Effect of Stereotactic Body Radiotherapy on the Growth Kinetics and Enhancement Pattern of Primary Renal Tumors

Abstract

OBJECTIVE. The objective of our study was to assess the growth rate and enhancement of renal masses before and after treatment with stereotactic body radiotherapy (SBRT). MATERIALS AND METHODS. This retrospective study included all patients with renal masses who underwent SBRT during a 5-year period. Orthogonal measurements of renal masses were obtained on pre- and posttreatment CT or MRI. Pre- and posttreatment growth rates were compared for renal mass diameter and volume using the t test. Pre- and posttreatment tumor enhancement values were compared for tumors that underwent multiphasic contrast-enhanced MRI. RESULTS. Forty patients underwent SBRT for the treatment of 41 renal tumors: clear cell renal cell carcinomas (RCCs) (n = 16), papillary RCCs (n = 6), oncocytic neoplasms (n = 8), unclassified RCCs (n = 2), urothelial carcinoma (n = 1), and no pathologic diagnosis (n = 8). The mean maximum tumor diameter before treatment was 3.9 cm (range, 1.6–8.3 cm). Three hundred thirty-eight pre- and posttreatment imaging studies were analyzed: 214 MRI studies and 124 CT studies. The mean pre- and posttreatment lengths of observation were 416 days (range, 2–1800 days) and 561 days (83–1366 days), respectively. The mean pretreatment tumor growth rate of 0.68 cm/y decreased to –0.37 cm/y post treatment (p < 0.0001), and the mean tumor volume growth rate of 21.2 cm3/y before treatment decreased to –5.35 cm3/y after treatment (p = 0.002). Local control—defined as less than 5 mm of growth—was achieved in 38 of 41 (92.7%) tumors. The Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 showed progression in one tumor (2.4%), stability in 31 tumors (75.6%), partial response in eight tumors (19.5%), and complete response in one tumor (2.4%). No statistically significant change in tumor enhancement was shown (mean follow-up, 142 days; range, 7–581 days). CONCLUSION. Renal tumors treated with SBRT show statistically significant reductions in growth rate and tumor size after treatment but do not show statistically significant differences in enhancement in the initial (mean, 142 days) posttreatment period.

Pooled analysis of stereotactic ablative radiotherapy for primary renal cell carcinoma: A report from the International Radiosurgery Oncology Consortium for Kidney (IROCK)

“…Inherent population‐level biases may have been introduced through data sampling of widely disparate populations from Japanese, European, North American, and Australian patients. Another limitation to the interpretation of data is the local response assessment after SABR; it is unclear whether Response Evaluation Criteria in Solid Tumors should remain the optimal assessment criteria in this setting …”

“…Another limitation to the interpretation of data is the local response assessment after SABR; it is unclear whether Response Evaluation Criteria in Solid Tumors should remain the optimal assessment criteria in this setting. 25 Local control, minimal complications, and preserved renal function are considered to constitute "the trifecta" after minimally invasive partial nephrectomy. 26 The current multi-institutional, pooled analysis marks an important step in demonstrating that SABR can achieve this trifecta in localized RCC.…”

Diffusion weighted and dynamic contrast enhanced MRI as an imaging biomarker for stereotactic ablative body radiotherapy (SABR) of primary renal cell carcinoma

“…Standard response assessments using morphological measurements and CT based contrast enhancement criteria after SABR for primary RCC are known to be challenging. In a recent study, it was shown that tumour growth rate and tumour size were reduced in primary RCC after SABR, however no significant differences in tumour signal enhancement were shown on multiphasic contrast-enhanced MRI during the initial post treatment period [ 28 ]. The authors concluded further studies were needed to determine the correlation between tumour enhancement and disease progression and specified the need for longer follow-up times.…”

“…Within this challenging context, we sought to carry out an exploratory analysis of diffusion and perfusion changes shown by DWI and DCE MRI after SABR for primary RCC and assess whether any correlate with treatment response shown on CT. We have carried out this assessment on patients with a consistent imaging protocol, acquired on the same MR scanner which has eliminated sequence and scanner variability. We have correlated changes in MRI parameters with percentage tumour volume change from consistent CT time points, while also assessing the last follow-up CT scan which we considered suitable as tumour shrinkage over time is typically slow and relatively linear [ 28 ]. This last follow-up CT was a median 761 days (range 385–1085 days) after SABR treatment, providing a long follow-up time for the analysis (see S1 Table ).…”

Stereotactic radiotherapy for primary renal cell carcinoma: time for larger‐scale prospective studies

“…Similarly to the study by Sun et al. it appears that stable or partial radiological responses will predominate in the early years after SABR and, unlike thermal ablation, changes in enhancement patterns can be very slow to evolve.…”