Study on the Focal Boost to the Dominant Intraprostatic Lesions Using Proton Therapy in High-Risk Prostate Cancer Patients with Pelvic Lymph Node Irradiation: Assessing Toxicity Using the Accumulated Dose Fitted NTCP Models

Ong, A.; Knight, K.; Panettieri, V.; Dimmock, M.; Tuan, J.K.L.; Tan, H.Q.; Wright, C.

Abstract

Purpose/Objective(s)
This feasibility study investigated focal boosts to the DILs and assessed the clinical impact based on physical dose-volume (DV) and biological metrics compared to the non-boost plans. The biological parameters were derived from the planned (DP) and accumulated (DA) DV data of 150 patients with high-risk prostate cancer (HR-PCa).

Materials/Methods
Ten HR-PCa patients with multiparametric MRI-defined DILs were investigated. Two intensity-modulated proton therapy (IMPT) plans were generated for each patient: one with and the other without focal boost. Evaluation metrics included DV metrics, TCP for DILs and the remaining prostate tissue, and NTCP for the rectum, bladder, and urethra. Data on TCP, NTCP and DV metrics were analyzed using the Wilcoxon signed-rank test (p<0.05). NTCP from QUANTEC (QT) was also used for comparison. A constant relative biological effectiveness (RBE) of 1.1 was assumed for proton therapy.

Results
A significantly higher Dmean was estimated to the DILs when comparing IMPT-boost (B) to IMPT-non-boost (NB) (IMPT-B: 68.1 GyRBE vs IMPT-NB: 60.8 GyRBE, p<0.01). TCPs for IMPT-B of the prostate-DILs and DILs were higher than for IMPT-NB for α/β of 1.5 and 3 Gy (p<0.001). The Rectal DA-NTCP corresponded to the highest GI toxicity risk of 5.4 % (IMPT-NB) -5.6% (IMPT-B) compared to DP and QT fitted LKB models. The differences in NTCPs were similar for both plans (Table 1).

Conclusion
Focal dose escalation using IMPT can achieve a higher TCP while keeping the NTCP comparable to that for IMPT-NB plans. The Rectal DA-NTCP resulted in a greater predicted GI toxicity compared to that for DP. The inclusion of DA to predict NTCP accounts for interfraction organ motion and could facilitate the reliability of the predicted toxicity while devising dose escalation strategies in patients with HR-PCa. Table 1: TCP and NTCP for the targets and organs at risk.

Citation

Ong, A., Knight, K., Panettieri, V., Dimmock, M., Tuan, J., Tan, H., & Wright, C. (in press). Study on the Focal Boost to the Dominant Intraprostatic Lesions Using Proton Therapy in High-Risk Prostate Cancer Patients with Pelvic Lymph Node Irradiation: Assessing Toxicity Using the Accumulated Dose Fitted NTCP Models. International Journal of Radiation Oncology - Biology - Physics, 120(2), Article e571. https://doi.org/10.1016/j.ijrobp.2024.07.1262

• Journal Article Type: Article
• Acceptance Date: Sep 27, 2024
• Online Publication Date: Sep 27, 2024
• Deposit Date: Dec 13, 2024
• Journal: International Journal of Radiation Oncology*Biology*Physics
• Print ISSN: 0360-3016
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 120
• Issue: 2
• Article Number: e571
• DOI: https://doi.org/10.1016/j.ijrobp.2024.07.1262
• Public URL: https://keele-repository.worktribe.com/output/948520
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S0360301624020248?via%3Dihub