Clinical comparative study of dose-volume and equivalent uniform  dose based predictions in post radiotherapy acute complications.
BACKGROUND
Single points placed on Dose-Volume Histograms (DVHs) for treatment plan acceptance are still widely used compared to the Equivalent Uniform Dose (EUD). The aim of this work is to retrospectively measure and compare the ability of both criteria in correctly predicting two clinical outcomes, RTOG grade 2 acute gastrointestinal (GI) and genitourinary (GU) complications in 137 patients treated for prostate cancer.


METHODS
For both complications,the best predictions have been achieved by fitting the EUD parameter and a tolerance dose (for a varying DVH point) by maximization of the Area Under the Receiver Operating Curve (AUROC). A complementary likelihood fitting of the Lyman's Normal Tissue Complication Probability (NTCP) allowed a graphical comparison between expected and observed frequencies, and to derive the associated parameters.


CONCLUSIONS
No significant differences were found in the AUROC values obtained by using dose-volume or EUD criteria, but all the results highlighted the role of high doses. Limiting V65 (for grade 2 GI) or V73 (for grade 2 GU) was as predictive as limiting EUD value, with n equal to 0.09 or 0.06 respectively, but in all cases AUROC values were low (< 0.7). Likelihood fitting gave m = 0.195 and TD50=72.5 Gy (fixing n=0.06 for acute GU) and m=0.19 and TD50=66 Gy (fixing n=0.09 for acute GI). Both AUROC and likelihood values revealed a better fit for acute GI than for acute GU. The use of a fractionation correction, new clinical contours or previous risk factors could improve these values.
Boulé
Thierry P
TP
Department of Medical Physiology and Biophysics, University of Seville, Avenida Sánchez Pizjuán 4, Seville, Spain. thierry_pascal_boule@hotmail.com
Gallardo Fuentes
M Isabel
MI
Roselló
Joan V
JV
Arrans Lara
Rafael
R
Torrecilla
José L
JL
Plaza
Antonio Leal
AL
D000208:Acute Disease; D019583:Dose Fractionation, Radiation; D005767:Gastrointestinal Diseases / Q000209:etiology*; D006801:Humans; D016013:Likelihood Functions; D008297:Male; D052801:Male Urogenital Diseases / Q000209:etiology*; D011237:Predictive Value of Tests; D011336:Probability; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D012372:ROC Curve; D011832:Radiation Injuries / Q000209:etiology; D011878:Radiotherapy / Q000009:adverse effects*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000009:adverse effects; D012189:Retrospective Studies; D012307:Risk Factors; D016896:Treatment Outcome