Abstract
Background and purpose: To compare the rectal wall and bladder volume in the high dose region with or without
the use of a balloon catheter with both three-dimensional (3D)-conformal and intensity
modulated radiation therapy (CRT, IMRT) approaches in the treatment of prostate cancer.
Material and methods: Five patients with a wide range of prostate volumes and treated with primary external
beam radiation therapy for localized prostate cancer were selected for analysis. Pinnacle™
treatment plans were generated utilizing a 3D conformal six-field design and an IMRT
seven coplanar-field plan with a novel, three-step optimization and with ultrasound
localization. Separate plans were devised with a rectal balloon deflated or air inflated
with and without inclusion of the seminal vesicles (SV) in the target volume. The
prescription dose was 76 Gy in 38 fractions of 2 Gy each. Cumulative dose–volume histograms (DVHs) were analyzed for the planning target
volume (PTV), rectal wall, and bladder with an inflated (60 cc air) or deflated balloon with and without SV included. The volumes of rectal wall
and bladder above 60, 65, and 70 Gy with each treatment approach were evaluated.
Results: Daily balloon placement was well-tolerated with good patient positional reproducibility.
Inflation of the rectal balloon in all cases resulted in a significant decrease in
the absolute volume of rectal wall receiving greater than 60, 65, or 70 Gy. The rectal sparing ratio (RSR), consisting of a structure's high dose volume with
the catheter inflated, divided by the volume with the catheter deflated, was calculated
for each patient with and without seminal vesicle inclusion for 3D-CRT and IMRT. For
3D-CRT, RSRs with SV included were 0.59, 0.59, and 0.56 and with SV excluded were
0.60, 0.58, and 0.54 at doses of greater than 60, 65, and 70 Gy, respectively. Similarly, for IMRT, the mean RSRs were 0.59, 0.59, and 0.63 including
SV and 0.71, 0.66, and 0.67 excluding SV at these same dose levels, respectively.
Averaged over all conditions, inflation of the rectal balloon resulted in a significant
reduction in rectal volume receiving ≥65 Gy to a mean ratio of 0.61 (P=0.01) or, in other words, a mean fractional high dose rectal sparing of 39%. There
was a slight overall increase to 1.13 in the relative volume of bladder receiving
at least 65 Gy; however, this was not significant (P=0.6). Use of an endorectal balloon with a non-image-guided 3D-CRT plan produced about
as much rectal dose sparing as a highly conformal, image-guided IMRT approach without
a balloon. However, inclusion of a balloon with IMRT produced further rectal sparing
still.
Conclusion: These results indicate that use of a rectal balloon with a 3D-CRT plan incorporating
typical treatment margins will produce significant high dose rectal sparing that is
comparable to that achieved by a highly conformal IMRT with ultrasound localization.
Further sparing is achieved with the inclusion of a balloon catheter in an IMRT plan.
Thus, in addition to a previously reported advantage of prostate immobilization, the
use of a rectal displacement balloon during daily treatment results in high dose rectal
wall sparing during both modestly and highly conformal radiotherapy. Such sparing
could assist in controlling and limiting rectal toxicity during increasingly aggressive
dose escalation.
Keywords
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Article info
Publication history
Accepted:
February 20,
2003
Received in revised form:
January 27,
2003
Received:
December 5,
2001
Identification
Copyright
© 2003 Elsevier Science Ireland Ltd. Published by Elsevier Inc. All rights reserved.
