Abstract
IntroductionGuidelines recommend that the proximal seminal vesicles (PrSV) should be included in the clinical target volume for locally advanced prostate cancer patients undergoing radiotherapy. Verification and margins for the prostate may not necessarily account for PrSV displacement. The purpose was to determine the inter‐fraction displacement of the PrSV relative to the prostate during radiotherapy.MethodsFiducials were inserted into the prostate, and right and left PrSV (RSV and LSV) in 30 prostate cancer patients. Correctional shifts for the prostate, right and left PrSV and pelvic bones were determined from each patient's 39 daily orthogonal portal images relative to reference digitally reconstructed radiographs.ResultsThere was a significant displacement of the RSV relative to the prostate in all directions: on average 0.38 mm (95% confidence interval (CI) 0.26 to 0.50) to the left, 0.80–0.81 mm (CI 0.68 to 0.93) superiorly and 1.51 mm (CI 1.36 to 1.65) posteriorly. The LSV was significantly displaced superiorly to the prostate 1.09–1.13 mm (CI 0.97 to 1.25) and posteriorly 1.81 mm (CI 1.67 to 1.96), but not laterally (mean 0.06, CI −0.06 to 0.18). The calculated PTV margins (left–right, superior–inferior, posterior–anterior) were 4.9, 5.3–5.6 and 4.8 mm for the prostate, 5.2, 7.1–8.0 and 9.7 mm for the RSV, and 7.2, 7.5–7.6 and 8.6 mm for the LSV.ConclusionThere is a significant displacement of the PrSV relative to the prostate during radiotherapy. Greater margins are recommended for the PrSV compared to the prostate.
Highlights
Guidelines recommend that the proximal seminal vesicles (PrSV) should be included in the clinical target volume for locally advanced prostate cancer patients undergoing radiotherapy
It is generally recommended that the seminal vesicle (SV) be included in the clinical target volume (CTV) for intermediate to high and very high-risk categories.[6,7]
The final cohort consisted of 30 men with locally advanced prostate cancer, that is two patients (7%) with NCCN7 very high risk, 13 (43%) with high risk and 15 (50%) with intermediate-risk prostate cancer
Summary
Guidelines recommend that the proximal seminal vesicles (PrSV) should be included in the clinical target volume for locally advanced prostate cancer patients undergoing radiotherapy. The purpose was to determine the inter-fraction displacement of the PrSV relative to the prostate during radiotherapy. Results: There was a significant displacement of the RSV relative to the prostate in all directions: on average 0.38 mm (95% confidence interval (CI) 0.26 to 0.50) to the left, 0.80–0.81 mm (CI 0.68 to 0.93) superiorly and 1.51 mm (CI 1.36 to 1.65) posteriorly. The risk for SVI in prostate cancer can be estimated using either Partins Tables or Roach’s formulae.[6] It is generally recommended that the seminal vesicle (SV) be included in the clinical target volume (CTV) for intermediate to high and very high-risk categories.[6,7]
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