68 Ga-PSMA-PET/CT imaging of localized primary prostate cancer patients for intensity modulated radiation therapy treatment planning with integrated boost

The purpose of our study was to show the feasibility and potential benefits of using68Ga-PSMA-PET/CT imaging for radiation therapy treatment planning of patients with primary prostate cancer using either integrated boost on the PET-positive volume or localized treatment of the PET-positive volume. The potential gain of such an approach, the improvement of tumor control, and reduction of the dose to organs-at-risk at the same time was analyzed using the QUANTEC biological model.

Twenty-one prostate cancer patients (70 years average) without previous local therapy received68Ga-PSMA-PET/CT imaging. Organs-at-risk and standard prostate target volumes were manually defined on the obtained datasets. A PET active volume (PTV_PET) was segmented with a 40% of the maximum activity uptake in the lesion as threshold followed by manual adaption. Five different treatment plan variations were calculated for each patient. Analysis of derived treatment plans was done according to QUANTEC with in-house developed software. Tumor control probability (TCP) and normal tissue complication probability (NTCP) was calculated for all plan variations.

Comparing the conventional plans to the plans with integrated boost and plans just treating the PET-positive tumor volume, we found that TCP increased to (95.2 ± 0.5%) for an integrated boost with 75.6 Gy, (98.1 ± 0.3%) for an integrated boost with 80 Gy, (94.7 ± 0.8%) for treatment of PET-positive volume with 75 Gy, and to (99.4 ± 0.1%) for treating PET-positive volume with 95 Gy (all p < 0.0001). For the integrated boost with 80 Gy, a significant increase of the median NTCP of the rectum was found, for all other plans no statistical significant increase in the NTCP neither of the rectum nor the bladder was found.

Our study demonstrates that the use of68Ga-PSMA-PET/CT image information allows for more individualized prostate treatment planning. TCP values of identified active tumor volumes were increased, while rectum and bladder NTCP values either remained the same or were even lower. However, further studies need to clarify the clinical benefit for the patients applying these techniques.

European journal of nuclear medicine and molecular imaging. 2018 Feb 21 [Epub ahead of print]

Lena Thomas, Steffi Kantz, Arthur Hung, Debra Monaco, Florian C Gaertner, Markus Essler, Holger Strunk, Wolfram Laub, Ralph A Bundschuh

Klinik und Poliklinik für Nuklearmedizin, Universitätsklinikum Bonn, Sigmund-Freud-Str. 25, 53127, Bonn, Germany. ., LMU Munich, Department of Radiation Oncology, Munich, Germany., Department of Radiation Medicine, Oregon Health and Science University, Portland, OR, USA., Klinik und Poliklinik für Nuklearmedizin, Universitätsklinikum Bonn, Sigmund-Freud-Str. 25, 53127, Bonn, Germany., Radiologische Klinik, Universitätsklinikum Bonn, Bonn, Germany., Department of Radiation Oncology and Molecular Radiation Sciences, The Johns Hopkins University School of Medicine, Baltimore, MD, USA.

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