Deterioration of Intended Target Volume Radiation Dose Due to Anatomical Changes in Patients with Head-and-Neck Cancer

SIMPLE SUMMARY: Delivered radiation dose in the patient during a course of 6–7 weeks of treatment can differ from intended radiation dose in the treatment planning. This study analyzes these dose differences in the target volumes in a set of 188 head-and-neck cancer patients. It was found that large dose deteriorations in targets occur in a minority of patients, although more frequently when smaller margins were used. The correlation to visual estimation of differences based on changing anatomy was poor. Therefore, dosimetric selection tools during treatment to assess differences seem warranted to identify patients at risk for under or overdosage. With such tools, patients at risk can be selected to adjust the treatment plan during treatment (adaptive radiotherapy) to correct the radiation dose. ABSTRACT: Delivered radiation dose can differ from intended dose. This study quantifies dose deterioration in targets, identifies predictive factors, and compares dosimetric to clinical patient selection for adaptive radiotherapy in head-and-neck cancer patients. One hundred and eighty-eight consecutive head-and-neck cancer patients treated up to 70 Gy were analyzed. Daily delivered dose was calculated, accumulated, and compared to the planned dose. Cutoff values (1 Gy/2 Gy) were used to assess plan deterioration in the highest/lowest dose percentile (D(1)/D(99)). Differences in clinical factors between patients with/without dosimetric deterioration were statistically tested. Dosimetric deterioration was evaluated in clinically selected patients for adaptive radiotherapy with CBCT. Respectively, 16% and 4% of patients had deterioration over 1 Gy in D(99) and D(1) in any of the targets, this was 5% (D(99)) and 2% (D(1)) over 2 Gy. Factors associated with deterioration of D(99) were higher baseline weight/BMI, weight gain early in treatment, and smaller PTV margins. The sensitivity of visual patient selection with CBCT was 22% for detection of dosimetric changes over 1 Gy. Large dose deteriorations in targets occur in a minority of patients. Clinical prediction based on patient characteristics or CBCT is challenging and dosimetric selection tools seem warranted to identify patients in need for ART, especially in treatment with small PTV margins.