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Impact of Prostate Focused Alignment On Pelvic Lymph Node Coverage

J Kilian-Meneghin

J Kilian-Meneghin1,2*, T Ma2 , L Kumaraswamy2 , (1) University at Buffalo, Buffalo, NY, (2) Roswell Park Cancer Institute, Buffalo, NY


SU-I-GPD-T-67 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Prostate patients with positive lymph node margins receive an initial course of 45Gy to the PTV comprised of prostate, seminal vesicles, and lymph nodes with a 1cm margin. The prostate is localized via implanted fiducial markers before each fraction is delivered using portal-imaging. However, the pelvic lymph nodes (PLN) are affixed to the bony anatomy and are not mobile in concert with the prostate. The aim of this study is to determine whether a significant difference in PLN coverage exists between planned and delivered external beam therapy treatments for these patients.

Methods: The recorded prostate motions were gathered for 15 patients; conjointly the PLN motions were determined by manual registration of the bony anatomy in the Kv-images. The difference between the prostate and the bony anatomy coordinates were input into Eclipse as field shifts to represent the deviation in planned vs delivered PLN coverage.

Results: Structure volume at D(100) was recorded for each patient for two structures: summed PLNs and PLNs+1cm margin to express their contribution to the PTV. For the PLNs+1cm, the average difference between the planned coverage and calculated delivered coverage was 3.9%, with a paired p-value of p=0.01. Based upon bony anatomy registration, only 33% of patients received the intended dose coverage based upon D(100) dose criteria for PLN+1cm. Dose value difference had a minimum of 3.3±3.43Gy, a mean of 0.34±0.34Gy, and a maximum of 0.68±0.42Gy between the two plans. For the PLNs, the average difference between the planned coverage and calculated delivered coverage was 0.8%, with a paired p-value of p=0.35.

Conclusion: The results indicate a significant difference exists between the planned coverage and calculated delivered coverage for the PLNs+1cm, with no significant difference for PLNs. We conclude that lymph node motion must be considered with the prostate motion when aligning patients before each fraction.

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