Clinical benefits of new immobilization system for hypofractionated radiotherapy of intrahepatic hepatocellular carcinoma by helical tomotherapy

Yong Hu, Yong-Kang Zhou, Yi-Xing Chen, Shi-Ming Shi, Zhao-Chong Zeng
Medical Dosimetry: Official Journal of the American Association of Medical Dosimetrists 2017, 42 (1): 37-41

OBJECTIVE: A comprehensive clinical evaluation was conducted, assessing the Body Pro-Lok immobilization and positioning system to facilitate hypofractionated radiotherapy of intrahepatic hepatocellular carcinoma (HCC), using helical tomotherapy to improve treatment precision.

METHODS: Clinical applications of the Body Pro-Lok system were investigated (as above) in terms of interfractional and intrafractional setup errors and compressive abdominal breath control. To assess interfractional setup errors, a total of 42 patients who were given 5 to 20 fractions of helical tomotherapy for intrahepatic HCC were analyzed. Overall, 15 patients were immobilized using simple vacuum cushion (group A), and the Body Pro-Lok system was used in 27 patients (group B), performing megavoltage computed tomography (MVCT) scans 196 times and 435 times, respectively. Pretreatment MVCT scans were registered to the planning kilovoltage computed tomography (KVCT) for error determination, and group comparisons were made. To establish intrafractional setup errors, 17 patients with intrahepatic HCC were selected at random for immobilization by Body Pro-Lok system, undergoing MVCT scans after helical tomotherapy every week. A total of 46 MVCT re-scans were analyzed for this purpose. In researching breath control, 12 patients, randomly selected, were immobilized by Body Pro-Lok system and subjected to 2-phase 4-dimensional CT (4DCT) scans, with compressive abdominal control or in freely breathing states, respectively. Respiratory-induced liver motion was then compared.

RESULTS: Mean interfractional setup errors were as follows: (1) group A: X, 2.97 ± 2.47mm; Y, 4.85 ± 4.04mm; and Z, 3.77 ± 3.21mm; pitch, 0.66 ± 0.62°; roll, 1.09 ± 1.06°; and yaw, 0.85 ± 0.82°; and (2) group B: X, 2.23 ± 1.79mm; Y, 4.10 ± 3.36mm; and Z, 1.67 ± 1.91mm; pitch, 0.45 ± 0.38°; roll, 0.77 ± 0.63°; and yaw, 0.52 ± 0.49°. Between-group differences were statistically significant in 6 directions (p < 0.05). Mean intrafractional setup errors with use of the Body Pro-Lok system were as follows: X, 0.41 ± 0.46mm; Y, 0.86 ± 0.80mm; Z, 0.33 ± 0.44mm; and roll, 0.12 ± 0.19°. Mean liver-induced respiratory motion determinations were as follows: (1) abdominal compression: X, 2.33 ± 1.22mm; Y, 5.11 ± 2.05mm; Z, 2.13 ± 1.05mm; and 3D vector, 6.22 ± 1.94mm; and (2) free breathing: X, 3.48 ± 1.14mm; Y, 9.83 ± 3.00mm; Z, 3.38 ± 1.59mm; and 3D vector, 11.07 ± 3.16mm. Between-group differences were statistically different in 4 directions (p < 0.05).

CONCLUSIONS: The Body Pro-Lok system is capable of improving interfractional and intrafractional setup accuracy and minimizing tumor movement owing to respirations in patients with intrahepatic HCC during hypofractionated helical tomotherapy.

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