MSOR04  Presentation Time: 8:45 AM: Outcomes with High Dose Rate Brachytherapy in Reirradiation of Head and Neck Cancers

Purpose Reirradiation of recurrent or second primary head and neck cancers (HNC) after prior therapy is a challenge. After prior definitive external beam radiotherapy (EBRT), reirradiation is limited by normal tissue tolerances and expected outcomes are modest with a minority achieving durable control. Outcomes of EBRT reirradiation have been widely variable, historically reporting 2-year locoregional control (LRC) rates of 40-60% and overall survival (OS) rates of 15-30%, with a small number of series achieving LRC rates up to ∼60%. Reirradiation can be associated with increased morbidity with high grade toxicity rates estimated at ∼25-50%. This study evaluated the hypothesis that high dose rate brachytherapy (HDR-BT) would improve cancer outcomes without worse toxicity. Materials and Methods Included were all patients treated with HDR-BT after having previously received definitive EBRT for primary HNC squamous cell carcinoma (SCC) from 2011-2021. Patients had either recurrent disease or second HNC primaries. Clinical and treatment characteristics and CTCAE-graded toxicity were summarized with descriptive statistics. Survival outcomes were estimated with the Kaplan Meier method. Results Twenty-three patients were evaluated. Median follow up time was 19mo (IQR 12-36mo). Median age at time of HDR-BT was 64 years (IQR 60-69 years). Thirteen patients (57%) were treated for recurrent HNC, of which 7 were in the oral cavity and 6 were in the oropharynx. Ten patients (43%) were treated for a second primary HNC, of which 5 were in the oral cavity and 5 were in the oropharynx. Median time from completion of prior EBRT to receiving HDR-BT was 41mo (IQR 14-73mo). Within their retreatment course, 11 patients (48%) were treated with HDR-BT after resection, 9 patients (39%) received concurrent hyperthermia, and 7 patients (30%) received chemotherapy. HDR-BT regimens included 600cGy x5 (N=11), 600cGy x6 (N=6), 450cGy x8 (N=1), 1500cGy x1 (N=1),1000cGy x1 (N=1), 500cGy x8 (N=1), and 700cGy x5 (N=1). One patient who was treated with two implants received 450cGy x 3 followed by 475cGy x5. Nine patients (39%) experienced grade ≥3 toxicity. These toxicities consisted of fistula, soft tissue necrosis, osteoradionecrosis, ulcer, hemorrhage, and dysphagia requiring a chronic feeding tube. Nine patients (39%) experienced a local recurrence with a median local control of 29mo. Three patients (13%) experienced regional relapse, and median regional control was not reached. Ten patients (43%) remained alive at the time of analysis, and median overall survival time was 17mo. Actuarial 2-year local control, regional control, and OS rates were 68%, 89%, and 62%, respectively. Conclusion Our data suggests that HDR-BT for re-irradiation of HNC can provide durable control compared to historical reports and should be further explored as a salvage treatment option for recurrent or second primary HNC. In addition, potential associated toxicities of HDR-BT do not apparently occur at a higher rate than expected with standard reirradiation. Reirradiation of recurrent or second primary head and neck cancers (HNC) after prior therapy is a challenge. After prior definitive external beam radiotherapy (EBRT), reirradiation is limited by normal tissue tolerances and expected outcomes are modest with a minority achieving durable control. Outcomes of EBRT reirradiation have been widely variable, historically reporting 2-year locoregional control (LRC) rates of 40-60% and overall survival (OS) rates of 15-30%, with a small number of series achieving LRC rates up to ∼60%. Reirradiation can be associated with increased morbidity with high grade toxicity rates estimated at ∼25-50%. This study evaluated the hypothesis that high dose rate brachytherapy (HDR-BT) would improve cancer outcomes without worse toxicity. Included were all patients treated with HDR-BT after having previously received definitive EBRT for primary HNC squamous cell carcinoma (SCC) from 2011-2021. Patients had either recurrent disease or second HNC primaries. Clinical and treatment characteristics and CTCAE-graded toxicity were summarized with descriptive statistics. Survival outcomes were estimated with the Kaplan Meier method. Twenty-three patients were evaluated. Median follow up time was 19mo (IQR 12-36mo). Median age at time of HDR-BT was 64 years (IQR 60-69 years). Thirteen patients (57%) were treated for recurrent HNC, of which 7 were in the oral cavity and 6 were in the oropharynx. Ten patients (43%) were treated for a second primary HNC, of which 5 were in the oral cavity and 5 were in the oropharynx. Median time from completion of prior EBRT to receiving HDR-BT was 41mo (IQR 14-73mo). Within their retreatment course, 11 patients (48%) were treated with HDR-BT after resection, 9 patients (39%) received concurrent hyperthermia, and 7 patients (30%) received chemotherapy. HDR-BT regimens included 600cGy x5 (N=11), 600cGy x6 (N=6), 450cGy x8 (N=1), 1500cGy x1 (N=1),1000cGy x1 (N=1), 500cGy x8 (N=1), and 700cGy x5 (N=1). One patient who was treated with two implants received 450cGy x 3 followed by 475cGy x5. Nine patients (39%) experienced grade ≥3 toxicity. These toxicities consisted of fistula, soft tissue necrosis, osteoradionecrosis, ulcer, hemorrhage, and dysphagia requiring a chronic feeding tube. Nine patients (39%) experienced a local recurrence with a median local control of 29mo. Three patients (13%) experienced regional relapse, and median regional control was not reached. Ten patients (43%) remained alive at the time of analysis, and median overall survival time was 17mo. Actuarial 2-year local control, regional control, and OS rates were 68%, 89%, and 62%, respectively. Our data suggests that HDR-BT for re-irradiation of HNC can provide durable control compared to historical reports and should be further explored as a salvage treatment option for recurrent or second primary HNC. In addition, potential associated toxicities of HDR-BT do not apparently occur at a higher rate than expected with standard reirradiation.