ABSTRACT
Purpose: Bladder preservation with trimodal therapy (TMT; maximal tumor resection followed by chemoradiation) is an effective paradigm for select patients with muscle invasive bladder cancer. We report our institutional experience of a TMT protocol using nonadaptive magnetic resonance imaging-guided radiation therapy (MRgRT) for partial bladder boost (PBB). Methods and Materials: A retrospective analysis was performed on consecutive patients with nonmetastatic muscle invasive bladder cancer who were treated with TMT using MRgRT between 2019 and 2022. Patients underwent intensity modulated RT-based nonadaptive MRgRT PBB contoured on True fast imaging with steady state precession (FISP) images (full bladder) followed sequentially by computed tomography-based RT to the whole empty bladder and pelvic lymph nodes with concurrent chemotherapy. MRgRT treatment time, table shifts, and dosimetric parameters of target coverage and normal tissue exposure were described. Prospectively assessed acute and late genitourinary and gastrointestinal (GI) toxicity were reported. Two-year local control was assessed with Kaplan-Meier methods. Results: Seventeen patients were identified for analysis. PBB planning target volume margins were ≤8 mm in 94% (n = 16) of cases. Dosimetric target coverage parameters were favorable and all normal tissue dose constraints were met. For MRgRT PBB fractions, median table shifts were 0.4 cm (range, 0-3.15), 0.45 cm (0-2.65), and 0.75 cm (0-4.8) in the X, Y, and Z planes, respectively. Median treatment time for MRgRT PBB fractions was 9 minutes (range, 6.9-17.4). We identified 32 out of 100 total MRgRT fractions that may have benefitted from online adaptation based on changes in organ position relative to planning target volume, predominantly because of small bowel (13/32, 41%) or rectum (8/32, 25%). Two patients discontinued RT prematurely. The incidence of highest-grade acute genitourinary toxicity was 1 to 2 (69%) and 3 (6%), whereas the incidence of acute GI toxicity was 1 to 2 (81%) and 3 (6%). There were no late grade 3 events; 17.6% had late grade 2 cystitis and none had late GI toxicity. With median follow-up of 18.2 months (95% CI, 12.4-22.5), the local control rate was 92%, and no patient has required salvage cystectomy. Conclusions: Nonadaptive MRgRT PBB is feasible with favorable dosimetry and low resource utilization. Larger studies are needed to evaluate for potential benefits in toxicity and local control associated with this approach in comparison to standard treatment techniques.
ABSTRACT
PURPOSE: This study aimed to retrospectively analyze the dosimetric and toxicity results from 272 patients with localized prostate cancer treated consecutively using loose or stranded radioactive seeds by transrectal ultrasound-guided transperineal permanent prostate seed brachytherapy. METHODS AND MATERIALS: Two hundred seventy-two patients with localized prostate cancer treated between February 2002 and June 2004 were analyzed. All patients were treated with radioactive iodine-125 or palladium-103 using unstranded or loose seeds (USS) (159 patients) or customized stranded seeds (CSS) at variable spacing (5-50 mm) (113 patients) (Vari-Strand; BrachySciences, Oxford, CT). A single experienced brachytherapist performed all implants. RESULTS: There was a slight improvement in the dosimetric parameter D90 between the CSS (101.9%) and USS (99.3%) groups (p = 0.041). However, overall implant quality based on Radiation Therapy Oncology Group (RTOG) guidelines was similar between both groups. CONCLUSIONS: We conclude that the D90 value calculated for CSS is statistically improved when compared to the USS cohort, but without a clinically significant difference. There was no difference in the toxicity scores in either group. Overall quality between groups is comparable in our institution.
