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Malignant salivary gland tumors are relatively rare and account for only 3%-4% of all head and neck cancers. Especially in adenoid cystic carcinoma, the incidence of local recurrence and distant metastases is influenced by the perineural spread of tumor. In advanced salivary gland tumors, surgery alone has a high incidence of local failure. The results of conventional radiotherapy are suboptimal in inoperable or not completely resected salivary gland tumors and in recurrent disease. The pooled data of some international series for low linear energy transfer radiation show a local control of only 28%. Especially in advanced salivary gland tumors, neutron therapy can improve local control. In Europe at least 570 patients with salivary gland tumors have been treated with neutrons alone or with combined modalities. The clinical data of different centers in Europe and the United States result in a similar local control rate of 67% in gross disease. An analysis of different European series shows on average a complication rate of 10.6% for severe radiation-related morbidity. Modern neutron machines and the use of three-dimensional treatment planning systems are now available in a few institutions and may further reduce side effects.

Chordomas are rare malignant neoplasms representing less than 3% of all primary bone tumors. They usually have a benign histological appearance and a slow growth rate. Their locoregional progression nearly always causes suffering and eventually death. Efforts to increase local control have included aggressive surgery, radiation therapy or combined approaches but locally free survival rates remain relatively low and have not exceeded 30% at 5 years. Sacrococcygeal chordomas, which represent approximately 50% of the localizations, have been investigated less frequently than those at the base of the skull or cervical region with primary or post-operative radiation therapy. The disappointing results with photon therapy in a multimodality approach and the good results reported by Schoenthaler with charged particles in the Lawrence Berkeley laboratory led us to propose fast neutron therapy in the management of inoperable or recurrent sacrococcygeal chordomas. Preliminary results obtained from only 12 patients indicate that high linear energy transfer (LET) therapy seems to be a good alternative for radical treatment of chordomas in the case of microscopic or macroscopic residual tumor.

Inoperable locally advanced or inoperable recurrent rectal cancer is a difficult problem. Tenesmus, discharge, bleeding and pelvic pain are frequently present and often are associated with infiltration of the sacral plexus. The value of radiotherapy in managing such patients is being appreciated, although up to 40% of the treated patients have no symptomatic response. Improvement in tumor response and control has been scored through efforts to overcome the radio resistance of the hypoxic tumor cells by neutron irradiation. This article is an account of the activity of neutron radiotherapy in such patients. Over 350 patients were entered in studies comparing neutrons used alone and neutrons used in a mixed-beam treatment schedule. At present no therapeutic gain for long-lasting survival has been achieved; however, local control and pain improvement seems to be better with neutrons than with photons.