When your MR linac is down: Can an automated pipeline bail you out of trouble?

PURPOSE: The unique treatment delivery technique provided by magnetic resonance guided radiotherapy (MRgRT) can represent a significant drawback when system fail occurs. This retrospective study proposes and evaluates a pipeline to completely automate the workflow necessary to shift a MRgRT treatment to a traditional radiotherapy linac. MATERIAL AND METHODS: Patients undergoing treatment during the last MRgRT system failure were retrospectively included in this study. The core of the proposed pipeline was based on a tool able to mimic the original MR linac dose distribution. The so obtained dose distribution (AUTO) has been compared with the distribution obtained in the conventional radiotherapy linac (MAN). Plan comparison has been performed in terms of time required to obtain the final dose distribution, DVH parameters, dosimetric indices and visual analogue scales scoring by radiation oncologists. RESULTS: AUTO plans generation has been obtained within 10 min for all the considered cases. All AUTO plans were found to be within clinical tolerance, showing a mean target coverage variation of 1.7% with a maximum value of 4.3% and a minimum of 0.6% when compared with MAN plans. The highest OARs mean variation has been found for rectum V60 (6.7%). Dosimetric indices showed no relevant differences, with smaller gradient measure in favour of AUTO plans. Visual analogue scales scoring has confirmed comparable plan quality for AUTO plans. CONCLUSION: The proposed workflow allows a fast and accurate generation of automatic treatment plans. AUTO plans can be considered equivalent to MAN ones, with limited clinical impact in the worst-case scenario.

Physicochemical characterization of neuroleptics. Relative stability of 7- and 9-hydroxyrisperidones and their protonated forms in gas phase and in solution.

Conventional ab initio and DFT-B3LYP calculations have been used to investigate on molecular conformation, dipole moments, intramolecular hydrogen bond and relative energies of 9-hydroxy and 7-hydroxyrisperidone metabolites of risperidone, in their neutral and mono-protonated forms in the gas phase and in solution. Three minimum energy conformations characterize the potential energy surface of 7-hydroxyrisperidone, while 9-hydroxyrisperidone is dominated by a strong intramolecular OH...N hydrogen bond of ca. 8 kcal/mol, which drastically reduces in water solution. In the gas phase, 9-hydroxyrisperidone is the most stable isomer both in the neutral and in the protonated forms. Solvent effects favour 7-hydroxyrisperidone rotamers owing to their higher dipole moment values. Under the physiological pH of 7.4, the protonated forms of both isomers in water coexist in almost equivalent amount, in qualitative agreement with the experiment. It is suggested that to stabilize the pharmacologically active 9-hydroxyrisperidone over the 7-OH isomer one has to increase its molecular dipole moment and the intramolecular OH...N hydrogen bond energy.