ESTRO 2024 - Abstract Book

S1513

Clinical - Lower GI

ESTRO 2024

Conclusion:

Survival was non-inferior than it would be expected suggesting that fit and medium-fit patients > 80 years with RC should be strongly considered for a curative treatment.

Keywords: rectal cancer, radiotherapy, elderly

1502

Digital Poster

PET/MR-based functional avoidance planning to protect bone marrow for rectal cancer patients

Zhe Zhang 1 , Zhixun Zhang 2,1 , Min Chen 1 , Mengqi Yang 1 , Changjun Tie 3 , Chao Zou 3 , Feng Jin 4 , Xin Li 1 , Lingling Guo 1 , Linlin Lu 1 , Xuehan Hu 5 , Ronghua Yan 5 , Zhibo Tan 1 1 Peking University Shenzhen Hospital, Radiation Oncology, Shenzhen, China. 2 Shantou University Medical College, PKU-Shenzhen Clinical Institute, Shenzhen, China. 3 Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen, China. 4 Peking University Shenzhen Hospital, Medical Oncology, Shenzhen, China. 5 Peking University Shenzhen Hospital, Medical Imaging, Shenzhen, China

Purpose/Objective:

Neoadjuvant radiotherapy is the standard therapy for patients with locally advanced rectal cancer or with difficulty in organ-preserving. More than 90% of rectal cancer patients receiving neoadjuvant radiotherapy suffered myelosuppression. The severity of myelosuppression is positively correlated with the exposure dose of active bone marrow (BM-a) with hematopoietic function. PET/MR can provide multiple information about bone marrow, such as morphology, fat content, cells and blood vessels, and metabolism, which can better show bone marrow's activity. In this study, PET/MR was used to delineate BM-a of pelvic, then, functional avoidance radiotherapy planning (FA-RT) was designed to minimize the exposure dose of BM-a. The dosimetry differences between FA-RT and routine radiotherapy planning (R-RT) were compared thereafter.

Material/Methods:

A total of 11 rectal cancer patients treated with neoadjuvant radiotherapy were selected from a clinical study (ChiCTR2200063005) and informed consent was obtained. Prior to the initial treatment, United-Imaging uPMR790 was used to acquire 18 F-FDG PET/MR images. The MR scanning followed relevant consensus. Radiotherapy target volume and organs at risk (OARs) were delineated according to guidelines, among which the whole bone marrow (BM-w) was defined as the entire medulla of the pelvic bone. Then, R-RT was designed using VMAT, with the following prescription dose: PGTVp/nd 50Gy/25f, PCTV 45Gy/25f. The dose limitation of OARs followed QUANTEC. Besides, PET/MR images were rigidly registrated on sim-CT to outline BM-a: the bone marrow areas with SUV value higher than 60% of the standardized SUV mean value of normal liver were defined as BM-a, and the rest was defined as inactive bone marrow (BM-ia). Then, FA-RT was optimized with additional limitation to reduce the dose of BM-a by 20%; the other dose restrictions were the same as in R-RT. The dosimetry differences between FA-RT