Renal SBRT
Impact of stereotactic radiotherapy on kidney function in primary renal cell carcinoma: Establishing a dose–response relationship

https://doi.org/10.1016/j.radonc.2016.01.027Get rights and content

Abstract

Background and purpose

To evaluate renal dysfunction after stereotactic ablative body radiotherapy (SABR) for inoperable primary renal cell carcinoma (RCC) using nuclear medicine assessments.

Materials and methods

In a prospective clinical trial, patients received single fraction renal SABR (26 Gy) for tumours <5 cm, or fractionated SABR (3 × 14 Gy) for tumours ⩾5 cm. Global and regional glomerular filtration rate (GFR) was calculated through 51Cr-EDTA and 99mTc-DMSA SPECT/CT, respectively, at baseline and post-treatment (14, 90 days and at 1-year). Regional loss in function was correlated to the absolute and biologically effective doses (BED) delivered.

Results

In 21 patients the mean (range) tumour size was 48 mm (21–75 mm). The mean ± SD GFR at baseline was 52 ± 24 ml/min. Net change in mean GFR was +0.6 ± 11.3, +3.2 ± 14.5 and −8.7 ± 13.4 ml/min (p = 0.03) at 2 weeks, 3 months and 1 year, respectively. For every 10 Gy of physical dose delivered, an exponential decline in affected kidney GFR was observed at 39% for 26 Gy/1 fraction and 25% for 42 Gy/3 fractions. When normalised to BED3Gy, the dose–response relationship for each treatment prescription was similar with a plateau beyond 100 Gy. The R50% conformity index correlated with GFR loss (p = 0.04). No patient required dialysis.

Conclusions

SABR results in clinically acceptable and dose-dependent renal dysfunction at 1-year. Sparing functional kidney from high-dose regions (>50% isodoses) may help reduce risk of functional loss.

Section snippets

Patients

The study received institutional ethical review board approval and was conducted as a translational substudy of a registered prospective clinical trial (clinicaltrials.gov identifier: NCT01676428). Eligible patients were medically inoperable, technically high risk for surgery or declined surgery, with an ECOG performance status of 0–2 inclusive. Patients with previous high-dose radiotherapy to the upper abdomen were excluded from the study. Patients underwent serial renal function assessments

Study population

In total, 21 patients were included in this study, with a median follow-up of 1.1 years. Pre-treatment patient characteristics can be found in Table 1. This was a patient population with significant comorbidities and pre-existing renal dysfunction with a median Charlson comorbidity score of 9 (range 3–12), mean ± standard deviation (SD) serum creatinine of 131 ± 28 μmol/L and calculated GFR of 52 ± 24 ml/min. Nine of the patients were referred for the clinical trial due to the perceived high risk of

Discussion

In this study we describe a dose-dependent relationship with regional kidney dysfunction secondary to radiation nephritis. Nephron sparing was observed at two weeks and three months after SABR, but late regional loss in function was observed at 1-year post treatment. We observed regional kidney dysfunction to be exponentially associated with physical delivered dose. Importantly, when normalising to BED using an α/β value of 3, both single and multi-fraction SABR displayed similar dose–response

Conflicts of interest statement

No disclosures.

Acknowledgment

This study was supported by the Royal Australian and New Zealand College of Radiologists FROGG – Ferring Fellowship Award, 2013.

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