gms | German Medical Science

48th Meeting of the Particle Therapy Co-Operative Group

Particle Therapy Co-Operative Group (PTCOG)

28.09. - 03.10.2009, Heidelberg

Cone-beam computed tomography and digital tomosynthesis using on-board x-ray projection system for an image-guided proton therapy

Meeting Abstract

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  • S. Y. Park - Proton Therapy Center, National Cancer Center, Goyang, Korea, Republic of Korea
  • M. K. Cho - Proton Therapy Center, National Cancer Center, Goyang, Korea, Republic of Korea
  • H. K. Kim - School of Mechanical Engineering, Pusan National University, Busan, Korea, Republic of Korea

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog156

DOI: 10.3205/09ptcog156, URN: urn:nbn:de:0183-09ptcog1560

Veröffentlicht: 24. September 2009

© 2009 Park et al.
Dieser Artikel ist ein Open Access-Artikel und steht unter den Creative Commons Lizenzbedingungen (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.de). Er darf vervielfältigt, verbreitet und öffentlich zugänglich gemacht werden, vorausgesetzt dass Autor und Quelle genannt werden.


Gliederung

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Purpose/Objective: Currently, only two orthogonal x-ray projections are used to register position of patient at treatment with that of radiation therapy planning (RTP). If tomograms of a patient can be directly acquired in the treatment room, it is possible to compare with the CT data of RTP, which gives us much more accurate registration results than the orthogonal alignment system. The purpose is to investigate the feasibility of CBCT (cone beam CT) and CBDT (cone beam digital tomosynthesis) methods in the treatment room for accurately aligning the patient in the proton beam.

Materials/methods: In the gantry treatment room for proton therapy at the National Cancer Center (Korea), pairs of x-ray imaging systems are orthogonally installed for patient positioning.

For image reconstruction, we employed the FDK algorithm with a Ram-Lak filter. For the quantitative analysis of CBCT performance, the AAPM CT QC phantom was scanned.

The theoretical work for DT is based on the work of Lauritsch and Härer that reported an FDK method in circular motion. We employed the combination filter with the weighted ramp filter for the scan angle, spectral apodizing filter to control high frequency noise and slice profile filter to suppress the frequency response of the out-of-plane blurring structures. For the implementation of both filters, we used a Hann window function.

Results: We evaluated the CBCT performances with the AAPM phantom. The worst error of the slice thicknesses was ~2.8%. We can distinguish the hole patterns up to 0.5 lp/mm. The largest HU error was observed for nylon by 3.5%. From the water region, we measured the SNR of ~20. The CNR between the inserts and water was also calculated and the best CNR was 2.54 (polycarbonate) and the worst CNR was 1.14 (acrylic). For acquiring CBCT data, the humanoid phantom was scanned with a rotational angle step of 2°. The quality of images is quite promising. The reconstructed images are illustrated in Figure 1a [Fig. 1].

We compared the images reconstructed by various approaches of DT; the shift-and-add (SAA) and filtered back-projection (FBP) methods with 21 projections for a 40° scan. While CBDT image (Figure 1b [Fig. 1]) using the SAA method exhibits a very blurred image as expected, the CBDT (Figure 1c [Fig. 1]) based on the FBP method provides a comparable quality to the CBCT image. The image sharpness of CBDT is preferred to that of CBCT.

Conclusion: CBCT/CBDT for image-guided radiation therapy has been developed and currently practically utilized. In this study, we have investigated the feasibility of CBCT/CBDT for image-guided proton therapy. From the reconstructed phantom images, the CBCT system in the gantry treatment room will be very useful as a primary patient alignment system for image-guided proton therapy. The CBDT may provide fast patient positioning with less motion artifact and patient dose.