| Intensity modulated radiation therapy (IMRT) for breast cancer decreases acute skin toxicity
One
problem with conventional photon radiation for breast cancer
using a standard tangential beam arrangement is the potential for
significant inhomogeneity of dose. This may negatively
impact upon the acute side effects and long-term cosmesis from
treatment. Presently, acute toxicity of conventional
radiation, including moist desquamation of the skin, is seen in
30-50% of women and is associated with decreased quality of life
during radiation. This
toxicity also increases with standard radiation as the patient
breast size increases. Our hypothesis was that measures to
decrease dose inhomogeneity within the breast and skin with intensity
modulated radiation therapy (IMRT) would reduce acute skin toxicity. We
treated 73
women with early stage breast cancer with breast-conserving surgery
and IMRT. The IMRT
technique involves an iteration method for optimization to generate the
IMRT plan, Monte Carlo dose calculation, and a step-and-shoot technique
using multi-leaf collimation for beam delivery.
Other aspects of the technique including the
clinical definition of the CTV by the physician, patient positioning,
tangential beam orientation, dose and field sizes were unchanged
compared conventional tangential radiation.
These patients
were matched one-to-one to a control group of 60 women treated with
conventional photon radiation by using their bra size and chest wall
separation. There
were no observed differences in the acute toxicity based upon common
terminology criteria for adverse events (CTC) for acute radiation
dermatitis. There was no
desquamation in 42% of IMRT patients, dry desquamation in 37% and moist
desquamation in 21%. The
degree of desquamation was greater for conventional patients compared to
IMRT patients - 52% grade 0, 10% grade 1 and 38% grade 2 (p=0.001).
Subgroup analysis showed desquamation was significantly lower
with IMRT for small (p=0.038) and large breast sizes (p=0.037), but not
medium sizes (p=0.454). For
large breast sizes, the incidence of moist desquamation grade 2 was 48%
with IMRT compared with 79% in controls.
Significant predictors of moist desquamation on stepwise logistic
regression were use of IMRT (p=0.0011) and breast size (P<0.0001). The principal
conclusion of this study is that IMRT for breast cancer was
associated with a decrease in the incidence of acute desquamation
compared with a matched control group treated with conventional
radiation therapy. This supported our hypothesis, and confirmed
our clinical impressions seen in the clinic since the use of IMRT was
initiated in 2003. Our physicians and nurses have been impressed
by the relatively mild acute dermatitis and patient symptoms seen in the
majority of patients treated with IMRT. However, the current CTC
grading system for acute radiation dermatitis may not have been sensitive
enough for this study to evaluate clinically important acute toxicity of
IMRT versus conventional treatment.
Reasons for this are the importance of erythema in the scoring
system, and the wide variation in classifying moist desquamation within
the category of grade 2. There
is a subjective nature to labeling erythema as mild, moderate or severe.
It may have little to no clinical relevance if it does not have
an impact on patient symptoms such as pain during treatment.
In addition, moist desquamation has a large heterogeneity as well
not reflected within the current scoring system.
Our impression was that the desquamation associated with IMRT was
generally less severe than with conventional radiation - however, the
study used highest recorded skin toxicity for comparisons, and could not
reliably gauge the onset, size, severity, and degree of patient symptoms
associated with moist desquamation between IMRT and control patients. We are continuing further study of patient symptoms, quality of life, and cosmesis needed to evaluate the benefit of IMRT for breast cancer.
Bibliographical reference:
Gary M. Freedman Department of Radiation Oncology, Fox Chase Cancer Center, Philadelphia, PA, USA
|