Presentation Treatment planning of carbon-ion scanning pancreatic therapy using 4DCT

Miki, Kentaro  ,  Mori, Shinichiro  ,  Yamada, Shigeru

Introduction:One of the advantages for pencil-beam scanning compared with passive scattering treatment isn’t to require either compensating boli or patient collimators. However the scanning treatment is more sensitive to the beam range variation due to intrafractional organ motion. Currently, the scanning treatment is applied limited parts not affected by intrafractional motion such as pelvic or head and neck regions in our facility. One of the solutions to deliver the prescribed dose to a moving tumor is respiratory-gating and phase-controlled rescanning. However residual motion with gating may be remained. Although internal target volume (ITV) is defined by the geometric union of target volume in all motions of 4DCT, it doesn’t fully include the beam range variation. To estimate the optimum margin for intrafractional range variation, we integrated the field-specific target volume (FTV) calculation to the treatment planning. Here, dose distribution was calculated of carbon-ion pancreatic therapy using 4DCT and FTV.Materials and Methods:14 pancreatic cancer patients who were planning to receive the conventional passive carbon-ion treatment, was conducted. The 4DCT images were acquired using 320 multi-slice CT under free breezing. The patient was fixed on the couch by immobilization shell device. One respiratory cycle was equally subdivided into 10 phases (peak inhalation and exhalation were expressed by T00 and T50 (reference phase), respectively). The oncologist contoured the gross target volume (GTV), clinical target volume (CTV), and organ at risks (cord, stomach, duodenum, and kidney) at reference phase. All contours at other respective phases were calculated by deformable image registration (DIR). Gating duty cycle was 30% around exhalation (T40 to T60). Beam spots and weights were optimized for the T50 to deliver more than 95% described dose to FTV, and dose calculations at respective phases were performed using optimized planning parameters of T50. DIR was then applied to warp the dose distributions back to T50 for the accumulating dose over the gating duty cycle. A prescribed dose of 55.2 Gy (RBE) was delivered with four beam ports from three fractions at 0, two fractions at 165, four fractions at 180, and three fractions at 270. The maximum dose to the duodenum and cord were required to be less than 42.0 Gy (RBE) and 24.3 Gy (RBE), respectively. The volumes for irradiating 15 Gy (RBE) were also calculated for kidney, duodenum, and stomach.Results:The mean over 14 patients of D95 were 96.5% for GTV and 95.0% for CTV to the prescribed dose. The mean maximal dose of first or second portion of duodenum (D1-2) was 37.7 Gy (RBE), third or fourth portion of duodenum (D3-4) was 32.8 Gy (RBE), and cord was 17.6 Gy (RBE). The volumes for irradiating 15 Gy (RBE) were 1.8% for right kidney, 7.9% for left kidney, 9.3% for D1-2, 5.9 for D3-4, and 2.2% for stomach.Conclusion:The treatment planning using 4DCT and FTV delivered sufficient dose distribution to the moving target. These results support us to implement this strategy to the clinical treatment for the carbon-ion scanning pancreatic therapy.
54th Annual Conference of the Particle Therapy Co-Operative Group (PTCOG54)

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