Adoption of Hybrid MRI-Linac Systems for the Treatment of Brain Tumors: A Systematic Review of the Current Literature Regarding Clinical and Technical Features.

BACKGROUND: Possible advantages of magnetic resonance (MR)-guided radiation therapy (MRgRT) for the treatment of brain tumors include improved definition of treatment volumes and organs at risk (OARs) that could allow margin reductions, resulting in limited dose to the OARs and/or dose escalation to target volumes. Recently, hybrid systems integrating a linear accelerator and an magnetic resonance imaging (MRI) scan (MRI-linacs, MRL) have been introduced, that could potentially lead to a fully MRI-based treatment workflow. METHODS: We performed a systematic review of the published literature regarding the adoption of MRL for the treatment of primary or secondary brain tumors (last update November 3, 2022), retrieving a total of 2487 records; after a selection based on title and abstracts, the full text of 74 articles was analyzed, finally resulting in the 52 papers included in this review. RESULTS AND DISCUSSION: Several solutions have been implemented to achieve a paradigm shift from CT-based radiotherapy to MRgRT, such as the management of geometric integrity and the definition of synthetic CT models that estimate electron density. Multiple sequences have been optimized to acquire images with adequate quality with on-board MR scanner in limited times. Various sophisticated algorithms have been developed to compensate the impact of magnetic field on dose distribution and calculate daily adaptive plans in a few minutes with satisfactory dosimetric parameters for the treatment of primary brain tumors and cerebral metastases. Dosimetric studies and preliminary clinical experiences demonstrated the feasibility of treating brain lesions with MRL. CONCLUSIONS: The adoption of an MRI-only workflow is feasible and could offer several advantages for the treatment of brain tumors, including superior image quality for lesions and OARs and the possibility to adapt the treatment plan on the basis of daily MRI. The growing body of clinical data will clarify the potential benefit in terms of toxicity and response to treatment.

Postoperative radiotherapy for prostate cancer: the sooner the better and potential to reduce toxicity even further.

PURPOSE: To evaluate biochemical relapse-free survival (bRFS), overall survival (OS), late rectal and bladder toxicities in a retrospective single institution series, also applying an in-house software for biological dose calculation. METHODS: 258 patients submitted to radiotherapy after prostatectomy were considered. Differences between groups were calculated using the log-rank test and the relevant clinical and therapeutic variables were considered for multivariate analysis. PRODVH is an in-house system able to calculate mean dose-volume histograms (DVHs) of a series of patients, to convert them in biologically effective DVHs (BEDVHs) and allowing to compare them with ANOVA and t Student test. RESULTS: Adjuvant radiotherapy (ART) and salvage radiotherapy (SRT) were performed in 131 (50.8%) and 127 patients (49.2%). At multivariate analysis advanced T stage, androgen deprivation total (ADT) and SRT resulted as independent variables related to a worst bRFS (p = 0.019, 0.001 and 0.02), while GS > 7 and SRT affected negatively OS (p 0.047 and 0.039). High grade toxicity events occurred mainly in patients treated with 3-dimensional conformal radiotherapy (3DCRT) (proctitis p = 0.006; cystitis: p = 0.041). A significantly more favorable mean rectum BEDVH for patients with G0 or G1 rectal toxicity was shown (p < 0.001). Mean BEDVH for both bladder (p < 0.01) and rectum (p < 0.05) were also significantly better for volumetric modulated arc therapy-image guided radiotherapy (VMAT-IGRT) plans than for 3DCRT plans. CONCLUSION: ART is better than SRT in terms of bRFS and OS, particularly for more aggressive cases, advanced T stage and higher Gleason Score. Postoperative prostate cancer radiotherapy should be applied as soon as possible after surgery. The use of modern techniques such as VMAT-IGRT significantly reduces toxicity.