3299 - Organ at Risk Dose Constraints in Conventionally Fractionated Pelvic Radiation Therapy: A Systematic Review of Clinical Trials

L. Tchelebi¹, P. Taylor², J. Lester¹, L. Lee¹, M. R. Folkert¹, J. M. Herman¹, and L. Potters¹; ¹Northwell, Lake Success, NY, ²Upstate Medical University, Syracuse, NY, United States

Purpose/Objective(s): Organ at risk (OAR) dose constraints are critical to minimize toxicity from radiation treatment (RT). There is limited evidence supporting optimal pelvic OAR constraints, resulting in heterogeneity across clinical trials involving pelvic disease sites. OAR dose constraints used in major clinical trials of conventionally fractionated RT (CFRT) for pelvic diseases were systematically evaluated to propose their consolidation to improve treatment planning efficiency and encourage standardization. Materials/

Methods: Site-specific directives providing guidance on treatment planning, including dose constraints, are used in our system to standardize treatment. A systematic review of the literature from 2014-2024 was conducted in Pubmed and Embase following the PRISMA guidelines to identify Phase II-III clinical trials for CFRT RT across pelvic disease sites conducted by large cooperative groups. Articles were imported into Covidence and reviewed by two reviewers. OAR constraints were derived from these manuscripts. All recommended OAR dose values were binned and the most frequent value for each dose level was assigned as the mandatory constraint. The proposed constraints were reviewed by our protocol directives committee and approved for use across our system.
Results: Of the 619 screened studies, 121 phase II-III cooperative group trials met our inclusion criteria. Nine additional studies were manually added. In compliance with AAPM TG-263 and to facilitate future data pooling efforts OARs were defined as: Rectum, Bowel_Bag, Bowel_Large, Bowel_Small, Femur_L/R, Bladder, and Colon_Sigmoid. We were able to consolidate 10 total sets of OAR constraints across pelvic CFRT directives to only one shown in the Table.
Conclusion: We found no standardization of OAR dose constraints used in clinical trials evaluating CFRT in pelvic diseases. This variability in OAR dose constraints creates challenges in creating a uniform standard of care for cancer patients. We developed a uniform set of OAR constraints to use across all pelvic disease sites to standardize our treatment planning process. We hypothesize that this will enhance efficiency across the radiation clinics in our system. We plan to test this hypothesis by analyzing treatment planning duration before and after the implementation of this process change.

Abstract 3299 – Table 1 * Planning constraint when brachytherapy boost will follow Abbreviations: Gy, Gray; cc, cubic centimeter; n/a, not applicable

Pelvic OAR Constraints (1.8-2.0 Gy/fx)

30Gy

35Gy

40Gy

45Gy

50Gy

54Gy

57.5Gy

60Gy

65Gy

70Gy

75Gy

80Gy

Bladder

n/a

n/a

75%

n/a

50%

n/a

n/a

n/a

50%, 150cc

n/a

25%

15%

Bowel_Bag

650cc

n/a

300cc

195cc

n/a

0.03cc

n/a

n/a

n/a

n/a

n/a

n/a

Bowel_Large

200cc

n/a

n/a

60cc

n/a

20cc

n/a

n/a

n/a

0.03cc

n/a

n/a

Bowel_Small

n/a

180cc

n/a

120cc

n/a

0.03cc

n/a

n/a

n/a

n/a

n/a

n/a

Colon_Sigmoid

n/a

n/a

80%*

n/a

60%*

n/a

0.03cc*

n/a

n/a

n/a

n/a

n/a

Femur_L/R

50%

n/a

n/a

25%

10%

0.03cc

n/a

n/a

n/a

n/a

n/a

n/a

Rectum

n/a

n/a

80%

60%

n/a

n/a

0.03cc*

50%, 40cc

35%, 30cc

25%, 20cc

15%, 10cc

5%