Abstract
BackgroundDespite combined modality treatment involving surgery and radiotherapy, a relevant proportion of skull-base chordoma and chondrosarcoma patients develop a local recurrence (LR). This study aims to analyze patterns of recurrence and correlate LR with a detailed dosimetric analysis.Methods222 patients were treated with proton radiotherapy for chordoma (n = 151) and chondrosarcoma (n = 71) at the PSI between 1998 and 2012. All patients underwent surgery, followed by pencil-beam scanning proton therapy to a mean dose of 72.5 ± 2.2GyRBE. A retrospective patterns of recurrence analysis was performed: LR were contoured on follow-up MRI, registered with planning-imaging and the overlap with initial target structures (GTV, PTVhigh-dose, PTVlow-dose) was calculated. DVH parameters of planning structures and recurrences were calculated and correlated with LR using univariate and multivariate cox regression.ResultsAfter a median follow-up of 50 months, 35 (16%) LR were observed. Follow-up MRI imaging was available for 27 (77%) of these recurring patients. Only one (3.7%) recurrence was located completely outside the initial PTV (surgical pathway recurrence). The mean proportions of LR covered by the initial target structures were 48% (range 0–86%) for the GTV, 70% (range 0–100%) for PTVhigh and 83% (range 0–100%) for PTVlow. In the univariate analysis, the following DVH parameters were significantly associated with LR: GTV(V < 66GyRBE, p = 0.01), GTV(volume, p = 0.02), PTVhigh(max, p = 0.02), PTVhigh(V < 66GyRBE, p = 0.03), PTVhigh(V < 59GyRBE, p = 0.02), PTVhigh(volume, p = 0.01) and GTV(D95, p = 0.05). In the multivariate analysis, only histology (chordoma vs. chondrosarcoma, p = 0.01), PTVhigh(volume, p = 0.05) and GTV(V < 66GyRBE, p = 0.02) were independent prognostic factors for LR.ConclusionThis study identified DVH parameters, which are associated with the risk of local recurrence after proton therapy using pencil-beam scanning for patients with skull-base chordoma and chondrosarcoma.
Highlights
Despite combined modality treatment involving surgery and radiotherapy, a relevant proportion of skull-base chordoma and chondrosarcoma patients develop a local recurrence (LR)
Chordoma and chondrosarcoma of the skull base are rare bone tumors [1–4] which are often located in close proximity to critical organs of risk (OAR), including but not limited to the brainstem, optic chiasm and optic nerves, making complete surgical resection of these tumors challenging and postoperative high-dose radiotherapy necessary in most cases [5]
Local control for chondrosarcomas was significantly better compared to chordomas (p = 0.04, Concordance index (CI) = 0.59). 5- and 7-year overall survival for the entire cohort were 86% and 80%, respectively [11]
Summary
Despite combined modality treatment involving surgery and radiotherapy, a relevant proportion of skull-base chordoma and chondrosarcoma patients develop a local recurrence (LR). Chordoma and chondrosarcoma of the skull base are rare bone tumors [1–4] which are often located in close proximity to critical organs of risk (OAR), including but not limited to the brainstem, optic chiasm and optic nerves, making complete surgical resection of these tumors challenging and postoperative high-dose radiotherapy necessary in most cases [5]. Despite combined modality treatment involving surgery and adjuvant radiotherapy, a relevant percentage of chordoma and chondrosarcoma patients develop a local recurrence [8–10], which is most likely explained by the locally aggressive growth pattern. The present study aims to analyze patterns of recurrence and correlate local control with a detailed dosimetric analysis
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