Comparison between the SGRT and the conventional setup method for patients undergoing VMAT for pelvic malignancies

Purpose: Surface Guided Radiation Treatment (SGRT) is a new method of positioning and monitoring patients on the linear accelerator's couch, using visual light cameras to monitor the skin's surface. The purpose of this study was to compare the SGRT with the conventional method, based on lasers and tattoos, in terms of accuracy and time expenditure, on patients with pelvic malignancies.

Materials and methods: A group of 34 patients were enrolled in this study, 24 males who underwent radiotherapy prostate treatment and 10 females who underwent gynecological radiation therapy. They were divided into two groups: Group A consisted of 17 (12 males and 5 females) patients positioned using tattoos/laser technique. Group Β also consisted of 17 (12 males and 5 females) patients positioned using the SGRT technique. For the verification of their position, all patients underwent cone beam computed tomography (CBCT) before each session. The corrections in the three directions recorded by the CBCT system were acquired for 419 and 358 sessions for groups A and B, respectively. The total corrections were also calculated. The positioning time was measured for 7 treatment sessions for each patient. The above corrections, along with the positioning duration, were statistically compared between the two groups.

Results: The Mann-Whitney U test shows that the corrections for Group B were significantly smaller (p < 0.05) than those for Group A. The comparison of the median values of each dataset shows that the corrections improved by 16.6% for the vertical direction, 36.7% for the lateral direction, and 33.3% for the longitudinal direction, while the total correction improved by 29.2%. The SGRT method also seems more consistent, as the average interquartile range (IQR) of the correction values of Group B was 0.25 cm, while the same value was 0.38 cm for Group A. The median positioning time was 1.6 ± 0.4 min for Group A and 2.0 ± 0.6 min for Group B. The positioning duration of patients in Group B was significantly elevated (Mann-Whitney U test, p < 0.001) in respect to that related to patients of Group A.

Conclusion: The above results show that SGRT increases the setup time compared to the conventional approach but it provides a more accurate positioning of patients subjected to VMAT for pelvic malignancies.