For head and neck cancer, they usually like to keep the "total treatment package" less than 100 days for better tumor control, survival. After the neck dissection, radiation is usually done within 4-6 weeks, depending on healing. Sounds like brachytherapy, which is an option for radiation or permament seeds, which I'm not as familiar with. There is low dose rate, LDR, and Hgh Dose Rate, HDR, Brachytherapy can be given solely or as a boost to EBRT, Extetnal Beam Radiation also, within 1-2 weeks. I had a newer form of Brachtherapy called High Dose Rate Intraoperative Radiation Therapy, HD-IORT, during resection of tumor, followed by IMRT after healing, and a 2nd one this year with Proton Therapy.

Good luck.