Crucial to all cancer therapy modalities, is a strong correlation between treatment and effect. Predictability of therapy success/failure allows for the optimization of treatment protocol and aids in the decision of whether additional treatment is necessary to prevent tumour progression. This work evaluated the relationship between cancer treatment and effect for intratumoural infusions of liposome-encapsulated 186 Re to head and neck squamous cell carcinoma xenografts of nude rats. Absorbed dose calculations using a dose point kernel convolution technique showed significant intratumoural dose heterogeneity due to the short range of the beta-particle emissions. The use of three separate tumour infusion locations improved dose homogeneity compared to a single infusion location as a result of a more uniform radioactivity distribution. An improved doseresponse correlation was obtained when using EUD calculations based on a generic set of radiobiological parameters (R 2 = 0.84) than when using average tumour absorbed dose (R 2 = 0.22). Varying radiobiological parameter values over ranges commonly used for all types of tumours showed little effect on EUD calculations which suggests that individualized parameter use is of little significance as long as the intratumoural dose heterogeneity is taken into consideration in the dose-response relationship. The improved predictability achieved when using EUD calculations for this cancer therapy modality may be useful for treatment planning and evaluation.
Purpose: Prostate specific antigen levels can be normalized by the prostate volume to give a prostate specific antigen density (PSAd). Magnetic resonance imaging (MRI) can more accurately determine prostate zonal anatomy and prostate volumes compared to transrectal ultrasound, and hence may lead to more accurate PSAd measurements. Methods: Imaging and pathology of men undergoing prostate MRI from April 2007 to May 2009 were reviewed in this retrospective study. 73 patients were included for analysis, of which 45 had prostate cancer and 28 did not have cancer. Total, transitional zone, and peripheral zone values were determined by ultrasound prolate ellipse, MRI prolate ellipse, and MRI segmentation methods. Results: The study population showed an average PSA of 6.3 ng/mL, with the control mean PSA (8.8 ng/mL) being greater than the cancer group (5.3 ng/mL). Transrectal ultrasound underestimated the prostate volume (mean 27.7 mL versus MRI volume of 38.3 mL, p ≤ 0.001). No difference was seen between cancer and control populations using PSAd. PSAd correctly categorized low (Gleason < 7) and high-grade cancers (Gleason ≥ 7) in patients with malignancy. Conclusion: Transrectal ultrasound underestimates prostate volumes and hence is inaccurate in calculating PSAd. MRI more accurately depicts PSAd, however PSAd is unable to differentiate between patients with cancer and benign disease such as BPH or prostatitis
Purpose To describe a rapid T2*-weighted (T2*W), three-dimensional (3D) echo planar imaging (EPI) sequence and its application in mapping local magnetic susceptibility variations in 3 Tesla (T) prostate MRI. To compare the sensitivity of T2*W EPI with routinely used T1-weighted turbo-spin echo sequence (T1W TSE) in detecting hemorrhage and the implications on sequences sensitive to field inhomogeneities such as MR spectroscopy (MRS). Materials and Methods B0 susceptibility weighted mapping was performed using a 3D EPI sequence featuring a 2D spatial excitation pulse with gradients of spiral k-space trajectory. A series of 11 subjects were imaged using 3T MRI and combination endorectal (ER) and six-channel phased array cardiac coils. T1W TSE and T2*W EPI sequences were analyzed quantitatively for hemorrhage contrast. Point resolved spectroscopy (PRESS MRS) was performed and data quality was analyzed. Results Two types of susceptibility variation were identified: hemorrhagic and nonhemorrhagic T2*W-positive areas. Post-biopsy hemorrhage lesions showed on average five times greater contrast on the T2*W images than T1W TSE images. Six nonhemorrhage regions of severe susceptibility artifact were apparent on the T2*W images that were not seen on standard T1W or T2W images. All nonhemorrhagic susceptibility artifact regions demonstrated compromised spectral quality on 3D MRS. Conclusion The fast T2*W EPI sequence identifies hemorrhagic and nonhemorrhagic areas of susceptibility variation that may be helpful in prostate MRI planning at 3.0T.
Purpose: This study investigates using MR imaging for prostate cancer targeted radiation therapy, including using MR imaging to localize tumor in prostate for focused radiation therapy, co‐registering MR images to CT or ultrasound images to guide or evaluate cancer radiation therapy, and determining tumor stage and its invasion to locoregional lymph nodes. Methods: Either endorectal (ER) or body RF coil has been used to acquire MR images. To determine the localization and volume of the prostate tumor from the MR images and to understand their correlation with the pathology slices, both pre‐surgery ER coil MR imaging and post‐surgery multi‐slice pathological analysis of the surgically excised tumor were studied (n=8). To avoid prostate dislocation caused by ER coil, multiple MR imaging protocols using the body coil were implemented to depict the structure of prostate and its surrounding tissues, pelvic lymph nodes, and obtain dynamics of contrast enhancement (n=37). MIM™ software was used to co‐register MR images to CT or ultrasound images for guiding treatment planning and evaluating prostate cancer brachytherapy. Results: The MR diagnosed tumor was proven by prostate pathology, which shows the rationale of using MRI guidance for focused treatment of prostate cancer to decrease toxicity and improve tumor control. It has been demonstrated that the capability of tumor localization and volume determination based on MR images are associated with tumor cell density. CT/MRI and ultrasound/MRI co‐registration provides excellent prostate micro‐structure, and surrounding tissue information for improved treatment planning, as well as post‐treatment evaluation. By using multi‐MR image synergistic co‐registration, T2‐weighted MR images can be accurately matched to CT image with <2 mm alignment error. Conclusion: MR image guidance is excellent for targeted prostate cancer radiation therapy, and it has been successfully used in our clinical practice.
Purpose: Vital to all cancer therapy modalities, is an effective relationship between treatment and effect. This work evaluated this relationship for intratumoral infusions of liposome‐encapsulated, 186Re for the treatment of human head and neck squamous cell carcinoma xenografts in nude rats. Methods: Rats were separated into three treatment groups receiving intratumoral infusions of, 186Re‐liposomes (5mCi/cm3 tumor; infused volume = 45% tumor volume): one group received a single infusion location, one group received multiple (3) infusion locations, and one group received multiple (3) infusion locations following two systemically injected bevacizumab treatments (1mg/rat). Planar gamma camera imaging was used to obtain tumor clearance kinetics. SPECT/CT images were used to obtain intratumoral activity distributions. Tumor sizes were periodically measured up to 43 days post‐treatment. Intratumoral dose calculations were performed using a dose‐point‐kernel convolution technique with co‐registered SPECT/CT images. Average dose and EUD values were calculated for individual tumors in attempt to correlate values with relative tumor shrinkage by comparing day 43 tumor volumes with day 0.Results: Intratumoral dose calculations showed significant intratumoral dose heterogeneity. The use of three separate tumor infusion locations improved dose homogeneity compared to a single infusion location as a result of a more uniform radioactivity distribution. An excellent dose‐response correlation was seen with EUD calculations (R, 2 = 0.84) compared with average tumor doses (R, 2 = 0.22). Varying radiobiological parameters over commonly used values showed little effect on relative EUD calculations among rats and suggests individualized parameter use is of little significance as long as the intratumoral dose heterogeneity is taken into consideration in the dose‐response relationship. Conclusions: This work showed a much improved treatment‐effect relationship for intratumoral delivery of, 186Re‐liposomes when using tumor EUD calculations. This is useful for treatment planning and evaluation with this radiation delivery technique.
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