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Purpose/objective(s) Management of progressive brain tumors following high dose radiotherapy is controversial. In select cases, surgical resection can provide rapid relief of regional mass effect and edema, and highly focal adjuvant re-irradiation can be administered in the form of brachytherapy. Permanent low-dose rate cesium-131 brachytherapy may offer dosimetric and radiobiologic advantages over other isotopes. The purpose of this study was to examine the safety and efficacy of intracranial cesium-131 brachytherapy after surgical resection in a heavily pre-treated patient cohort. Materials/methods A retrospective chart review was conducted of all patients treated with intraoperative intracranial cesium-131 brachytherapy from an institutional database. Treatment consisted of maximal safe resection followed by implantation of suture-stranded cesium-131 seeds, maintaining approximately 10mm spacing between seeds, with a planned target dose of 80 Gy to 5mm depth. Local failure was defined as recurrence in or contacting the resection cavity after salvage resection and brachytherapy. Regional failure was defined as recurrence within 10mm of the resection cavity. Recurrence was defined as a new lesion or growth of ≥25% in any axial dimension on interval MRI. Toxicity was collected based on CTCAE 4.0. Results A total of 35 patients with a median imaging follow up of 17.0 months (interquartile range [IQR] 9.7-25.9) underwent 41 consecutive cesium-131 implants between 2016 and 2020. 20 patients (59%; N = 22 implants) were treated for recurrent brain metastasis, 12 patients (34%; N = 16 implants) were treated for recurrent atypical (N = 8) or anaplastic meningioma (N = 4), and 3 patients (9%) were treated for recurrent glioma (N = 2) or hemangiopericytoma (N = 1). A majority of lesions had received prior surgery (N = 28, 66.7%, range 0-3 prior surgeries) and 34 patients had received prior high dose radiation. 34 of 41 (82.9%) tumors had received prior radiosurgery, and 12 (29.2%) had undergone prior external beam radiation (range 50-60 Gy). 17 of 41 lesions (41.5%) had radiologic evidence of adverse radiation/treatment effect (ARE) prior to salvage therapy. Median tumor size was 3.0cm (IQR 2.3-3.7). Overall actuarial local/loco-regional control at 1-year was 91.6%/84.7% (89.8%/88.9% for metastases and 100%/82.5% for meningiomas). Crude loco-regional control was 86.3% for metastases, 75% for meningiomas, and 66.7% for other lesions. Symptomatic ARE following treatment was observed in 9.8% (N = 4) resection cavities. The surgical complication rate was 14.6% (N = 6 total, N = 3 [7.3%] grade 3-5) including 1 peri-operative death. Conclusion Cesium-131 brachytherapy in this heavily pre-treated cohort resulted in good local control and an acceptable rate of symptomatic adverse radiation effect and toxicity and may be a reasonable treatment option for this select population. Author disclosure W.C. Chen: None. M. Lafreniere: None. C. Phuong: None. M. Lometti: None. O. Morin: None. B.P. Ziemer: None. H. Vasudevan: Research Grant; Children's Tumor Foundation. Patent/License Fees/Copyright; Genentech, Eli Lilly. S. Hervey-Jumper: None. P.V. Theodosopoulos: None. S. Magill: None. S.E. Fogh: Independent Contractor; Accuray. J.L. Nakamura: None. L. Boreta: None. P.K. Sneed: None. M.W. McDermott: Chair; Miami Baptist. D. Raleigh: None. S.E. Braunstein: Advisory Board; Radiation Oncology Questions, LLC.

