Dose rate correction in medium dose rate brachytherapy for XXXX .

@entity1 @entity189
PURPOSE: To establish the magnitude of brachytherapy dose reduction required for stage IIB and III @entity189 @entity1 treated by external radiation and medium dose rate (MDR) brachytherapy at a dose rate of 220+/-10 cGy/h at point A. MATERIALS AND METHODS: In study-I, at the time of MDR brachytherapy application at a dose rate of 220+/-10 cGy/h at point A, @entity1 received either 3060 cGy, a 12.5% dose reduction (MDR-12.5), or 2450 cGy, a 30% dose reduction (MDR-30), to point A and they were compared to a group of previously treated LDR @entity1 who received 3500 cGy to point A at a dose rate of 55-65 cGy/h. Study-II was a prospective randomized trial and @entity1 received either 2450 cGy, a 30% dose reduction (MDR-II (30)) or 2800 cGy, a 20% dose reduction (MDR-II (20)), at point A. @entity1 were evaluated for local control of disease and morbidity. RESULTS: In study-I the 5-year actuarial local control rate in the MDR-30 and MDR-12.5 groups was 71.7+/-10% and 70.5+/-10%, respectively, compared to 63.4+/-10% in the LDR group. However, the actuarial morbidity (all grades) in the MDR-12.5 group was 58.5+/-14% as against 34.9+/-9% in the LDR group (P < 0.05). Similarly, the grade III and IV morbidity also in the MDR-12.5 group was 12.5+/-9% as against 5.3+/-5% in the LDR group (P < 0.05). No statistically significant difference in morbidity was seen between the MDR-30 and LDR groups. In study-II the 3-year actuarial local control rate in the MDR-II (30) and MDR-II (20) groups was 66.6+/-10% and 74.8+/-9%, respectively. There was a significant correlation between the rectal BED received and the percentage of @entity1 developing rectal morbidity. Only 10% of @entity1 receiving a rectal BED of (100 < 120) Gy3 developed complication as against 62.5% of those receiving a rectal BED of (140 < 160) Gy3 (chi2 = 46.43; P < 0.001). CONCLUSION: We suggest that at a dose rate of 220+/-10 cGy/h at point A the brachytherapy dose reduction factor should be around 30%, as suggested by radiobiological data, to keep the morbidity as low as possible without compromising the local control rates.
