Irradiation in the management of tumours of the head and neck

The effect of customized beam shaping on normal tissue complications in radiation therapy of parotid gland tumors

The impact of customized beam shaping was studied for five patients with parotid tumors treated with a paired wedged field technique. For each patient two plans were generated. The standard plan had unblocked portals with field sizes defined by the largest target contour found in any CT slice. In the second plan customized beam's eye view (BEV) designed blocks were added to both beams. The differences in the dose distributions between the two types of plans were evaluated using dose-volume histograms (DVH). As expected, the dose distribution within the target volume showed no difference. However, a considerable sparing of normal tissue was observed for the plans with customized blocks. The volume of unnecessary exposed normal tissue that received more than 90% of the prescribed dose, was reduced by a factor of about 4: from 165 to 44% on average, if the volume is expressed as a percentage of the target volume in each patient. In particular, the homolateral mandible showed a mean decrease of 21% of integral dose when blocks were used. Normal tissue complication probabilities (NTCP) were calculated. For a tumor dose of 70 Gy, the average bone necrosis probability was reduced from 8.4% (no blocks) to 4.1% (blocks). For other normal tissues such as nervous tissue, other soft tissues and bones a substantial reduction of integral dose was found for all patients when individual blocks were used.

Irradiation of malignant tumors of the parotid gland

The treatment results in a series of 30 patients with parotid gland carcinoma are reported. Postoperative irradiation to the parotid bed and regional lymph node appears to improve the result of treatment. No difference in the results or complications was found between the group of patients treated by external irradiation or external irradiation combined with radium implantation. Irradiation of residual disease was more effective than irradiation of the recurrences.

Carcinoma of the parotid gland

Sixty-nine patients with parotid gland cancer were studied at the Cancer Control Agency of British Columbia; half were treated successfully. Localized cancers should be treated by total parotidectomy with facial nerve preservation. Facial nerve sacrifice and radical neck dissection for metastatic lymph nodes may be required. If adequate surgery has been done, the histologic type of the tumor significantly determines the outcome. Postoperative radiation to the parotid bed in the more malignant types of tumor is advocated and appears to improve the results of treatment.