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Usefulness of positron-emission tomographic images after proton therapy
Int. J. Radiation Oncology Biol. Phys., Vol. 53, No. 5, pp. 1388 –1391, 2002 Copyright © 2002 Elsevier Science Inc. Printed in the USA. All rights reserved 0360-3016/02/$–see front matter
PII S0360-3016(02)02887-0
PHYSICS CONTRIBUTION
USEFULNESS OF POSITRON-EMISSION TOMOGRAPHIC IMAGES AFTER PROTON THERAPY YOSHIO HISHIKAWA, M.D.,*† KAZUFUMI KAGAWA, M.D.,* MASAO MURAKAMI, M.D.,*† HIROTO SAKAI, PH.D.,* TAKASHI AKAGI, PH.D.,* AND MITSUYUKI ABE, M.D.* *Department of Radiology, Hyogo Ion Beam Medical Center, Hyogo, Japan; †Division of Imaging Medicine and Ion Beam Therapy, Kobe University Graduate School of Medicine, Kobe, Japan Purpose: To examine the positron emission tomography (PET) image obtained after proton irradiation and investigate the usefulness of the image for confirmation of the irradiated volume in proton radiotherapy (RT). Methods and Materials: A homogenous phantom was irradiated separately by carbon-ion and proton beams and the images obtained were compared. The PET images of cancer patients just after proton RT were then taken after informed consent. Results: In the PET image produced by carbon-ion beams, the high pixel counts in the image corresponded to the Bragg peak; however, in that produced by proton beams, they were visible throughout the entire track of the proton beams and were not related to the Bragg peak. The PET image of patients treated with proton RT was similar to that of the phantom experiment. Conclusion: The PET image after proton RT was different from that of carbon-ion RT. It was found that the PET image was very useful in proton RT to verify treatment planning. © 2002 Elsevier Science Inc. Positron emission tomography, Proton, Carbon ion, Proton therapy.
INTRODUCTION
and proton RT in the phantoms are demonstrated, and the usefulness of PET images in proton RT is reported.
Although more than 20 facilities provide ion beam cancer treatment worldwide, each facility uses either proton or carbon-ion beams. Our facility was opened in April 2001 as the Hyogo Ion Beam Medical Center, the first medical center to use both proton and carbon-ion beams for cancer therapy. Positron emission tomography (PET) images obtained after carbon-ion beam radiotherapy (RT) have already been used to verify the treatment volume (1), but the application to proton RT has not yet been made. The well-known fact that positron emitters are generated during proton RT led us to the idea that PET images obtained immediately after proton RT could be used to confirm the irradiation field. Our clinical trial of proton RT has been under way since May 2001. Before the trial, phantom studies were performed. The phantom PET image was first obtained after carbon-ion RT, which showed the autoactivation of 12C beams. The phantom PET image was then obtained after proton RT. Patients participating in the clinical trial were informed about PET imaging after RT. The PET image was obtained just after proton RT and then fused with the CT image. In this paper, the PET images obtained after carbon-ion
METHODS AND MATERIALS Phantom study Carbon-ion and proton RT was performed with the Hyogo Ion Beam Treatment System (Mitsubishi Electric, Kobe, Japan). Homogenous phantoms were irradiated separately by a monoenergetic carbon-ion beam with the narrow Bragg peak and the carbon-ion beam with 6-cm-wide spreadout Bragg peak (6 cm–SOBP), and a monoenergetic proton beam, and the proton beam with 6-cm–SOBP. The energy of carbon-ion beams was 320 MeV and that of proton beams 150 MeV. The phantoms were irradiated through a field of 15 ⫻ 15 cm by carbon-ion and proton beams. It was found that both carbon-ion and proton beams traveled 15 cm into the phantom. The image data were obtained using a PET camera (SET-2300W, Shimadzu, Kyoto, Japan) during 5–20 minutes after each irradiation. Clinical application A patient was transported from the treatment theater to the PET room immediately after proton RT. The emission
Reprint requests to: Yoshio Hishikawa, M.D., Department of Radiology, Hyogo Ion Beam Medical Center, 1-2-1, Kouto, Shingu-cho, Ito-gun, Hyogo 679-5165, Japan. Tel: ⫹81 791 58 0100; Fax: ⫹81 791 58 2600; E-mail: [email protected]
Supported by Grant-in-aid for Cancer Research No. 11-6 from the Ministry of Health, Labor and Welfare, Japan. Received Dec 26, 2001. Accepted for publication Mar 25, 2002. 1388
PET after proton therapy
Fig. 1. PET image of carbon-ion beams in a phantom. High pixel counts are recognized (A) at the narrow Bragg peak of a monoenergetic carbon-ion beam and (B) at the 6-cm–SOBP.
