Predictive value of linear-quadratic model in the treatment of cervical cancer using high-dose-rate brachytherapy

Abstract Purpose : To determine whether a dose-response relationship exists between the biologic effective dose (BED) at Point A and the bladder and rectum and the clinical outcomes in our experience with external beam radiotherapy (EBRT) and high-dose-rate brachytherapy in the treatment of cervical carcinoma. Methods and Materials : This was a retrospective study. A total of 49 patients with cervical cancer were treated with a combination of EBRT (median 45 Gy, range 41.4–50.4) and high-dose-rate brachytherapy (median 18 Gy; range 18–19, in two fractions). Twenty-three patients received concomitant cisplatin-based chemotherapy. The cumulative BEDs were calculated at Point A (BED 10 ) and at bladder and rectal reference points (BED 3 ) using the linear-quadratic equation. The BED 10 values, after incorporating a time factor (BED 10 tf) in the formula, were also calculated. Results : In patients treated with RT alone, the local failure rate was 10% (1 of 10) and 19% (3 of 16) in patients receiving a BED 10 >89 Gy 10 or 10 to Point A, respectively ( p = 0.2). The corresponding local failure rates were 20% (3 of 15) and 0% (0 of 8) in patients treated with concomitant chemotherapy ( p = 0.3). In patients treated with RT alone, the local failure rate was 7.7% (1 of 13) and 23% (3 of 13) in patients with a BED 10 tf >64 Gy 10 or 10 ( p = 0.1), respectively. The median BED 3 values at the rectal and bladder point was 95.5 Gy 3 and 103.6 Gy 3, respectively. Only 1 case of Grade 2 late rectal toxicity (2%) and no late bladder toxicity occurred. Conclusion : In patients treated with RT alone, a BED 10 >89 Gy and a BED 10 tf >64 Gy indicated a trend toward a better local control rate. This difference was not observed in patients receiving chemotherapy. A BED 3 3 was associated with negligible late toxicity. Although the BED 10 in our study was about 10–15 Gy 10 less than that in the published data, the 4-year local control rate of 80% and 83% and disease-free survival rate of 75% and 70% with and without chemotherapy, respectively, compare well with the rates in other studies in the literature.