Effects of continuous hyperfractionated accelerated and conventionally fractionated radiotherapy on the parotid and submandibular salivary glands of rhesus monkeys

Radiotherapy is a major treatment modality for head and neck cancer. It is often not possible to exclude the salivary glands from the treatment fields. The unique susceptibility of the serous cells of the salivary glands to irradiation often results in xerostomia with ensuing secondary complications and discomfort to the patients. Recent reports have suggested that continuous hyperfractionated accelerated radiotherapy (CHART) can lead to considerably less reduction in salivary flow of the parotid salivary gland than conventional radiotherapy. This study was undertaken to assess histologic changes of salivary glands induced by CHART and conventional radiation fractionation schedules. The parotid and submandibular salivary glands of adult rhesus monkeys were irradiated with cobalt-60 γ radiation at 50 Gy/20 fractions/4 weeks, 55 Gy/25 fractions/5 weeks, or 54 Gy/36 fractions/12 days (CHART). Salivary tissues were harvested at 16 weeks following irradiation and evaluated histopathologically. Microscopically, the glands receiving 50 Gy, 55 Gy, or CHART were virtually indistinguishable. There was severe atrophy and fibrosis of all glands. Quantitative analysis revealed that 50 Gy, 55 Gy, and CHART induced a reduction of serous acini in parotid glands by 86.4%, 84.8%, and 88.8%, respectively. In submandibular glands, serous acini were reduced by 99.4%, 99.0%, and 100%, respectively. The corresponding reduction in mucous acini were 98.4%, 98.4%, and 99.2%, respectively. These histopathologic and quantitative morphologic studies show that the magnitude of serous gland atrophy in the parotid and submandibular salivary glands of rhesus monkeys was similar at 16 weeks after receiving 50 Gy in 20 fractions, 55 Gy in 25 fractions, or CHART