Innovative technique for pulsed dose rate brachytherpy in mobile and base of tongue carcinomas

Abstract

Purpose Continuous low-dose rate interstitial brachytherapy using Pernot's plastic tubes afterloading with loop technique was a well-established treatment modality for localized tongue carcinomas. With the stop sale of iridium wires we must use pulse-dose rate brachytherapy, and replace each loop is by two straight catheters, leading to underdosage at the top of the clinical target volume. To obtain a correct clinical target volume coverage, dwell time of distal dwell positions must be increased creating a risk of mucosa necrosis by overdose. We evaluated the use of a bolus in pulsed-dose rate brachytherapy to mimic the continuous low-dose rate iridium wire loop technique. Materials and methods Three consecutive patients with base of tongue carcinomas referred for interstitial brachytherapy were included. We used pulsed-dose rate brachytherapy with interstitial plastic straight. We replaced the loop technique with catheters protruding above the tongue to ensure that the distal dwell position was above the tongue surface. Catheters were protruding through plastic buttons placed at the top end of the catheter for the control patient and plastic button more one bolus (5 mm-thickness) for two experimental patients. The Paris system for dosimetry was applied. Dose distribution was optimized by increased dwell time for the three distal dwell positions. Dosimetric comparison was performed between control patient and the two experimental patients. Results Six catheters were implanted for the control patient and the first experimental patient and 4 for the second. Ratio between dwell time for the distal dwell positions and the other positions was 2,6 for the control patient, 1,9 and 1,4 for the first and second experimental patients respectively, as to cover at least 98% of the clinical target volume. All patients could receive the whole pulsed-dose rate treatment and the bolus was well tolerated. Conclusion Pulsed-dose rate brachytherapy with bolus application could be an effective and safe alternative to continuous low dose rate iridium wire technique for localized tongue carcinomas treatment.