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Pencil Beam Scanning Proton Bragg Peak Conformal FLASH in Prostate Cancer Stereotactic Body Radiotherapy.
Tyler Kaulfers1, Grant Lattery1, Chingyun Cheng2
1Department of Physics and Astronomy, Hofstra University, Hempstead, NY 11549, USA.
Cancers
|February 24, 2024
Summary
Bragg peak FLASH radiotherapy, a novel ultra-high dose technique, shows comparable organ-at-risk sparing to conventional proton therapy for prostate cancer. This method preserves excellent dose coverage and FLASH dose rate delivery, making it suitable for prostate stereotactic body radiotherapy.
Area of Science:
- Radiation Oncology
- Medical Physics
- Proton Therapy
Background:
- Conventional proton stereotactic body radiotherapy (SBRT) uses pencil beam scanning (PBS).
- FLASH radiotherapy (RT) offers potential for improved normal tissue sparing due to ultra-high dose rates.
- Bragg peak FLASH RT with distal tracking aims to eliminate exit doses and enhance organ-at-risk (OAR) sparing.
Purpose of the Study:
- To investigate the feasibility and efficacy of Bragg peak FLASH-RT for prostate cancer.
- To compare dosimetric outcomes between conventional PBS and Bragg peak FLASH-RT plans.
- To assess OAR sparing and dose rate coverage in prostate FLASH-RT.
Main Methods:
- Developed an in-house platform for intensity-modulated proton therapy (IMPT) planning using single-energy Bragg peak distal tracking.
- Optimized four-beam FLASH plans for patients previously treated with 40 Gy/5 fractions PBS SBRT.
- Compared dose metrics (including Dmax and V40Gy/s) between conventional PBS and Bragg peak FLASH plans.
Main Results:
- Bragg peak FLASH plans showed comparable OAR dose metrics (rectum, bladder, femur heads, large bowel, penile bulb) to conventional plans, except for Dmax.
- The CTV Dmax was higher in FLASH plans (116.9%) compared to clinical plans (103.3%).
- Rectal V40Gy/s reached 94% (composite) and 93% (single-field) at 1 Gy threshold; FLASH ratio approached 100% at 5 Gy threshold.
Conclusions:
- Bragg peak distal tracking enables comparable plan quality in most OARs for prostate SBRT.
- The technique preserves sufficient FLASH dose rate coverage, demonstrating applicability of ultra-high dose rates in prostate FLASH SBRT.
