Contrast filled endorectal balloons (ERBs) were evaluated as an alternative to prostate gland fiducial markers for target localization and alignment in post-prostatectomy proton therapy. ERBs were well-tolerated by patients and found to be a reliable, reproducible method for daily alignment. Treatment plans using ERBs achieved similar rectal dose sparing as plans using fiducial markers. ERB patients experienced on average half as many daily table shifts compared to patients aligned using fiducial markers alone. The study concluded that ERBs are an effective tool for localization and alignment in post-prostatectomy proton therapy.

1. 1
Contrast Filled Rectal Balloons in Post-Prostatectomy
Proton Therapy Alignment
Rachel Rendall, B.S. R.T.(T), Lauren Curran, B.S. R.T.(T), John Han-Chih
Chang, MD, Mingcheng Gao, PhD, Daniel Spring, B.S. R.T.(R)(T),
Charles Yoo, B.S., MBA, Mark Pankuch, PhD, William Hartsell, MD
CDH Proton Center, a ProCure Center – Warrenville, IL, USA
Sagittal, axial and coronal view of ERB in XIO for treatment planning. Green outlines TV,
brown outlines the rectum, red outlines the ERB.
Axial, Coronal, Sagittal, and 3D views of planning CT with Re-CT overlay. Position of ERB is
confirmed to be reproducible throughout treatment.
Orthogonal films taken during treatment showing
proper alignment of ERB within contour and
bony anatomy.
Graph 1: Difference in amount of table shifts per fraction.
Graphs 2 and 3: Evaluation of rectum receiving dose. Red line is deviation tolerance.
Introduction
The use of prostate gland fiducial markers in prostate alignment is a
commonly used practice in photon therapy and proton therapy. These
fiducials assist in image fusion, anatomy contouring, creation of
target volumes (TV), and is used for daily target alignment for image
guidance. In the absence of the prostate gland, the localization of
treatment targets is more challenging. Some prostatectomy surgeries
leave surgical clips which can be contoured as a fiducial, however
some surgeries leave no clips. These patients need an alternative way
to localize the prostate bed that can also be used as an alignment
device. Proper immobilization using endorectal balloons (ERB) is
essential to reduce margins, which reduce the dose to normal
structures. ERBs serve as a setup reference device by distending the
rectal wall out of the treatment volume, decreasing the amount of
high dose to the rectum volume.
Methods and Materials
In patients with gold or carbon prostate gland fiducials, the fiducial is
contoured in dosimetry planning with a margin of 1mm to aid in daily
setup. An ERB is contoured with no margin due to the size differential
between the balloon and fiducial. After all contours are finished, the
dosimetrist and physician must evaluate the TV, ERB and rectum
contours. The rectum contour must be outside of the ERB contour
and the TV contour must not overlap the ERB contour.
Results
Discussion and Conclusion
Contrast filled ERBs have shown equivalent results compared to
patients with fiducial markers. Using ERBs is now an alternative
procedure to allow patients without fiducial markers or surgical clips
to be treated at CDH Proton Center, a ProCure Center. ERBs have
shown to be well-tolerated, reliable, reproducible, and an effective
tool for alignment of post-prostatectomy patients as well as efficient
device for treatment planning, so that proper dose sparing of normal
tissue can occur in post-prostatectomy patients.
The entire ERB contour is forced to a
density of 1.0, using the relative
stopping power ratio of the contrast
mix inserted in the ERB to the water
tissue equivalent based on Hounsfield
units. Beam arrangement for ERB
patients are picked to give minimal
dose to the bladder and rectum. The
ideal beamline position has been
determined to be opposing right and
left laterals. After the range and
modulation are determined, the plan is
then checked for deviations regarding
dose limitations and tolerances of
surrounding tissue. If deviations are
present, the dosimetrist will continue
to optimize the plan by editing
apertures and compensators. Once the
plan is determined optimal for the
patient, it is then ready to be exported
to milling, quality assurance and the
treatment room.
Preparation of the ERB is very
important because it is used
as an immobilization device as
well as an alignment device. A
syringe is filled with a pre-
determined amount of
contrast and attached to the
ERB. During the simulation process, it is evaluated whether barium
contrast or a 50-50 Cystografin-water will be used during treatment.
When the patient is positioned on the treatment table, orthogonal x-
rays are taken and the patient is aligned using the anterior ERB
border with the planned ERB contour. Bony anatomy is used to align
the patient superiorly and right to left. A verification film is taken after
table shifts to confirm proper alignment.
Axial and sagittal views of isodose
lines for planned treatment. Red
shaded area is TV, purple outline is
ERB, brown outline is rectum, inner
yellow line is conedown shape.
Evaluation of the dosage to the tumor volume and areas requiring
protection from the proton particle beam compared to the patients
with fiducials show a similar rectal dose to the 50% volume and 70%
volume tolerance limit.
The number of table shifts in prostate patients with fiducial markers
averages two per fraction compared to ERB patients’ average of one
per fraction.
In this study, the ERB patient’s setup parameters and outcomes were
compared to 10 patients who were aligned with fiducial markers daily.
ERB patients did not have any additional acute complications
compared to those with fiducial markers. The highest reported
urinary frequency toxicity was grade one. ERBs average the same
size of localized offset corrections as fiducials, but reduce the
average number of table shifts per treatment by half.