The recent FLAME trial has demonstrated improved local control of intermediate to high-risk prostate cancer after focal dose escalation of the visible tumor. To visualize the tumor, MRI... Show moreThe recent FLAME trial has demonstrated improved local control of intermediate to high-risk prostate cancer after focal dose escalation of the visible tumor. To visualize the tumor, MRI examinations were taken in which prostate tissue characteristics were visualized. Since this treatment strategy improves the clinical outcome of the patient, a technical analysis of the FLAME dataset is useful for the further optimization of focal dose escalation strategies.Delineation of the prostate tumor appeared to be performed differently in the participating radiotherapy departments. Considering the impact on the realized tumor dose, this analysis demonstrated the need for guidelines of tumor delineation on MRI. Due to the complex nature of the treatment plans, in addition a prediction model was developed, which identified patients for which a higher tumor dose could be planned.The application of MRI was also investigated for ‘dose painting by numbers’, in which MRI values are translated to prescription dose without interference of manual tumor delineations. Dose prescription based on MRI appeared robust to daily patient variations, a prerequisite for further development of ‘dose painting by numbers’. However, because of the absence of significant tumor changes during the treatment course, MRI was considered not suitable for early adaptive treatment. Show less
PurposeIn a randomized focal dose escalation radiation therapy trial for prostate cancer (FLAME), up to 95 Gy was prescribed to the tumor in the dose-escalated arm, with 77 Gy to the entire... Show morePurposeIn a randomized focal dose escalation radiation therapy trial for prostate cancer (FLAME), up to 95 Gy was prescribed to the tumor in the dose-escalated arm, with 77 Gy to the entire prostate in both arms. As dose constraints to organs at risk had priority over dose escalation and suboptimal planning could occur, we investigated how well the dose to the tumor was boosted. We developed an anatomy-based prediction model to identify plans with suboptimal tumor dose and performed replanning to validate our model.Methods and MaterialsWe derived dose-volume parameters from planned dose distributions of 539 FLAME trial patients in 4 institutions and compared them between both arms. In the dose-escalated arm, we determined overlap volume histograms and derived features representing patient anatomy. We predicted tumor D98% with a linear regression on anatomic features and performed replanning on 21 plans.ResultsIn the dose-escalated arm, the median tumor D50% and D98% were 93.0 and 84.7 Gy, and 99% of the tumors had a dose escalation greater than 82.4 Gy (107% of 77 Gy). In both arms organs at risk constraints were met. Five out of 73 anatomic features were found to be predictive for tumor D98%. Median predicted tumor D98% was 4.4 Gy higher than planned D98%. Upon replanning, median tumor D98% increased by 3.0 Gy. A strong correlation between predicted increase in D98% and realized increase upon replanning was found (ρ = 0.86).ConclusionsFocal dose escalation in prostate cancer was feasible with a dose escalation to 99% of the tumors. Replanning resulted in an increased tumor dose that correlated well with the prediction model. The model was able to identify tumors on which a higher boost dose could be planned. The model has potential as a quality assessment tool in focal dose escalated treatment plans. Show less
Romeijn, R.J.; Gorski, M.M.; Schie, M.A. van; Noordermeer, J.N.; Mullenders, L.H.; Ferro, W.; Pastink, A. 2005
The decision of whether and where to cross the midline, an evolutionarily conserved line of bilateral symmetry in the central nervous system, is the first task for many newly extending axons. We... Show moreThe decision of whether and where to cross the midline, an evolutionarily conserved line of bilateral symmetry in the central nervous system, is the first task for many newly extending axons. We show that Wnt5, a member of the conserved Wnt secreted glycoprotein family, is required for the formation of the anterior of the two midline-crossing commissures present in each Drosophila hemisegment. Initial path finding of pioneering neurons across the midline in both commissures is normal in wnt5 mutant embryos; however, the subsequent separation of the early midline-crossing axons into two distinct commissures does not occur. The majority of the follower axons that normally cross the midline in the anterior commissure fail to do so, remaining tightly associated near their cell bodies, or projecting inappropriately across the midline in between the commissures. The lateral and intermediate longitudinal pathways also fail to form correctly, similarly reflecting earlier failures in pathway defasciculation. Panneural expression of Wnt5 in a wnt5 mutant background rescues both the commissural and longitudinal defects. We show that the Wnt5 protein is predominantly present on posterior commissural axons and at a low level on the anterior commissure and longitudinal projections. Finally, we demonstrate that transcriptional repression of wnt5 in AC neurons by the recently described Wnt5 receptor, Derailed, contributes to this largely posterior commissural localization of Wnt5 protein. Show less
