Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2018 Jun 27;63(13):13NT01.
doi: 10.1088/1361-6560/aaca1b.

Mid-range probing-towards range-guided particle therapy

Mingli Chen  1 , Yuncheng Zhong, Yiping Shao, Steve Jiang, Weiguo Lu
Affiliations

Mid-range probing-towards range-guided particle therapy

Mingli Chen et al. Phys Med Biol. .

Abstract

Particle therapy can achieve excellent dose localization but is sensitive to range uncertainty. Therefore, online in vivo range verification before treatment is critical for treatment safety and quality assurance. We introduce a novel range-probing technique that uses mid-range treatment spots selected from the treatment plan as probing beams to be delivered before other treatment spots in pencil beam scanning. The probing spot signal can be acquired by an in-beam positron emission tomography (PET) scanner, and the reconstructed spot positions are compared with pre-calculated positions to measure the range shift. Mid-range probing ensures that the Bragg peaks stay inside the tumor even with significant range variation from the plan. Single-layered spots enable easier spot detection than multi-layered spots without cross-layered spot smearing. With therapeutic dose, the probing beam offers higher positron activities and range detectability than the low-dose imaging beam by up to two orders of magnitude, without exposing patients to extra radiation. Higher positron activities allow sufficient signal statistics in shorter acquisition time, therefore reducing metabolic washout of positron emitters. Thus, range shifts from the plan can be measured easily. We also describe two online range-compensated plan modification methods. We apply correction, if the range shift is above a certain tolerance. We studied feasibility using simulated particle treatment plans with online anatomical changes. For illustration, we demonstrate range shift measurement using simulated probing dose. The proposed range probing and correction effectively handled range shifts in the simulated cases. Both range-compensated adaptation and optimization accounted for online changes so that the delivered dose matched the planned dose. With a dedicated online in-beam PET scanner and phantom and clinical studies, which are currently being developed, this novel strategy may open up a range-guided particle therapy1 paradigm.

PubMed Disclaimer

Figures

Figure 1
Figure 1
RGPT workflow. The shaded blocks indicate automatic steps unique to RGPT.
Figure 2
Figure 2
Planned mid-range spots and online pre-treatment probing spots. Left: planned situation. The circles in the tumor represent the planned spots with the shaded ones indicating the mid-range spots. Right: online situation. Mid-range probing spots become anterior and posterior to the planned positions due to an unexpected bony object and air pocket, respectively, on the beam path. Nevertheless, the midrange spots remain inside the tumor, but other spots may shift outside the tumor.
Figure 3
Figure 3
Crescent-shaped target with the treatment spots depicted by circles. Mid-range spots are indicated by shaded circles. The long blue arrow lines indicate beam paths.
Figure 4
Figure 4
Range shift ΔR measured in WEPL between the probing spot and planned mid-range spot.
Figure 5
Figure 5
Range probing with anatomical mid-ranges or single energy mid-ranges and their respective probing beam dose. Top row (left to right): (a) CT with contours of target (crescent shape), body (large outer circle), and OAR (small inner circle); (b) WEPL in target according to horizontal beam direction from negative to positive position, and red curve indicating the mid-values of WEPL; (c) plan dose with red curve indicating the dose peaks on the beam paths, and three horizontal lines (dashed, dash-dot, and dotted) indicating the positions of three dose profiles shown in the inset. Middle row (left to right): (d) treatment plan (beam intensity map) with red curve indicating the anatomical mid-range; (e) mid-range probing beam intensity extracted from the treatment plan; (f) probing dose with red curve indicating the dose peaks along the beam paths, and three horizontal lines (dashed, dash-dot, and dotted) indicating the positions of three probing beam dose profiles shown in the inset. Bottom row ((g), (h), and (i)): same as the middle row, except for the single-energy mid-range.
Figure 6
Figure 6
Dose overlay on online CT in TCS views with countoured place holder (in pink), tumor (in red), and OAR (in yellow) along the beam path. (a) Plan dose on planning CT. (b) and (c) Doses of the same plan delivered to the online images with an air pocket and bony structure, respectively, at the place holder.
Figure 7
Figure 7
Dose of modified treatment plan based on range-compensated adaptation with (a) air and (b) bony material at the placeholder. The modified plan doses are similar to that of the original plan shown in figure 6(a).
Figure 8
Figure 8
DVH comparison for two online scenarios: (a) an air pocket at the place holder and (b) a bony structure at the place holder. Solid curves: Range-compensated adaptation. Dashed curves: online delivery of the unmodified plan. Dash-dotted curves: the reference DVH. Range-compensated adapation produced similar results to those of the original plan.
See this image and copyright information in PMC

References

    1. Assmann W, Kellnberger S, Reinhardt S, Lehrack S, Edlich A, Thirolf PG, Moser M, Dollinger G, Omar M, Ntziachristos V and Parodi K 2015. Ionoacoustic characterization of the proton Bragg peak with submillimeter accuracy Med Phys 42 (2) 567–574. - PubMed
    1. Attanasi F, Belcari N, Del Guerra A, Enghardt W, Moehrs S, Parodi K, Rosso V and Vecchio S 2009. Comparison of two dedicated ‘in beam’ PET systems via simultaneous imaging of C-12-induced beta(+)-activity Physics in Medicine and Biology 54 (2) N29–N35. - PubMed
    1. Dendooven P, Buitenhuis HJ, Diblen F, Heeres PN, Biegun AK, Fiedler F, van Goethem MJ, van der Graaf ER and Brandenburg S 2015. Short-lived positron emitters in beam-on PET imaging during proton therapy Phys Med Biol 60 (23) 8923–8947. - PubMed
    1. Dong L, Cheung JP and Zhu RX (2012) Image-Guided Proton and Carbon Ion Therapy Proton and Carbon Ion Therapy. Ma C and Lomax T, CRC Press: 127–149.
    1. Enghardt W, Crespo P, Fiedler F, Hinz R, Parodi K, Pawelke J and Ponisch F 2004. Charged hadron tumour therapy monitoring by means of PET Nuclear Instruments & Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment 525 (1–2) 284–288.

Publication types

LinkOut - more resources