Simple immobilization for stereotactic radiotherapy aimed at pelvic metastases.

Stereotactic body radiotherapy (SBRT) is increasingly applied for pelvic oligometastases of prostate cancer, and currently no simple immobilization method is available for cone beam computed tomography (CBCT)-guided treatment. We assessed patient set-up and intrafraction motion using simple immobilization during CBCT-guided pelvic SBRT. Forty patients were immobilized with basic arm- head- and knee support and either a thermoplastic cushion or a foam cushion. Analysis of 454 CBCTs showed mean intrafraction translation <3.0 mm in 94% of fractions and mean intrafraction rotation <1.5° in 95% of fractions. Therefore, simple immobilization ensured stable patient positioning during CBCT-guided pelvic SBRT.