MR-guided online adaptive stereotactic body radiation therapy (SBRT) for prostate cancer aims to reduce toxicity by full compensation of interfractional uncertainties. However, the process of online ...adaptation currently takes approximately 45 min during which intrafractional movements remain unaccounted for. This study aims to analyze the dosimetric benefit of online adaptation and to evaluate its robustness over the duration of one treatment fraction.
Baseline MR-scans at a MR-linear accelerator were acquired for ten healthy male volunteers for generation of mock-prostate SBRT plans with a dose prescription of 5 × 7.25 Gy. On a separate day, online MR-guided adaptation (ViewRay
MRIdian) was performed, and thereafter MR images were acquired every 15 min for 1 h to assess the stability of the adapted plan.
A dosimetric benefit of online MR-guided adaptive re-planning was observed in 90% of volunteers. The median D
CTV- and D
PTV-coverage was improved from 34.8 to 35.5 Gy and from 30.7 to 34.6 Gy, respectively. Improved target coverage was not associated with higher dose to the organs at risk, most importantly the rectum (median D
rectum baseline plan vs. adapted plan 33.3 Gy vs. 32.3 Gy). The benefit of online adaptation remained stable over 45 min for all volunteers. However, at 60 min, CTV-coverage was below a threshold of 32.5 Gy in 30% of volunteers (30.6 Gy, 32.0 Gy, 32.3 Gy).
The dosimetric benefit of MR-guided online adaptation for prostate SBRT was robust over 45 min in all volunteers. However, intrafractional uncertainties became dosimetrically relevant at 60 min and we therefore recommend verification imaging before delivery of MR-guided online adapted SBRT.
Automated treatment planning and/or optimization systems (ATPS) are in the process of broad clinical implementation aiming at reducing inter-planner variability, reducing the planning time allocated ...for the optimization process and improving plan quality. Five different ATPS used clinically were evaluated for advanced head and neck cancer (HNC).
Three radiation oncology departments compared 5 different ATPS: 1) Automatic Interactive Optimizer (AIO) in combination with RapidArc (in-house developed and Varian Medical Systems); 2) Auto-Planning (AP) (Philips Radiation Oncology Systems); 3) RapidPlan version 13.6 (RP1) with HNC model from University Hospital A (Varian Medical Systems, Palo Alto, USA); 4) RapidPlan version 13.7 (RP2) combined with scripting for automated setup of fields with HNC model from University Hospital B; 5) Raystation multicriteria optimization algorithm version 5 (RS) (Laboratories AB, Stockholm, Sweden). Eight randomly selected HNC cases from institution A and 8 from institution B were used. PTV coverage, mean and maximum dose to the organs at risk and effective planning time were compared. Ranking was done based on 3 Gy increments for the parallel organs.
All planning systems achieved the hard dose constraints for the PTVs and serial organs for all patients. Overall, AP achieved the best ranking for the parallel organs followed by RS, AIO, RP2 and RP1. The oral cavity mean dose was the lowest for RS (31.3 ± 17.6 Gy), followed by AP (33.8 ± 17.8 Gy), RP1 (34.1 ± 16.7 Gy), AIO (36.1 ± 16.8 Gy) and RP2 (36.3 ± 16.2 Gy). The submandibular glands mean dose was 33.6 ± 10.8 Gy (AP), 35.2 ± 8.4 Gy (AIO), 35.5 ± 9.3 Gy (RP2), 36.9 ± 7.6 Gy (RS) and 38.2 ± 7.0 Gy (RP1). The average effective planning working time was substantially different between the five ATPS (in minutes): < 2 ± 1 for AIO and RP2, 5 ± 1 for AP, 15 ± 2 for RP1 and 340 ± 48 for RS, respectively.
All ATPS were able to achieve all planning DVH constraints and the effective working time was kept bellow 20 min for each ATPS except for RS. For the parallel organs, AP performed the best, although the differences were small.
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