Bone metastases
Predictive model for survival in patients having repeat radiation treatment for painful bone metastases

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Abstract

Purpose

To establish a survival prediction model in the setting of a randomized trial of re-irradiation for painful bone metastases.

Methods

Data were randomly divided into training and testing sets with an approximately 3:2 ratio. Baseline factors of gender, primary cancer site, KPS, worst-pain score and age were included with backward variable selection to derive a model using the training set. A partial score was assigned by dividing the value of each statistically significant regression coefficient by the smallest statistically significant regression coefficient. The survival prediction score (SPS) was obtained by adding together partial scores for the variables that were statistically significant. Three risk groups were modelled.

Results

The training set included 460 patients and the testing set 351 patients. Only KPS and primary cancer site reached the 5%-significance level. Summing up the partial scores assigned to KPS (90–100, 0; 70–80, 1; 50–60, 2) and primary cancer site (breast, 0; prostate, 1.3; other, 2.6; lung, 3) totalled the SPS. The 1/3 and 2/3 percentiles of the SPS were 2 and 3.6. For the testing set, the median survival of the 3 groups was not reached, 11.3 (95% C.I. 8.5 – not reached) and 5.2 months (95% C.I. 3.7–6.5). The 3, 6 and 12 month survival rates for the worst group were 64.4% (95% C.I. 55.3–72.1%), 43.0% (95% C.I. 34.0–51.8%) and 19.7% (95% C.I. 12.4–28.1%) respectively, similar to that in the training set.

Conclusion

This survival prediction model will assist in choosing dose fractionation. We recommend a single 8 Gy in the worst group identified.

Section snippets

Methods

We employed the database of NCIC Clinical Trials Group Symptom Control.20 trial (SC-20) randomizing patients with painful bone metastases requiring repeat radiation to a single or multiple fractions. The eligible patients were 18 years or older with a proven diagnosis of cancer with radiologically confirmed bone metastases that had previously received radiation. Patients with clinical or radiological evidence of spinal cord compression, a pathological fracture, or an impending fracture that

Results

From the SC.20 dataset of 850 patients, 39 patients with missing data were excluded. The training set was made up of 460 patients and the testing set 351 patients. The training and testing sets were comparable among the baseline factors (Table 1). Only KPS and primary cancer site reached the 5% significance level for prediction of survival (Table 2). The partial scores assigned were KPS (90–100, 0; 70–80, 1; 50–60, 2) and primary cancer site (breast, 0; prostate, 1.3; other, 2.6; lung, 3).

Discussion

The NCIC Clinical Trials Group SC.20 randomized trial shows that repeat radiation therapy benefits in patients with bone metastases irrespective of radiation dose schedules and in those who responded or did not respond to the initial radiation [1]. A secondary analysis confirmed that patients responding to reirradiation experienced better QOL scores and less functional interference associated with pain [2].

The major limitation of the trial is lack of concordance between the intention-to-treat

Conflicts of interest

None.

Acknowledgements

This study was supported by the NCIC CTG’s programmatic grants from the Canadian Cancer Society Research Institute; the RTOG grant U10 CA21661 and CCOP grant U10 CA37422 from the National Cancer Institute in the US. Funding for Australia & New Zealand was from Cancer Council Australia (Grant for International Infrastructure Support) and Royal Adelaide Hospital (Special Purposes Fund Research Grant). The Dutch Cancer Society funded the national data management for Dutch patients (Dutch Cancer

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