Intrafractional variation of breath-hold radiotherapy for gastric lymphoma.

BACKGROUND

Radiotherapy (RT) for localized gastric lymphoma requires large margins due to respiratory motion. Breath-hold RT is performed to reduce respiratory motion. However, intrafractional variation (IV) during breath-hold RT has not been fully evaluated. We quantitatively evaluated IV during breath-hold RT for gastric lymphoma.

METHODS

Twenty-one patients with localized gastric lymphoma underwent breath-hold RT between 2013 and 2023. They underwent 3-4 computed tomography (CT) simulation scans with breath-holding during the end-expiratory phase of the respiratory cycle. Two radiation oncologists jointly defined a clinical target volume (CTV), and the sum of all CTVs (CTVsum) was defined as the volume covering the CTVs of all CT images. We evaluated CTV changes, displacement of the CTV center, and displacement of each CTV border from the CTVsum. The maximum displacement of the initial breath-hold CT scan (CT1) from the CTVsum was compared with the mean of subsequent breath-hold CT scans (CT2-4) in each direction (anterior-posterior [AP], left-right [LR], superior-inferior [SI]) and across all directions (overall). Factors influencing the maximum overall displacement were assessed using the Mann-Whitney U test (p < 0.05).

RESULTS

Mean CTV was 209 ± 86 cm³, with all patients showing maximum volumetric changes within 4% of the mean CTV. Mean CTV center displacement from the mean center position was 1.6 ± 1.0 mm (AP), 1.1 ± 0.9 mm (LR), and 2.1 ± 1.6 mm (SI). Mean displacement of each CTV border from the CTVsum was 7.5 ± 2.5, 7.2 ± 2.6, 7.2 ± 2.5, and 8.0 ± 2.6 mm for AP, LR, SI, and overall directions, respectively. The displacement of CT1 was significantly larger than that of CT2-4 in all directions (p < 0.001). The overall displacement in patients aged ≥ 70 years was significantly larger than in patients aged < 70 years (10.1 ± 2.5 mm vs. 6.9 ± 2.0 mm; p = 0.01).

CONCLUSIONS

Breath-hold RT for gastric lymphoma achieves a small IV, but significantly larger IVs were observed in CT1 than CT2-4 and in elderly patients. Multiple breath-hold CT scans at simulation are recommended to assess the IV, and application of breath-hold RT in elderly patients should be individualized.