Proposed method to study the factors affecting local control with combined external beam and interstitial implantation of mobile tongue and floor of mouth

Twenty‐seven patients with squamous cell carcinoma of the mobile tongue and floor of the mouth were treated with external beam and interstitial radiation. Good prognostic factors were T 1 N 0 , T 2 N 0 , superficial tumors, tumor shrinkage by 75% with external beam, and no apparent tumor clinically 2 months after treatment. On the other hand, T 3 N 0 , T 1‐3 N 1 , and deeply necrotic tumors had a poor prognosis. We recommend using a flexible afterloading system to implant the initial local tumor volume (not just the residual nidus) that does not exceed 45 cm 3 . The minimum (reference) dose was prescribed to a surface 1/2 cm beyond the most peripheral rim of radioactive sources. For acceptable local control and complication rates, our suggested minimum (reference) doses are ⩽7,500 rads for T 1 (or a time‐dose‐fractionation [TDF] of 131‐140), <8,000 rads for T 2 (TDF of 131‐140), and probably < 8,500 rads for T 3 (TDF of ⩽ 150). These guidelines should be considered preliminary.