232 Radiation Oncology, Biology, Physics Volume 32, Supplement 1 1019 PROSIATE CANCER VOLUME ADDS SIGNIFICANTLY TO PROSIATE SPECIFIC ANTIGEN IN IHE PREDICI-ION OF EARLY BIOCHEMICAL FAILURE AFTER EXTERNAL BEAM RADIATION 1HERAPY D'Amico, A.V., Propert, K.J. Joint Center for Radiation Therapy, Harvard Medical School, Boston, Ma. Purpose A new clinical !ore treatment quantity that closely approximates the Irue prostate cancer volume is defined. Materials and Methods The cancer specific prostate specific antigen, PSA density, prostale cancer volume (Vco] and the volume fraction of the gland involved w/th carcinoma ( Vco fx ) were calculated for 227 prostate cancer patients managed definitively s,*dth external beam radiation therapy. A Cox regression mulitvariate analysis was employed to test if any of these clinical pre-treatment parameters added significantly to PSA in predicting early post-radiation PSA failure. Cancel- specific PSA = PSA - [PSA ITom benign epithelial tissue]* Vco = Cancer specific PSA/[PSA in serum per cm3ot cancer]** Vco fx = Vc=/ultrasound prostate gland volume *Lepor el al. Urology 44:199 1994 **Aihara el al. J Urology 151 ;1558,1994 Results The prostate cancer volume ( p = .039 ) and the volume fl'action of the gland involved by carcinoma ( p = .035 ) significantly added to the PSA in predicting post-radiation PSA failure on multivariate analysis. Conversely, the PSA density and the cancer specific PSA did not add significantly (p > .05) to PSA in predicting post-radiation PSA failure, Numbe[ Vco 20 month actuarial PSA failure Number at risk at 20 months 44 < 0.5 cm ~ 8% 13 129 0.5 - 4.0 cm a 20% 26 54 > 4.0 cm 3 50% I 1 I P = .00004 median follow up: 12 months Conclusion The volume of cancer { Vco } and the resulting volume fraction of cancer both added significantly to PSA in their ability to predict for early posl-radiafion PSA failure. These new parameters may be used to optimize lhe selection of patients in prospective randomized trials that examine the efficacy of combining radiation and androgen ablative therapy in patients vdth clinically localized disease but who are at high risk for early post-radiation PSA failure. 1020 USING PRE-TREATIMENT PSA ANt) GLEASON SCORE TO PREDICT FOR EXTRA CAPSULAR EXTENSION AMONG PATIENTS WITH CLINIC,M,LY STAGED ORGAN CONFINED PROSTATE CANCER AnitaChen, M.D.I, Mack Roach llI. MD I. Aldna,gl)iaz, M.D.l CarollvtarquczMD2. DanChinnMD. I,LoliColcmanMD. l, Jo.,;cph Presti, M.D. 4, Peter Camfli, M.D L IDepartments of Radiation ()ncohlgy. Llnr,.eislty el Calilornia San Flancisco {UCSF). 2()rosen Health Sciences University 2Depaltments tlf Urnlngy. University nl ('alihllTiia Sail Francisco,. :'Fret Mile) Vctmans Adminisl~ati~m Medical Ccnlcr IVAMC} Purpose/Objectives: The patients most suitablc lul a radtcal prustatcct(m~y (RP] ale those with (~lgan con[lncd disease. At least 1/3 el patients with clinically staged organ continual disease will bc Iqund to have extra capsuhu cxtcnsiun (ECE] h,lh~wmg RP. The purpose of this sludy is to assess the predictive vatue of an equation hn predicting the risk ~t ECE based ~m the pre treatment pl(mtalic spcclfic antigen (PSA) and Gieason score (GS) in patients with clinical stage TI/'T2 ploslatc cancel Materials & Methods: Two hundred and [W¢11[~ b.%! patio[/[ ~, wll(~ clndelwent RP at cidlci tilt San [=lancisco VAMC O1" U C , ~ F hctwccn 19g~ and 1994 were eligible hn- thi.s analysis. Patients ~cic considclcd eligible il the pathological stage, pro t~pclativc PSA and GS wcrc available. Among these patients the median pro upclativc P.RA was 9 nginll (range 0 195 ng/ml), and the Incdian p,c-operali,..e GS was 6 (lange 2- I0). The empirically derived equations lusted were I 1.5 x PS;A + iGS • ~;) x ll)l (Roach. J. Ullfl.. 151): 192~ 1924. 1993) as >,'ell as a recent i'nndiliu'ation hi this cqoation ItIIPSA + (GS - 3.5) x ll)l Fol the~,c CClUa[ilms, [11c ]an'go 01 calculated risk was limited tu II lOOt/,. Results: The rcsuhs el using these two equauon,, aic slmv,'n giaphically t.sin,g the modilicd equatbm. ;sith a calculalcd ~isk tCR) el <25c~ and an average calculated risk (ACR) of 15.4%. the observed incidence (OI)o1 ECE was I ,7.2c~. Among the patients with a CR of 26 to 51T% and an ACR of 36.1%, die O/ of ECE was 38.4q. Among the patients with aCR el 51 to ?5% and an ACR ot 611.4~,the OIof ECE was62.7c~. Finally, among the patients with a CR of 76 to llll)D and an ACR ~I 77 3g,. the OI of ECE was 85.7~. Transrccta] uhrasound (TRUS) or magnetic resonance imaging (MRI) reports wclc available in 72 patients, Correlation with "I'I~,IJS dmnlmstratcd a sensitivity and specificty of 52.4% and 56. l % respectively. Conclation with MRI shuwcd a sensitivity c~l 579'/, and a spccilicit 5 el 45.5% The use of cilher MRI el TRL.TS in predicting advanced localized disease had a sensllivily c~l 636'/, and a spccificily t)l44g