This study compares conventional and robotic intensity modulated radiation therapy (IMRT) plans for prostate boost treatments and provides clinical insight into the strengths and weaknesses of each. The potential for dose escalation with robotic IMRT is further investigated using the “critical volume tolerance” method proposed by Roach et al. Three clinically acceptable treatment plans were generated for 10 prostate boost patients: (1) a robotic IMRT plan using fixed cones, (2) a robotic IMRT plan using the Iris variable aperture collimator, and (3) a conventional linac based IMRT (c-IMRT) plan. Target coverage, critical structure doses, homogeneity, conformity, dose fall-off, and treatment time, were compared across plans. The average bladder and rectum V75 was 17.1%, 20.0%, and 21.4%, and 8.5%, 11.9%, and 14.1% for the Iris, fixed, and c-IMRT plans, respectively. On average the conformity index (nCI) was 1.20, 1.30, and 1.46 for the Iris, fixed, and c-IMRT plans. Differences between the Iris and the c-IMRT plans were statistically significant for the bladder V75 (P= .016), rectum V75 (P= .0013), and average nCI (P =.002). Dose to normal tissue in terms of R50 was 4.30, 5.87, and 8.37 for the Iris, fixed and c-IMRT plans, respectively, with statistically significant differences between the Iris and c-IMRT (P = .0013) and the fixed and c-IMRT (P = .001) plans. In general, the robotic IMRT plans generated using the Iris were significantly better compared to c-IMRT plans, and showed average dose gains of up to 34% for a critical rectal volume of 5%.

The purpose of this report was to evaluate the magnitude of the error that would be introduced if only a lateral (LAT) portal image, as opposed to a pair of orthogonal images, was used to verify and correct daily setup errors and organ motion in external beam radiation therapy (EBRT) of prostate cancer. The 3-dimensional (3D) coordinates of gold markers from 12 consecutive prostate patients were reconstructed using a pair of orthogonal images. The data were re-analyzed using only the LAT images. Couch moves from the 2-dimensional (2D)-only data were compared with the complete 3D data set. The 2D-only data provided couch moves that differed on average from the 3D data by 2.3 ± 3.0, 0.0 ± 0.0, and 0.8 ± 1.0 mm in the Lat, AP, and SI directions, respectively. Along AP and SI axes, the LAT image provided positional information similar to the orthogonal pair. The error along the LAT axis may be acceptable provided lateral margins are large enough. A LAT-only setup protocol reduces patient treatment times and increases patient throughput. In most circumstances, with exceptions such as morbidly obese patients, acquisition of only a LAT image for daily targeting of the prostate will provide adequate positional precision.

Purpose: The aim of this study was to measure interfraction prostate bed motion, setup error, and total positioning error in 10 consecutive patients undergoing postprostatectomy radiotherapy. Methods and Materials: Daily image-guided target localization and alignment using electronic portal imaging of gold seed fiducials implanted into the prostate bed under transrectal ultrasound guidance was used in 10 patients undergoing adjuvant or salvage radiotherapy after prostatectomy. Prostate bed motion, setup error, and total positioning error were measured by analysis of gold seed fiducial location on the daily electronic portal images compared with the digitally reconstructed radiographs from the treatment-planning CT. Results: Mean (± standard deviation) prostate bed motion was 0.3 ± 0.9 mm, 0.4 ± 2.4 mm, and −1.1 ± 2.1 mm in the left–right (LR), superior–inferior (SI), and anterior–posterior (AP) axes, respectively. Mean set-up error was 0.1 ± 4.5 mm, 1.1 ± 3.9 mm, and −0.2 ± 5.1 mm in the LR, SI, and AP axes, respectively. Mean total positioning error was 0.2 ± 4.5 mm, 1.2 ± 5.1 mm, and −0.3 ± 4.5 mm in the LR, SI, and AP axes, respectively. Total positioning errors >5 mm occurred in 14.1%, 38.7%, and 28.2% of all fractions in the LR, SI, and AP axes, respectively. There was no significant migration of the gold marker seeds. Conclusions: This study validates the use of daily image-guided target localization and alignment using electronic portal imaging of implanted gold seed fiducials as a valuable method to correct for interfraction target motion and to improve precision in the delivery of postprostatectomy radiotherapy.