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Berghen et al. J Cancer Metastasis Treat 2021;7:58 https://dx.doi.org/10.20517/2394-4722.2021.123 Page 7 of 10

PBT and CIRT for metastatic RCC
Nakao et al. (abstract only) reported a case of a 70-year-old woman treated with CIRT for lung and lymph
[52]
node metastases five years after previous radical nephrectomy. They observed 100% LC in the irradiated
lesions at the time of last follow-up. We could not find any other studies with PBT/CIRT for RCC. Planning
studies have shown that SBRT plans for spinal metastases for proton and carbon ion RT were feasible [53,54] .
For equivalent tumoral coverage, the maximum spinal cord dose was lower for PBT/CIRT, and the
treatment time was shorter . Future prospective trials will need to elaborate the real benefit of PBT and/or
[53]
CIRT for metastatic RCC.

Challenges and future prospects
Organ movements (e.g., by breathing) and variability in setup (positioning of the patient) can cause
uncertainties in administrating the correct dose. Knowing that motion management is already a challenge in
photon SBRT for primary RCC and metastatic lesions subject to motion, this is even more so for particle
therapy [55,56] due to density changes along the beam path that may cause the Bragg peak to occur at a
different location than planned, and the interplay between organ motion (especially breathing motion) and
beam delivery technique . Range uncertainty, due to patient positioning and movement, is seen as a
[57]
limiting factor. Robust optimization for treatment planning, four-dimensional planning CT (coping with
breathing), and image-guided RT are essential parts of the treatment, to mitigate the potentially
deteriorating impact of range uncertainty and inter- and intrafraction motion on the dose distribution [55,58] .

Although many other trials are underway regarding SBRT for primary or (oligo)metastatic RCC with
photon beam radiotherapy, we are not aware of any ongoing trials with PBT or CIRT for these indications.
Prospective trials are badly needed. However, this type of research is limited due to the availability of
particle therapy, as well as the higher treatment costs that require appropriate patient selection to ensure a
cost-effective implementation of the techniques in daily practice .
[59]

CONCLUSION
Encouraging results are seen with both photon and particle (SB)RT for the treatment of primary RCC, but
prospective trials are needed with a longer follow-up and sufficient patient numbers. PBT and/or CIRT may
also be important for the treatment of metastatic lesions adjacent to critical organs. CIRT in particular
shows promising results because of its advantages in dose distribution and biological effect.

DECLARATIONS
Acknowledgments
Charlien Berghen is a PhD student at KU Leuven, receiving a grant from “Kom op tegen kanker” (Stand up
to Cancer). Kato Rans is a PhD student at KU Leuven, receiving a grant from “Stichting tegen Kanker”.
Steven Joniau is a senior clinical researcher of the FWO (research foundation flanders). No writing
assistance was utilized in the production of this manuscript.

Authors’ contribution
Literature search, content of the manuscript, data collection, data interpretation, writing of the manuscript:
Berghen C
Critical review of the manuscript, advice on surgical items: Albersen M
Creation of figure 1 and 2, critical review of the manuscript, advice on technical parts of radiation therapy:
De Roover R
Critical review of the manuscript: Rans K