Parotid glands in whole-brain radiotherapy: 2D versus 3D technique for no sparing or sparing

Whole-brain radiotherapy is performed as standard therapy in patients with multiple brain metastases and in patients with more favourable prognosis such as lymphoma and small-cell lung carcinoma in the prophylactic setting. Because of the prognosis and the total prescribed dose, the parotid glands are not usually regarded as an organ at risk in whole-brain radiotherapy. Long-term survival can be expected in some of these patients and late toxicity can be observed, becoming essential to evaluate organs at risk, particularly the parotid glands even in metastatic patients. We compared the 2D with 3D technique to evaluate parotid glands involvement and received dose, and coverage of the clinical target volume.

Seven patients were considered. The prescribed dose was 30 Gy in ten fractions. On the same day and with the same set-up, all the treatment planning were performed using a 2D and 3D technique. A treatment plan was performed following same technical characteristics as the 2D technique. The parotid glands and whole brain were delineated. Dose-volume statistics were analysed.

Dose-volume histograms of the parotid glands showed that 2/7 patients (28 %) received a mean dose >20 Gy. We found a lack of coverage of the clinical target volume in 6/7 patients.

Planning whole-brain radiotherapy with only the 2D technique involves a risk of including parotid glands in the field and not covering the clinical target volume. The 3D technique should be systematically performed and the parotid glands should be regarded as an organ at risk in whole-brain radiotherapy.