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Fig. 2. PET image of proton beams in a phantom. High pixel counts are recognized throughout the proton beam track (A) in the monoenergetic beam and (B) also in the 6-cm–SOBP proton beam.
6-cm–SOBP, the distal end of the beam was dull compared with the image obtained by the monoenergetic beam. and transmission data were obtained within 5–20 minutes after treatment. The transmission and CT images were then displayed on the screen. An alignment parameter was established between the CT and PET images by moving the transmission image to the CT image. Finally, the emission images were transformed by the same parameter and displayed on the CT images. We call this fused image “CTPET.” Image processing of CT-PET took approximately 30 minutes.
RESULTS Phantom study The PET image obtained after carbon-ion RT showed the high pixel counts at the Bragg peak in the monoenergetic beam (Fig. 1A) and in the 6-cm–SOBP beam (Fig. 1B). Low pixel counts were visible before and after the Bragg peak in both images. On the other hand, the PET image obtained after proton RT showed the proton beam track as high pixel counts in the monoenergetic beam (Fig. 2A). and also in the 6-cm–SOBP beam (Fig. 2B). However, in the image of
Clinical application Figure 3 shows the CT-PET images after proton RT for a patient with ethmoid sinus carcinoma. Each autoactivation image after proton RT corresponded well to the prescribed planning field (Fig. 4). DISCUSSION Charged particles produce positron emitters in human tissues. Therefore, PET has been widely used in carbon-ion RT for the verification of treatment planning (1) and on-line control of the beams (2). 11 C plays the most important role in PET imaging after both carbon-ion and proton RT, because other isotopes (except for 13N) decay within 2 min, and the cross-section of 13N is 7 myoglobin (mb) smaller than the 54 mb of 11C. In the phantom study, the PET image obtained after carbon-ion RT was different from that of proton RT. The high pixel counts in the image after carbon-ion RT were mostly visible in the Bragg peak, and those were observed over the entire tract after proton RT. Kraft (2) reported that
1390
I. J. Radiation Oncology
● Biology ● Physics
Volume 53, Number 5, 2002
Fig. 3. CT-PET image of patient with ethmoid sinus cancer treated by proton beams.
Fig. 4. Comparison between the (A) CT-PET image and (B) treatment planning at the slice of the treatment center. The CT-PET image corresponded well to the planning field.
PET after proton therapy
in the case of target fragmentation, positron emitters are smeared out over the particle path, whereas in the case of projectile fragmentation, they have nearly the same range because of their similar mass-to-charge ratio and the strongly forward-peaked reaction kinematics. This suggests that the PET image after proton RT is due to the target fragmentation occurring throughout the track of proton beams and that the PET image obtained after carbon-ion therapy is mostly due to the projectile fragmentation of 12C
● Y. HISHIKAWA et al.
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to 11C. The distal end of the 6-cm–SOBP proton beams was dull in the PET image. This seems to be no longer active in tissue at the last millimeters of its range (3). From our studies, it was found that the PET image obtained by proton RT does not demonstrate the dose distribution but the irradiation field. We think the PET image is clinically useful for the quality assurance of proton RT because it allows verification of whether the target is precisely irradiated.
REFERENCES 1. Tomitani T, Yoshikawa K, Kanazawa M, et al. Imaging of 11 C distribution in patients induced by autoactivation of 12C beams. In: Amaldi U, Larsson B, Lemoigne Y, editors. Advances in hadrontherapy. Amsterdam: Elsevier; 1997. p. 339 –345.
2. Kraft G. Heavy ion therapy in GSI. In: Linz U, editor. Ion beam in tumor therapy. London: Chapman & Hall; 1995. p. 341–349. 3. Vynckier S, Derreumaux S, Richrd F, et al. Is it possible to verify directly a proton-treatment plan using positron emission tomography? Radiother Oncol 1993;26:275–277.
