Optimizing the dose-averaged linear energy transfer for the dominant intraprostatic lesions in high-risk localized prostate cancer patients

Abstract

Background and purpose

Radiotherapy for localized prostate cancer often targets the entire prostate with a uniform dose despite the presence of high-risk dominant intraprostatic lesions (DILs). This study investigated the feasibility of focal dose-averaged linear energy transfer (LET_d) boost for prostate carbon-ion radiotherapy to deposit higher LET_d to DILs while ensuring desired relative biological effectiveness weighted dose coverage to targets and sparing organs at risk (OARs).

Materials and methods

A retrospective planning study was conducted on 15 localized prostate cancer cases. The DILs were identified on multiparametric MRI and used to define the boost target (PTV_boost). Two treatment plans were designed for each patient: 1) conventional plan optimized by the single-field uniform dose technique, and 2) boost plan optimized by the multifield optimization and LET painting technique, to achieve LET_d boost within the PTV_boost. Dose and LET_d metrics of the targets and OARs were compared between the two plans.

Results

Compared to the conventional plans, the boost plans delivered clinically acceptable dose coverage (D_90% and D_50%) to the target (PTV2) within 1% differences while significantly increasing the minimum LET_d by 16 ∼ 24 keV/μm for the PTV_boost (63.9 ± 2.8 vs. 44.0 ± 1.3 keV/μm, p < 0.001). Furthermore, these improvements were consistent across all cases, irrespective of their anatomical features, including the boost volume’s size, location, and shape.

Conclusion

Focal LET_d boost was a feasible strategy for prostate carbon-ion radiotherapy. This investigation demonstrated its superiority in delivering LET_d boost without depending on tumor location and volume across different cases.