Search

Background The analysis aimed to compare the radiotracers [68Ga]-Ga-PSMA-11 and [18F]-F-PSMA-1007 intraindividually in terms of malignant lesions, mi(molecular-imaging)TNM staging and presumable unspecific lesions retrospectively as used in routine clinical practice. Methods A retrospective analysis of 46 prostate cancer patients (median age: 71 years) who underwent consecutive [18Ga]-Ga-PSMA-11- and [18F]-F-PSMA-1007-PET/CT or PET/MRI within a mean of 12 ± 8.0 days was performed. MiTNM staging was performed in both studies by two nuclear medicine physicians who were blinded to the results of the other tracer. After intradisciplinary and interdisciplinary consensus with two radiologists was reached, differences in both malignant and presumable nonspecific tracer accumulation were analyzed. Results Differences in terms of miTNM stages in both studies occurred in nine of the 46 patients (19.6%). The miT stages differed in five patients (10.9%), the miN stages differed in three patients (6.5%), and different miM stages occurred only in one patient who was upstaged in [18F]-F-PSMA-1007 PET. Concordant miTNM stages were obtained in 37 patients (80.4%). There was no significant difference between [18F]-F-PSMA-1007 and [68Ga]-Ga-PSMA-11 in the SUVmax locally (31.5 vs. 32.7; p = 0.658), in lymph node metastases (28.9 vs. 24.9; p = 0.30) or in bone metastases (22.9 vs. 27.6; p = 0.286). In [18F]-F-PSMA-1007 PET, more patients featured presumable unspecific uptake in the lymph nodes (52.2% vs. 28.3%; p: 18F]-F-PSMA-1007-positive lesions mainly occurred in the ribs (58.7%), axillary lymph nodes (39.1%) and cervical ganglia (28.3%). Conclusion In terms of miTNM staging, both tracers appeared widely exchangeable, as no tracer relevantly outperformed the other. The differences between the two tracers were far more common in presumable unspecific lesions than in malignant spots. A routinely performed two-tracer study could not be shown to be superior. Since it seems at least challenging for most nuclear medicine departments to provide both [18F]-F-PSMA-1007 and [68Ga]-Ga-PSMA-11, it appears reasonable to choose the PSMA radiotracer depending on local availability with attention to the greater occurrence of nonspecific bone findings with [18F]-F-PSMA-1007.

The study presents the first series of daily in-room CT images acquired from the first 12 prostate cancer patients after proton-specific immobilization and positioning procedures and followed by actual proton radiotherapy at the University Proton Therapy Dresden. Based on this unique dataset, the actually delivered proton dose is calculated retrospectively for each fraction, analyzed for inter-fractional variability and accumulated to a total dose for comparison with the treatment plan. Introduction: The steep dose gradients and small number of treatment fields require reproducible anatomical geometry and positioning in proton therapy to secure an accurate dose delivery. Prostate cancer is known to be subjected to inter-fractional variation due to day-to-day variation in bowel, rectum and bladder filling. Adequate positioning and treatment protocols were investigated prior the start of proton therapy to prostate cancer patients in our institute [1]. The presented study analyzes the suitability of these protocols by means of a retrospective evaluation of actually delivered proton dose in comparison to the treatment plan. Material and Methods: Inter-fractional motion in prostate cancer patients treated at the University Proton Therapy Dresden is counteracted by water-filled endorectal ballon and bladder filling protocol. Patient positioning is based on bony anatomy match utilizing orthogonal X-Ray imaging. Stability of implanted fiducial markers and anatomy were checked in the first 12 patients by daily scheduled in-room control CT (cCT) after immobilization and positioning. Typical plans (XiO, Elekta Instruments AB, Stockholm) for 74 Gy(RBE) sequential boost treatment in 37 fractions include two series of opposing lateral double-scattered proton beams covering the respective internal clinical target volume (iCTV). In RayStation 4.6 (RaySearch Laboritories AB, Stockholm), all cCTs are delineated retrospectively and the treatment plans were recalculated on the planning CT and the registered cCTs. All fraction doses were accumulated on the planning CT after deformable registration. Parameters of delivered dose to iCTV (D98% > 95%, D2% < 107%), bladder (V75Gy < 15%, V70Gy < 25%, V65Gy < 30%), rectum (V70Gy < 10%, V50Gy < 40%) and femoral heads (V50Gy < 5%) are compared to those in the treatment plan. Intra-therapy variation is represented in DVH bands. Result: Due to CT maintenance, physician’s decision and initial workflow optimization, the median number of actually acquired cCTs within 37 fractions was 32 (range: 27-37). Seven patients received the sequential boost series prior the nominal series due to concerns that anatomy might change noticeably during six weeks of therapy and then margin concepts might be insufficient. One patient received a nominal plan of 37 fractions to an iCTV excluding seminal vesicles. First intra-therapy variability analysis in 5 patients showed no time-dependent parameter drift and revealed strongest variability for bladder dose. In some fractions, iCTV coverage (D98%) and rectum V70Gy was missed. An illustration of the dosimetric evaluation is shown for an exemplary patient in Figure 1. No alarming differences (cp. Table 1) were observed between planned and retrospectively accumulated dose for all 12 patients: iCTV constraints were met, except for one patient (D98% = 94.4% in non-boosted iCTV). Considered bladder and femoral head dosimetric values were below the limits. Rectum V70Gy was slightly exceeded (

Purpose: Retrospective calculation of the delivered proton dose in prostate cancer patients based on a unique dataset of daily CT images. Methods: Inter-fractional motion in prostate cancer patients treated at our proton facility is counteracted by water-filled endorectal ballon and bladder filling protocol. Typical plans (XiO, Elekta Instruments AB, Stockholm) for 74 Gy(RBE) sequential boost treatment in 37 fractions include two series of opposing lateral double-scattered proton beams covering the respective iCTV. Stability of fiducial markers and anatomy were checked in 12 patients by daily scheduled in-room control CT (cCT) after immobilization and positioning according to bony anatomy utilizing orthogonal X-ray. In RayStation 4.6 (RaySearch Laboritories AB, Stockholm), all cCTs are delineated retrospectively and the treatment plans were recalculated on the planning CT and the registered cCTs. All fraction doses were accumulated on the planning CT after deformable registration. Parameters of delivered dose to iCTV (D98%>95%, D2%75Gy70Gy65Gy70Gy50Gy50Gy98%=94.6% in non-boosted iCTV). Considered bladder and femoral head values were below the limits. Rectum V70Gy was slightly exceeded (98%) and rectum V70Gy was missed. Conclusion: Double scattered proton plans are accurately delivered to prostate cancer patients due to fractionation effects and the applied precise positioning and immobilization protocols. As a result of rare interventions after daily 3D imaging of the first 12 patients, in-room CT frequency for prostate cancer patients was reduced. The presented study supports this decision.