@article{525e858bc5a340a69ea0a3dcfccff599,
title = "Use of treatment log files in spot scanning proton therapy as part of patient-specific quality assurance",
abstract = "Purpose: The purpose of this work was to assess the monitor unit (MU) values and position accuracy of spot scanning proton beams as recorded by the daily treatment logs of the treatment control system, and furthermore establish the feasibility of using the delivered spot positions and MU values to calculate and evaluate delivered doses to patients. Methods: To validate the accuracy of the recorded spot positions, the authors generated and executed a test treatment plan containing nine spot positions, to which the authors delivered ten MU each. The spot positions were measured with radiographic films and Matrixx 2D ion-chambers array placed at the isocenter plane and compared for displacements from the planned and recorded positions. Treatment logs for 14 patients were then used to determine the spot MU values and position accuracy of the scanning proton beam delivery system. Univariate analysis was used to detect any systematic error or large variation between patients, treatment dates, proton energies, gantry angles, and planned spot positions. The recorded patient spot positions and MU values were then used to replace the spot positions and MU values in the plan, and the treatment planning system was used to calculate the delivered doses to patients. The results were compared with the treatment plan. Results: Within a treatment session, spot positions were reproducible within ±0.2 mm. The spot positions measured by film agreed with the planned positions within ±1 mm and with the recorded positions within ±0.5 mm. The maximum day-to-day variation for any given spot position was within ±1 mm. For all 14 patients, with ∼1 500 000 spots recorded, the total MU accuracy was within 0.1% of the planned MU values, the mean (x, y) spot displacement from the planned value was (-0.03 mm, -0.01 mm), the maximum (x, y) displacement was (1.68 mm, 2.27 mm), and the (x, y) standard deviation was (0.26 mm, 0.42 mm). The maximum dose difference between calculated dose to the patient based on the plan and recorded data was within 2%. Conclusions: The authors have shown that the treatment log file in a spot scanning proton beam delivery system is precise enough to serve as a quality assurance tool to monitor variation in spot position and MU value, as well as the delivered dose uncertainty from the treatment delivery system. The analysis tool developed here could be useful for assessing spot position uncertainty and thus dose uncertainty for any patient receiving spot scanning proton beam therapy.",
keywords = "dose verification, patient specific QA, proton therapy, scanning beam proton therapy",
author = "Heng Li and Narayan Sahoo and Falk Poenisch and Kazumichi Suzuki and Yupeng Li and Xiaoqiang Li and Xiaodong Zhang and Lee, {Andrew K.} and Gillin, {Michael T.} and Zhu, {X. Ronald}",
note = "Funding Information: We thank Kathryn Carnes, Sarah Bronson, and Sunita Patterson from the Department of Scientific Publications at MD Anderson Cancer Center for editorial review of this manuscript. MD Anderson Cancer Center is supported by the National Institutes of Health (Grant No. CA16672). FIG. 1. Diagram of relevant components in the proton scanning beam delivery system studied. FIG. 2. Diagram of the method used to calculate spot position at the isocenter plane on the x axis, (a) considering the focusing effect of the pencil beam and (b) ignoring the focusing effect. FIG. 3. Film results for three energies of the proton scanning beam: (a) 146.9 MeV, (b) 173.7 MeV, and (c) 198.3 MeV. Ten MU (250 spots of 0.04 MU each) were delivered to each location and measured at isocenter in air. FIG. 4. Results for the 173.7 MeV proton scanning beam. Ten MU (250 spots of 0.04 MU each) were delivered to each location and measured at isocenter in air. (a) Recorded, planned, and film-measured positions. (b) Zoom-in for spot position (100 mm, 100 mm). FIG. 5. Results of MU values in the treatment plan and recorded in the delivery system for 14 patients. (a) Recorded MU deviations vs planned MUs. (b) Histogram of planned MUs for all patients. (c) Spot and total MU deviations from planned values (as a percentage) for each patient. For each patient, spot MU deviations were calculated for all single spots delivered, and total MU deviation was the deviation of the cumulative MUs in each fraction. Error bars represent 95% confidence intervals. FIG. 6. Spot position map from the treatment planning system and from recorded data for a single proton energy (163.9 MeV). (a) Recorded position vs planned position. (b) Zoom-in for spot position (27.6 mm, 36.8 mm). This spot had the maximum mean displacement from the planned position. (c) Displacement of daily recorded position from planned position for spots with an energy of 163.9 MeV. Dots of different colors represent spot positions recorded on different days. (d) Displacement from the planned position of the mean recorded position for each spot position (total of 48) and mean displacement from the planned position for all recorded spots at this energy. FIG. 7. Displacement of spot recorded position from planned position for all patients. (a) Scatter plot of all spots with the red cross at ( $\mu _{E_x }$ μ E x , $\mu _{E_y }$ μ E y ). (b) Histogram of the percentage distances from recorded position to planned position. (c) Histogram of displacements of spot position on the x axis. (d) Histogram of displacements of spot position on the y axis. FIG. 8. Displacement of recorded position from planned position for different patients and dates. Means and 95% CIs (error bars) for distance to planned position on the x and y axes for (a) different patients and (b) different treatment dates. FIG. 9. Displacement of recorded position from planned position for different energies and gantry angles. Means and 95% CIs (error bars) for distance to planned position on the x and y axes for (a) different energies and (b) different gantry angles. (c) Polar plot of the mean distance vs angle. FIG. 10. Displacement of recorded position vs planned position. Means and 95% CIs (error bars) for distance to planned position on the x and y axes for (a) different planned positions on the x axis and (b) different planned positions on the y axis. FIG. 11. Reconstructed patient dose with delivered spot positions and MUs compared to the planned dose for a prostate patient (a) at isocenter plane, plan (left) vs log (right). (b) Dose volume histogram, plan (solid) vs log (dash). ",
year = "2013",
month = feb,
doi = "10.1118/1.4773312",
language = "English (US)",
volume = "40",
journal = "Medical physics",
issn = "0094-2405",
publisher = "AAPM - American Association of Physicists in Medicine",
number = "2",
}