An excess mortality risk analysis of proton beam versus optimal photon radiotherapy for mediastinal Hodgkin lymphoma: who may benefit most?
Ntentas, G. Dedeckova, K. Andrilik, M. Shakir, R. Aznar, Marianne Camille Ramroth, J. Begum, R. Darby, S. Mikhaeel, G. Cutter, D.
Ntentas, G.
Dedeckova, K.
Andrilik, M.
Shakir, R.
Aznar, Marianne Camille
Ramroth, J.
Begum, R.
Darby, S.
Mikhaeel, G.
Cutter, D.
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Abstract
Purpose/Objective(s): Previous studies have shown that proton beam
therapy (PBT) can reduce radiation exposure of normal tissues in patients
with mediastinal lymphoma compared to photon radiotherapy (RT).
However, most studies were small, did not use intensity modulated
radiotherapy (IMRT) which avoids low dose bath and focused mainly on
dosimetric endpoints. Our purpose was to compare PBT to best available
photon RT in a large cohort to identify which patients benefited most from
PBT both dosimetrically and in terms of predicted excess mortality risk
(EMR) from cardiovascular disease (CVD) and second cancers (SC).
Materials/Methods: Between 2015 and 2019, 80 supradiaphragmatic
Hodgkin lymphoma patients with mediastinal disease were treated with
pencil beam scanning PBT in deep inspiration breath hold (DIBH). We replanned
this cohort using Butterfly-VMAT (BVMAT) in DIBH to provide
a comparison between clinical PBT and “best-plan” photon RT. We predicted
EMR from CVD and SC (breast, lung and esophagus) using
established dose-response relationships and mean organ doses. Doses to
cardiac substructures (left ventricle, valves) and to carotids were also
included in the prediction of EMR from CVD, as was the chemotherapyrelated
EMR. The two RT methods were compared using within-patient
multiple regression. Results: Compared to BVMAT, PBT substantially reduced cardiac doses
and EMR from CVD but only for those patients whose clinical target
volume (CTV) overlapped longitudinally with the heart by >40% (n Z
23). For those with 40% overlap (n Z 57), there was no substantial
difference between PBT and BVMAT. Mean lung dose and EMR from
lung SC was reduced substantially for all patients with PBT, but an
additional benefit was observed for those with axillary disease (n Z 25).
The EMR from breast cancer was halved for female patients with axillary
disease, but this was a small effect in absolute terms. (Table 1) The integral
dose was doubled with BVMAT compared to PBT (4.7 Gy from 2.3 Gy).
Conclusion: PBT reduced radiation exposure to normal tissues to varying
degrees in different patients. Only patients with >40% longitudinal
overlap of CTV with the heart received substantial reduction of EMR from
CVD. EMR from lung SC was reduced for all patients, and those with
axillary involvement received the greatest benefit in terms of EMR from
lung and breast SC. The EMR from breast SC, however, was low for both
methods, attributable to the excellent sparing of the female breasts with
both RT techniques.
Affiliation
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Date
2020
Publisher
Collections
Keywords
Type
Meetings and Proceedings
Citation
Ntentas G, Dedeckova K, Andrilik M, Shakir R, Aznar MC, Ramroth J, et al. An excess mortality risk analysis of proton beam versus optimal photon radiotherapy for mediastinal Hodgkin lymphoma: who may benefit most? International Journal of Radiation Oncology Biology Physics. 2020;108(3):S140-S1