Variability in MRI vs. ultrasound measures of prostate volume and its impact on treatment recommendations for favorable-risk prostate cancer patients: a case series.

BACKGROUND: Prostate volume can affect whether patients qualify for brachytherapy (desired size ≥20 mL and ≤60 mL) and/or active surveillance (desired PSA density ≤0.15 for very low risk disease). This study examines variability in prostate volume measurements depending on imaging modality used (ultrasound versus MRI) and volume calculation technique (contouring versus ellipsoid) and quantifies the impact of this variability on treatment recommendations for men with favorable-risk prostate cancer. METHODS: We examined 70 patients who presented consecutively for consideration of brachytherapy for favorable-risk prostate cancer who had volume estimates by three methods: contoured axial ultrasound slices, ultrasound ellipsoid (height × width × length × 0.523) calculation, and endorectal coil MRI (erMRI) ellipsoid calculation. RESULTS: Average gland size by the contoured ultrasound, ellipsoid ultrasound, and erMRI methods were 33.99, 37.16, and 39.62 mLs, respectively. All pairwise comparisons between methods were statistically significant (all p < 0.015). Of the 66 patients who volumetrically qualified for brachytherapy on ellipsoid ultrasound measures, 22 (33.33%) did not qualify on ellipsoid erMRI or contoured ultrasound measures. 38 patients (54.28%) had PSA density ≤0.15 ng/dl as calculated using ellipsoid ultrasound volumes, compared to 34 (48.57%) and 38 patients (54.28%) using contoured ultrasound and ellipsoid erMRI volumes, respectively. CONCLUSIONS: The ultrasound ellipsoid and erMRI ellipsoid methods appeared to overestimate ultrasound contoured volume by an average of 9.34% and 16.57% respectively. 33.33% of those who qualified for brachytherapy based on ellipsoid ultrasound volume would be disqualified based on ultrasound contoured and/or erMRI ellipsoid volume. As treatment recommendations increasingly rely on estimates of prostate size, clinicians must consider method of volume estimation.

High-dose-rate brachytherapy for prostate cancer in a previously radiated patient with polyethylene glycol hydrogel spacing to reduce rectal dose: case report and review of the literature.

PURPOSE: To describe the use of a temporary spacer to reduce rectal dose prior to prostate radiation in a man with prior pelvic radiotherapy and review the relevant literature. METHODS AND MATERIALS: A healthy 57-year-old man presented with high-risk prostate cancer (Gleason score of 8, prostate-specific antigen level [PSA] 12.6 ng/mL, T3a by magnetic resonance imaging [MRI]), only 2.5 years after a low anterior resection followed by pelvic chemo-radiotherapy to 50.4 Gy for a locally advanced rectal cancer. Due to the prior radiation, he was not felt to be a candidate for surgery or external beam radiation, so he chose long-term androgen deprivation therapy (ADT) plus high-dose-rate brachytherapy to 36 Gy in 6 fractions. To reduce the radiation dose to the anterior rectal wall, 10 mL of a polyethylene glycol hydrogel spacer was injected between the prostate and rectum and created between 1.4 and 1.5 cm of separation along the length of the prostate. RESULTS: Two randomized trials demonstrating that local therapy plus ADT improves overall survival compared to ADT alone provided the rationale for additional prostate radiotherapy in this otherwise healthy patient. Salvage brachytherapy is associated with a 3.4% rate of rectal fistula among the 251 cases reported in the literature from 2000-2007, with rates as high as 12% in one series. The spacer allowed the rectal dose constraint goals to be easily met. CONCLUSIONS: Injecting an absorbable polyethylene glycol hydrogel to separate the prostate and rectum appears to be associated with decreased maximum and mean rectal doses, and may have particular utility in previously irradiated patients.

Two solutions for registration of ultrasound to MRI for image-guided prostate interventions.

Ultrasound-guided prostate interventions could benefit from incorporating the radiologic localization of the tumor which can be acquired from multiparametric MRI. To enable this integration, we propose and compare two solutions for registration of T2 weighted MR images with transrectal ultrasound. Firstly, we propose an innovative and practical approach based on deformable registration of binary label maps obtained from manual segmentation of the gland in the two modalities. This resulted in a target registration error of 3.6±1.7 mm. Secondly, we report a novel surface-based registration method that uses a biomechanical model of the tissue and results in registration error of 3.2±1.3 mm. We compare the two methods in terms of accuracy, clinical use and technical limitations.

Technological advancements and error rates in radiation therapy delivery.

PURPOSE: Technological advances in radiation therapy (RT) delivery have the potential to reduce errors via increased automation and built-in quality assurance (QA) safeguards, yet may also introduce new types of errors. Intensity-modulated RT (IMRT) is an increasingly used technology that is more technically complex than three-dimensional (3D)-conformal RT and conventional RT. We determined the rate of reported errors in RT delivery among IMRT and 3D/conventional RT treatments and characterized the errors associated with the respective techniques to improve existing QA processes. METHODS AND MATERIALS: All errors in external beam RT delivery were prospectively recorded via a nonpunitive error-reporting system at Brigham & Women's Hospital/Dana Farber Cancer Institute. Errors are defined as any unplanned deviation from the intended RT treatment and are reviewed during monthly departmental quality improvement meetings. We analyzed all reported errors since the routine use of IMRT in our department, from January 2004 to July 2009. Fisher's exact test was used to determine the association between treatment technique (IMRT vs. 3D/conventional) and specific error types. Effect estimates were computed using logistic regression. RESULTS: There were 155 errors in RT delivery among 241,546 fractions (0.06%), and none were clinically significant. IMRT was commonly associated with errors in machine parameters (nine of 19 errors) and data entry and interpretation (six of 19 errors). IMRT was associated with a lower rate of reported errors compared with 3D/conventional RT (0.03% vs. 0.07%, p = 0.001) and specifically fewer accessory errors (odds ratio, 0.11; 95% confidence interval, 0.01-0.78) and setup errors (odds ratio, 0.24; 95% confidence interval, 0.08-0.79). CONCLUSIONS: The rate of errors in RT delivery is low. The types of errors differ significantly between IMRT and 3D/conventional RT, suggesting that QA processes must be uniquely adapted for each technique. There was a lower error rate with IMRT compared with 3D/conventional RT, highlighting the need for sustained vigilance against errors common to more traditional treatment techniques.

Angular dose dependence of Matrixx TM and its calibration.

One of the applications of MatriXX (IBA Dosimetry) is experimental verification of dose for IMRT, VMAT, and tomotherapy. For cumulative plan verification, dose is delivered for all the treatment gantry angles to a stationary detector. Experimental calibration of MatriXX detector recommended by the manufacturer involves only AP calibration fields and does not address angular dependency of MatriXX. Angular dependency may introduce dose bias in cumulative plan verification if not corrected. For this reason, we characterized angular dependency of MatriXX and developed a method for its calibration. We found relatively large discrepancies in responses to posterior vs. anterior fields for four MatriXX (Evolution series) detectors (up to 11%), and relatively large variability of responses as a function of gantry angle in the gantry angle ranges of 91 degrees-110 degrees and 269 degrees-260 degrees. With our calibration method, the bias due to angular dependency is effectively removed in experimental verification of IMRT and VMAT plans.