Main Session
Sep 27
PQA 01 - Gastrointestinal Cancer and Central Nervous System

2112 - Enhanced Normal Tissue Sparing in Hippocampal-Avoidance Whole Brain Radiotherapy: A Dosimetric Study

03:00pm - 04:00pm ET
Poster Hall - Exhibit Hall A
Screen: 9
POSTER

Presenter(s)

Racha Khodor, MD - American University of Beirut Medical Center, Beirut, Beirut

R. Khodor1, A. Al Zein1, T. Mobayed2, L. Bodgi1, Z. Reda3, Z. Mazeh3, J. Sebaaly V2, A. H. Shmoury3, T. Al Bitar3, Z. Dandash3, L. Hilal1, M. Al beainy1, Z. Ayoub1, T. A. Eid1, O. Mohamad1, and B. Y. Youssef1; 1American University of Beirut Medical Center, Beirut, Lebanon, 2American University of Beirut, Beirut, Beyrouth, Lebanon, 3American University of Beirut Medical center, Beirut, Lebanon

Purpose/Objective(s):

Hippocampal-avoidance whole brain radiotherapy (HA-WBRT) aims to preserve neurocognitive function while maintaining target coverage. It prioritizes hippocampal sparing with limited emphasis on additional organs at risk (OAR). We hypothesized that incorporating lenses, cochleas, brainstem, and oral cavity structures into plan optimization could reduce dose to OARs and potentially decrease subsequent risks of cataracts, hearing loss, and dysgeusia. We also sought to reduce dose inhomogeneity by minimizing high-dose regions within the target volume through reducing brain D2%. We performed a dosimetric study comparing HA-WBRT planned as per the NRG-CC001 to an enhanced normal tissue sparing HA-WBRT.

Materials/Methods:

Fourteen patients previously treated with HA-WBRT (30 Gy in 10 fractions) were identified. Two VMAT plans were generated per patient using identical targets and contours for paired comparison. Plan 1 represented standard optimization meeting NRG-CC001 constraints. Plan 2 incorporated additional prioritization of the lens, cochlea, tongue, and soft palate. It also sought to reduce high-dose regions within the brainstem and the brain. Dosimetric endpoints included target coverage parameters per NRG-CC001, and OARs sparing per Timmerman; cochlear V25 and Dmax, ocular and oral cavity mean doses, brain D2% and Dmax, and brainstem Dmax. Dependent t-tests were used for analysis.

Results:

Plan 2 maintained equivalent target coverage while significantly reducing cochlear, ocular, oral cavity, brainstem doses and brain hotspots (Table 1). Cochlear Dmax and V25 decreased bilaterally (p < 0.001) with major reductions in lens Dmax. Brainstem Dmax and brain high-dose metrics (D2%, overall Dmax) were significantly reduced, indicating improved dose homogeneity.

Table1

Conclusion:

Enhanced HA-WBRT optimization improved organ-at-risk sparing and reduced dose inhomogeneity without compromising target coverage, supporting the feasibility of refined planning strategies that may reduce treatment-related toxicity.
Plan 1 (Mean ± SD)

 Plan 2 (Mean ± SD)

 p-value
Brain

D2% <3750 (cGy)

 3612.2 (123%) ± 91.1

 3317.3 (110%) ± 22.1

 <0.001
Dmax overall (%)

 141.22 ± 12.28

 117.95 ± 1.76

 <0.001
Brainstem

 Dmax (cGy)

 3968.8 ± 154.3

 3483.0 ± 46.1

 <0.001
Cochlea

 Max Rt (cGy)

 3143.9 ± 194.9

 2455.7 ± 73.0

 <0.001
Max Lt (cGy)

 3062.1 ± 257.6

 2468.8 ± 71.1

 <0.001
V25 Rt <0.5 cc

 0.0687 ± 0.0297

 0.00564 ± 0.0200

 <0.001
V25 Lt <0.5 cc

 0.0571 ± 0.0347

 0.00579 ± 0.0199

 <0.001
Lens

 Max Rt (cGy)

 1588.7 ± 296.3

 562.4 ± 51.7

 <0.001
Max Lt (cGy)

 1618.3 ± 340.9

 569.4 ± 34.2

 <0.001
Tongue

 Mean dose (cGy)

 653.7 ± 174.9

 383.6 ± 145.2

 <0.001
Soft palate

 Mean dose (cGy)

 1045.4 ± 271.6

 584.2 ± 230.4

 <0.001