Evaluation of setup errors of immobilization device for radiation therapy in companion animals

Abstract

Background: Intensity-modulated radiotherapy (IMRT), which allows generating steep dose gradients, is a beneficial treatment for companion animals with adjacent target and risk organs. IMRT is essential for high setup accuracy for avoiding overdose to risk organs, and optimal radiotherapy is important for evaluating the setup accuracy of companion animals. Aim: To use an immobilization device to evaluate setup errors in radiotherapy for companion animals Materials and methods: We calculated setup errors in radiotherapy for 386 animals (dogs and cats; 3261 registration images) that underwent radiotherapy between 2016 and 2022. The companion animals were immobilized with a customized bite block and vacuum lock device. A quantile–quantile plot with 95% confidence interval (CI) was used to evaluate the histogram of the setup errors, and the systematic and random setup errors were calculated for each region (brain, head and neck, chest and abdomen, pelvis, and spine). Results: The setup error in each direction presented an extremely narrow-interval histogram, with the following lower and upper 95% CIs: cranial–caudal (−0.08, −0.06 cm); left–right (−0.04, −0.02 cm); and dorsal–ventral (−0.13, −0.11 cm). The mean systematic setup error was 0.16 cm (range: 0.12–0.36 cm), and the random error was 0.15 cm (range: 0.08–0.34 cm). The pelvis showed the highest systematic and random setup errors (mean: 0.36 and 0.23 cm, respectively). Conclusion: The use of an immobilization device enables highly accurate radiotherapy for companion animals (95% CI < 0.15 cm).

Comparison of a new immobilization method using a reusable 3‐point fixation cylinder system and bite‐block type immobilization methods in veterinary radiotherapy

“…No previous studies have focused on the mandible. [6][7][8][9][10][11][12][13][14][15] Tracheal intubation under general anesthesia is necessary during radiotherapy for small animals, and the tracheal tube may be fixed to the mandible. 18 In this case, the tracheal tube may have affected mandibular movement.…”

“…In cases where the radiotherapy irradiation area extends to the mandible, such as mandibular tumors, mandibular immobilization is also important. No previous studies have focused on the mandible 6–15 . Tracheal intubation under general anesthesia is necessary during radiotherapy for small animals, and the tracheal tube may be fixed to the mandible 18 .…”

“…5 Various immobilization methods have been reported for head radiotherapy in veterinary medicine. [6][7][8][9][10][11][12][13][14][15] In recent years, the need for a sustainable society has been emphasized, and an action agenda for sustainable development goals (SDGs) has been defined. 16 From this perspective, there is an increasing emphasis on reusable immobilization methods in radiotherapy.…”

“…Various immobilization methods have been reported for head radiotherapy in veterinary medicine 6–15 . In recent years, the need for a sustainable society has been emphasized, and an action agenda for sustainable development goals (SDGs) has been defined 16 .…”