Relationship between pressure levels on the occipital region and intrafraction motion using an individualized head support for intracranial treatment

Abstract

The purpose of this study was to evaluate the relationship between pressure on the occipital region and intrafraction motion using an individualized vacuum pillow and a thermoplastic mask for intracranial treatment. We calculated head displacement during treatment from 8811 image verifications in 59 patients and divided them into two groups according to the magnitude of the mean and standard deviation (SD) of the displacement in the 59 patients. Pressure was compared between the small (n = 29) and large (n = 30) displacement groups using Welch’s t-test for the mean and SD of displacement. The mean head displacement in the small and large groups was (0.3, 0.3, 0.4) and (0.5, 0.6, 0.7) (unit: mm) for the vector length and 10 mm and 30 mm radius targets, respectively. The mean SD of head displacement in the small and large groups was (0.2, 0.2, 0.2) and (0.3, 0.3, 0.4) (unit: mm) for the vector length and 10 mm and 30 mm radius targets, respectively. Significant differences were observed in the SD of the displacement in the vector length and 10 mm radius target between the two groups. The SD of the displacement under a pressure of 15 kPa was smaller than that under a pressure of 11 kPa. The intrafraction motion under a high-pressure level on the occipital region was less than that under a low-pressure level. Management of pressure on the occipital region may result in less intrafraction motion in clinical practice.

Optimal mask fixation method for frameless radiosurgery with Leksell Gamma Knife IconTM

“…Inata et al showed that patient motion was reduced when the force on the occipital area was larger. 15 As shown in Figure 3 , the forces on the occipital bone at 1.5 h after the initial application were approximately 4 N in Plain and Folded methods. The force reached 80% of the maximum value in about 30 min in the Folded method, while it took about 1 h in the Plain and Wide methods.…”

Estimation of imaging intervals and intrafraction displacement in CyberKnife image‐guided radiotherapy for intracranial lesions

“…The measurement sensitivity of our monitoring system may have improved because the coefficient of displacement became smaller as the image interval became longer. We reported that the SD of the intrafraction displacement became small when an immobilizing pressure on the head was maintained at a high pressure level 20 . Hence, if a larger imaging interval is set, radiation exposure may be reduced with high positioning precision by means of maintaining a high pressure.…”

“…A baseplate (MT‐20108, CIVCO), a vacuum pillow (YCI‐01; Engineering System), and a mask (RT‐1779KS; Qfix) were used to immobilize the patients. The intrafraction displacement could be reduced by increasing the pressure in the occipital region to 15 kPa or more, as feasible 20 . Therefore, we inserted a foam sheet (made from natural rubber origin, with a thickness of 3 mm and a density of 0.100 ± 0.03 kg/m 3 ) under the pressure sensors to improve the sensitivity and equalization of pressure in the occipital region as compared to the procedure followed in our previous study 12 …”

“…The intrafraction displacement could be reduced by increasing the pressure in the occipital region to 15 kPa or more, as feasible. 20 Therefore, we inserted a foam sheet (made from natural rubber origin, with a thickness of 3 mm and a density of 0.100 ± 0.03 kg/m 3 ) under the pressure sensors to improve the sensitivity and equalization of pressure in the occipital region as compared to the procedure followed in our previous study. 12 As the pressure sensors in this system make angles that reflect the shape of the back of the head in a horizontal direction, the displacement could measure pressure based on Equation (3) (unless head displacement moved in parallel for each axis).…”

“…We reported that the SD of the intrafraction displacement became small when an immobilizing pressure on the head was maintained at a high pressure level. 20 Hence, if a larger imaging interval is set, radiation exposure may be reduced with high positioning precision by means of maintaining a high pressure.…”