Log file based Monte Carlo calculations for proton pencil beam scanning therapy

Abstract

Patient specific quality assurance is crucial to guarantee safety in proton pencil beam scanning. In current clinical practice, this requires extensive, time consuming measurements. Additionally, these measurements do not consider the influence of density heterogeneities in the patient and are insensitive to delivery errors. In this work, we investigate the use of log file based Monte Carlo calculations for dose reconstructions in the patient CT, which takes the combined influence of calculational and delivery errors into account. For one example field, 87%/90% of the voxels agree within ±3% when taking either calculational or delivery uncertainties into account (analytical versus Monte Carlo calculation/Monte Carlo from planned versus Monte Carlo from log file). 78% agree when considering both uncertainties simultaneously (nominal field versus Monte Carlo from log files). We then show the application of the log file based Monte Carlo calculations as a patient specific quality assurance tool for a set of five patients (16 fields) treated for different indications. For all fields, absolute dose scaling factors based on the log file Monte Carlo agree within ±3% to the measurement based absolute dose scaling. Relative comparison shows that more than 90% of the voxels agree within ± 5% between the analytical calculated plan and the Monte Carlo based on log files. The log file based Monte Carlo approach is an end-to-end test incorporating all requirements of patient specific quality assurance. It has the potential to reduce the workload and therefore to increase the patient throughput, while simultaneously enabling more accurate dose verification directly in the patient geometry.

Dosimetric influence of deformable image registration uncertainties on propagated structures for online daily adaptive proton therapy of lung cancer patients

“…A full plan reoptimisation used in this study (a new spot placement, constraint optimisation [27,28]) has the advantage that it allows for an improved plan quality in case of favourable anatomy and also works in the case of major anatomical changes, where the simpler approach of restoring the dose on the new anatomy independent from the daily structures [67] might fail. As part of the offline quality assurance after the delivery, the delivered DAPT dose can then be reconstructed from the delivery logfile, using the daily CT and a MC dose calculation [30,68], as in such an online workflow, no patient specific dose measurements are possible. The daily DVHs should then be evaluated with these offline corrected structures.…”

“…In the DAPT workflow a daily CT is acquired in treatment position, contours are transferred and a plan is reoptimised online [27], followed by a fast clinical and measurement-free physical quality assurance [28]. After the delivery, the dose is reconstructed on the planning CT [29,30]. One of the main requirements to deliver an online adaptive workflow is speed.…”

Daily Adaptive Proton Therapy: Is it Appropriate to Use Analytical Dose Calculations for Plan Adaption?

“…In addition, MC calculations can also be incorporated into an analytical based DAPT workflow. For instance, after delivery of each adapted fraction, a full MC dose reconstruction could be performed on the anatomy of the day, by also taking into account information from the log-files of the delivered treatment (37). Such a log-file based MC dose calculation could then be used for offline QA and dose accumulation.…”

“…The number of protons per pencil beam in the MC simulations were calculated directly from the number of protons provided by the treatment planning system, divided by 1000. This results in statistical fluctuations of less than 1% (37). Each MC field was normalized to the same mean PTV dose as the corresponding analytical field (19).…”

Estudo dos Efeitos de Composição e Densidade de Materiais Tecido Equivalentes na Distribuição de Dose Longitudinal em Protonterapia

“…Isso é alcançado através da introdução de moduladores e atenuadores que alteram o feixe original. A garantia de qualidade específica para cada paciente é crucial para garantir a segurança na técnica de PBS 15 . As distribuições de dose podem ser significativamente influenciadas pelas heterogeneidades dos tecidos.…”