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Dosimetric Advantages of Partial Prostate SBRT Compared to Whole-Gland SBRT

C Langmack1*, B Traughber1,2, M Kharouta1,2, R Ellis1,3, E Fredman1,2, L Ponsky1,2, M Machtay1,2, T Baig1, K Xu1, T Podder1,2, (1) University Hospitals, Cleveland, OH, (2) Case Western Reserve University, Cleveland, OH, (3) Penn State Cancer Institute, Hershey, PA,

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: institution has previously reported the feasibility and tolerability of a multiparametric MRI (mpMRI)-directed, targeted partial gland radiotherapy technique using focal SBRT (f-SBRT) in patients with a single focus of low-intermediate risk prostate cancer. We hypothesize that irradiation of the primary lesion alone will allow for better organ-at-risk (OAR) sparing with comparable clinical outcomes. In the current study, we report a dosimetric comparison of f-SBRT with standard whole-gland SBRT (w-SBRT) plans in patients treated as per our institutional protocol.

Methods: patients with prostate cancer treated with f-SBRT after confirming the primary lesion using mp-MRI and histopathology were analyzed. Each case was re-planned to receive the same dose scheme (2925 cGy at 975cGy/fractionx3fractions) for whole-gland SBRT (w-SBRT). A comparison was made of percent volumes relative to their completed f-SBRT plans. The w-SBRT plans are normalized such that 95% of the whole prostate PTV receives prescription dose. We analyzed the dose to each OAR by comparison of the V30%, V50%, V70%, and V90%.

Results: f-SBRT plan spares more volume of OARs than the corresponding w-SBRT plan. Averaging over all planned patients, the f-SBRT plans meet the constraints set by IRB approved protocol CASE-11813, and the w-SBRT plans meet all the volumetric constraints to OARs. When comparing the mean V50% between w-SBRT and f-SBRT plans, the f-SBRT plans spared 23% more of the bladder, 32% of the rectum, 35% of the urethra, and 47% of the rest of the prostate at the 50% isodose level (IDL). Similar benefits were observed at all analyzed IDLs across all OARs.

Conclusion: study reveals that prostate f-SBRT dosimetrically outperforms w-SBRT in the sparing of OARs. Therefore, f-SBRT is expected to yield improved clinical outcomes, especially reduced toxicity and improved quality of life, for appropriately selected patients. Longer-term follow-up and additional study in a larger cohort is warranted.

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Keywords

Stereotactic Radiosurgery, Prostate Therapy

Taxonomy

Not Applicable / None Entered.

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