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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

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 ± 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.


Related in: MedlinePlus

Linear regression graph of anterior-posterior (AP) setup error and weight loss normalized by planning target volume (PTV) (R2 = 0.059, p < 0.001).
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j_raon-2016-0047_fig_004: Linear regression graph of anterior-posterior (AP) setup error and weight loss normalized by planning target volume (PTV) (R2 = 0.059, p < 0.001).

Mentions: Treatment volume strongly depended on gross disease volume, neck girth, and target margins. To control the effect of treatment volume on weight loss, we normalized the amount of weight loss to PTV. We calculated the normalized weight loss by the ratio of the percentage of weight loss over PTV (cc). As shown in Figure 4, normalized weight loss correlated significantly with setup displacement in the AP direction (R2= 0.059, p < 0.001). For every one percent increase in weight loss normalized to PTV, AP setup error was increased by 0.06 mm (y = 0.055x + 2.927, x: percentage of weight loss/PTV, y: AP setup displacement).


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
Linear regression graph of anterior-posterior (AP) setup error and weight loss normalized by planning target volume (PTV) (R2 = 0.059, p < 0.001).
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5120582&req=5

j_raon-2016-0047_fig_004: Linear regression graph of anterior-posterior (AP) setup error and weight loss normalized by planning target volume (PTV) (R2 = 0.059, p < 0.001).
Mentions: Treatment volume strongly depended on gross disease volume, neck girth, and target margins. To control the effect of treatment volume on weight loss, we normalized the amount of weight loss to PTV. We calculated the normalized weight loss by the ratio of the percentage of weight loss over PTV (cc). As shown in Figure 4, normalized weight loss correlated significantly with setup displacement in the AP direction (R2= 0.059, p < 0.001). For every one percent increase in weight loss normalized to PTV, AP setup error was increased by 0.06 mm (y = 0.055x + 2.927, x: percentage of weight loss/PTV, y: AP setup displacement).

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.


Related in: MedlinePlus