Multiple
toxicity concerns exist for
patients undergoing combined
modality therapy, including
xerostomia, mucositis, taste
changes, and so forth. However,
among these toxicities, the most
serious and distressing to
patients are related to
swallowing function.
Multiple studies have directly
related patient-assessed quality
of life after head-and-neck
treatment to their swallowing
function
With the
advent of IMRT and the
flexibility to achieve more
complex dose distributions,
radiation oncologists have the
opportunity to attempt to more
precisely sculpt the dose
distributions toward the targets
and away from critical
structures. To use IMRT to
prevent swallowing
complications, one needs to
determine which clinical factors
or anatomic structures, if
changed or spared, would lead to
a reduction in these toxicities.
Therefore, the primary aim of
this study was to find a
relationship between aspiration
and/or stricture formation and
the radiation dose to structures
involved in swallowing function.
The only
clinical predictor of swallowing
toxicity in our study was a
history of smoking. This finding
was not surprising, because
previous work has associated
smoking with more toxicity
during CRT. What was interesting
was the lack of significance of
the primary site and type of
chemotherapy, either in regimen
or sequence. It is possible that
we did not have sufficient power
in this study to identify these
relationships. However, we
believe that the dose effects of
RT are so powerful that they
minimize any small effects of
these other clinical factors.
Published
reports directed at correlating
the radiation dose to the
specific anatomic structures
involved in swallowing have been
limited. Eisbruch hypothesized
that the possible candidate
structures for predicting
complications related to
swallowing included the
pharyngeal constrictors and
glottic and supraglottic larynx.
When tested in a recently
reported prospective study, they
found that the mean dose to the
pharyngeal constrictors and the
partial organ dose for both
constrictors and larynx >50 Gy
both correlated significantly
with the occurrence of
aspiration. They found that the
dose to the superior constrictor
was of greatest significance
When we
examined our data, our results
mirrored those of the University
of Michigan group. We found that
the mean dose to the larynx and
inferior constrictors and the
volume of the larynx receiving
≥50 Gy were the most significant
predictors for aspiration.
However, we did not find as
great a correlation with the
superior constrictor dose.
Because their study (n = 36) was
limited to oropharynx and
nasopharynx patients, we
performed a subset analysis of
our data limiting it to the same
patient group (n = 66). This did
not change the significance of
the doses to the larynx and
inferior constrictor; however,
we did find a stronger
association with the dose to the
superior constrictor (p = 0.01).
The implications of these
two data sets are that avoidance
of either the pharyngeal
constrictors or the laryngeal
structures can prevent
aspiration. Clinicians
should choose the structure that
best fits the clinical scenario
and the limits of their
optimization system. However,
it is our contention that the
larynx is a more realistic
avoidance structure than the
pharyngeal constrictors. In
addition, two recent reports
have correlated swallowing
complications with the dose to
larynx, one correlating the dose
to the laryngeal edema and the
other relating laryngeal dose to
speech-related quality of life
The result of
our study (i.e., that the dose
to the larynx correlated with
aspiration) should not be
surprising. In
two-dimensional head-and-neck
treatment planning, a larynx
block is traditionally inserted
in the low anterior neck to
shield the larynx from RT. How
to translate this practice to
the IMRT setting is a subject of
some controversy. Some have
advocated split-field IMRT
preserving the low neck anterior
approach with the larynx block.
Others have argued a full-neck
IMRT program because of concerns
for low-neck failure with
split-field techniques. We share
the concern for the use of
split-field IMRT, especially
when contouring the posterior
neck nodes in Level V. We have
found that only full-neck IMRT
adequately addresses these nodes
because they often lie deeper
than the depth of a single
anteroposterior photon field. In
addition,
the present study results have
demonstrated no incidences of
aspiration in nearly 100
patients when the dose to the
larynx was limited to 48.2 Gy.
The implication is that if our
constraints are followed, it is
not necessary to use the
split-field technique. However,
we recognize that this will
continue to be an area of
controversy and good reasons
exist to justify both
approaches.
In the
present study, we found a
37% radiographic stricture rate
in our patients.
All these strictures were at the
laryngeal–cricoid level.
None of the patients who had
received a mean inferior
pharyngeal constrictor muscle
dose of <53.9 Gy developed a
stricture. It was
difficult to correlate these
data with the published data,
because robust data on stricture
vs. dose are limited. In a study
by Lee of 199 patients
after concurrent CRT for HNSCC,
21% of the patients developed
stricture. When they
analyzed the prognostic factors,
twice-daily radiation
fractionation, female gender,
and hypopharyngeal primary site
were significant. Our study is
the first, to our knowledge, to
find a dosimetric relationship
between the dose to specific
structures and stricture
formation. We did not find that
patients with laryngeal/hypopharyngeal
primary cancer or patients who
had undergone surgery before RT
were more likely to develop a
stricture. Importantly, we chose
to be aggressive with the
management of these strictures
as detected on video swallow
study and 31 of the 36 patients
underwent immediate dilation,
with only two long-term
strictures. Our overall
stricture rate might appear
high; however, this could have
been a result of a detection
bias. The rate of long-term
strictures in this study was
consistent with both our own
experience and that of other
institutes
Finally, it is important to
emphasize that in addition to
the dosimetric avoidance of the
swallowing structures, a
critical component to improving
swallowing in these patients is
the use of swallowing exercises
and interventions by speech and
swallowing therapists. Studies
have shown the importance of
early intervention by speech and
swallowing therapists and the
improvements that swallowing
exercises can have on
restoration of function
An important
limitation of our study was the
retrospective nature of the
analysis. As such, we did not
have good data on pretreatment
swallowing function. However,
even if we had had this
information, it might not have
contributed significantly to the
results because the swallowing
dysfunction of patients before
treatment is more likely to be
related to tumor burden and
might actually improve during
treatment rather than contribute
to acute on chronic toxicity and
could have confused the present
results. In addition, we used
video fluoroscopy only for
patients who had clinical signs
of swallowing dysfunction at
their initial swallowing
evaluation. This might have
missed some “silent aspirators.”
However, the patients we were
primarily concerned were with
those with clinically relevant
swallowing toxicity; thus,
patients with no swallowing
deficit at all after treatment
were excluded. In, addition in
the study by Feng from the
University of Michigan, >90% of
their patients were free of any
pathologic findings on the
pretreatment evaluation,
confirming our recollection of
our own patients that these
deficits were quite limited.
Nevertheless, more prospective
studies in which all patients
undergo detailed swallowing
analyses are needed to validate
our results.