Assessment of Anatomic Surface Contour Variations During Radiation Therapy in Oral Cavity Cancer Patients with Flap Reconstruction by Co-Registering Planning CT and Cone Beam CT Scan.

BACKGROUND

Oral cavity cancer (OCC) patients undergoing flap reconstruction during surgery present unique anatomical challenges during postoperative radiation therapy (PORT). Variations in body contour and internal anatomy can affect dose distribution and necessitate adaptive radiotherapy (ART). However, limited data is available regarding the frequency, timing, and causes of re-planning.

OBJECTIVE

To evaluate anatomical surface contour variations and the need for adaptive re-planning in OCC patients with flap reconstruction (OCCwFR) receiving PORT using co-registration of planning CT and cone-beam CT (CBCT).

METHODS

This prospective observational study included adult OCCwFR patients treated with curative-intent PORT. Daily portal imaging and weekly CBCTs were analyzed. Variations greater than 1 cm across three or more consecutive CBCTs were considered significant. Changes were categorized as progression, regression, internal target motion, or setup error. Factors associated with adaptive re-planning were recorded.

RESULTS

Among 111 patients, 39 (35%) required re-planning. Regression was the predominant change (92%), mainly due to weight loss (80%), followed by edema resolution and tumor response. Re-planning occurred mostly around the 20th fraction. Progression-related changes were rare (5%) and occurred earlier (3rd week). No association was found between flap type and re-planning (p= 0.21). Weight loss strongly correlated with re-planning (χ²= 45.5, p< 0.0001) and mean volume reduction of 50 cc.

CONCLUSION

Anatomical changes during PORT in OCCwFR patients are frequent, predominantly due to weight loss. Mid-treatment ART around the 5th week and proactive nutritional support are essential to maintain dosimetric accuracy and treatment efficacy.