A simple algorithm to assess patient suitability for Calypso-seed implantation for four-dimensional prostate localization

Abstract

Purpose: To retrospectively determine the proportion of prostate cancer patients who are appropriate candidates for prostate localization with Calypso (Calypso Medical, Seattle, WA); to assess the accuracy of surface-anatomy in predicting prostate depth; and, to describe a simple clinical-algorithm predicting patient’s appropriateness for Calypso localization.

Methods: Medical records and archived CT scans of all patients treated for localized prostate cancer at our institution between 2006 and 2007 were reviewed. Association between the feasibility of Calypso use, the depth of the prostate from the anterior torso, and a variety of anatomic factors were assessed (ANOVA, linear regression, and ROC).

Results: Patients were appropriate for the Calypso system in 91% of cases (localize and track, 52%; localize only, 39%). Strong correlation between greater trochanter location and the posterior prostate was seen (r²=0.91, mean difference 0.6 cm). The negative predictive value of the greater trochanter measurements was 31%. 31/45 patients (69%) who were deemed inappropriate for Calypso based on greater trochanter to anterior torso measurements were eligible on the basis of CT-based measurements of prostate depth. Weight, BMI, waist circumference, and hip circumference) correlated with distance from the prostate to the anterior torso and were predictive of Calypso appropriateness. All patients with weight ?100 kg, BMI ?30, or waist/hip circumference ?100cm, were eligible for Calypso.

Conclusions: Most prostate cancer patients are candidates for Calypso localization +/- tracking. The greater trochanter to anterior torso distance underestimates the number of eligible patients. Weight, BMI and waist/hip circumference are good predictors for Calypso appropriateness.