Program Information
Effects of Megavoltage Computed Tomographic Scan Methodology On Setup Verification and Adaptive Dose Calculation in Helical TomoTherapy
J Zhu1*, T Bai2 , J Gu3 , Z Sun4 , Y Wei5 , B Li6 , Y Yin7 , (1) Shandong Cancer Hospital Affiliated to Shandong University, Jinan, Shandong, (2) Shandong Cancer Hospital Affiliated to Shandong University, Jinan, Shandong, (3) Shandong Cancer Hospital Affiliated to Shandong University, Jinan, Shandong, (4) Affiliated Hospital of Shandong Academy of Medical Sciences, Jinan, Shandong, (5) Shandong Cancer Hospital Affiliated to Shandong University, Jinan, Shandong, (6) Shandong Cancer Hospital Affiliated to Shandong University, Jinan, Shandong, (7) Shandong Cancer Hospital Affiliated to Shandong University, Jinan, Shandong
Presentations
SU-I-GPD-J-115 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To evaluate the effect of pretreatment megavoltage computed tomographic (MVCT) scan methodology on setup verification and adaptive dose calculation in helical TomoTherapy.
Methods: Both anthropomorphic heterogeneous chest and pelvic phantoms were scanned with Tomo megavoltage image-guided radiotherapy (IGRT) system consisted of six groups o options: three different acquisition pitches (APs) of ‘fine’, ‘normal’ and ‘coarse’ multiplying 2 different corresponding reconstruction intervals (RIs). In order to mimic patient setup variations, each phantom was shifted 5 mm away manually in three orthogonal directions respectively.
Results: MVCT scanning time with pitch ‘fine’ was approximately twice than ‘normal’ and 3 times than ‘coarse’, all which will not be affected by RI options. MVCT with different APs delivered almost identical CT numbers and image noise inside 7 selected regions with various densities. DVH curves from adaptive dose calculation with MVCT images acquired by varied pitches overlapped together, where as there are no significance in all p values of intercept & slope of emulational spinal cord (p=0.761 & 0.277), heart (p=0.984 & 0.978), lungs (p=0.992 & 0.980), soft tissue (p=0.319 & 0.951) and bony structures (p=0.960 & 0.929) between the most elaborated and roughest MVCT. On chest phantom, all registration errors larger than 1 mm appeared at superior-inferior axis, which cannot be avoided with the smallest AP and RI. On pelvic phantom, craniocaudal errors are much smaller than chest, however, ‘coarse’ presents larger registration errors which can be reduced from 2.90mm to 0.22mm by registration technique ‘full image’.
Conclusion: AP of ‘coarse’ with RI of 6mm is recommended in adaptive radiotherapy (ART) planning. While considering the trade-off between IGRT and ART, AP of ‘normal’ with RI of 2mm was highly recommended in daily practice. The scan length should encompass at least one entire vertebra body in craniospinal irradiation, to avoid the misalignment in image scanning.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the National Natural Science Foundation of China (grant numbers 81671785 and 81530060), the Taishan Scholar Foundation (grant number ts20120505), the China Postdoctoral Science Foundation (grant number 2016T90412) and the Natural Science Foundation of Shandong Province (grant number 2016ZRC03118, ZR2014YL034).
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