AAPM Task Group Report 290: Respiratory motion management for particle therapy

Abstract

Dose uncertainty induced by respiratory motion remains a major concern for treating thoracic and abdominal lesions using particle beams. This Task Group report reviews the impact of tumor motion and dosimetric considerations in particle radiotherapy, current motion-management techniques, and limitations for different particle-beam delivery modes (i.e., passive scattering, uniform scanning, and pencil-beam scanning). Furthermore, the report provides guidance and risk analysis for quality assurance of the motion-management procedures to ensure consistency and accuracy, and discusses future development and emerging motion-management strategies. This report supplements previously published AAPM report TG76, and considers aspects of motion management that are crucial to the accurate and safe delivery of particle-beam therapy. To that end, this report produces general recommendations for commissioning and facility-specific dosimetric characterization, motion assessment, treatment planning, active and passive motion-management techniques, image guidance and related decision-making, monitoring throughout therapy, and recommendations for vendors. Key among these recommendations are that: (1) facilities should perform thorough planning studies (using retrospective data) and develop standard operating procedures that address all aspects of therapy for any treatment site involving respiratory motion; (2) a risk-based methodology should be adopted for quality management and ongoing process improvement.

Keywords: motion management; particle therapy.

FIGURE 1

Dosimetric impact of motion on particle beam. (a) A two‐phase respiratory motion model, where the target did not move, but the high‐Z (bone) structure moved in and out of a single particle beam. The average image (AVG) was generated by taking the pixel‐by‐pixel average of the two phases (T0 and T1). (b) 3D plan that was created using AVG, where a single spot (yellow) was used. The dose distribution for the same plan was then recalculated on both T0 and T1. The 4DD was then calculated by deforming dose distributions onto T1, and taking the average of all deformed doses. (c) 4D plan was created using both T0 and T1, where two spots (purple and green) with different energies were used to ensure coverage on both phases. The dose was then recalculated on AVG, and 4DD was also calculated. (d) Dynamic dose calculation for the 4D plan was simulated. For two spots and two phases, there were four possible dynamic delivery scenarios. Assuming the two spots were delivered independently and to each phase with equal chance, the weighted average of the four possible scenarios yielded the same result as 4DD

FIGURE 2

(a) Reference MIP DVH (black) and phase averaged 4DCT DVH (grey) for the ITV for 61 single‐beam plans for patient 1. The plans were normalized to obtain V95  = 95%, as can be seen in the zoom region, where all reference DVH cross this point. Doses and volumes are given as a percentage of the total. (b) Scatter plot for patients 1 to 3 showing the strong association for each patient between the V95 reduction with the mean ΔWEPL. The values for the linear correlation coefficients are 0.98, 0.92, and 0.96 for patients 1, 2 and 3, respectively (p < 0.01). ([a] Figure 1 and [b] Figure 5 from Oscar Casares‐Magaz et al., A method for selection of beam angles robust to intrafractional motion in proton therapy of lung cancer. Acta. Oncol. 2014;53(8):1058–1063. Note that the (%) reduction in (b) appears to be decimal)

FIGURE 3

An illustration of the hardware differences between passive scattering (top), uniform scanning (middle panel), and active scanning (a synonym for PBS) modalities. For active scanning (bottom row), the resulting radiation field is the sum of all of the individual spots, which may have different intensities. In the illustration, each spot contributes to the total dose indicated by the red dashed line. (Figure 2 from James SS, Grassberger C, Lu HM. Considerations when treating lung cancer with passive scattered or active scanning proton therapy. Transl. Lung Cancer Res. 2018;7(2):210–215)

FIGURE 4

Illustration of the scan path within an energy layer for the three scanned particle delivery techniques: spot scanning, raster scanning, and line scanning (from left to right). Axes T and U span the energy iso‐layer plane. Klimpki et al. Phys. Med. Biol. 2018;63:145006. https://doi.org/10.1088/1361‐6560/aacd27

FIGURE 5

Rescanning strategies: (a) volumetric rescanning, (b) layered rescanning, (c) breath sampled layered rescanning, and (d) continuous breath‐sampled layered rescanning. The energy switching time, t_es , is dictated by the machine, while the time delay between the layers, ∆t, is introduced in the breath‐sampled techniques to spread the layer rescans of an energy level over the full breathing cycle (line thicknesses illustrate the relative weight of each layer). Engwall et al. Phys. Med. Biol. 2018;63: 095006. https://doi.org/10.1088/1361‐6560

FIGURE 6

4DD accumulation to investigate the influence of the gating window size in treatment of liver cancer with a carbon beam. (a) T00–T90. (b) T30–T70. (c) T50. (d) Panels (a)–(c). (e) Panels (b)–(c). (f) CTV (from Mori S, Karube M, Yasuda S, et al. Gating window dependency on scanned carbon‐ion beam dose distribution and imaging dose for thoracoabdominal treatment. Br J Radiol. 2017;90(1074):20160936)

FIGURE 7

Examples of dose reconstruction in hepatocellular carcinoma treatments for a patient treated with abdominal compression (a) and a patient treated with gating (b). (From Richter D, Saito N, Chaudhri N., et al. Four‐dimensional patient dose reconstruction for scanned ion beam therapy of moving liver tumors. Int J Radiat Oncol Biol Phys. 2014;89(1):175–181)

FIGURE 8

Weekly 3D trajectories of the gross tumor volume center of mass during respiration for two patients (Figure 6 from Britton KR, Starkschall G, Tucker SL, et al. Assessment of gross tumor volume regression and motion changes during radiotherapy for non‐small‐cell lung cancer as measured by four‐dimensional computed tomography. Int J Radiat Oncol Biol Phys. 2007;68:1036–1046)

FIGURE 9

Polar plots of the absolute change in water‐equivalent path length (ΔWEPL) as a function of beam angle for patients with right‐sided tumors (a–c) and left‐sided tumors (d), respectively. Patient 17 (PT17) has a maximum ΔWEPL of 41.1 mm (outside the range of the plot). As examples of large WEPL, the polar plots for patients 1 and 28 are overlaid to the image registration in (e, f). Figure 3 from Gorgisyan J, Perrin R, Lomax AJ, et al. Impact of beam angle choice on pencil‐beam scanning breath‐hold proton therapy for lung lesions. Acta Oncol. 2017;56(6):853‐859)

FIGURE 10

An example of qualitative comparison of active motion‐management techniques currently proposed for implementation during particle therapy. The required participation or the effect of active motion‐management techniques (tracking, apneic oxygenation, abdominal compression, breath‐hold, respiratory gating) were estimated for each of the evaluation metrics using a numerical scale (1 to 5 [highest])

FIGURE 11

Sample workflow for motion management in particle therapy. *WED water‐equivalent depth, a synonym of WEPL