Inter-fraction motion robustness in a prospective phase II trial on dose-escalated proton reirradiation for locally recurrent rectal cancer

TY - JOUR

T1 - Inter-fraction motion robustness in a prospective phase II trial on dose-escalated proton reirradiation for locally recurrent rectal cancer

AU - Truelsen, C. G.

AU - Rønde, H. S.

AU - Kallehauge, J. F.

AU - Poulsen, L.

AU - Havelund, B. M.

AU - Pedersen, B. G.

AU - Iversen, L. H.

AU - Spindler, K. G.

AU - Kronborg, C. S.

N1 - Publisher Copyright: © 2024

PY - 2024/7

Y1 - 2024/7

N2 - Background and purpose: Intensity modulated proton therapy (IMPT) enables generation of conformal dose plans with organ at risk (OAR) sparing potential. However, pelvic IMPT robustness is challenged by inter-fraction motion caused by constant anatomical variations. In this study, the dosimetric impact of inter-fraction motion on target coverage and dose to OAR was quantified in the prospective phase II study ReRad-II on dose-escalated proton reirradiation for locally recurrent rectal cancer (LRRC). Materials and methods: The inter-fraction motion robustness was assessed for the initial twelve patients enrolled in the ReRad-II study. Patients with resectable LRRC were assessed for neoadjuvant IMPT (55 Gy(RBE)/44Fx) and unresectable recurrences for definitive IMPT (57.5–65 Gy(RBE)/ 46-52Fx). Target coverage and dose to OAR were assessed for robustly optimised three-field IMPT, on 12 plan computerized tomography (CT) scans (pCT) − and 47 repetitive control CT scans (cCTs) during the treatment. The target coverage and doses to OAR were re-calculated on each cCT and the mean dose ratio (pCT/cCT-ratio) and target coverage (V95%) was evaluated. Results: The target coverage was robust with a mean dose pCT/cCT-ratio of 1.00 (+/-1%). The V95% target coverage for every cCT were above the accepted worst-case scenario in the robust evaluation. Considerable variation in bladder-, bowel bag-, and bowel loop volume was observed. The OAR with the largest variation in ratio was the bladder (pCT/cCT-ratio: 1.3 (range: 0.5–4.7). Conclusions: IMPT for dose-escalated reirradiation of LRRC provided anatomically robust target coverage despite OAR changes. Inter-fraction motion resulted in OAR doses varying within clinically acceptable range.

AB - Background and purpose: Intensity modulated proton therapy (IMPT) enables generation of conformal dose plans with organ at risk (OAR) sparing potential. However, pelvic IMPT robustness is challenged by inter-fraction motion caused by constant anatomical variations. In this study, the dosimetric impact of inter-fraction motion on target coverage and dose to OAR was quantified in the prospective phase II study ReRad-II on dose-escalated proton reirradiation for locally recurrent rectal cancer (LRRC). Materials and methods: The inter-fraction motion robustness was assessed for the initial twelve patients enrolled in the ReRad-II study. Patients with resectable LRRC were assessed for neoadjuvant IMPT (55 Gy(RBE)/44Fx) and unresectable recurrences for definitive IMPT (57.5–65 Gy(RBE)/ 46-52Fx). Target coverage and dose to OAR were assessed for robustly optimised three-field IMPT, on 12 plan computerized tomography (CT) scans (pCT) − and 47 repetitive control CT scans (cCTs) during the treatment. The target coverage and doses to OAR were re-calculated on each cCT and the mean dose ratio (pCT/cCT-ratio) and target coverage (V95%) was evaluated. Results: The target coverage was robust with a mean dose pCT/cCT-ratio of 1.00 (+/-1%). The V95% target coverage for every cCT were above the accepted worst-case scenario in the robust evaluation. Considerable variation in bladder-, bowel bag-, and bowel loop volume was observed. The OAR with the largest variation in ratio was the bladder (pCT/cCT-ratio: 1.3 (range: 0.5–4.7). Conclusions: IMPT for dose-escalated reirradiation of LRRC provided anatomically robust target coverage despite OAR changes. Inter-fraction motion resulted in OAR doses varying within clinically acceptable range.

KW - Intensity-modulated proton therapy (IMPT)

KW - Inter-fraction motion robustness

KW - Locally recurrent rectal cancer

KW - Organs at risk

KW - Reirradiation

UR - http://www.scopus.com/inward/record.url?scp=85202718731&partnerID=8YFLogxK

U2 - 10.1016/j.phro.2024.100634

DO - 10.1016/j.phro.2024.100634

M3 - Journal article

C2 - 39286771

AN - SCOPUS:85202718731

SN - 2405-6316

VL - 31

JO - Physics and Imaging in Radiation Oncology

JF - Physics and Imaging in Radiation Oncology

M1 - 100634

ER -