Magnetic resonance spectroscopy of the malignant prostate gland after radiotherapy: A histopathologic study of diagnostic validity

Purpose: Accurate spatial representation of tumor clearance after conformal radiotherapy is an endpoint of clinical importance. Magnetic resonance spe ctroscopy (MRS) can diagnose malignancy in the untreated prostate gland thr ough measurements of cellular metabolites, In this study we sought to descr ibe spectral metabolic changes in prostatic tissue after radiotherapy and v alidate a multivariate analytic strategy (based on MRS) that could identify viable tumor. Methods and Materials: Transrectal ultrasound-guided prostate biopsies from 35 patients were obtained 18-36 months after external beam radiotherapy. O ne hundred sixteen tissue specimens were subjected to H-1 MRS, submitted to histopathology, and analyzed for correlation with a multivariate strategy specifically developed for biomedical spectra, Results: The sensitivity and specificity of MRS in identifying a malignant biopsy were 88.9% and 92% respectively, with an overall classification accu racy of 91.4%, The diagnostic spectral regions identified by our algorithm included those due to choline, creatine, glutamine, and lipid. Citrate, an important discriminating resonance in the untreated prostate gland, was inv isible in all spectra, regardless of histology, Conclusions: Although the spectral features of prostate tissue markedly cha nge after radiotherapy, MRS combined with multivariate methods of analysis can accurately identify histologically malignant biopsies. MRS shows promis e as a modality that could integrate three-dimensional measures of tumor re sponse. (C) 2001 Elsevier Science Inc.