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Written Assignment #1- Part 2
Concept Map:
History of Breast
Cancer
Treatment Breast
Conservation Therapy
Treatment
Mastectomy
Treatment Concers:
Lung V20, Hotspots
and Breast Bridge
Sep.
Supine Treatment
Position
Prone Treatment
Position
Methods
Methods
Results
Results
Discussion and
Conclusion
Discussion and
Conclusion
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“Comparing Critical Structure Dose: Prone vs Supine Breast Treatments”1, by Richard McKinnes and
Kevin Collins, objectively compare prone versus supine breast treatment for early stage breast cancer.
The authors clearly state their objectives in the purpose section and continue to adhere to “research
article” format throughout the peer review. The purpose (abstract) section was followed by an
introductory section which chronicled the history of breast cancer treatment through present day. It
emphasized that conservative therapy, although the current treatment of choice is not without its
challenges. A major consideration of treatment is the V20, the volume of lung that receives 20 Gray
(Gy). This value is not only an indication of radiation pneumonitis, but may play a factor in these
patients developing lung cancer according to a 2006 literature review study by Levi. This study inclusion
is relevant to the peer review because it examines the incidence of lung cancer in patients that have
received radiotherapy versus another form of treatment for breast cancer.
The methods section stated that the number of participants for this peer review was 25. This is a small
sample population, but final results could warrant continued research with a larger population. A “t”
test was used to compare the three variables that were to be indicative of the effectiveness of prone
versus supine treatment. The “t” test is used to define the difference in variables and illustrate if two
samples differ significantly from each other. The three variables to be compared included lung V20,
global max spot and breast bridge separation. The 25 patients were planned using the Varian Eclipse
treatment planning system. Of the 25 patients, 14 were treated supine and 11 prone, all utilized
tangent only treatment fields and all were right breasts. The authors did not indicate the criteria for how
the patient position was chosen. It was also indicated that one prone patient’s V20 was not recorded,
but a reason was not mentioned. The three variables selected appeared to be objective and reliable.
The results were clearly stated in table formats. The lung V20 mean of patients treated in the prone
position (1.49%, SD=2.42%) was significantly less than the mean of patients treated in the supine
position (10.92%, SD=3.53%). The mean scores for the global max hot spots for both sets of patients also
exhibited a significant difference. The global max hot spot for supine patients (115.14%, SD=5.26%) was
higher than that for prone patients (107.57%, SD=2.5%). Finally, the mean for the breast bridge
separation of prone patients (17.78cm, SD=3.51cm) was significantly smaller than the mean for supine
patients (24.87cm, SD=4.73cm). The “t” test format appeared to be an adequate and objective research
tool for this peer review.
The discussion section logically evaluated the results of each of the tested variables. It stated that the
reason for the low V20 in prone breast patient was because this technique allowed gravity to force the
breast tissue away from the chest wall, thus allowing good coverage of the breast tissue, reducing lung
volume and eliminating the lung from the field. Dose volume histogram results were also listed to
compare prone versus supine treatment lung volume. The discussion alluded to the global max hot spot
being lower because of the decreased breast bridge diameter when the patient was prone. The thinner
the body part, the lower the hot spot. The prone breast contour displayed on the included transverse
slice resembled a rectangle. The presented information did not appear to be biased.
The conclusion adequately summarized the peer review. It stated that its findings offered viable
solutions to physicians that are concerned with breast treatment lung dose. The discussion also noted
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that since the elongated prone breast resembled more of a uniform structure than the supine breast,
less “field-in-field” segments could be used to achieve a uniform plan distribution. It was also noted that
although prone breast irradiation has its merits, it is not ideal for all patients. Obese patients and those
not very mobile may find the prone position difficult to achieve. If the patient is unable to hold the
position because of discomfort, this will necessitate more time on the treatment table and a setup that
is not reproducible.
In conclusion, the prone position technique should be considered as a method to help reduce the
magnitude of hot spots and the lung volume in a field. The limitations observed in this study include a
small sample size and exclusion of patients planned in both positions. Further research is needed to
evaluate patients simulated in both positions, thus allowing all variables to remain constant with only
the treatment position changing.
References:
1. McKinnes, R, Collins, K. Comparing Critical Structure Dose: Prone vs Supine Breast Treatments. ASRT
Radiation Therapist. 2011;20(2):103-107.