Radioimmunoscintigraphy for post-prostatectomy radiotherapy: Analysis of toxicity and biochemical control

Abstract

4660 Background: To evaluate the role of radioimmunoscintigraphy (RIS) directed against prostate specific membrane antigen (PSMA) [ProstaScint] in influencing post-radical retropubic prostatectomy (RRP) radiotherapy (RT) toxicity and biochemical failure-free survival (BFFS). Methods: The records of 107 consecutive post-RRP patients who underwent RT were reviewed. The group for whom no RIS scan was obtained (Group A, n=54, mean follow-up (FU) 26.7 months) was identified, as was the group for whom RIS was obtained (Group B, n=53, mean FU 21.3 months). Group B was comprised of those who had a RIS/computed tomography (CT) correlation to aid in treatment planning (Subgroup B1, n=40) and those who did not (Subgroup B2, n=13). The acute and late gastrointestinal (GI) and genitourinary (GU) toxicity were reviewed. BFFS curves were constructed, using two successive PSA rises after a nadir to a value > 0.2 ng/mL as the definition of failure. Results: No significant differences in late toxicity were observed between any Group/Subgroup. However, acute GI toxicity was higher for Group B vs A (p=0.026), and acute GU toxicity was higher in Subgroup B2 vs B1 (p=0.050). Most toxicity was Grade 1 or Grade 2; only 1 case of Grade 3 toxicity and no cases of Grade 4 or Grade 5 toxicity were seen. 3-year BFFS was higher for Group B vs A (80.7 vs 75.5%) and for Subgroup B1 vs Subgroup B2 (84.5 vs 71.6%). On multivariate analysis of patient (age, race), surgical (stage, grade, margin status, extracapsular extension, seminal vesicle invasion, post-RRP PSA nadir, post-RRP PSA max, and RRP to RT interval), and treatment (hormone therapy, RT dose, RT technique, RIS scan, and RIS/CT correlation) factors on BFFS, only RIS/CT correlation (p=0.042) reached significance. Conclusions: A BFFS advantage was observed in patients for whom RIS was obtained; however, this advantage only reached significance for the population in which RIS/CT correlation was used to guide RT target definition. The improved PSA control using RIS was achieved with a small increase in acute toxicity, but with no observed change in late toxicity. These findings can serve as the basis for prospective studies in this area. No significant financial relationships to disclose.