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The ratio of weight loss to planning target volume significantly impacts setup errors in nasopharyngeal cancer patients undergoing helical tomotherapy with daily megavoltage computed tomography

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ABSTRACT

Background: Changes in head and neck anatomy during radiation therapy (RT) produce setup uncertainties of nasopharyngeal cancer (NPC) irradiation. We retrospectively analyzed image guidance data to identify clinical predictors of setup errors.

Patients and methods: The data of 217 NPC patients undergoing definitive RT on a helical tomotherapy (HT) unit were analyzed. Factors including tumor stage, body mass index, weight loss, and planning target volume (PTV) were assessed as predictors of daily megavoltage computed tomography (MVCT) setup displacements, which were automatically registered using software.

Results: Mean daily setup displacements (in mm) were 1.2 ± 0.6, 1.8 ± 0.8, 3.4 ± 1.4 in the medial-lateral (ML), superior-inferior (SI), and anterior-posterior (AP) directions, respectively. Mean weight loss was 4.6 ± 3.3 kg (6.8 ± 4.9%). Patients with weight loss > 5% had significantly larger setup displacements in the AP (3.6 ± 1.5 vs. 2.9 ± 1.1 mm, p < 0.001) and SI (1.6 ± 0.7 vs. 1.9 ± 0.9 mm, p = 0.01) direction, but not in the ML direction (p = 0.279). The AP setup error increased 0.06 mm (y = 0.055x + 2.927, x: percentage of weight loss/PTV, y: AP displacement) per one percent increase in weight loss normalized to PTV.

Conclusions: Patients with weight loss > 5% and smaller PTVs, possibly because of small body frame or neck girth, were more likely to have increased setup errors in the AP direction.

No MeSH data available.


Setup error of the anterior-posterior (AP) direction at each treatment fraction.
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j_raon-2016-0047_fig_003: Setup error of the anterior-posterior (AP) direction at each treatment fraction.

Mentions: Mean daily setup displacements (in mm) were 1.2 ± 0.6, 1.8 ± 0.8, and 3.4 ± 1.4 in the ML, SI, and AP directions, respectively (Table 2). The displacement was significantly larger in the AP direction than in the ML (p < 0.001) and SI (p < 0.001) directions. The displacement was also significantly larger in SI direction than in the ML direction (p < 0.001). Setup errors greater than 3 mm occurred for 6.1%, 18.0%, and 59.1% of treatment fractions in the ML, SI, and AP directions, respectively (Table 3). There was a trend of increased setup errors toward the end of treatment course, especially in the AP direction (Figures 1–3).


The ratio of weight loss to planning target volume significantly impacts setup errors in nasopharyngeal cancer patients undergoing helical tomotherapy with daily megavoltage computed tomography
Setup error of the anterior-posterior (AP) direction at each treatment fraction.
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Related In: Results  -  Collection

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j_raon-2016-0047_fig_003: Setup error of the anterior-posterior (AP) direction at each treatment fraction.
Mentions: Mean daily setup displacements (in mm) were 1.2 ± 0.6, 1.8 ± 0.8, and 3.4 ± 1.4 in the ML, SI, and AP directions, respectively (Table 2). The displacement was significantly larger in the AP direction than in the ML (p < 0.001) and SI (p < 0.001) directions. The displacement was also significantly larger in SI direction than in the ML direction (p < 0.001). Setup errors greater than 3 mm occurred for 6.1%, 18.0%, and 59.1% of treatment fractions in the ML, SI, and AP directions, respectively (Table 3). There was a trend of increased setup errors toward the end of treatment course, especially in the AP direction (Figures 1–3).

View Article: PubMed Central - PubMed

ABSTRACT

Background: Changes in head and neck anatomy during radiation therapy (RT) produce setup uncertainties of nasopharyngeal cancer (NPC) irradiation. We retrospectively analyzed image guidance data to identify clinical predictors of setup errors.

Patients and methods: The data of 217 NPC patients undergoing definitive RT on a helical tomotherapy (HT) unit were analyzed. Factors including tumor stage, body mass index, weight loss, and planning target volume (PTV) were assessed as predictors of daily megavoltage computed tomography (MVCT) setup displacements, which were automatically registered using software.

Results: Mean daily setup displacements (in mm) were 1.2 &plusmn; 0.6, 1.8 &plusmn; 0.8, 3.4 &plusmn; 1.4 in the medial-lateral (ML), superior-inferior (SI), and anterior-posterior (AP) directions, respectively. Mean weight loss was 4.6 &plusmn; 3.3 kg (6.8 &plusmn; 4.9%). Patients with weight loss &gt; 5% had significantly larger setup displacements in the AP (3.6 &plusmn; 1.5 vs. 2.9 &plusmn; 1.1 mm, p &lt; 0.001) and SI (1.6 &plusmn; 0.7 vs. 1.9 &plusmn; 0.9 mm, p = 0.01) direction, but not in the ML direction (p = 0.279). The AP setup error increased 0.06 mm (y = 0.055x + 2.927, x: percentage of weight loss/PTV, y: AP displacement) per one percent increase in weight loss normalized to PTV.

Conclusions: Patients with weight loss &gt; 5% and smaller PTVs, possibly because of small body frame or neck girth, were more likely to have increased setup errors in the AP direction.

No MeSH data available.