|
High Dose Rate Conformal Brachytherapy - "The Other Brachytherapy": A Three Institution Consortium Reports Long Term Outcome
(May 2004)
Most times when
prostate brachytherapy is mentioned the technique that comes to mind is
the permanent placement into the prostate of radioactive seeds, either
with the isotope Iodine 125 or Palladium 103 as the source. The prefix "brachy-"
stems from the Greek meaning" short". High dose rate brachytherapy (HDR-BT)
involves the delivery of radiation to the prostate and to as far as 5mm
beyond the capsule through 12 or more temporarily placed catheters. Each
catheter becomes a conduit through which a wire tipped with an Iridium
192 radiation source delivers a planned dose and is then withdrawn. The
length of time that the source remains at its target site determines the
dose to that location. Each catheter is employed sequentially. HDR-BT is
accompanied by treatment with external beam radiotherapy (EBRT).
Multiple authors working in Germany, Michigan, and Seattle (including
Drs. Tim Mate and Steve Eulau) have reported treatment outcome data at a
median follow-up of five years in their article: "Long-term outcome by
risk factors using conformal high-dose-rate brachytherapy (HDR-BT) boost
with or without neoadjuvant androgen suppression of localized prostate
cancer" (Int. J. Radiation Oncology Biol Phys, Vol. 58(4) 1048-1055,
2004). There is considerable overlap in the tumor characteristics of
patients undergoing treatment for prostate cancer with surgery,
permanent seeds, HDR-BT, or EBRT. However, with regard to men being
considered for treatment with radiation therapy, an imperfect
generalization would suggest that low to intermediate risk patients
thought to have organ confined disease are optimal candidates for
treatment with permanent seeds, and HDR-BT and EBRT are a better fit for
intermediate and high risk patients. For patients with significant
medical comorbidities, large prostate glands, significant urinary
obstructive symptoms, or prominent TURP defects, EBRT may be the better
modality. The practitioners of HDR-BT cite advantages for this technique
principally stemming from the positive control over radiation
distribution and the customized dose intensity that this modality
affords. Once the catheters are placed, the HDR delivery system allows
varying the intensity of radiation dose to different areas within the
prostate to as to address varying locations of tumor. They claim that
94% of the targeted areas get 100% of the planned radiation and consider
their technique especially well suited to tumors with a high likelihood
of multifocal disease and extracapsular extension, since the radiation
may be tailored to extend up to 5m beyond the capsule. Even after the
HDR-BT has been completed, further dose targeting can be customized, if
needed, in the EBRT phase. They assert excellent radiation coverage base
to apex, and point out that by carefully shaping the dose distribution
radiation to the urethra can be minimized. The flexibility to customize
the radiation dose afforded by HDR-BT, and the possibility of delivering
higher total doses to the prostate with the HDR-BT/EBRT combination than
can be safely achieved by EBRT alone lead to fewer treatment side
effects, proponents believe. A negative feature for HDR-BT is that it is
heavily labor intensive. As currently practiced in Seattle, HDR-BT
requires an overnight hospitalization during which two applications of 8
to 9 Gy of irradiation are delivered via the catheters (only one
catheter implant procedure required). This HDR-BT dose is approximately
the equivalent of 40 to 50 Gy if delivered by standard EBRT. After HDR-BT,
an additional 45 to 50 Gy EBRT is delivered, for a combined EBRT dose
equivalent of 85 to 90 Gy. The total treatment time is approximately 6
to 7 weeks. EBRT to pelvic nodes is only offered in situations where the
likelihood of nodal spread is considerable, i.e. estimated to be at a
risk greater than 15%.
What are the results of
the HDR-BT/EBRT treatment? The article by Mate, Eulau, et al. presents
the outcome of 593 patients categorized into three risk groups: Group I
(low risk, 46 men) stage < T2a (UICC'92), Gleason score < 6, and initial
PSA < 10 ng/ml; Group II (intermediate risk, 188 men) comprising men who
had one of the following higher risk features, clinical stage > T2b,
Gleason score > 7, or iPSA > 10, replacing a Group I element; and, Group
III (high risk, 359 men) comprising men with two or three of the higher
risk features. The biochemical control rate (as defined by ASTRO) at a
mean follow-up of 5 years for Groups I, II, and III were 96%, 88%, and
69% respectively. The cancer specific survival was 100%, 99%, and 95%
and the overall survival 88%, 86%, and 85%, again respectively.
How do these results
compare to EBRT alone? Kupelian et al. recently reported treatment
outcome of a series of 1352 men with T1-T3 disease treated at the
Cleveland Clinic with EBRT alone (CANCER, March 15, 2004. pp 1283-1292)?
The risk groups were generally similar. However, although the ultimate
goal for comparison between studies is "apples to apples", but most
times it's more like Macintosh to Granny Smith. The biochemical relapse
free survival at a median of 5 years follow-up for the low,
intermediate, and high risk groups was 93%, 83%, and 71% respectively.
Their analysis allowed this encouraging observation: "The most
remarkable observation in the current series was that, among patients
who actually experienced biochemical failure after RT, only 28%
developed a clinical failure (either local or distant) at 10 years after
the failure date." Just as the Vanguard investment guru, John Bogle,
constantly stresses, "cost matters", so in radiotherapy for prostate
cancer, "dose matters". The HRT-BT dose has gradually increased to a
near maximum effectiveness. The total dose delivered by monotherapy with
permanent seed implantation is approximately equivalent to 120 Gy EBRT.
The results I've cited from the Kupelian study are for only those men
who received > 72 Gy, since lesser doses clearly yielded inferior
results. Current doses with conformal 3-D and IMRT technology are
pushing into the 80 and 90 Gy. and local control is steadily improving
with increased irradiation dosage.
Bottom Line:
High dose rate brachytherapy is an effective technique for prostate
cancer treatment and is especially suited for selected patients.
«
Back to Article List
|