PII S0360-3016(02)02887-0
PHYSICS CONTRIBUTION
USEFULNESS OF POSITRON-EMISSION TOMOGRAPHIC IMAGES AFTER PROTON THERAPY YOSHIO HISHIKAWA, M.D.,*† KAZUFUMI KAGAWA, M.D.,* MASAO MURAKAMI, M.D.,*† HIROTO SAKAI, PH.D.,* TAKASHI AKAGI, PH.D.,* AND MITSUYUKI ABE, M.D.* *Department of Radiology, Hyogo Ion Beam Medical Center, Hyogo, Japan; †Division of Imaging Medicine and Ion Beam Therapy, Kobe University Graduate School of Medicine, Kobe, Japan Purpose: To examine the positron emission tomography (PET) image obtained after proton irradiation and investigate the usefulness of the image for confirmation of the irradiated volume in proton radiotherapy (RT). Methods and Materials: A homogenous phantom was irradiated separately by carbon-ion and proton beams and the images obtained were compared. The PET images of cancer patients just after proton RT were then taken after informed consent. Results: In the PET image produced by carbon-ion beams, the high pixel counts in the image corresponded to the Bragg peak; however, in that produced by proton beams, they were visible throughout the entire track of the proton beams and were not related to the Bragg peak. The PET image of patients treated with proton RT was similar to that of the phantom experiment. Conclusion: The PET image after proton RT was different from that of carbon-ion RT. It was found that the PET image was very useful in proton RT to verify treatment planning. © 2002 Elsevier Science Inc. Positron emission tomography, Proton, Carbon ion, Proton therapy.
INTRODUCTION
and proton RT in the phantoms are demonstrated, and the usefulness of PET images in proton RT is reported.
Although more than 20 facilities provide ion beam cancer treatment worldwide, each facility uses either proton or carbon-ion beams. Our facility was opened in April 2001 as the Hyogo Ion Beam Medical Center, the first medical center to use both proton and carbon-ion beams for cancer therapy. Positron emission tomography (PET) images obtained after carbon-ion beam radiotherapy (RT) have already been used to verify the treatment volume (1), but the application to proton RT has not yet been made. The well-known fact that positron emitters are generated during proton RT led us to the idea that PET images obtained immediately after proton RT could be used to confirm the irradiation field. Our clinical trial of proton RT has been under way since May 2001. Before the trial, phantom studies were performed. The phantom PET image was first obtained after carbon-ion RT, which showed the autoactivation of 12C beams. The phantom PET image was then obtained after proton RT. Patients participating in the clinical trial were informed about PET imaging after RT. The PET image was obtained just after proton RT and then fused with the CT image. In this paper, the PET images obtained after carbon-ion
METHODS AND MATERIALS Phantom study Carbon-ion and proton RT was performed with the Hyogo Ion Beam Treatment System (Mitsubishi Electric, Kobe, Japan). Homogenous phantoms were irradiated separately by a monoenergetic carbon-ion beam with the narrow Bragg peak and the carbon-ion beam with 6-cm-wide spreadout Bragg peak (6 cm–SOBP), and a monoenergetic proton beam, and the proton beam with 6-cm–SOBP. The energy of carbon-ion beams was 320 MeV and that of proton beams 150 MeV. The phantoms were irradiated through a field of 15 ⫻ 15 cm by carbon-ion and proton beams. It was found that both carbon-ion and proton beams traveled 15 cm into the phantom. The image data were obtained using a PET camera (SET-2300W, Shimadzu, Kyoto, Japan) during 5–20 minutes after each irradiation. Clinical application A patient was transported from the treatment theater to the PET room immediately after proton RT. The emission
Reprint requests to: Yoshio Hishikawa, M.D., Department of Radiology, Hyogo Ion Beam Medical Center, 1-2-1, Kouto, Shingu-cho, Ito-gun, Hyogo 679-5165, Japan. Tel: ⫹81 791 58 0100; Fax: ⫹81 791 58 2600; E-mail: [email protected]
Supported by Grant-in-aid for Cancer Research No. 11-6 from the Ministry of Health, Labor and Welfare, Japan. Received Dec 26, 2001. Accepted for publication Mar 25, 2002. 1388
PET after proton therapy
Fig. 1. PET image of carbon-ion beams in a phantom. High pixel counts are recognized (A) at the narrow Bragg peak of a monoenergetic carbon-ion beam and (B) at the 6-cm–SOBP.
