Inter-fraction target and OARs reproducibility in cervical cancer: Influence of immobilization systems and patient positioning verified by daily fan beam CT.

INTRODUCTION

To assess radiotherapy plans quality, the reproducibility of the targets and organs at risk (OARs) in cervical cancer radiotherapy with different immobilizations and positioning.

METHODS

Sixty definitive cervical cancer patients were enrolled and immobilized with the Orfit Rack (prone), the Personalized Prone Plate (PPP) (prone), and the vacuum bag (VB) (supine), respectively. Dosimetric metrics and daily reproducibility of the targets and OARs on fan beam CT (FBCT) were analyzed.

RESULTS

The Orfit Rack and PPP (prone position) provided slight advantage in OARs protection. The reproducibility rates of targets were 56.64 % (Orfit Rack), 64.95 % (PPP), 77.88 % (VB), and 61.25 % (prone). The VB (supine position) showed smaller shifts in Superior-Inferior and Anterior-Posterior direction, p < 0.05. For OARs, the VB had the best reproducibility for small intestine in PTVs (0-30 mm), the Orfit Rack provided the best reproducibility for the colon in PTVs (0, 3, 20, 30 mm) (p < 0.0167). The supine position exhibited better reproducibility for small intestine in PTVs (0-30 mm) and colon in PTV, p < 0.05.

CONCLUSIONS

Compared to the PPP and Orfit Rack (prone position), the VB (supine position) can provide better targets and OARs reproducibility and make patient set-up more convenient during the radiotherapy treatment, yet OAR dose constraints must be considered in treatment planning to ensure safety and efficacy.

IMPLICATIONS FOR PRACTICE: It is recommended to use the VB immobilization (supine) to ensure the reproducibility of target and OARs during treatment.