The Role of Adaptive Radiotherapy in Definitive Radiation of Nasopharyngeal Cancer: A Review of Dosimetry

OBJECTIVE This study aimed to evaluate the dosimetry changes and provide an overview of the time for radiation planning adjustments. METHODS This prospective cohort study recruited nasopharyngeal cancer patients aged 18 or older. Radiation planning adjustment was performed if at least one normal organ at-risk or target volume deviated from the criteria. RESULTS A total of 11 patients were included as study subjects. After completing up to the 30^th fraction of radi-ation, 8 of 11 patients lost more than 10% of their weight and required adjustments in their radiation plan. The analysis of the relationship between the fractionation time and planning adjustment showed the greatest increase in fractions 11 to 16, RR: 2.83 (1.74–4.61) and 4.76 (2.35–9.65), with a statistically significant result (p=0.000). The widest neck separation demonstrated the highest sensitivity of plan adjustment need (93.3%) and specificity (87.5%) at 1.21 cm with an area under the curve (AUC) of 0.951 and a 95% CI of 0.905–0.996 (p<0.001). The mastoid tip separation showed the highest plan adjustment need sensitivity of 93.3% and specificity of 40.6% at 0.435 cm with an AUC of 0.741, 95% CI 0.631–0.852 (p<0.001). The Δ body weight percentage showed the plan adjustment needs a sensitivity of 91.1% and specificity of 81.2% at 4.49 with an AUC of 0.911, 95% CI 0.844–0978 (p<0.001). CONCLUSION The radiation planning adjustment in patients with locally advanced nasopharyngeal cancer is suggested at the 16^th fraction, the 3^rd week. It is recommended at the widest lymph node area separation of 1.21 cm or a weight loss percentage of 4.49%.