of prostate
cancer the Technetium-99M bone scan has a low efficiency - about 1% - for
detecting metastatic cancer when PSA values are less than 20 ng/mL.
However, there is data that indicates that in presentations with Gleason
scores >8 this level might better be lowered so that bone scanning
may be safely avoided at PSA values of <10 ng/mL. An entirely different
issue is what is the diagnostic efficiency of the Technetium scan in the
diagnosis of bone metastases when the disease is recurrent
after primary surgical or irradiation treatment?
This issue
was addressed by Chodak, Iverson, McLeod et al. in J. Urol., July 2006:
"Are Bone Scans Necessary in Men With Low Prostate Specific Antigen Levels
Following Localized Therapy?". Their data base was the Early Prostate
Cancer trial comparing treatment with bicalutamide (4052 men) to a placebo
(4061 men) in men diagnosed with T1-4, MO and N+, N-, or Nx disease.
Serial bone scans (a total of 10,389) were performed at approximately
yearly intervals regardless of PSA levels. Results: "In the groups treated
with radiation therapy or radical prostatectomy, regardless of the
addition of bicalutamide, the incidence of positive bone scans was low
(0.2% to 1.4%) at prostate specific antigen levels of less then 5 ng/mL".
Specifically, for the placebo-treated RP group with PSA levels of <5 ng/mL
only 15 of 2465 (0.6%) scans were positive. In the bicalutamide-treated
post-RP group 5 of 2594 (0.2%) were positive. In the radiation therapy
cohort receiving the placebo 9 of 643 (1.4%) showed positive scans, and in
the bicalutamide treatment RT group 7 of 794 (0.9%) scans were positive at
PSA level of < 5 ng/mL. A "watchful waiting" group was included in the
trial and also received bicalutamide vs. placebo. In this cohort the
positive bone scan rate for PSA values <5 ng/mL was 0.7% vs. 1.3%,
respectively; and for PSA range 5 - 10 ng/mL, 2.3% vs. 2.2%; and for PSA
range 10-20 ng/mL, 3.2% vs. 1.4% - for an overall positivity of less than
2%. The data from the "watchful waiting" group led the authors to conclude
that the level below which a bone scan may be omitted "can be increased to
20 ng/mL with caution in those patients treated with watchful waiting".
This study
deserves credibility since it is the largest of its kind addressing this
issue, and in the authors' opinion "provides sufficient support for
clinicians to eliminate routine bone scans in patients [after primary
therapy] with PSA less than 5 ng/mL".
In the JCO,
March 20,2005, article Kattan et al.,"Pattern of Prostate -Specific
Antigen (PSA) Failure Dictates the Probability of a Positive Bone Scan in
Patients With an Increasing PSA After Radical Prostatectomy", reported
that the PSA level [as discussed above] and post-treatment PSAV were the
only significant predictors of a positive scan. The median PSAV for
positive scans was 1.4 ng/mL/mo vs. 0.12 ng/mL/mo for negative results.
Based on their data a multi-parameter nomogram was constructed to predict
the likelihood of a positive bone scan.
However,
with the increasing use and increased specificity and sensitivity of the
newer non-specific bone tracer, 18F-Fluoride, results from studies using
Fluoride-18 PET/CT for skeletal evaluation will likely lead to revised
parameters for bone scanning. Comparison analyses between the planar scan
using the Technetium tracer and the F-18 PET/CT have shown that the F-18
radioisotope provides improved spacial resolution ( to about 5-6 mm ), and
the associated CT offers more precise anatomic correlation and structural
detail. The current combination of the two in a single procedure offers a
more confident differentiation between benign and malignant lesions. It is
very likely that a lower value will be established for the PSA level at
which scanning provides informative results. In a 2006 review of the new
tracers for scanning in Seminars in Nuclear Medicine, Langsteger et al,
conclude "Therefore, in high risk patients (GsC >7 or PSA doubling time <
3 months) we recommend 18F-fluoride PET/CT and not BS as the primary
staging procedure".
It is
possible that even further changes are afoot in bone scanning technique.
Dr. David Djang, Seattle Nuclear Medicine, commented, "The anatomy is so
good with the F-18 PET that I feel adding the CT gains nothing or
extremely little for anatomical localization. There are some lytic lesion
that will show better on CT, but this is hardly ever the case with the
blastic lesions of prostate cancer. With F-18 PET's greater accuracy
compared to traditional bone scans, I suggest that far fewer MRIs would be
necessary for confirmation/exclusion of disease, and omitting the CT would
save the system money."
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