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Effectiveness of Dynamic Adaptive Proton Therapy with Computed Tomography Image Guidance in Abdomen

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S Moriya

S Moriya1*, H Tachibana2 , K Hotta2 , N Nakamura2 , T Sakae1 , T Akimoto2 , (1) University of Tsukuba, Tsukuba, Ibaraki, (2) National Cancer Center, Kashiwa, Chiba,


SU-I-GPD-T-198 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To show the effectiveness of a dynamic adaptive system using CT-based three-dimensional image guidance in abdomen.

Methods: A retrospective analysis of a patient who received proton beam therapy with curative intent for abdominal lymph node metastases from ascending colon cancer using the original plan (OP) and in-room CT images were acquired once every four fractions was performed. The OP, which had a total dose of 60 GyE, was generated using six fields in a passive scattering method. Two image registrations were performed on each pretreatment daily CT image dataset, using either a bone- or tumor-based registration method (BR and TR, respectively), to shift the isocenter. In addition to it, the system automatically adapted the range shifter (range adaptive method, RA) after the TR. The dose distributions for the three methods were calculated using the simplified Monte Carlo. To assess the effectiveness of the system, the three dose distributions were compared to the OP using the dosimetric parameters. The following parameters were compared: D99%, D95%, D1%, D5%-D95% and mean dose for the CTV. The parameters of OARs also were compared included mean dose and D2cm³ for the kidneys, small intestine and stomach, and D2cm³ for the spinal cord.

Results: The RA showed more comparable CTV coverage to the OP than the BR and TR (D95% = 51.8 GyE for the OP compared with 43.8 ± 2.8 GyE, 45.6 ± 2.4 GyE and 54.7 ± 0.9 GyE for the BR, TR and RA, respectively). For OARs, the RA achieved similar dosimetric parameters in comparison with the OP; however, the RA slightly increased the D2cm³ of the small intestine and stomach.

Conclusion: Our system would achieve a more robust irradiation, while maintaining tumor dose coverage and higher geometric accuracy. Further improvements of range optimization algorithm would be needed for OARs.

Funding Support, Disclosures, and Conflict of Interest: This research is partially supported by Japan Agency for Medical Research and Development (AMED).

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