The comparison between the conventional and the hypofractionated arm allowed to evaluate the response of rectal toxicity to changes in fractionation. The similar rate of late toxicity
in the two arms seems to indicate the feasibility of hypofractionated regimes in prostate cancer. Our study led to an estimation of α/β ratio value for late rectal toxicity very close to 3 Gy; however further prospective studies need to be performed to definitely establish the value of the α/β ratio Selleck Vismodegib in a larger cohort of patients enhancing the accuracy of the radiobiological modeling. Appendix 1 For the LKB model [9, 10], assuming a uniform irradiation of a fraction v of the organ at dose D, NTCP can be calculated by (A.1) where t is defined as (A.2) and (A.3) As known, the parameters n, m and TD50(1) determine the volume dependence of NTCP, the slope of NTCP vs. dose and the tolerance dose to the whole organ leading to a 50% complication probability, respectively. The effective volume method  was chosen as histogram reduction scheme for non uniform organ irradiations: (A.4) where D i is the dose delivered to the volume fraction v i and N is the number
of points of the differential DVH. By (A.4), an inhomogeneous dose distribution is converted to an equivalent uniform irradiation of a fraction v eff of the organ at the maximum dose D max . Before applying the above equations, a correction is performed to D i , to take into GSK872 order account the fractionation inside each volume fraction v i . In this way, the physical dose D in each volume fraction v is converted to the biologically equivalent total dose normalized to the standard fraction of 2 Gy (NTD2). (A.5) where the parameters α and β are the coefficients of the linear and quadratic dose contributions to damage in the linear-quadratic model of the cell survival curve and n fr is the number of fractions. References 1. Brenner DJ, Hall EJ: Fractionation and protraction for radiotherapy of prostate carcinoma. Int Int J Radiat Biol Oncol Phys 1999, 43: 1095–1101.CrossRef 2. Fowler JF, Chappell RJ, Ritter MA: Is α/β for prostate tumors really low? Int J Radiat Biol Oncol Phys 2001, 50: 1021–1031.CrossRef 3.
Brenner ADAMTS5 DJ, Martinez AA, Edmundson GK, Mitchell C, Thames HD, Armour EP: Direct evidence that prostate tumors show high sensitivity to fractionation (low α/β ratio) comparable to late-responding normal tissue. Int J Radiat Biol Oncol Phys 2002, 52: 6–13.CrossRef 4. Fowler JF, Chappell R, Ritter MA: The CYC202 prospects for new treatments for prostate cancer. Int J Radiat Biol Oncol Phys 2002, 52: 3–5.CrossRef 5. Brenner JD: Hypofractionation for prostate cancer radiotherapy. What are the issues? Int J Radiat Oncol Biol Phys 2003, 57: 912–914.CrossRefPubMed 6. Duchesne GM, Peters LJ: What is the α/β ratio for prostate cancer? Rationale for hypofractionated high-dose-rate brachytherapy. Int J Radiat Biol Oncol Phys 1999, 44: 747–748.CrossRef 7.