Presenter of 1 Presentation
Treatment Planning And Dose-Rate Distributions For Conventionally Fractionated Head And Neck Cancer Using Uhdr Transmission Beam Proton Therapy
Abstract
Background and Aims
Transmission beam (TB) proton therapy (PT) uses single, high energy beams with Bragg-peak behind the target, sharp penumbras and simplified planning/delivery. TB facilitates ultra-high dose-rates (UHDRs, e.g. ≥40Gy/s), which is a requirement for the FLASH-effect. FLASH may also require a dose threshold, but this remains uncertain and UHDR-distribution investigation is of interest for head-and-neck cancer treatment.
Methods
We investigated (1) plan quality for conventionally-fractionated head-and-neck cancer treatment using spot-scanning proton TBs, intensity-modulated PT (IMPT) and photon volumetric-modulated arc therapy (VMAT); (2) UHDR-metrics. VMAT, 3-field IMPT and 10-field TB-plans, delivering 70/54.25Gy in 35 fractions to boost/elective volumes, were compared (n=10 patients). To increase spot peak dose-rates (SPDRs), TB-plans were split into three subplans, with varying spot monitor units and different gantry currents.
Results
Despite the lack of Bragg-peak advantages, average TB-plan OAR-sparing was comparable to IMPT: mean oral cavity/body dose were 4.1/2.5Gy higher than IMPT (9.3/2.0Gy lower than VMAT); most other OAR (salivary glands, larynx, pharynx) mean doses differed by <2Gy (2.0-12.1Gy lower than VMAT). Average percentage of dose delivered at UHDRs was 46%/12% for split/non-split TB-plans and mean dose-averaged dose-rate 46/21Gy/s. Average total beam-on irradiation time was 1.9/3.8s for split/non-split plans and overall time including scanning 8.9/7.6s.
Conclusions
Conventionally-fractionated proton TB-plans achieved comparable OAR-sparing to IMPT and better than VMAT, with total beam-on irradiation times <10s. Splitting TB-plans increased the UHDR, demonstrating the advantage of gantry current variation per spot. If a FLASH-effect can be demonstrated at conventional dose/fraction, this would further improve plan quality and TB-protons would be a suitable delivery system.
Author Of 2 Presentations
FLASH PROTON THERAPY FOR WHOLE BREAST IRRADIATION: EXPLORING MACHINE REQUIREMENTS
Abstract
Background and Aims
With a sizeable patient population, a target largely comprising healthy tissue, and clinically relevant late effects, FLASH whole breast irradiation (WBI) merits consideration. Transmission beams provide a practical way to deliver ultra-high dose rate proton therapy. However, the large WBI volumes make it harder to achieve FLASH dose rates with pencil-beam-scanning (PBS). We therefore performed a simulation study to identify PBS machine characteristics needed for such treatments.
Methods
For a left-sided breast case (861cc) a single-field spot-reduced plan was generated using 250MeV transmission beams. ‘PBS dose rates’ were calculated, considering the total time (including dead-times) to deliver 95% of the dose in each voxel. We varied maximum beam current at isocenter (200, 400, 800nA), energy-layer-wise or spot-wise current, minimum spot duration (0.5, 1, 2ms), and fraction dose (5x5.7Gy, 2x9.74Gy; equivalent BED3). The percentage of dose delivered above FLASH thresholds was evaluated, considering dose rate thresholds of 40Gy/s and 100Gy/s, and dose thresholds of 4Gy and 8Gy.
Results
For 40Gy/s dose rate threshold, spot-wise currents generally provided >70% of dose delivered above FLASH thresholds, with little dependence on beam current and spot duration (Figure 1). When using energy-layer-wise currents, comparable FLASH dose was achieved only for 9.74Gy fraction dose and 0.5ms minimum spot duration. For 100Gy/s dose rate threshold, substantial FLASH dose was obtained only with extreme machine settings (i.e. 800nA, spot-wise, <=1ms).
Conclusions
Assuming large fields do not necessarily preclude a FLASH effect, FLASH WBI is theoretically achievable, but may require large fraction sizes, and may be (too) demanding for current PBS machines.
Treatment Planning And Dose-Rate Distributions For Conventionally Fractionated Head And Neck Cancer Using Uhdr Transmission Beam Proton Therapy
Abstract
Background and Aims
Transmission beam (TB) proton therapy (PT) uses single, high energy beams with Bragg-peak behind the target, sharp penumbras and simplified planning/delivery. TB facilitates ultra-high dose-rates (UHDRs, e.g. ≥40Gy/s), which is a requirement for the FLASH-effect. FLASH may also require a dose threshold, but this remains uncertain and UHDR-distribution investigation is of interest for head-and-neck cancer treatment.
Methods
We investigated (1) plan quality for conventionally-fractionated head-and-neck cancer treatment using spot-scanning proton TBs, intensity-modulated PT (IMPT) and photon volumetric-modulated arc therapy (VMAT); (2) UHDR-metrics. VMAT, 3-field IMPT and 10-field TB-plans, delivering 70/54.25Gy in 35 fractions to boost/elective volumes, were compared (n=10 patients). To increase spot peak dose-rates (SPDRs), TB-plans were split into three subplans, with varying spot monitor units and different gantry currents.
Results
Despite the lack of Bragg-peak advantages, average TB-plan OAR-sparing was comparable to IMPT: mean oral cavity/body dose were 4.1/2.5Gy higher than IMPT (9.3/2.0Gy lower than VMAT); most other OAR (salivary glands, larynx, pharynx) mean doses differed by <2Gy (2.0-12.1Gy lower than VMAT). Average percentage of dose delivered at UHDRs was 46%/12% for split/non-split TB-plans and mean dose-averaged dose-rate 46/21Gy/s. Average total beam-on irradiation time was 1.9/3.8s for split/non-split plans and overall time including scanning 8.9/7.6s.
Conclusions
Conventionally-fractionated proton TB-plans achieved comparable OAR-sparing to IMPT and better than VMAT, with total beam-on irradiation times <10s. Splitting TB-plans increased the UHDR, demonstrating the advantage of gantry current variation per spot. If a FLASH-effect can be demonstrated at conventional dose/fraction, this would further improve plan quality and TB-protons would be a suitable delivery system.