Comparison of Dosimetric and Biologic Effective Dose Parameters for Prostate and Urethra Using 131Cs and 125I for Prostate Permanent Implant Brachytherapy

• Published in: International journal of radiation oncology, biology, physics Vol. 72; no. 1; pp. 247 - 254
• Main Authors: Sahgal, Arjun, Jabbari, Siavash, Chen, Josephine, Pickett, Barbie, Roach, Mack, Weinberg, Vivian, Hsu, I-Chow, Pouliot, Jean
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.09.2008
• Subjects: 125I; 131Cs; Biologic effective dose; Cesium-131; Dosimetric comparisons; Iodine-125; Prostate brachytherapy; 125I; Iodine-125; 131Cs; Biologic effective dose; Cesium-131; Dosimetric comparisons; Prostate brachytherapy
• ISSN: 0360-3016; 1879-355X
• DOI: 10.1016/j.ijrobp.2008.05.013

To compare the urethral and prostate absolute and biologic effective doses (BEDs) for 131Cs and 125I prostate permanent implant brachytherapy (PPI). Eight previously implanted manually planned 125I PPI patients were replanned manually with 131Cs, and re-planned using Inverse Planning Simulated Annealing. 131Cs activity and the prescribed dose (115 Gy) were determined from that recommended by IsoRay. The BED was calculated for the prostate and urethra using an α/β ratio of 2 and was also calculated for the prostate using an α/β ratio of 6 and a urethral α/β ratio of 2. The primary endpoints of this study were the prostate D 90 BED (pD 90BED) and urethral D 30 BED normalized to the maximal potential prostate D 90 BED (nuD 30BED). The manual plan comparison (α/β = 2) yielded no significant difference in the prostate D 90 BED (median, 192 Gy 2 for both isotopes). No significant difference was observed for the nuD 30BED (median, 199 Gy 2 and 202 Gy 2 for 125I and 131Cs, respectively). For the inverse planning simulated annealing plan comparisons (α/β = 2), the prostate D 90 BED was significantly lower with 131Cs than with 125I (median, 177 Gy 2 vs. 187 Gy 2, respectively; p = 0.01). However, the nuD 30BED was significantly greater with 131Cs than with 125I (median, 192 Gy 2 vs. 189 Gy 2, respectively; p = 0.01). Both the manual and the inverse planning simulated annealing plans resulted in a significantly lower prostate D 90 BED ( p = 0.01) and significantly greater nuD 30BED for 131Cs ( p = 0.01), compared with 125I, when the prostate α/β ratio was 6 and the urethral α/β ratio was 2. This report highlights the controversy in comparing the dose to both the prostate and the organs at risk with different radionuclides.