Local ablative stereotactic body radiotherapy for oligometastatic prostate cancer.

PURPOSE OF REVIEW: The oligometastases is considered an intermediate state of the disease between localized and wide spread metastases. Local ablative therapy to oligometastatic prostate cancer is gaining significant traction and stereotactic body radiotherapy (SBRT) is an emerging treatment modality for this patient population. In this review, we report our literature review of SBRT to prostate oligometastases. Current evidence on the role of SBRT in oligometastatic prostate cancer reported in the last 10 years was summarized. Criteria for inclusion included studies with prostate cancer only as the primary site. RECENT FINDINGS: The unique properties of the oligometastatic prostate cancer appear to carry a better prognosis than wide spread metastatic disease, especially if these metastases are amenable to local ablative therapies. Our literature review revealed that local ablative therapy, using SBRT to prostate oligometastases, is associated with significant 2-years local control and acceptable toxicity profile. SUMMARY: SBRT to oligometastatic prostate cancer patients is feasible and carries an acceptable toxicity profile. The randomized phase II and III trials, currently underway, should clearly define the real benefit of this approach on progression-free and overall survival outcomes.

Magnitude of speed of sound aberration corrections for ultrasound image guided radiotherapy for prostate and other anatomical sites.

PURPOSE: The purpose of this work is to assess the magnitude of speed of sound (SOS) aberrations in three-dimensional ultrasound (US) imaging systems in image guided radiotherapy. The discrepancy between the fixed SOS value of 1540 m∕s assumed by US systems in human soft tissues and its actual nonhomogeneous distribution in patients produces small but systematic errors of up to a few millimeters in the positions of scanned structures. METHODS: A correction, provided by a previously published density-based algorithm, was applied to a set of five prostate, five liver, and five breast cancer patients. The shifts of the centroids of target structures and the change in shape were evaluated. RESULTS: After the correction the prostate cases showed shifts up to 3.6 mm toward the US probe, which may explain largely the reported positioning discrepancies in the literature on US systems versus other imaging modalities. Liver cases showed the largest changes in volume of the organ, up to almost 9%, and shifts of the centroids up to more than 6 mm either away or toward the US probe. Breast images showed systematic small shifts of the centroids toward the US probe with a maximum magnitude of 1.3 mm. CONCLUSIONS: The applied correction in prostate and liver cancer patients shows positioning errors of several mm due to SOS aberration; the errors are smaller in breast cancer cases, but possibly becoming more important when breast tissue thickness increases.

Analytical modelling of regional radiotherapy dose response of lung.

Knowledge of the dose-response of radiation-induced lung disease (RILD) is necessary for optimization of radiotherapy (RT) treatment plans involving thoracic cavity irradiation. This study models the time-dependent relationship between local radiation dose and post-treatment lung tissue damage measured by computed tomography (CT) imaging. Fifty-eight follow-up diagnostic CT scans from 21 non-small-cell lung cancer patients were examined. The extent of RILD was segmented on the follow-up CT images based on the increase of physical density relative to the pre-treatment CT image. The segmented RILD was locally correlated with dose distribution calculated by analytical anisotropic algorithm and the Monte Carlo method to generate the corresponding dose-response curves. The Lyman-Kutcher-Burman (LKB) model was fit to the dose-response curves at six post-RT time periods, and temporal change in the LKB parameters was recorded. In this study, we observed significant correlation between the probability of lung tissue damage and the local dose for 96% of the follow-up studies. Dose-injury correlation at the first three months after RT was significantly different from later follow-up periods in terms of steepness and threshold dose as estimated from the LKB model. Dependence of dose response on superior-inferior tumour position was also observed. The time-dependent analytical modelling of RILD might provide better understanding of the long-term behaviour of the disease and could potentially be applied to improve inverse treatment planning optimization.

A deformable phantom for 4D radiotherapy verification: design and image registration evaluation.

Motion of thoracic tumors with respiration presents a challenge for three-dimensional (3D) conformal radiation therapy treatment. Validation of techniques aimed at measuring and minimizing the effects of respiratory motion requires a realistic deformable phantom for use as a gold standard. The purpose of this study was to develop and study the characteristics of a reproducible, tissue equivalent, deformable lung phantom. The phantom consists of a Lucite cylinder filled with water containing a latex balloon stuffed with dampened natural sponges. The balloon is attached to a piston that mimics the human diaphragm. Nylon wires and Lucite beads, emulating vascular and bronchial bifurcations, were uniformly glued at various locations throughout the sponges. The phantom is capable of simulating programmed irregular breathing patterns with varying periods and amplitudes. A tissue equivalent tumor, suitable for holding radiochromic film for dose measurements was embedded in the sponge. To assess phantom motion, eight 3D computed tomography data sets of the static phantom were acquired for eight equally spaced positions of the piston. The 3D trajectories of 12 manually chosen point landmarks and the tumor center-of-mass were studied. Motion reproducibility tests of the deformed phantom were established on seven repeat scans of three different states of compression. Deformable image registration (DIR) of the extreme breathing phases was performed. The accuracy of the DIR was evaluated by visual inspection of image overlays and quantified by the distance-to-agreement (DTA) of manually chosen point landmarks and triangulated surfaces obtained from 3D contoured structures. In initial tests of the phantom, a 20-mm excursion of the piston resulted in deformations of the balloon of 20 mm superior-inferior, 4 mm anterior-posterior, and 5 mm left-right. The change in the phantom mean lung density ranged from 0.24 (0.12 SD) g/cm3 at peak exhale to 0.19 (0.12 SD) g/cm3 at peak inhale. The SI displacement of the landmarks varied between 94% and 3% of the piston excursion for positions closer and farther away from the piston, respectively. The reproducibility of the phantom deformation was within the image resolution (0.7 x 0.7 x 1.25 mm3). Vector average registration accuracy based on point landmarks was found to be 0.5 (0.4 SD) mm. The tumor and lung mean 3D DTA obtained from triangulated surfaces were 0.4 (0.1 SD) mm and 1.0 (0.8 SD) mm, respectively. This phantom is capable of reproducibly emulating the physically realistic lung features and deformations and has a wide range of potential applications, including four-dimensional (4D) imaging, evaluation of deformable registration accuracy, 4D planning and dose delivery.

Local correlation between monte-carlo dose and radiation-induced fibrosis in lung cancer patients.

PURPOSE: To present a new method of evaluating the correlation between radiotherapy (RT)-induced fibrosis and the local dose delivered to non-small-cell lung cancer patients. METHODS AND MATERIALS: Treatment plans were generated using the CadPlan treatment planning system (pencil beam, no heterogeneity corrections), and RT delivery was based on these plans. Retrospective Monte-Carlo dose calculations were performed, and the Monte-Carlo distributions of dose to real tissue were calculated using the planning computed tomography (CT) images and the number of monitor units actually delivered. After registration of the follow-up CT images with the planning CT images, different grades of radiologic fibrosis were automatically segmented on the follow-up CT images. Subsequently, patient-specific fibrosis probabilities were studied as a function of the local dose and a function of time after RT completion. RESULTS: A strong patient-specific variation in the fibrosis volumes was found during the follow-up period. For both lungs, the threshold dose for which the probability of fibrosis became significant coincided with the threshold dose at which significant volumes of the lung were exposed. At later stages, only fibrosis localized in the high-dose regions persisted for both lungs. Overall, the Monte-Carlo dose distributions correlated much better with the probability of RT-induced fibrosis than did the CadPlan dose distributions. CONCLUSION: The presented method allows for an accurate, systematic, patient-specific and post-RT time-dependent numeric study of the relationship between RT-induced fibrosis and the local dose.