Proton SBRT for Isolated Nodal Recurrence in Gynecological Cancers

Abstract

<h3>Purpose/Objective(s)</h3> Stereotactic body radiotherapy (SBRT) for isolated lymph node recurrence has been shown to have good rates of local control (LC) in gynecological cancers. However there exists the risk of toxicities to nearby organs. This single institution, retrospective outcome and dosimetric analysis assesses treatment response, associated GI and GU toxicities and associated characteristics for improved or worsened outcomes with proton based SBRT, hypothesizing that there will be low rates of toxicities while maintaining beneficial outcomes. <h3>Materials/Methods</h3> Adult patients diagnosed with primary gynecologic malignancy with isolated nodal recurrence treated with proton SBRT from 2006-2021 at a single institution were included. Toxicities were evaluated using RTOG/EORTC and CTCAE grading. Descriptive statistics were used to describe characteristics associated with local recurrence, toxicity, and survival. <h3>Results</h3> Fourteen patients with 21 nodal lesions were treated with 19 courses of proton SBRT. Median age was 64.5 (range: 47-78) years at time of initial cancer diagnosis and median of 66.0 (range: 51- 80) years at initial lymph node recurrence. Patients recurred within an average of 13.00 (range: 0.66- 31.41) months from end of initial treatment. Primary cancer sites included endometrium (n= 9), cervix (n= 2), ovary (n= 2), and vagina (n= 2). SBRT doses ranged from 30- 50 Gy (median 40 Gy) in 5-15 fractions with mean BED (alpha beta 10) of 69.93 (range: 48.00- 100.00) and mean BED (alpha beta 3) of 139.95 (range: 72.00- 216.67). Nodal locations treated included para-aortic (n= 7), pelvis (n= 5), iliacs (n= 4), and distant nodes (n= 3, supraclavicular, perirectal, periadrenal). Three pelvic and iliac lesions recurred locally at a median of 2.9 months (range 1.25-29.23) and 50% of patients developed local or distant recurrence. Local control at 3 months, 6 months, 1 year, and 2 years was 84.6%, 83.3%, 81.8%, and 70.0% respectively. Local recurrence free survival (LRFS) at 1 year and 2 years was 80.0%, 75.0% and overall survival (OS) was 54.5%, 44.4% respectively. Six patients developed grade 1 or 2 GI treatment related toxicity (Grade 1: 3, Grade 2: 3). 2 patients developed grade 1 GU toxicity. There were no GI grade 3-5 toxicities or GU grade 2-5 toxicities. Average Dmax to bladder was 14.42 Gy (median 18.62 Gy), range (0.6- 30.6). Average rectum Dmax was 15.75 Gy (range: 0.1- 34.2), median: 15.8 Gy. Median small bowel D2cc was 27 Gy (range: 10- 50.5) <h3>Conclusion</h3> Patients treated with proton SBRT had excellent rates of LC and LRFS and low rates of GI and GU toxicity. Dosimetric analysis also demonstrates low dose to nearby OARs. Based on these findings, Phase I/II trials evaluating dose escalation using proton techniques to further improve local control of isolated nodal recurrences should be considered.