Inter-fraction motion robustness and organ sparing potential of proton therapy for cervical cancer

Abstract

Large-field photon radiotherapy is current standard in the treatment of cervical cancer patients. However, with the increasing availability of Pencil Beam Scanning Proton Therapy (PBS-PT) and robust treatment planning techniques, protons may have significant advantages for cervical cancer patients in the reduction of toxicity. In this study, PBS-PT and photon Volumetric Modulated Arc Therapy (VMAT) were compared, examining target coverage and organ at risk (OAR) dose, taking inter-and intrafraction motion into account. Materials and methods: Twelve cervical cancer patients were included in this in-silico planning study. In all cases, a planning CT scan, five weekly repeat CT scans (reCTs) and an additional reCT 10 min after the first reCT were available. Two-arc VMAT and robustly optimised two-and four-field (2F and 4F) PBS-PT plans were robustly evaluated on planCTs and reCTs using setup and range uncertainty. Nominal OAR doses and voxel-wise minimum target coverage robustness were compared. Results: Average voxel-wise minimum accumulated doses for pelvic target structures over all patients were adequate for both photon and proton treatment techniques (D98 > 95%, [91.7-99.3%]). Average accumulated dose of the para-aortic region was lower than the required 95%, D98 > 94.4% [91.1-98.2%]. With PBS-PT 4F, dose to all OARs was significantly lower than with VMAT. Major differences were observed for mean bowel bag V 15Gy : 60% [39-70%] for VMAT vs 30% [10-52%] and 32% [9-54%] for PBS-PT 2F and 4F and for mean bone marrow V 10Gy : 88% [82-97%] for VMAT vs 66% [60-73%] and 67% [60-75%] for PBS-PT 2F and 4F. Conclusion: Robustly optimised PBS-PT for cervical cancer patients shows equivalent target robustness against inter-and intra-fraction variability compared to VMAT, and offers significantly better OAR sparing.

Impact of interfractional target motion in locally advanced cervical cancer patients treated with spot scanning proton therapy using an internal target volume strategy

“…Our results are in line with the ones of Gort et al [17] which showed by analyzing repeat CT scans, that ITV-based treatment plans with PBS-PT and photon therapy were equally robust to interfractional motion. However, it is interesting to note that their worst D98% dose degradation of the uterus was of less than 30%, while in our study fractions with dose degradation greater than 80% was observed in one patient.…”

“…Berger et al [6] showed that gas cavities and outline variations had minor impact on target and OARs doses. In addition, the study by Gort et al [17] indicated that, with all sources of uncertainties considered, robustly optimized PBS-PT was equally robust against inter-and intrafraction variability compared to photon therapy and provides better OARs sparing.…”

“…ITV strategies can also be combined with adaptive replanning as demonstrated by Jensen et al [16] with a CBCT monitoring strategy in photon radiotherapy. Furthermore, a recent study by Gort et al [17] compared the robustness of ITV-based treatment plans with Pencil Beam Scanning PT (PBS-PT) and photon therapy. Based on the analysis of repeat CT scans they found PT to be equally robust to photons, in addition to significantly reducing the OARs doses.…”

Intensity modulated proton therapy planning study for organ at risk sparing in rectal cancer re-irradiation

“…Posterior fields are often used in pelvic proton therapy, to reduce impact from changing bowel gas/fillings, weight and other variable conditions [13,18]. This can result in slightly higher dose to the parts of the sacral bone close to the CTV.…”

Correlations between bone marrow radiation dose and hematologic toxicity in locally advanced cervical cancer patients receiving chemoradiation with cisplatin: a systematic review

“…The beneficial physical characteristics of proton therapy and its ability to achieve satisfactory target dose distributions using only a few beams enables BMS [22,23]. Gort et al and Dinges et al showed significantly better BMS for proton therapy when compared to photon therapy [22,24]. However, knowledge on the spatial location of bone marrow sparing and the required degree of sparing is essential for the development of BMS-radiotherapy techniques [25].…”