Maskless SGRT improved initial pelvic setup and shortened positioning time

KEY POINTS

• The prospective E-SAMM study randomized 100 patients receiving pelvic radiotherapy for cervical, endometrial, rectal or prostate cancer to maskless AlignRT surface-guided positioning or six-clamp thermoplastic-mask laser alignment. Treatment doses ranged from 45–68 Gy in 25–28 fractions, and 2,376 fractions were analyzed.
• Both groups still underwent daily CBCT verification on a TrueBeam with a six-degree-of-freedom couch. SGRT therefore replaced initial mask/laser positioning, not internal image guidance.
• Mean pre-correction translational error was lower with SGRT in the mediolateral direction (1.97±1.54 vs 2.63±2.06 mm; p=0.03) and craniocaudal direction (3.13±2.34 vs 4.03±2.67 mm; p=0.001). AP shifts were larger with SGRT, while rotational differences were not significant (p=0.14).
• Overall three-dimensional vector displacement was also lower with SGRT: 1.91±0.36 versus 2.26±0.48 mm (p<0.05), supporting better reproducibility of the initial external setup.
• Van Herk margins calculated from pre-correction CBCT shifts were smaller with SGRT in every direction: 4.9 vs 6.8 mm mediolaterally, 8.1 vs 9.9 mm craniocaudally and 7.7 vs 8.7 mm anteroposteriorly.
• Mean setup time decreased from 3.55±0.99 to 2.51±0.81 minutes (p=0.007)—approximately a 29% reduction—providing a concrete workflow advantage alongside elimination of thermoplastic pelvic immobilization.
• The calculated margins represent pre-correction setup reproducibility, not residual geometric uncertainty during beam delivery, because daily CBCT corrections were performed before every fraction. The study also did not quantify intrafraction motion using the continuous SGRT data, so the results should not be interpreted as direct validation of smaller clinical PTV margins.

CLINICAL TAKEAWAY

SOURCE

Strahlentherapie und Onkologie