Cone beam CT-based dose accumulation and analysis of delivered dose to the dominant intraprostatic lesion in primary radiotherapy of prostate cancer

Jörg Tamihardja; Sinan Cirsi; Patrick Kessler; Gary Razinskas; Florian Exner; Anne Richter; Bülent Polat; Michael Flentje

doi:10.1186/s13014-021-01933-z

Cone beam CT-based dose accumulation and analysis of delivered dose to the dominant intraprostatic lesion in primary radiotherapy of prostate cancer

Radiat Oncol. 2021 Oct 26;16(1):205. doi: 10.1186/s13014-021-01933-z.

Authors

Jörg Tamihardja¹, Sinan Cirsi², Patrick Kessler², Gary Razinskas², Florian Exner², Anne Richter², Bülent Polat², Michael Flentje²

Affiliations

¹ Department of Radiation Oncology, University of Wuerzburg, Josef-Schneider-Str. 11, 97080, Würzburg, Germany. tamihardja_j@ukw.de.
² Department of Radiation Oncology, University of Wuerzburg, Josef-Schneider-Str. 11, 97080, Würzburg, Germany.

Abstract

Background: Evaluation of delivered dose to the dominant intraprostatic lesion (DIL) for moderately hypofractionated radiotherapy of prostate cancer by cone beam computed tomography (CBCT)-based dose accumulation and target coverage analysis.

Methods: Twenty-three patients with localized prostate cancer treated with moderately hypofractionated prostate radiotherapy with simultaneous integrated boost (SIB) between December 2016 and February 2020 were retrospectively analyzed. Included patients were required to have an identifiable DIL on bi-parametric planning magnetic resonance imaging (MRI). After import into the RayStation treatment planning system and application of a step-wise density override, the fractional doses were computed on each CBCT and were consecutively mapped onto the planning CT via a deformation vector field derived from deformable image registration. Fractional doses were accumulated for all CBCTs and interpolated for missing CBCTs, resulting in the delivered dose for PTV_DIL, PTV_Boost, PTV, and the organs at risk. The location of the index lesions was recorded according to the sector map of the Prostate Imaging Reporting and Data System (PIRADS) Version 2.1. Target coverage of the index lesions was evaluated and stratified for location.

Results: In total, 338 CBCTs were available for analysis. Dose accumulation target coverage of PTV_DIL, PTV_Boost, and PTV was excellent and no cases of underdosage in D_Mean, D_95%, D_02%, and D_98% could be detected. Delivered rectum D_Mean did not significantly differ from the planned dose. Bladder mean D_Mean was higher than planned with 19.4 ± 7.4 Gy versus 18.8 ± 7.5 Gy, p < 0.001. The penile bulb showed a decreased delivered mean D_Mean with 29.1 ± 14.0 Gy versus 29.8 ± 14.4 Gy, p < 0.001. Dorsal DILs, defined as DILs in the posterior medial peripheral zone of the prostate, showed a significantly lower delivered dose with a mean D_Mean difference of 2.2 Gy (95% CI 1.3-3.1 Gy, p < 0.001) compared to ventral lesions.

Conclusions: CBCT-based dose accumulation showed an adequate delivered dose to the dominant intraprostatic lesion and organs at risk within planning limits. Cautious evaluation of the target coverage for index lesions adjacent to the rectum is warranted to avoid underdosage.

Keywords: Adaptive radiotherapy; Deformable image registration; Dominant intraprostatic lesion; Dose accumulation; Prostate Imaging Reporting and Data System; Prostate cancer.

MeSH terms

Aged
Aged, 80 and over
Cone-Beam Computed Tomography / methods*
Humans
Image Processing, Computer-Assisted / methods
Male
Middle Aged
Organs at Risk / radiation effects
Prognosis
Prostatic Neoplasms / diagnostic imaging
Prostatic Neoplasms / pathology*
Prostatic Neoplasms / radiotherapy
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted / methods*
Radiotherapy, Intensity-Modulated / methods*
Retrospective Studies