PV QA 1 - Poster Viewing Q&A 1
Purpose/Objective(s): In order to evaluate the tolerability of escalating doses of stereotactic body radiotherapy (SBRT) as the primary treatment of localized renal cell carcinoma (RCC) in poor surgical candidates we expanded on our initial experience which prospectively treated patients with up to 48 Gy in 4 fractions by extending the study to evaluate the safety of treating patients with dose levels up to 60 Gy in 3 fractions.
Materials/Methods: Eligible patients included those with clinically localized, biopsy-confirmed RCC and comorbid medical illness which precluded surgery. Groups of patients were assigned to one of three dose levels (48, 54, and 60 Gy all in 3 fractions) beginning at the lowest dose level. Escalation to the next dose level was allowed to occur only if 4 patients in the previous dose level did not experience any dose-limiting toxicities (DLTs), defined as grade 3 or worse gastrointestinal/genitourinary toxicity by CTCAEv4 up to 6 months post-treatment. Per protocol, patients were assessed for toxicities 1, 3, and 6 months post-treatment and then every 6 months for 3 years. Tumor response was assessed by RECIST v1.1 measurements every 6 months for 3 years with MRI or CT of the chest and abdomen, and patients were recommended post-treatment biopsy at 6 - 12 months for histologic analysis of treatment effect.
Results: An additional 11 patients were treated in the second and final phase of the dose-escalation protocol. Groups of 4, 4, and 3 patients respectively received 48, 54, and 60 Gy in 3 fractions. The median age of patients in the second cohort was 72 years (range, 61 – 86), median maximal lesion dimension was 3.65 cm (range, 1.7 – 9.5), and median follow-up was 1.7 years (range, 0.5 – 3.7). No patients reported significant grade 1 or greater acute GI/GU toxicities related to treatment. 1 patient was hospitalized for pyelonephritis possibly contributed to by SBRT. All patients had at least 6-month follow-up imaging assessment (range, 6 – 42). 1 patient had partial response, 9 patients had stable disease, and 1 patient had disease progression in the primary lesion. 1 patient with stable disease at the primary site developed evidence of distant metastasis 3.5 years post SBRT. 5 of 11 patients consented to post-treatment biopsies at a median time of 6 months following SBRT (range, 4.5 – 10.5). All 5 patients had positive histologic findings of residual tumor. Of these 5 patients one died from comorbid illness without evidence of local progression or distant metastasis, one was treated with cryotherapy with no evidence of progression, and three have received no further therapy with no evidence of disease progression on imaging 14.5 - 25 months after post-SBRT biopsy.
Conclusion: Dose escalation with SBRT to 60 Gy in 3 fractions was achieved without dose-limiting toxicity. Further investigation of this dose-fractionation scheme in conjunction with targeted agents for primary renal tumor treatment in localized and metastatic disease is warranted. The role of post-SBRT biopsy in RCC is yet to be determined.
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