ESTRO 2024 - Abstract Book

S4378

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

For patients with stage II and III rectal cancer, preoperative radiotherapy has proven to be an effective treatment. In our radiotherapy department, the mean time to treatment after first consultation to start with radiation treatment is currently 15 days, due to the arrangement of a planning CT scan and radiotherapy treatment plan. In addition, part of the patients treated with concurrent chemotherapy also require consultation at the department of oncology and work-up for chemotherapy. During this delay, patients often suffer from rectal pain and rectal bleeding. The primary aim of this study is to reduce the mean time to treatment to ≤7 days in these patients, using an online adaptive radiotherapy workflow with the treatment preparation done on the available diagnostic CT scan, instead of the planning CT scan. Secondary aims are to evaluate the online adaptive workflow with respect to timing and plan characteristics, and to assess patient-reported quality of life.

Material/Methods:

Twenty rectal patients requiring preoperative (chemo)radiotherapy are eligible for inclusion in this prospective, ethics approved clinical study (MEC-2023-0445), started in September 2023. Per week, 1-2 patients are expected to be included. The workflow starts with consultation by a radiation oncologist. The diagnostic CT scan is used for preplanning, on which a reference treatment plan with intensity-modulated radiotherapy (IMRT) is made. The clinical target volume (CTV) is delineated according to standard guidelines, the planning target volume (PTV) margin consists of 5 mm in laterodorsal direction, and 8 mm in anterior and craniocaudal direction. Organs at risk include the bladder, femur heads and bowelbag. Patients are treated with IMRT on an Ethos system (Varian Medical system). Throughout the radiotherapy treatment, before, during and directly after each treatment fraction, a high-quality cone beam CT scan (HyperSight CBCT, Varian Medical Systems) is made, which enables online contour and treatment plan adaptation. The evaluation of the adaptive workflow consists of description of on-coach treatment time (time in minutes between first and third HyperSight CBCT). Plan characteristics are evaluated by analysing dosimetric data of the adapted and initial reference treatment plan calculated on the daily anatomy of the HyperSight CBCT. The clinical goals include PTV: V95%≥99 % and V107%<1 %, CTV: V97% ≥ 99 %, bladder V80%<40% and derived bowelbag structure V80%<100 cc.

To assess patient-reported quality of life, questionnaires (i.e., EORTC QLQ-C30 and EORTC QLQ-CR29) are distributed at baseline, at the end of treatment and 8-12 weeks after end of treatment.

Results:

Adaptive plan on daily HyperSight CBCT

Scheduled plan on daily HyperSight CBCT

p-value

PTV V 95% in %

100 (0.2)

98.2 (4.2)

< 0.001*

PTV V 107% in %

0.0 (0.0)

0.2 (0.6)

< 0.001*

CTV V 97% in %

99.9 (0.1)

99.3 (3.8)

< 0.001*

Bladder V 80% in %

3.0 (13.6)

10.9 (13.9)

< 0.001*

Bowelbag V 80 % in cc

28.8 (30.5)

84.0 (63.5)

< 0.001*