Christian S Adame González1,2, José Trinidad Álvarez Romero3, Mario Moranchel Y Rodríguez2, Armando Félix Leyva4, Michelle Aline Villavicencio Queijeiro5, María Yicel Bautista Hernández6. 1. Departamento de Física Médica, Centro Médico Nacional 20 de Noviembre, Ciudad de México, Mexico. 2. Instituto Politécnico Nacional, Escuela Superior de Física y Matemáticas, Ciudad de México, Mexico. 3. LSCD, Instituto Nacional de Investigaciones Nucleares, La Marquesa, Ocoyoacac, México. 4. Departamento de Radioterapia, Hospital de Oncología, Centro Médico Nacional, Siglo XXI, Ciudad de México, Mexico. 5. Departamento de Radioterapia, Centro Médico Nacional 20 de Noviembre, Ciudad de México, Mexico. 6. Departamento de Radioterapia, Hospital General de México, Dr. Eduardo Liceaga, Ciudad de México, Mexico.
Abstract
BACKGROUND: The aim of the study was to Estimate and compare the radiobiological ratio α/β with the heuristic method for a cohort of Mexican patients with prostate cancer (PCa) who were treated with external radiotherapy (RT) techniques at three Hospital Institutions in Mexico City. With the Kaplan-Meier technique and the Cox proportional hazards model, the biochemical relapse-free survival (bRFS) is determined and characterized for cohorts of Mexican patients with PCa who received treatment with external RT. Using these clinical outcomes, the radiobiological parameter α/β is determined using the heuristic methodology of Pedicini et. al. MATERIALS AND METHODS: The α/β is calculated from the survival curves for different treatment schemes implemented at three distinct hospitals. The Pedicini's techniques allow to determine the parameters α/β, k and N 0 when treatments are not radiobiologically equivalent, therefore, are built up of a set of curved pairs for the biologically effective dose (BED) versus the ratio α/β, where the ratio is given by the intersection for each pair of curves. RESULTS: Six different values of α/β were found: the first α/β = 2.46 Gy, the second α/β = 3.30 Gy, the third for α/β = 3.25 Gy, the fourth α/β = 3.24 Gy, the fifth α/β = 3.38 Gy and the last α/β = 4.08 Gy. These values can be explained as follows: a) The bRFS of the schemes presents a statistical variation; b) The absorbed doses given to the patient present uncertainties on the physical dosimetry that are not on the modeling; c) Finally, in the model for the bRFS of Eq. (3), there are parameters that have to be considered, such as: the number of clonogenic tumor cells N 0 , the overall treatment time (OTT), the kick-off time for tumor repopulation T k and the repopulation doubling time. Therefore, the mean value to α/β for all schemes has an average value of 3.29 (± 0.52) Gy. CONCLUSIONS: The value of α / β ¯ = 3.29 ( ± 0.52 ) Gy is determined from cohorts of Mexican patients with PC a treated with external radiotherapy using the time-dependent LQ model, which is a higher value with respect to the "dogma" value of α/β 1.5 Gy obtained with the LQ model without temporal dependence. Therefore, there is a possibility of optimizing treatments radiobiologically and improving the results of bRFS in Mexican patients with PCa treated with external radiotherapy.
BACKGROUND: The aim of the study was to Estimate and compare the radiobiological ratio α/β with the heuristic method for a cohort of Mexican patients with prostate cancer (PCa) who were treated with external radiotherapy (RT) techniques at three Hospital Institutions in Mexico City. With the Kaplan-Meier technique and the Cox proportional hazards model, the biochemical relapse-free survival (bRFS) is determined and characterized for cohorts of Mexican patients with PCa who received treatment with external RT. Using these clinical outcomes, the radiobiological parameter α/β is determined using the heuristic methodology of Pedicini et. al. MATERIALS AND METHODS: The α/β is calculated from the survival curves for different treatment schemes implemented at three distinct hospitals. The Pedicini's techniques allow to determine the parameters α/β, k and N 0 when treatments are not radiobiologically equivalent, therefore, are built up of a set of curved pairs for the biologically effective dose (BED) versus the ratio α/β, where the ratio is given by the intersection for each pair of curves. RESULTS: Six different values of α/β were found: the first α/β = 2.46 Gy, the second α/β = 3.30 Gy, the third for α/β = 3.25 Gy, the fourth α/β = 3.24 Gy, the fifth α/β = 3.38 Gy and the last α/β = 4.08 Gy. These values can be explained as follows: a) The bRFS of the schemes presents a statistical variation; b) The absorbed doses given to the patient present uncertainties on the physical dosimetry that are not on the modeling; c) Finally, in the model for the bRFS of Eq. (3), there are parameters that have to be considered, such as: the number of clonogenic tumor cells N 0 , the overall treatment time (OTT), the kick-off time for tumor repopulation T k and the repopulation doubling time. Therefore, the mean value to α/β for all schemes has an average value of 3.29 (± 0.52) Gy. CONCLUSIONS: The value of α / β ¯ = 3.29 ( ± 0.52 ) Gy is determined from cohorts of Mexican patients with PC a treated with external radiotherapy using the time-dependent LQ model, which is a higher value with respect to the "dogma" value of α/β 1.5 Gy obtained with the LQ model without temporal dependence. Therefore, there is a possibility of optimizing treatments radiobiologically and improving the results of bRFS in Mexican patients with PCa treated with external radiotherapy.
Authors: Raymond Miralbell; Stephen A Roberts; Eduardo Zubizarreta; Jolyon H Hendry Journal: Int J Radiat Oncol Biol Phys Date: 2011-02-15 Impact factor: 7.038
Authors: Christopher A Haiman; Gary K Chen; William J Blot; Sara S Strom; Sonja I Berndt; Rick A Kittles; Benjamin A Rybicki; William B Isaacs; Sue A Ingles; Janet L Stanford; W Ryan Diver; John S Witte; Stephen J Chanock; Suzanne Kolb; Lisa B Signorello; Yuko Yamamura; Christine Neslund-Dudas; Michael J Thun; Adam Murphy; Graham Casey; Xin Sheng; Peggy Wan; Loreall C Pooler; Kristine R Monroe; Kevin M Waters; Loic Le Marchand; Laurence N Kolonel; Daniel O Stram; Brian E Henderson Journal: PLoS Genet Date: 2011-05-26 Impact factor: 5.917