Optimizing radiotherapy strategies for skull base chordoma: a comprehensive meta-analysis and systematic review of treatment modalities and outcomes
Authors: Palavani Lucca B. , Borges Pedro , Andreão Filipi Fim , Borges Jordana , Batista Sávio , Oliveira Leonardo B. , Ferreira Márcio Yuri , Reis Pedro C. Abrahão , Pontes Julia , Negri Herika , Beer-Furlan Andre , Krishna Chandan , Bertani Raphael , Rassi Marcio S. 
Published: May 2024

OBJECTIVE
In the treatment of skull base chordoma (SBC) surgery is considered the mainstay approach, and gross-total resection has an established relationship with progression-free survival (PFS) and overall survival (OS). However, the tumor’s location often interferes with attempts at complete resection. In this case, surgery for maximal resection followed by high-dose radiotherapy has been demonstrated to be the standard treatment. In this context, various modalities are available, yet no consensus exists on the most effective. This systematic review and meta-analysis aimed to evaluate the efficacy and safety of different radiotherapy modalities for SBC.

METHODS
Following PRISMA guidelines, the authors systematically searched for the treatment of SBC with radiation modalities in the PubMed, Cochrane, Web of Science, and EMBASE databases. Outcomes assessed for each modality were as follows: OS, PFS, local control (LC), and complications. The random-effects model was adopted. A single-proportion analysis with 95% CI was used to measure the effects in single-arm analysis. For the comparative analysis, the OR with 95% CI was used to compare outcome treatment effects. Heterogeneity was assessed using I2 statistics, and statistical significance was defined as p < 0.05.

RESULTS
A total of 32 studies comprising 3663 patients, with 2322 patients who were treated with radiotherapeutic modalities, were included. Regarding 5-year OS findings in each modality study, the findings were as follows: in photon fractionated radiotherapy, an estimated rate of 77% (69%–84%, 568 patients); in conventional fractionated radiotherapy, 76% (65%–87%, 517 cases); in proton-based + carbon ion–based radiotherapy, 85% (82%–88%, 622 cases); and in a comparative analysis of proton-based and carbon ion–based therapy, there was an OR of 1.2 (95% CI 0.59–2.43, 306 cases). Regarding the 5-year PFS estimate, the rates were as follows: 35% (26%–45%, 95 cases) for photon fractionated therapy; 35% (25%–45%, 85 cases) for stereotactic radiotherapy; 77% (50%–100%, 180 cases) for proton-based and carbon ion–based radiotherapy; and 74% (45%–100%, 102 cases) for proton-based radiotherapy. Regarding LC in periods of 3 and 5 years after proton- and carbon ion–based therapy, the overall estimated rates were 84% (78%–90%, 326 cases) and 75% (65%–85%, 448 cases), respectively. For proton-based radiotherapy and carbon ion–based therapy, the 5-year LC rates were 76% (67%–86%, 259 cases) and 75% (59%–91%, 189 cases), respectively.

CONCLUSIONS
The analysis highlights the finding that particle-based modalities like proton beam radiotherapy and carbon ion radiotherapy are the most effective radiation therapies available for the treatment of SBC. Furthermore, it reinforces the idea that surgery followed by radiotherapy constitutes the standard treatment.