BWT vs. Other technologies heating:
Contrary to the simplicity
of the conductive-heat mechanism, the "sophisticated” heating is
notoriously known to be non-homogeneous with "hot spots”– burns (in the bladder,
at the posterior bladder wall), and "cold spots” - places of ineffective
heating (in the bladder, at the dome and near the trigone). The claim to fame of the
"other" thermo-chemotherapy for NMIBC is the use of cooled drug that is not
heated while the energy is used to heat only the bladder wall. This
claim is misleading as the precooled drug solution is well heated in two places
during circulation: in the catheter were the drug flows very slowly in the same
lumen where the very hot radiating antenna resides and in the bladder
where the drug stays for a long time close to the catheter with the radiating
antenna. Due to the slow flow in the microwave system, bladder content replaced
every 12-20 minutes – about 60 times slower than in BWT. In the microwave
system, the bladder wall tissue temperature is measured on the surface of
bladder lumen, at the drug-tissue interface. According to physics, with that
slow flow, it is impossible that at this interface the drug is "cold” and the
tissue is "hot” as these two temperatures should be very close to each other.In a standard microwave
procedure this temperature does not exceed 42oC.
Considerations in bladder thermo-chemotherapy:
Efficacy of bladder thermo-chemotherapy in NMIBC is
temperature dependent as proved by a microwave system (Synergo®, targeted
treatment temperature 42oC), where treatments performed above 42oC compared to those performed below 42oC showed 44% increase in
efficacy. Because "heat is heat", efficacy is independent of
the heat source as long as the heat is uniform and does not affect the drug.
Compared to microwave, BWT is performed at a higher uniform temperature (range
Temperatures in the
Large surface area of
the unique conical heat exchanger and the high flow circulation allow a small
temperature delta of only 2OC above the treatment temperature in the
bladder which means that the drug is exposed to very moderate temperature to
maintain its potency. Due to the high flow, the temperature gradient between
entry and exit of the catheter is only 0.8OC to 1.2OC.
Therefore, the uniform temperature inside the bladder is 0.4OC to
0.6OC below the temperature measured at the entry of the catheter and
measuring the temperature inside the bladder is not required.
From bladder surface
down to the bladder wall, bio-physics allows moderate temperature gradient to
about 42OC at 4mm depth (about 0.6OC per 1mm).
® Drug exposure to
The indifference to the heat source is valid as long as the
drug is not exposed to a too high temperature which damages it. In BWT, due to the high-flow circulation of the carefully
heated drug solution, only a small temperature gradient between heat-source and
treatment-site is required to induce an effective heating of the bladder wall. In the microwave system, the drug is exposed to a very high
temperature in the catheter and high temperature in the bladder.
Efficacy of thermo-chemotherapy in NMIBC is also
drug-concentration dependent and it is agreed that higher drug concentration
results in better efficacy. In microwave procedure (which comprises 2
sub-sessions lasting 30 minutes each), the full dose 40mg or 80mg MMC is
divided into two half doses of 20mg or 40mg MMC and each half dissolved in 50ml
water. In contrast, BWT is a 50 minute continuous session where the full dose
40mg or 80mg MMC dissolved in 50ml water.
® Adverse events
and patients’ tolerance
BWT provides better patients’ tolerance and less adverse
events than microwave due to the absence of "hot” spots and to the non-traumatic
insertion of the BWT flexible catheter (which does not include any rigid part).
® Ease of
Compared to microwave, BWT is easier to perform as no
adjustments required during the procedure.
BWT is much more economic than microwave where the BWT
console costs only a fraction of the microwave console and the disposable set
is 50%-70% less than the cost of the microwave one.
Office-based procedures with best patient's tolerance:
· No pain; performed with topical anesthesia only.
· No post-procedure Catheter.
· No rectal, bladder or tissue temperature probes.
· Patient returns back to normal activities the same day.