Estimating Potential Benefits to Neurocognition with Proton Therapy in Adults with Brain Tumors

Mariana Petruccelli; Amy Parent; Michael Holwell; Hitesh Dama; Grace Tsui; Zhihui Amy Liu; Derek S Tsang

doi:10.14338/IJPT-22-00024.1

Estimating Potential Benefits to Neurocognition with Proton Therapy in Adults with Brain Tumors

Int J Part Ther. 2023 Mar 16;9(4):261-268. doi: 10.14338/IJPT-22-00024.1. eCollection 2023 Spring.

Authors

Mariana Petruccelli¹, Amy Parent¹, Michael Holwell¹, Hitesh Dama¹, Grace Tsui¹, Zhihui Amy Liu², Derek S Tsang¹

Affiliations

¹ Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada.
² Department of Biostatistics, Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada.

Abstract

Purpose: Photon radiation therapy (RT) is important in the treatment of many brain tumors but can negatively affect neurocognition. Proton therapy (PT) can reduce doses to normal brain structures. We compared photon and proton plans to estimate the potential benefit in cognition if the patient were treated with PT.

Materials and methods: We analyzed 23 adult patients with proton and photon plans for the treatment of a primary brain tumor. Cognitive outcomes were predicted using converted equivalent dose (EQD2) with an α/β ratio of 3 to left temporal lobe and normal brain tissue. Risks of cognitive decline on 2 specific tests, the Controlled Oral Word Association Test (COWAT [letter S], a test of verbal fluency) and the Wechler Adult Intelligence Scale (WAIS-IV Coding Test, a test of processing speed) were derived from a previously published model.

Results: Dose reductions to left temporal lobe and normal brain tissue translated into lower estimated probabilities of impairment in specific neurocognitive test scores after PT. With a mean dose reduction from 1490 to 1092 cGy in EQD2 to the left temporal lobe (P < .001), there was reduction in probability of impairment in the COWAT (Letter S) test from 6.8% to 5.4%. Similar results were seen with the normal brain (750 to 451 cGy in EQD2, P < .001), with reduction in probability of impairment in the WAIS-IV Coding test from 5% to 4.1%. Other structures experiencing dose reduction with PT included each cochlea, posterior fossa, each temporal lobe, and each hippocampus.

Conclusion: We confirmed an association between PT and lower doses to brain substructures, which is expected to result in a modest decrease in probability of impairment in neurocognitive test scoring. These findings should be confirmed in prospective cohorts of patients treated with PT.

Keywords: brain neoplasms; cognition; computer-assisted; proton therapy; radiation therapy planning; survivorship.

Grants and funding

Funding: This study was funded by the Adam Coules Research Grant from the Patient & Family Advisory Committee (PFAC) of the Gerry & Nancy Pencer Brain Tumor Centre at Princess Margaret Cancer Centre via the Princess Margaret Cancer Foundation.