J.P. Cuijpers

Fast and robust online adaptive planning in stereotactic MR-guided adaptive radiation therapy (SMART) for pancreatic cancer

BACKGROUND AND PURPOSE To implement a robust and fast stereotactic MR-guided adaptive radiation therapy (SMART) online strategy in locally advanced pancreatic cancer (LAPC). MATERIAL AND METHODS SMART strategy for plan adaptation was implemented with the MRIdian system (ViewRay Inc.). At each fraction, OAR (re-)contouring is done within a distance of 3cm from the PTV surface. Online plan re-optimization is based on robust prediction of OAR dose and optimization objectives, obtained by building an artificial neural network (ANN). Proposed limited re-contouring strategy for plan adaptation (SMART3CM) is evaluated by comparing 50 previously delivered fractions against a standard (re-)planning method using full-scale OAR (re-)contouring (FULLOAR). Plan quality was assessed using PTV coverage (V95%, Dmean, D1cc) and institutional OAR constraints (e.g. V33Gy). RESULTS SMART3CM required a significant lower number of optimizations than FULLOAR (4 vs 18 on average) to generate a plan meeting all objectives and institutional OAR constraints. PTV coverage with both strategies was identical (mean V95%=89%). Adaptive plans with SMART3CM exhibited significant lower intermediate and high doses to all OARs than FULLOAR, which also failed in 36% of the cases to adhere to the V33Gy dose constraint. CONCLUSIONS SMART3CM approach for LAPC allows good OAR sparing and adequate target coverage while requiring only limited online (re-)contouring from clinicians.

On the practice of the clinical implementation of enhanced dynamic wedges.

Practical aspects of the clinical implementation of enhanced dynamic wedges (EDW) replacing manual wedges are presented and discussed extensively. A comparison between measured and calculated data is also presented. Relative dose distributions and wedge factors were calculated with a commercially available treatment planning system and measured in a water-phantom and with an ionization chamber. Wedge factor calculations and measurements were also compared with an independent method of wedge factor calculations available from the literature. Aspects of the clinical implementation, such as safety and quality assurance, were evaluated. Measurements and calculations agreed very well and were slightly better than results of previous studies. Profiles and percentage depth doses (PDDs) agreed within 1% to 1.5% and within 0.5%, respectively. Measured and calculated wedge factors ratios agreed within 0.5% to 1%. Calculated and measured EDW dose distributions showed excellent agreement, both relative and absolute. However, for safe and practical use, specific aspects need to be taken into consideration. Once the treatment planning system is commissioned properly, the clinical implementation of EDW is rather straightforward.