Treatment of Prostate Cancer with Radiotherapy: Should the Entire Seminal Vesicles be Included in the CTV

Ryan Smith, MD
University of Pennsylvania Cancer Center
Last Modified: November 7, 2001

Presenter: L.L. Kestin
Presenter's Affiliation: William Beaumont Hospital
Type of Session: Scientific

Background

Dose escalation (to upper 70s to >80 Gy) has been shown to be efficacious in the treatment of prostate cancer.

With this escalation, patients will likely experience toxicity directly related to volume treated, and the inclusion of the seminal vesicles (SVs).

Hence, there is great importance to accurately define the CTV that is needed to be treated.

This study was done to attempt to determine the appropriate amount of SV to include in the CTV.

Materials and Methods

Study of 344 patients with T1-2N0 prostate cancer, all treated with radical prostatectomy.

A majority of patients had Gleason Score (GS) of 3-6 with a relative minority having a GS of 9-10.

Longitudinal sectioning was done in 66% of specimens to directly measure the length of tumor extension from the prostate junction to the farthest cell.

Transverse sectioning was done in 34% of patients, where the distance was estimated.

Results

Total median SV length was 3.5 cm, with the 90th percentile being 5.2 cm.

There were 81 (+) SVs in 51 patients (15% of patient population).

86% of patients had contiguous spread of disease (so 14% had "skip" lesions).

The median length of SVs involved was 1.0 cm, with the 90th percentile being 2.0 cm.

Predictors of SV involvement was high PSA (>20=38% involvement), high GS (7=33%, 8-10=37% involvement), and T stage (T2b=39% involvement)

Author's Conclusions

A portion of the SVs should only be included for those patients at high risk of involvement (PSA >10, GS >6, Stage T2b or higher)

When treating the SVs, only the proximal 2 cm (50% of total) should be included in the CTV.

Clinical/Scientific Implications
The standard dose of radiation delivered in the treatment of prostate cancer has increased in recent years. This is being done with a paucity of data regarding long term toxicity. With increasing doses, it is important to limit the volume being treated. This study makes strides in defining the extent of SVs that need to be treated. As expected, with higher "classic" prognostic factors (high PSA, higher Gleason Score, higher T stage) comes a a higher involvement of the SVs. Regardless of the prognostic factors, the authors recommend treating, at the most, the proximal 2 cm of the SVs in patients with clinical T1-2 tumors. It should be noted, that also presented during this session, was a paper also looking into SV involvement (Davis, et al, Abstract #250). These authors reached the opposite conclusion, notably that the entire SVs should be treated in those patients at risk for SV involvement. In this study, however, a majority (75%) had stage T2b or higher tumors, and all had Gleason Score >6. In addition, the length of SVs was measured differently in terms of pathologic sectioning. This likely accounts for the discrepency, and the indiviaual patient should be considered when evaluating these data.

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