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. 2016 May 26:11:73.
doi: 10.1186/s13014-016-0646-2.

Integration of (68)Ga-PSMA-PET imaging in planning of primary definitive radiotherapy in prostate cancer: a retrospective study

Sabrina Dewes  1 , Kilian Schiller  2 , Katharina Sauter  2 , Matthias Eiber  2 , Tobias Maurer  2 , Markus Schwaiger  2 , Jürgen E Gschwend  2 , Stephanie E Combs  2 , Gregor Habl  2
Affiliations

Integration of (68)Ga-PSMA-PET imaging in planning of primary definitive radiotherapy in prostate cancer: a retrospective study

Sabrina Dewes et al. Radiat Oncol. .

Abstract

Background: Prostate cancer (PC) is one of the most commonly treated cancer entities with radiation therapy (RT). Risk group-adapted treatment and avoidance of unnecessary toxicities relies primarily on accurate tumor staging. Thus, the introduction of prostate-specific membrane antigen (PSMA) in diagnosis and treatment of PC is a highly interesting development in radiation oncology of urologic tumors. The present work is to evaluate the integration of (68)Ga-PSMA-PET imaging into standard radiation planning of primary definitive treatment of PC and to determine the impact of PSMA imaging on tumor staging.

Methods: The data of 15 patients treated for PC between August 2013 and April 2015 were evaluated. Treatment planning included (68)Ga-PSMA-PET imaging. We analyzed whether the use of PSMA-imaging led to a change of the TNM stage and if it influenced the RT treatment approach or the target volume, due to changes in the gross tumor volume (GTV) or clinical target volume (CTV), in the final treatment plan.

Results: In 53.3 % of the analyzed patients a change occurred in the TNM stage based on (68)Ga-PSMA-PET examination. The RT concept changed in 33.3 % of all patients, leading to relevant changes in the planning target volume. Among these, an additional irradiation of the pelvic lymph drainage due to tracer uptake in lymph nodes was performed in 25 %. Furthermore, boost volumes of PET-positive lymph nodes were added in 80 % of these cases. A down staging due to the (68)Ga-PSMA-PET examination occurred in 13.3 % of all cases.

Conclusions: The integration of (68)Ga-PSMA-PET-imaging into the RT treatment planning process can be useful for detailed target volume planning. The performance of a (68)Ga-PSMA-PET frequently leads to changes in the TNM stage, altering the RT treatment regimen and the target volume. A prospective trial is underway to evaluate the impact of (68)Ga-PSMA-PET based treatment planning on outcome.

Keywords: PSMA-PET; Prostate cancer; Radiation oncology; Radiation therapy; Treatment planning.

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Figures

Fig. 1
Fig. 1
Down-staging by 68Ga-PSMA-PET. Choline-PET-CT (a) with elevated tracer uptake of left iliac lymph node. 68Ga-PSMA-PET (b) does not confirm the questionable involvement seen by Choline-PET-CT
Fig. 2
Fig. 2
Up-staging due to extra capsular spread by 68Ga-PSMA-PET. Questionable extra capsular spread on MRI (a). In 68Ga-PSMA-PET imaging (b) is strong tracer uptake in the bladder and dorsal, as indicated by the arrow, in the extra capsular region, suggesting a strong possibility of its involvement
Fig. 3
Fig. 3
Up-staging due to lymph node involvement by 68Ga-PSMA-PET. Non-suspicious lymph nodes on MRI (a) presacral. In 68Ga-PSMA-PET imaging (b), the lymph node displays enhancement and was thus treated with a higher radiation dose
Fig. 4
Fig. 4
Treatment plan comparison. Basic treatment plan (a), including lymph node irradiation up to 45 Gy à 1.8 Gy. Based on the information obtained by 68Ga-PSMA-PET imaging, PET-positive nodes receive a simultaneous integrated boost to 54 Gy à 2.17 Gy. In comparison with Fig. 4a an example of the dose distribution (b) without the knowledge through the 68Ga-PSMA-PET; the lymph node involvement would not have been suspected and therefore only the prostate itself would have been treated
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