Phase II prospective study of the use of conformal high-dose-rate brachytherapy as monotherapy for the treatment of favorable stage prostate cancer: A feasibility report

Purpose: To evaluate the technical feasibility and tolerance of image-guide d transperineal conformal high-dose-rate (C-HDR) brachytherapy as the sole treatment modality for favorable, localized cancer of the prostate, and to analyze possible intrafraction and interfraction volume changes in the pros tate gland which may affect dosimetric quality. Methods and Materials: Patients were eligible for this prospective Phase IT trial if they had biopsy proven adenocarcinoma of the prostate with favora ble prognostic factors (Gleason score less than or equal to7, PSA less than or equal to 10 ng/ml and Stage less than or equal to T2a). The technique c onsisted of a transperineal implant procedure using a template with transre ctal ultrasound (TRUS) guidance. An interactive on-line real-time planning system was utilized with geometric optimization. This allowed dosimetry to be generated and modified as required intraoperatively. Prescription was to the minimum dose point in the implanted volume, assuring conformal coverag e of the prostate at its widest dimension with no margin. Total dose was 38 00 cGy in 4 fractions of 950 cGy each, delivered twice a day over 2 days. T he dose to any segment of rectum and urethra was limited to less than or eq ual to 75% and less than or equal to 125% of the prescription dose, respect ively. Before each fraction, needle positions were verified under fluorosco py and adjusted as required. For the last 10 patients, the adjustments requ ired were measured in a prospective fashion in representative extrema of th e gland. TRUS images were recorded for all patients before any needle manip ulation, again just before delivering the first fraction and immediately af ter the last fraction. This typically meant approximately 36 h to pass betw een the first and last measurements. Implant quality was assessed via dose- volume histograms (DVH). Results: Between 3/99 and 6/00, 41 patients received C-HDR interstitial bra chytherapy as their only treatment for prostate cancer at our institution. Median age was 64 years (range 51-79). Stage distribution was 27 T1c patien ts and 14 T2a patients. Three patients had Gleason score (GS) of 5; 34 had GS of 6; 4 patients had GS of 7. Median pretreatment PSA was 4.7 ng/ml (ran ge 0.8-13.3). All patients tolerated the treatment well with minimal discom fort. For 23 patients, data on volume changes in the gland during the impla nt were tabulated. They demonstrated a mean prostate volume of 30.7 cc befo re any manipulation with needles, 37.0 cc at the end of fraction 1, and 38. 2 cc at the end of fraction 4. In addition, for those 10 patients prospecti vely evaluated for required adjustments, the overall mean adjustment betwee n fraction 1 and fraction 2 was 2.0 cm, between fraction 2 and 3 was 0.4 cm , and between fractions 3 and 4 was 0.4 cm. For 10 consecutive patients, th e average prescriptions dose -D90 for fractions 1 and 4 were 104% and 100%, respectively. The corresponding average urethral D10 for fractions 1 and 4 were 122% and 132%. Conclusions: Our protocol using C-HDR interstitial brachytherapy as monothe rapy for early cancer of the prostate was feasible and well tolerated by 41 patients treated. Changes in interfraction prostate volume do not appear t o be significant enough to warrant modification of dosimetry for each fract ion. Both excellent dose coverage of the prostate gland and low urethral do se are achieved as measured by DVH. However, paramount attention should be given to needle displacement before each fraction. Needle movement is most significant between fractions 1 and 2. Acute toxicity (RTOG) has been modes t. Late toxicity and tumor control rates will be reported as longer follow- up allows. (C) 2001 Elsevier Science Inc.