Prostate deformation during hypofractionated radiotherapy: an analysis of implanted fiducial marker displacement.

BACKGROUND: To report prostate deformation during treatment, based on an analysis of fiducial marker positional differences in a large sample. MATERIAL AND METHODS: This study included 144 patients treated with prostate stereotactic body radiation therapy after implantation in each of 4 gold fiducial markers (FMs), which were located and numbered consistently. The center of mass of the FMs was recorded for every pair of X-ray images taken during treatment. The distance between each pair of fiducials in the live X-ray images is calculated and compared with the respective distances as determined in the CT volume. The RBE is the difference between these distances. Mean RBE and intrafraction and interfraction RBE were evaluated. The intrafraction and intefraction RBE variability were defined as the standard deviation, respectively, of all RBE during 1 treatment fraction and of the mean daily RBE over the whole treatment course. RESULTS: We analyzed 720 treatment fractions comprising 24,453 orthogonal X-ray image acquisitions. We observed a trend to higher RBE related to FM4 (apex) during treatment. The fiducial marker in the prostate apex could not be used in 16% of observations, in which RBE was > 2.5 mm. The mean RBEavg was 0.93 ± 0.39 mm (range 0.32-1.79 mm) over the 5 fractions. The RBEavg was significantly lower for the first and second fraction compared with the others (P < .001). The interfraction variability of RBEavg was 0.26 ± 0.16 mm (range 0.04-0.74 mm). The mean intrafraction variability of all FMs was 0.45 ± 0.25 mm. The highest Pearson correlation coefficient was observed between FM2 and FM3 (middle left and right prostate) (R = 0.78; P < .001). Every combination with FM4 yielded lower coefficients (range 0.66-0.71; P < .001), indicating different deformation of the prostate apex. CONCLUSIONS: Ideally, prostate deformation is generally small, but it is very sensitive to rectal and bladder filling. We observed RBE up to 11.3 mm. The overall correlation between FMs was affected by shifts of individual fiducials, indicating that the prostate is not a "rigid" organ. Systematic change of RBE average between subsequent fractions indicates a systematic change in prostate shape.

Monitoring of CRT-D devices during radiation therapy in vitro.

BACKGROUND: Using of active cardiac medical devices increases steadily. In Europe, there were 183 implants of ICD and 944 implants of PM, 119 of biventricular ICD and 41 of biventricular PM, all per million inhabitants in 2014. Healthcare environments, including radiotherapy treatment rooms, are considered challenging for these implantable devices. Exposure to radiation may cause the device to experience premature elective replacement indicator, decreased pacing amplitude or pacing inhibition, inappropriate shocks or inhibition of tachyarrhythmia therapy and loss of device function. These impacts may be temporary or permanent. The aim of this study was to evaluate the influence of linear accelerator ionizing radiation dose of 10 Gy on the activity of the biventricular cardioverter-defibrillator in different position in radiation beam. METHODS: Two identical wireless communication devices with all three leads were used for the measurement. Both systems were soused into solution saline and exposed in different position in the beam of linear accelerator per 10 Gy fractions. In comparison of usually used maximum recommended dose of 2 Gy, the radiation doses used in test were five times higher. Using the simultaneous monitoring wireless communication between device and its programmer allowed watching of the devices activities, noise occurrence or drop of biventricular pacing on the programmer screen, observed by local television loop camera. RESULTS: At any device position in radiation beam, there were no influences of the device activity at dose of 10 Gy neither a significant increase of a solution saline temperature in any of the measured positions of CRT-D systems in linear accelerator. CONCLUSIONS: The results of the study indicated, that the recommendation dose for treating the patients with implantable devices are too conservative and the risk of device failure is not so high. The systems can easily withstand the dose fractions of tens Gy, which would allow current single-dose-procedure treatment in radiation therapy. Even though the process of the random alteration of device memory and electrical components by scatter particles not allowed to specify a safe dose during ionizing radiation, this study showed that the safe limit are above the today used dose fractions.