Materials/Methods:
1453 men with prostate cancer underwent low dose rate brachytherapy using either an 125I implant, a 103Pd implant or the combination of external beam radiotherapy with a 103Pd implant and had a minimum of two year follow-up. All patients were followed prospectively at six-month intervals and given an American Urological Association Symptom Score (AUASS) sheet pre-implant and at the time of follow-up evaluation. CT based post-implant dosimetry was done at one month following the implant and the dose to 90 percent of the prostate (D90) was used for the calculation of the LDR component of the total treatment BED. The linear quadratic model was used to determine the BED using the equation, BED=nd[1+(d/α/β)], for external beam radiotherapy. The equation used to calculate the BED for LDR implants was BED=(R0/λ){1+[R0/(μ+λ)(α/β)]}. The α/β ratio was hypothesized to be similar to late responding normal tissues and assigned a value of 2Gy for prostate mediated urinary bother. For analysis, patients were divided into four BED groups: 140-169, 170-209, 210-239, 240-270. The mean AUASS was compared for each BED achieved by either LDRM or LDREBRT using the Student T-test at each follow-up interval. The intervals were between 1-6 months, 6-12 months, 12-24 months, 24-36 months and 36-48 months. Results: 533 patients achieved a mean BED of 206 Gy (range 158-266) with LDREBRT compared to 194 Gy (range 140-260) for 919 patients treated with LDRM (p=0.000). There was no significant difference between the mean AUASS of patients who achieved a BED of between 140-169 Gy treated with either LDREBRT or LDRM at any follow-up interval. There was a significant difference in mean AUASS among the group treated to a BED of 170-209 at the 6 month interval, LDREBRT mean AUASS of 11.7 versus 13.1 for LDRM (p=0.02). In addition, a significant difference was found in the group treated to a BED of 210-239, with the mean AUASS of LDREBRT 11.1 versus 14.7 at six months (p=0.000). No difference in mean AUASS was noted for the relatively small group (45 patients) achieving a BED of 240-270. Conclusions: The LDREBRT approach to radiotherapy dose escalation for prostate cancer appears to offer clinically meaningful benefit to patient's urinary quality of life by affording a relative decrease in urinary bother over LDRM at very high radiotherapy doses, above what is commonly prescribed. Should dose escalation be considered, the patient and care team may consider combination therapy more attractive than monotherapy because of the decrease in acute urinary morbidity. Author Disclosure: J.A. Cesaretti, DOD, B. Research Grant; CR BARD, F. Consultant/Advisory Board; R.G. Stock, CR BARD, F. Consultant/Advisory Board; N.N. Stone, Prologics, E. Ownership Interest; B.S. Rosenstein, None. |
