Evaluation of Biology-Guided Radiotherapy Treatment Delivery Patterns Based on Beamlet Sequence Log Data from Daily Treatments
Abstract
Purpose
To evaluate beamlet sequence delivery patterns in biology-guided radiotherapy (BgRT) on a linac machine with an integrated PET scanner and a binary multileaf collimator (MLC) using beamlet sequence log data from daily treatments.
Methods
Beamlet sequence data from both the treatment plan and daily treatment delivery were retrieved for patients treated by BgRT at our institution. Nine patients were treated to bone lesions with non-periodic motion while eleven patients treated to bone or lung lesions with periodic motion. The prescription dose ranged from 7 to 18 Gy per fraction in one to five fractions. A 64-leaf binary MLC modulates the beam at 50 gantry firing positions in each gantry rotation while the gantry rotates at 60 RPM. In delivery, the couch makes four passes (couch travel into or out of the gantry). Gantry angle, couch position, delivered monitor units (MU), and MLC leaf opening status were recorded at each beam firing position and were analyzed.
Results
The BgRT treatment plans had an average MU per fraction of 6,684±1,880 MU (range: 2,860 – 9,898) with an average total gantry firing positions of 15,835±4,391 (range: 9,566 – 21,817). In daily delivery, the average percentage of MU delivered in the first pass was 39.5±5.1% (range: 30.4 – 47.9%), which was significantly higher than those in the other three passes (two-tailed p-value < 0.05 in paired t-tests for targets with both periodic and non-periodic motion). The delivered MU showed an average increase of 3.3±3.9% (range: -6.5 – 13.0%) compared to the plan MU, with no statistically significant difference between targets with periodic motion and those with non-periodic motion.
Conclusion
Delivery in the first pass of BgRT treatment is more important for delivery accuracy as significantly higher percentage of total MU is given. This is true for targets with both periodic and non-periodic motions.