Permanent prostate brachytherapy extracapsular radiation dose distributions: analysis of a multi-institutional database

Abstract

PurposePeriprostatic brachytherapy doses impact biochemical control. In this study, we evaluate extracapsular volumetric dosimetry following permanent prostate brachytherapy in patients entered in a multi-institutional community database.Material and methodsIn the database, 4547 patients underwent brachytherapy (3094 – 125I, 1437 – 103Pd and 16 – 131Cs). Using the originally determined prostate volume, a 5 mm, 3-dimensional peri-prostatic anulus was constructed around the prostate (except for a 2 mm posterior margin), and evaluated in its entirety and in 90° segments. Prostate dosimetric parameters consisted of a V100 and D90 while the annular dosimetry was reported as a V100.ResultsThe intraprostatic V100 and D90 for 103Pd, and 125I were statistically comparable when stratified by isotope and/or monotherapy vs. boost. The overall mean V100 for the periprostatic annulus was 62.8%. The mean V100 at the base (51.6%) was substantially less than the apex (73.5%) and midgland (65.9%). In addition, for all patients, the anterior V100 (45.7%) was less than the lateral (68.8%) and the posterior (75.0%). The geometric V100 annular differences were consistent when evaluated by isotope. Overall, the V100 was higher in the 125I cohort.ConclusionsThe optimal extracapsular brachytherapy dose and radial extent remains unknown, but will prove increasingly important with reductions and/or elimination of supplemental external beam radiation therapy. The large multi-institutional community database demonstrates periprostatic annular doses that are not as robust as those in selected high volume brachytherapy centers, and may be inadequate for optimal biochemical control following monotherapeutic brachytherapy, especially in higher risk patients.

The impact of body mass index on dosimetric quality in low-dose-rate prostate brachytherapy

“…In a multi-institutional analysis of 4547 patients, Merrick et al . found that the V 100 was less at the base (51.5%) and anterior (45.7%) of the gland when compared to the lateral (68.8%), posterior (75%), and mid gland (65.9%) [21]. We postulate that increased perirectal and periprostatic fat in patients with higher BMI values may lead to difficulties accessing the anterior prostate, thereby resulting in an inferior D 90 .…”

Dosimetric evaluation of clinical target volume in the postimplant analysis of low-dose-rate brachytherapy for prostate cancer

“…Merrick et al (21) analyzed permanent prostate brachytherapy extracapsular radiation dose distributions in a multi-institutional database and found that the overall mean V 100 for the periprostatic annulus was 62.8%. The authors concluded that in multi-institutional community health centers, periprostatic annular doses are not as robust as those in selected high-volume brachytherapy centers and may be inadequate for optimal biochemical control after monotherapeutic brachytherapy, especially in high-risk patients (21).…”

“…The authors concluded that in multi-institutional community health centers, periprostatic annular doses are not as robust as those in selected high-volume brachytherapy centers and may be inadequate for optimal biochemical control after monotherapeutic brachytherapy, especially in high-risk patients (21). Merrick et al (22) evaluated the postimplant 5 mm, three-dimensional periprostatic annulus dosimetric coverage using CT scan within 2 h of the prostate seed implantation procedure.…”

Perineal recurrence of prostate cancer six years after trans-perineal brachytherapy

“…Merrick et al . [ 7 ] reported in a series of 4547 patients a significant underdosage in the first 5 mm outside the prostate in patients treated with brachytherapy. They describe a V 100 (the volume of prostate receiving the prescription dose) as low as 45% in this 5 mm annulus.…”