Radioimmunoscintigraphy for postprostatectomy radiotherapy: analysis of toxicity and biochemical control

Our goal was to evaluate the role of radioimmunoscintigraphy (RIS) directed against prostate-specific membrane antigen (PSMA) in influencing postprostatectomy radiotherapy (RT) toxicity and biochemical control.

The records of 107 postprostatectomy RT patients were reviewed. The group for whom no RIS scan was obtained (group A, n = 54) was identified as was the group for whom a RIS scan was obtained (group B, n = 53). Group B was further subdivided into those who had a RIS and CT-scan correlation to aid in treatment planning (subgroup B1, n = 40) versus those who did not (subgroup B2, n = 13). Gastrointestinal (GI) and genitourinary (GU) toxicities were reviewed for each of these groups and subgroups and compared. Biochemical failures (defined as 2 successive PSA rises after a nadir of >or=0.2 ng/mL) were identified to generate biochemical failure-free survival (BFFS) curves for each of the groups and subgroups.

No significant differences in late toxicity were observed between any group or subgroup. However, acute GI toxicity was higher in group B versus group A (P = 0.026), and acute GU toxicity was higher in subgroup B2 versus subgroup B1 (P = 0.050). Overall, most toxicity was grade 1 or 2; only one case of grade 3 toxicity and no cases of grade 4 or 5 toxicity were observed. Three-year BFFS was higher for group B versus group A (80.7% vs. 75.5%) and for subgroup B1 versus subgroup B2 (84.5% vs. 71.6%). On multivariate analysis of pretreatment (age, race), surgical/staging (stage, grade, margin status, extracapsular extension, lymph node status, seminal vesicle invasion, post-radical retropubic prostatectomy [RRP] prostate-specific antigen [PSA] nadir, maximum post-RRP PSA, and RRP-to-RT interval), and treatment (hormone therapy, RT dose, RT technique, RIS scan, and RIS/CT correlation) factors on BFFS, the only covariate reaching significance was RIS/CT correlation (P = 0.042).

A small BFFS advantage was observed in patients for whom RIS was used to guide RT decision making and treatment planning; however, this advantage only reached significance in this study for those for whom the RIS/CT correlation was used to guide 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 of investigation.