Main Session
Sep 29
PQA 05 - Physics

3093 - Personalizing Adaptive Radiotherapy for Rectal Cancer: Three-Arm Comparison with Introduction of a Hybrid Adaptive Approach

12:30pm - 01:45pm ET
Poster Hall - Exhibit Hall A
Screen: 4
POSTER

Presenter(s)

Madhav Patel, MD, BS - Columbia Presbyterian Medical Center, New York, NY

M. Patel, R. Z. Rajkumar, A. Sangal, K. M. Daniell, A. W. Lee, L. A. Kachnic, Y. F. Wang, and D. P. Horowitz; Department of Radiation Oncology, Columbia University Irving Medical Center, New York, NY

Purpose/Objective(s): Studies have shown advantages to daily online adaptive radiation therapy (oART) for rectal adenocarcinoma (RA), with enhanced target coverage and organ at risk (OAR) sparing. However, daily oART may be resource intensive and time-consuming, making patient selection and workflow optimization critical for appropriate use. We present an innovative hybrid oART strategy involving physician-guided adaptation once-per-week, and compare dosimetric outcomes to existing non-adaptive and daily-adaptive approaches.

Materials/Methods: Ten previously treated RA patients undergoing CBCT-guided daily oART were retrospectively identified. Primary tumor/gross nodes were treated to 50Gy and elective nodes to 45Gy in 25 fractions, with a 4Gy in 2 fraction boost to residual tumor volume. The first 10 fractions were used to simulate a weekly adaptation model. Dosimetric variables for targets (PTV45, PTV50) and OARs (bladder, bowel) were extracted for non-adapted, daily adaptive, and weekly adaptive plans. Python 3.9.12 was utilized to calculate median/interquartile range (IQR) for dosimetric variables, with three-group and pairwise comparisons performed with Kruskal–Wallis and Mann-Whitney U test, respectively.

Results: Median age and Karnofsky performance score were 56 years and 90. Most patients were with T3 (67%) and N1/N2 (40%, each) disease and did not receive prior neoadjuvant chemotherapy (70%). For PTV45 and PTV50 D95% and V98%, daily oART provided superior coverage among all groups, and weekly oART demonstrated improved coverage vs. non-adapted group (Table 1; p<0.001, all). D30% and V45Gy for bowel, and D50% for bladder did not significantly differ. Max dose to bladder/bowel were significantly higher for the hybrid weekly adaptive group but met final OAR constraints.

Table 1. PTV45/50 Coverage Comparisons. Boldface denotes statistical significance; *comparison of all three groups, †non-adaptive vs. daily adaptive, ‡non-adaptive vs. weekly adaptive, §daily adaptive vs. weekly adaptive

Conclusion: Hybrid oART with weekly adaptation significantly improved coverage to target volumes (PTV45, PTV50) vs. conventional scheduled radiotherapy, while daily oART yielded superior dosimetry across all groups. More frequent interval adaptation may be investigated to optimize the hybrid adaptive radiotherapy approach. Future studies with increased sample size and fractionation data are necessitated to further comprehend and refine hybrid adaptive radiotherapy for rectal cancer.

Non-adaptive (Median, IQR)

 Daily Adaptive (Median, IQR)

 Weekly Adaptive (Median, IQR)

 p-value*

 p-value†

 p-value‡

 p-value§
PTV45 D95%

 179 cGy (177-181)

 184 cGy (183-184)

 183 cGy (180-184)

 <0.001

 <0.001

 <0.001

 <0.001
PTV45 V98%

 96.8% (95.2-97.9)

 99.7% (99.3-99.9)

 97.9% (96.4-99.0)

 <0.001

 <0.001

 <0.001

 <0.001
PTV50 D95%

194 cGy (191-197)

 201 cGy (200-201)

 199 cGy (195-201)

 <0.001

 <0.001

 <0.001

 <0.001
PTV50 V98%

 92.7% (88.5-95.8)

 99.4% (99.1-99.6)

 97.7% (93.9-99.2)

 <0.001

 <0.001

 <0.001

 <0.001