International Journal of Radiation Oncology*Biology*Physics
Clinical InvestigationSafety and Efficacy of Stereotactic Ablative Radiation Therapy for Renal Cell Carcinoma Extracranial Metastases
Introduction
The standard of care for metastatic renal cell carcinoma (mRCC) is systemic therapy, whereas local treatment still remains controversial. A surgical series suggested that selected patients receiving curative-intent metastasectomy survived with a longer disease-free interval compared with patients who had not received it (1). Another series showed improved survival after resections of multiple limited metastases (2). The Mayo Clinic reviewed 887 mRCC patients and found improved cancer-specific survival with complete metastasectomy compared with less aggressive surgery, especially for pulmonary metastases (3). These findings suggested that selected patients with oligometastatic mRCC disease (4) can survive longer with improved quality of life when treated with complete metastasectomy (5).
Radiation therapy has historically been used for palliative purposes, and its practice in renal cell carcinoma (RCC) has been limited by perceived radioresistance to conventional fractionation (6). “Radioresistance” may be overcome with dose escalation, particularly by increasing the dose per fraction (7), as suggested by studies in preclinical models of human RCC xenografts (8). Stereotactic ablative radiation therapy (SAbR), or stereotactic body radiation therapy, has shown encouraging efficacy in mRCC 9, 10. SAbR relies on sophisticated image guidance and immobilization devices to deliver highly conformal ablative radiation doses to the tumor while sparing surrounding organs. However, factors associated with failure in mRCC are poorly understood. We report the safety and efficacy of SAbR and highlight its limitations for extracranial mRCC.
Section snippets
Patients
We retrospectively reviewed patients with extracranial mRCC treated with SAbR between 2005 and 2015 at our institution with >2 months’ follow-up (to obtain a scan to assess efficacy). Conventional fractionated radiation therapy and intracranial lesions were excluded. Pathologic confirmation was required to establish metastases. Patients treated with SAbR were divided into 2 radiation therapy intent categories: “curative,” in which all progressing lesions were treated, and “palliative,” in which
Tumor characteristics and radiation therapy regimens
Lesions (N=175) were identified from 84 patients treated over 124 SAbR sessions (Table 1). Most patients (72.6%) had localized disease at initial presentation but later had metastases develop. Most lesions (90%) were detected in patients with favorable or intermediate International Metastatic Renal Cell Carcinoma Database Consortium prognosis groups at the time of diagnosis with metastatic disease. The median dose per fraction was 11 Gy, and the median fraction number was 3. The median target
Discussion
We conducted a detailed analysis of our institutional SAbR experience for extracranial mRCC and showed satisfactory LC rates, confirming SAbR's safety and efficacy as a local therapy. More than half of the analyzed lesions were located in regions with significant internal motion (eg, chest, abdomen, or kidney). Despite the internal motion, adequate LC was achieved, indicating that modern radiation therapy techniques can accurately treat moving targets. A recent experience from the University of
Conclusions
SAbR exerts favorable LC with minimum acute and late complications and should be considered a treatment modality in selected RCC patients with limited metastases. No failures were observed when SAbR regimens of 24 Gy in 1 fraction, 12 Gy in 3 fractions, or 8 Gy in 5 fractions were used with ≥95% PTV coverage. These regimens may have been underestimated, as longer follow-up periods may result in additional failures. Lesions in patients in whom systemic therapy failed may require a higher dose.
Acknowledgments
The authors thank Dr. Damiana Chiavolini for scientific editing of the manuscript.
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Note—An online CME test for this article can be taken at http://astro.org/MOC.
Conflict of interest: none.