Abstract
BackgroundThe purpose of this study was to identify clinical and dosimetric factors associated with radiotherapy induced bone injury (RIBI) following stereotactic lung radiotherapy.MethodsInoperable patients with early stage non-small cell lung cancer, treated with SBRT, who received 54 or 60 Gy in 3 fractions, and had a minimum of 6 months follow up were reviewed. Archived treatment plans were retrieved, ribs delineated individually and treatment plans re-computed using heterogeneity correction. Clinical and dosimetric factors were evaluated for their association with rib fracture using logistic regression analysis; a dose-event curve and nomogram were created.Results46 consecutive patients treated between Oct 2004 and Dec 2008 with median follow-up 25 months (m) (range 6 – 51 m) were eligible. 41 fractured ribs were detected in 17 patients; median time to fracture was 21 m (range 7 – 40 m). The mean maximum point dose in non-fractured ribs (n = 1054) was 10.5 Gy ± 10.2 Gy, this was higher in fractured ribs (n = 41) 48.5 Gy ± 24.3 Gy (p < 0.0001). On univariate analysis, age, dose to 0.5 cc of the ribs (D0.5), and the volume of the rib receiving at least 25 Gy (V25), were significantly associated with RIBI. As D0.5 and V25 were cross-correlated (Spearman correlation coefficient: 0.57, p < 0.001), we selected D0.5 as a representative dose parameter. On multivariate analysis, age (odds ratio: 1.121, 95% CI: 1.04 – 1.21, p = 0.003), female gender (odds ratio: 4.43, 95% CI: 1.68 – 11.68, p = 0.003), and rib D0.5 (odds ratio: 1.0009, 95% CI: 1.0007 – 1.001, p < 0.0001) were significantly associated with rib fracture.Using D0.5, a dose-event curve was constructed estimating risk of fracture from dose at the median follow up of 25 months after treatment. In our cohort, a 50% risk of rib fracture was associated with a D0.5 of 60 Gy.ConclusionsDosimetric and clinical factors contribute to risk of RIBI and both should be included when modeling risk of toxicity. A nomogram is presented using D0.5, age, and female gender to estimate risk of RIBI following SBRT. This requires validation.
Highlights
The purpose of this study was to identify clinical and dosimetric factors associated with radiotherapy induced bone injury (RIBI) following stereotactic lung radiotherapy
* Correspondence: mojgan.taremi@rmp.uhn.on.ca 1Radiation Medicine Program, Princess Margaret Hospital, Toronto, ON, Canada 2Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada Full list of author information is available at the end of the article fracture following SBRT has been reported by a number of groups [3,4,5] including our own [5] - we previously found that out of 42 patients treated with 54 or 60 Gy in 3 fractions, 9 patients developed a total of 15 fractured ribs after a median follow-up of 17 months
Patient characteristics From Oct 2004 to Dec 2008, 48 consecutive patients were treated with 18 or 20 Gy × 3 fractions and followed for > 6 months, two were excluded from this analysis one had rib fracture at baseline, pre-SBRT, the other had rib fracture associated with a bone metastasis
Summary
The purpose of this study was to identify clinical and dosimetric factors associated with radiotherapy induced bone injury (RIBI) following stereotactic lung radiotherapy. SBRT has superior local tumor control when compared to conventionally fractionated radiotherapy [1]. Due to the large doses per fraction, the risk of late normal tissue toxicities such as radiation induced bone injury (RIBI) such as rib fracture may be increased [2]. Rib nomogram estimating risk of rib fracture from these factors
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