Proton versus photon therapy for high-risk prostate cancer with dose escalation of dominant intraprostatic lesions: a preliminary planning study

Ashley Li Kuan Ong; Kellie Knight; Vanessa Panettieri; Mathew Dimmock; Jeffrey Kit Loong Tuan; Hong Qi Tan; Caroline Wright

doi:10.3389/fonc.2023.1241711

Proton versus photon therapy for high-risk prostate cancer with dose escalation of dominant intraprostatic lesions: a preliminary planning study

Front Oncol. 2023 Nov 8:13:1241711. doi: 10.3389/fonc.2023.1241711. eCollection 2023.

Authors

Ashley Li Kuan Ong^{1

2}, Kellie Knight², Vanessa Panettieri^{2

3

4

5}, Mathew Dimmock^{2

6}, Jeffrey Kit Loong Tuan¹, Hong Qi Tan¹, Caroline Wright²

Affiliations

¹ Division of Radiation Oncology, National Cancer Centre Singapore, Singapore, Singapore.
² Department of Medical Imaging and Radiation Sciences, Monash University, Clayton, VIC, Australia.
³ Department of Physical Sciences, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia.
⁴ Sir Peter MacCallum Department of Oncology, The University of Melbourne, Victoria, VIC, Australia.
⁵ Central Clinical School, Monash University, Melbourne, VIC, Australia.
⁶ School of Allied Health Professions, Keele University, Staffordshire, United Kingdom.

Abstract

Background and purpose: This study aimed to investigate the feasibility of safe-dose escalation to dominant intraprostatic lesions (DILs) and assess the clinical impact using dose-volume (DV) and biological metrics in photon and proton therapy. Biological parameters defined as late grade ≥ 2 gastrointestinal (GI) and genitourinary (GU) derived from planned (D _P) and accumulated dose (D _A) were utilized.

Materials and methods: In total, 10 patients with high-risk prostate cancer with multiparametric MRI-defined DILs were investigated. Each patient had two plans with a focal boost to the DILs using intensity-modulated proton therapy (IMPT) and volumetric-modulated arc therapy (VMAT). Plans were optimized to obtain DIL coverage while respecting the mandatory organ-at-risk constraints. For the planning evaluation, DV metrics, tumor control probability (TCP) for the DILs and whole prostate excluding the DILs (prostate-DILs), and normal tissue complication probability (NTCP) for the rectum and bladder were calculated. Wilcoxon signed-rank test was used for analyzing TCP and NTCP data.

Results: IMPT achieved a higher Dmean for the DILs compared to VMAT (IMPT: 68.1 GyRBE vs. VMAT: 66.6 Gy, p < 0.05). Intermediate-high rectal and bladder doses were lower for IMPT (p < 0.05), while the high-dose region (V60 Gy) remained comparable. IMPT-TCP for prostate-DIL were higher compared to VMAT (IMPT: 86%; α/β = 3, 94.3%; α/β = 1.5 vs. VMAT: 84.7%; α/β = 3, 93.9%; α/β = 1.5, p < 0.05). Likewise, IMPT obtained a moderately higher DIL TCP (IMPT: 97%; α/β = 3, 99.3%; α/β = 1.5 vs. VMAT: 95.9%; α/β = 3, 98.9%; α/β = 1.5, p < 0.05). Rectal D _A-NTCP displayed the highest GI toxicity risk at 5.6%, and IMPT has a lower GI toxicity risk compared to VMAT-predicted Quantec-NTCP (p < 0.05). Bladder D _P-NTCP projected a higher GU toxicity than D _A-NTCP, with VMAT having the highest risk (p < 0.05).

Conclusion: Dose escalation using IMPT is able to achieve a high TCP for the DILs, with the lowest rectal and bladder DV doses at the intermediate-high-dose range. The reduction in physical dose was translated into a lower NTCP (p < 0.05) for the bladder, although rectal toxicity remained equivalent.

Keywords: biological modeling; high-risk prostate cancer; intraprostatic lesions; magnetic resonance imaging; proton therapy.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This work was funded by the AM/ACP-Designated Philanthropic Fund award (Research Program of Proton Physics; Project Ref: 08/FY2021/EX/12-A42).