ESTRO 2024 - Abstract Book

S4232

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

ESTRO 2024

1191

Digital Poster

Comparison of adaptive vs. delivered plan for CBCT based adaptive radiation therapy

Suresh Chaudhari 1 , Naveen M 1 , Sagar Warang 1 , Suneetha M 1 , Harjot Bajwa 1 , Vinitha Reddy Palwai 1 , Prasanth Kandra 1 , Mahaboob Basha Syed 1 , Parisa Shamsesfandabadi 2 , Sushil Beriwal 2,3 1 American Oncology Institute, Radiation Oncology, Hyderabad, India. 2 Allegheny Health Network, Radiation Oncology, Pittsburgh, USA. 3 Varian Medical Systems, Medical Affairs, Pittsburgh, USA

Purpose/Objective:

Online adaptive radiotherapy has the potential to improve coverage and/or reduce toxicities for patients treated for pelvic malignancies. The adaptive workflow can take 15-25 mins which may introduce intrafraction motion especially with rectal and bladder filling. It can change the dosimetry between adapted vs. delivered plans. The goal of this study was to assess difference in dosimetry between adapted and delivered plans for pelvic malignancies.

Material/Methods:

Nine consecutive patients of cervix (n=3), rectal (n=4) and prostate (n=2) treated on CBCT based Ethos™ were analyzed. The PTV margin for nodal region was 5 mm for all patients. All patients were treated with daily adaptive radiation therapy and had another CBCT obtained after treatment to assess the dosimetry of delivered plan. The DVH parameters common to all including V95, Dmax and V105% for PTV, mean dose to bladder and V45 for bowel bag were compared between initial/scheduled, adaptive and delivered plans.

Results:

Total of 225 fractions for nine patients were evaluated. The average total time including set up, 1 st CBCT, target and influencer propagation and review, replanning, quality assurance, treatment delivery and repeat CBCT was 23.66 (20.49-28.93) minutes. The total time between adaptive plan and delivered plan CBCT was 18 (17.03-21.78) minutes. The dosimetry parameters between scheduled (if no adaptation done with CBCT), adaptive and delivered plans are highlighted in Table 1. There was improvement in coverage (V95) between scheduled vs adaptive plans (96.5% vs. 99.9% p= .0042)) with no difference in doses to bladder and bowel bag. The adaptive plans were chosen for most fractions and there was no difference between adaptive plan and delivered plans for coverage with V95 being 99.9% vs. 99.5% respectively. Similarly mean dose to bladder and V45 for bowel bags were 33.2 Gy vs. 32.6 Gy (p=.68) and 44cc and 45.4 cc (p=.16) respectively.