● Y. HISHIKAWA et al.
1389
Fig. 2. PET image of proton beams in a phantom. High pixel counts are recognized throughout the proton beam track (A) in the monoenergetic beam and (B) also in the 6-cm–SOBP proton beam.
6-cm–SOBP, the distal end of the beam was dull compared with the image obtained by the monoenergetic beam. and transmission data were obtained within 5–20 minutes after treatment. The transmission and CT images were then displayed on the screen. An alignment parameter was established between the CT and PET images by moving the transmission image to the CT image. Finally, the emission images were transformed by the same parameter and displayed on the CT images. We call this fused image “CTPET.” Image processing of CT-PET took approximately 30 minutes.
RESULTS Phantom study The PET image obtained after carbon-ion RT showed the high pixel counts at the Bragg peak in the monoenergetic beam (Fig. 1A) and in the 6-cm–SOBP beam (Fig. 1B). Low pixel counts were visible before and after the Bragg peak in both images. On the other hand, the PET image obtained after proton RT showed the proton beam track as high pixel counts in the monoenergetic beam (Fig. 2A). and also in the 6-cm–SOBP beam (Fig. 2B). However, in the image of
Clinical application Figure 3 shows the CT-PET images after proton RT for a patient with ethmoid sinus carcinoma. Each autoactivation image after proton RT corresponded well to the prescribed planning field (Fig. 4). DISCUSSION Charged particles produce positron emitters in human tissues. Therefore, PET has been widely used in carbon-ion RT for the verification of treatment planning (1) and on-line control of the beams (2). 11 C plays the most important role in PET imaging after both carbon-ion and proton RT, because other isotopes (except for 13N) decay within 2 min, and the cross-section of 13N is 7 myoglobin (mb) smaller than the 54 mb of 11C. In the phantom study, the PET image obtained after carbon-ion RT was different from that of proton RT. The high pixel counts in the image after carbon-ion RT were mostly visible in the Bragg peak, and those were observed over the entire tract after proton RT. Kraft (2) reported that
1390
I. J. Radiation Oncology
● Biology ● Physics
Volume 53, Number 5, 2002
Fig. 3. CT-PET image of patient with ethmoid sinus cancer treated by proton beams.
Fig. 4. Comparison between the (A) CT-PET image and (B) treatment planning at the slice of the treatment center. The CT-PET image corresponded well to the planning field.
PET after proton therapy
in the case of target fragmentation, positron emitters are smeared out over the particle path, whereas in the case of projectile fragmentation, they have nearly the same range because of their similar mass-to-charge ratio and the strongly forward-peaked reaction kinematics. This suggests that the PET image after proton RT is due to the target fragmentation occurring throughout the track of proton beams and that the PET image obtained after carbon-ion therapy is mostly due to the projectile fragmentation of 12C
● Y. HISHIKAWA et al.
1391
to 11C. The distal end of the 6-cm–SOBP proton beams was dull in the PET image. This seems to be no longer active in tissue at the last millimeters of its range (3). From our studies, it was found that the PET image obtained by proton RT does not demonstrate the dose distribution but the irradiation field. We think the PET image is clinically useful for the quality assurance of proton RT because it allows verification of whether the target is precisely irradiated.
REFERENCES 1. Tomitani T, Yoshikawa K, Kanazawa M, et al. Imaging of 11 C distribution in patients induced by autoactivation of 12C beams. In: Amaldi U, Larsson B, Lemoigne Y, editors. Advances in hadrontherapy. Amsterdam: Elsevier; 1997. p. 339 –345.
2. Kraft G. Heavy ion therapy in GSI. In: Linz U, editor. Ion beam in tumor therapy. London: Chapman & Hall; 1995. p. 341–349. 3. Vynckier S, Derreumaux S, Richrd F, et al. Is it possible to verify directly a proton-treatment plan using positron emission tomography? Radiother Oncol 1993;26:275–277.