Proton therapy reduces the incidence of severe lymphopenia compared with photon
Abravan, Azadeh Sitch, Peter Gaito, Simona McPartlin, Andrew J Sashidaran, S. Smith, Ed Whitfield, Gillian A Pan, Shermaine
Abravan, Azadeh
Sitch, Peter
Gaito, Simona
McPartlin, Andrew J
Sashidaran, S.
Smith, Ed
Whitfield, Gillian A
Pan, Shermaine
Citations
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Abstract
Purpose or Objective
Radiotherapy-induced lymphopenia may be associated with adverse outcome and reduced survival in various cancer types.
Due to unique dosimetric characteristics, proton therapy can reduce the volumes of healthy tissue irradiated, potentially
sparing lymphocytes. We investigated the incidence of severe lymphopenia in patients treated with either photons or
protons, whose radiation treatment site included head and neck (H&N) and central nervous system (CNS).
Materials and Methods
Data from 44 patients treated with proton therapy and 44 with photon therapy at a single institute for H&N (n=52) or CNS
(n=36) were included. Base of skull treatment were included in the H&N category. All patients had lymphocyte counts at
baseline (< 90 days prior to radiotherapy) and during radiotherapy. Severe lymphopenia grade 3 or higher was based on
lymphocytes at nadir during RT < 0.5x109/L (CTCAE v5.0). If case of multiple clinical target volumes (CTVs), the largest CTV
was used in the analysis. Vx was calculated from RT images and is a volume receiving x Gy or higher in the body normalized
to body weight to account for patients’ size. For patients without weight data, it is imputed using a 3rd power fit of weight
vs age from the available data. Multivariable logistic analysis was conducted to investigate the association between the
incidence of severe lymphopenia and patients’ clinical, demographics, and dosimetric factors. To avoid multi-collinearity,
dosimetric parameters were included in the multivariable regression one at a time together with other factors known to
affect lymphocytes.
Results
Four (9%) and 17 (39%) of the patients developed grade 3 lymphopenia in the proton and photon treatment arm,
respectively. There was a good match of baseline lymphocytes and CTV between proton and photon arms for each disease
site (Table 1). However, lymphocyte counts during radiotherapy and the incidence of grade 2 and grade 3 lymphopenia was
significantly lower in the proton arm. As seen in Table 2, in the univariable model, proton therapy was associated with the
reduced risk of lymphopenia, however, it became insignificant when including dosimetric parameters in the multivariable
model. Multivariable logistic regression adjusted for age, gender, treatment arm, and disease site suggested that lower
baseline lymphocytes and larger volumes receiving 2‒30 Gy (V2, V5, V10, V20, V30) are associated with higher risk of
developing grade 3 or higher lymphopenia during radiotherapy. Conclusion
Our study suggests that in H&N and CNS treatment, protons reduce the risk of severe treatment-related lymphopenia.
Proton therapy reduces the volume receiving low to intermediate doses (V2 -V30) and subsequently reduces grade 3 or higher
lymphopenia.
Description
Date
2022
Publisher
Collections
Keywords
Type
Meetings and Proceedings
Citation
Abravan A, Sitch P, van Herk M, Gaito S, McPartlin A, Sashidaran S, et al. Proton therapy reduces the incidence of severe lymphopenia compared with photon. Radiotherapy and Oncology. 2022 May;170:S140-S1. PubMed PMID: WOS:000806759200139.