Helical Tomotherapy For Radiochemotherapy In Esophageal Cancer: A Preferred Plan?
J Thorac Dis 2009;1:3-4. DOI: 10.3978/j.issn.2072-1439.2009.12.01.e02
Editorial
Helical Tomotherapy For Radiochemotherapy In Esophageal Cancer: A Preferred Plan?
J Thorac Dis 2009;1:3-4. DOI: 10.3978/j.issn.2072-1439.2009.12.01.e02
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Emerging radiation technologies are aimed at improving that therapeutic ratio in this disease
where the results remain modest at best, and morbidity is significant. Intensity modulated radiation
therapy (IMRT) offer the opportunity to “shape”radiation dose, optimally sparing normal tissue
while allowing adequate coverage to tumor volumes. Dosimetrically, the use of IMRT could be of
benefit in the treatment of esophageal cancer where the target is surrounded by radiosensitive tissues.
Helical tomotherapy is a form of IMRT delivered on a continuous helix, with the source being collimated to a fan beam which is modulated with a binary multi-leaf collimator (7). During treatment,
the patient is moved through a ring gantry resulting in a helical beam delivery. Image-guidance is in
the form of daily pre-treatment megavoltage CT. In this issue of the Journal of Thoracic Disease,
Chen et al. report their results utilizing helical tomotherapy in the definitive and pre-operative management of patient with locally advanced esophageal cancer (8). To date, there is very limited published data on the use of tomotherapy in esophageal cancer. On the basis of dosimetric analysis, one
previous study by Chen et al. found that based on isodose distributions and dose-volume histograms
(DVHs), tomotherapy allowed for sharper dose gradients, more conformal coverage, and better homogeneity when compared with step-and-shoot IMRT or 3D-Conformal Radiotherapy (3D-CRT)
(9). In addition the volume of lung receiving at least 20 Gy (V20) and the volume of heart receiving
V30 and V45 were significantly reduced with tomotherapy. It is notable; however, that tomotherapy
resulted in larger lung volume receiving V10 when compared to 3D-CRT.
In the current study, 20 consecutive patients are treated with concurrent chemoradiation, with ten
receiving definitive 10 patients receiving definitive therapy and 10 going on to surgery. The total
dose to the gross disease was 50 Gy in standard fractionation, with 45 Gy delivered simultaneously to
the regions of subclinical disease, while surrounding normal tissue limits were established prior to
planning. All patients were able to complete the prescribed
chemoradiation with 60% of patients receiving definitive treatment
achieving radiographic complete response (cCR). In addition, 20%
of patients undergoing esophagectomy had a pathologic CR, with
another 40% (4/10) having only microscopic disease. The overall
survival rates for the entire cohort, the definitive chemoradiation,
and tri-modality group were 64.3%, 50.0%, and 78.8% respectively. The rate of acute grade 3 toxicity was 45%, while post-operative morbidity was seen in 60% of patients, including 5 anastomotic leaks and 2 cases of pneumonitis.
The outcomes from this single institution study compare favorably with published studies evaluating both definitive chemoradiation and tri-modality therapy. In addition, the rate of grade 3 acute
toxicity is promising. It is also worth noting that of 8 patients
planned from the start of therapy to undergo neoadjuvant chemoradiation follow by esophagectomy, 7 of those patients were able to
complete that prescribed regimen. As the authors alluded to in the
discussion, the location of the esophagus as a central structure in
the thorax allows for maximal conformal benefit of the tomotherapy technology. In addition, normal tissue is further spared by field
margin reduction on the target that is permitted by utilizing daily
axial imaging.
Helical tomotherapy appears well-suited for the definitive
non-surgical management of locally advanced esophageal cancer.
Dosimetric analysis has shown tomotherapy’ ability to reduce
s
lung V20 and cardiac V30 and V45, dosimetric parameters used to
predict treatment toxicity (9). Among patients receiving non-surgical management, this has translated to a favorable outcome and
toxicity profile in the current study. There may be slightly more
hesitation regarding its widespread use for neoadjuvant therapy.
When chemoradiation is followed by esophagectomy, it appears
that different dosimetric parameters may need to be considered. In
particular, the dose and volume of lung irradiation need to be
strongly considered. Pulmonary toxicity in the setting of
esophagectomy is critical as evidenced by one study reporting a
15% rate of significant pulmonary complications that accounted for
55% of mortality following esophagectomy (10). As mentioned in
the current study, Lee et al. found that with tri-modality therapy,
the dose-threshold for lung volume may be less than expected for
non-surgical treatment, with pulmonary complications noted more
often (35% vs. 8%, p = 0.014) when the pulmonary V10 was at
least 40% vs. less than 40% and when the V15 was at least 30% vs.
less than 30% (33% vs. 10%, p = 0.036) (11). A follow-up study
by Wang et al. found on multivariate analysis that the volume of
the lung spared from doses of at least 5 Gy was the only independent dosimetric factor predictive of pulmonary complication (12).
These data suggest that small doses of radiation, previously felt to
be relatively meaningless, affect the rate of post-operative pulmonary complication and may negatively impact on peri-operative
morbidity and mortality. By the helical nature of tomotherapy dose
delivery small amounts of radiation are deposited in a relatively
large portion of normal tissue depending on tumor location and
size. The authors have identified this potential hazard and in found
the 2 cases of post-operative pulmonary complications that the patients had a V10 of at least 40%.
Overall, the results of this study are promising and warrant further investigation. This technology may allow for dose escalation
where previous studies have failed to demonstrate a benefit. Local
failure continues to be a concern in these patients and perhaps further study of dose escalation with modern technology may improve
upon those results. Additionally, its use in tri-modality therapy
should be further investigated as meaningful dosimetric parameters
of normal tissue toxicity continue to be developed and refined.
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References
Cite this article as: Yang GY. Helical Tomotherapy For Radiochemotherapy In Esophageal Cancer: A Preferred Plan? J Thorac Dis 2009;1:3-4. doi: 10.3978/j.issn.2072-1439.2009.12.01.e02
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