ESTRO 2021 Abstract Book

S330

ESTRO 2021

Conclusion Going beyond the current approach to test a facility’s ability to deliver a selected audit test case, this novel audit methodology evaluates local clinically used PSQA procedures. After the audit is completed, its impact continues for ongoing PSQA, thus improving quality and impacting many patients. The new audit system is administered fully remotely. This provides advantages in cost, environmental impact and logistics. References

[1] Peters et al 2010 doi.org/10.1200/JCO.2009.27.4498 [2] Kry et al 2014 doi.org/10.1016/j.ijrobp.2014.08.334

Poster highlights: Poster highlights 15: Image-guided innovations in radiotherapy

PH-0429 Feasibility of tracking skeletal muscle mass changes by CBCT in HNC patients during radiotherapy W. Huang 1 , Y. Pan 2 , P. Tan 3 , X. Gao 3 , H. Zhang 3 , Z. Li 4 , H. Lin 3 1 Guangdong provincial people's hospital, Guangdong Academy of Medical Sciences, School of Medicine, South China University of Technology, Radiation Oncology, Guangzhou, China; 2 Guangdong provincial people's hospital ， Guangdong Academy of Medical Sciences, School of Medicine, South China University of Technology, Radiation Oncology,, Guangzhou, China; 3 Guangdong provincial people's hospital ， Guangdong Academy of Medical Sciences, School of Medicine, South China University of Technology, Radiation Oncology, Guangzhou, China; 4 Guangdong provincial people's hospital ， Guangdong Academy of Medical Sciences, School of Medicine, South China University of Technology, Department of nutrition, Guangzhou, China Purpose or Objective Malnutrition is present in 44-88% patients with locally advanced head and neck cancer (HNC) during radiotherapy. Malnutrition leads to loss of skeletal muscle mass (SMM) which is associated with adverse clinical outcomes. Timely and accurate measurement of SMM in malnourished individuals is emerging as the new challenge in clinical practice. Cross-sectional skeletal muscle areas (SMA) at the level of third cervical vertebra (C3) on computed tomography (CT) are shown to provide accurate surrogates of SMM in HNC patients, but high cost and radiation exposure limit its use. Cone beam CT (CBCT) has been routinely used as an image- guided radiotherapy tool for ensuring the precise and accurate position of the patients, which is usually performed once a week during radiotherapy. We aim to assess the feasibility and reliability of measuring SMM and tracking its changes by CBCT in HNC patients during radiotherapy. Materials and Methods The study enrolled HNC patients receiving radical radiotherapy and was done in two parts: I) CT scan performed on 0th fraction (N=32); II) CT scan obtained on the 0th, 15th and 25th fractions and body weight measured on the 0th, 5th, 10th, 15th and 25thfractions (N=24). CBCT was performed once a week. Cross- sectional SMA at C3 was defined as the area of paravertebral and sternocleidomastoid muscles. SMA on both CT and CBCT scans (3 times point) were delineated by three independent senior radiation oncologists. SMA on other CBCT images were contoured by one investigator. The interobserver agreement and correlation of SMA