Patterns of failure after radical prostatectomy in prostate cancer - implications for radiation therapy planning after Ga-PSMA-PET imaging.

BACKGROUND

Salvage radiotherapy (SRT) after radical prostatectomy (RPE) and lymphadenectomy (LAE) is the appropriate radiotherapy option for patients with persistent/ recurrent prostate cancer (PC). Ga-PSMA-PET imaging has been shown to accurately detect PC lesions in a primary setting as well as for local recurrence or for lymph node (LN) metastases.

OBJECTIVE

In this study we evaluated the patterns of recurrence after RPE in patients with PC, putting a highlight on the differentiation between sites that would have been covered by a standard radiation therapy (RT) field in consensus after the RTOG consensus and others that would have not.

METHODS AND MATERIALS

Thirty-one out of 83 patients (37%) with high-risk PC were the subject of our study. Information from Ga-PSMA-PET imaging was used to individualize treatment plans to include suspicious lesions as well as possibly boost sites with tracer uptake in LN or the prostate bed. For evaluation, Ga-PSMA-PET-positive LN were contoured in a patient dataset with a standard lymph drainage (RTOG consensus on CTV definition of pelvic lymph nodes) radiation field depicting color-coded nodes that would have been infield or outfield of that standard lymph drainage field and thereby visualizing typical patterns of failure of a "blind" radiation therapy after RPE and LAE.

RESULTS

Compared to negative conventional imaging (CT/MRI), lesions suspicious for PC were detected in 27/31 cases (87.1%) by Ga-PSMA-PET imaging, which resulted in changes to the radiation concept. There were 16/31 patients (51.6%) that received a simultaneous integrated boost (SIB) to a subarea of the prostate bed (in only three cases this dose escalation would have been planned without the additional knowledge of Ga-PSMA-PET imaging) and 18/31 (58.1%) to uncommon (namely presacral, paravesical, pararectal, preacetabular and obturatoric) LN sites. Furthermore, 14 patients (45.2%) had a changed TNM staging result by means of Ga-PSMA-PET imaging.

CONCLUSION

Compared to conventional CT or MRI staging, Ga-PSMA-PET imaging detects more PC lesions and, thus, significantly influences radiation planning in recurrent prostate cancer patients enabling individually tailored treatment.