Potential Impact of ⁶⁸Ga-PSMA-11 PET/CT on the Planning of Definitive Radiation Therapy for Prostate Cancer

Abstract

Standard-of-care imaging for initial staging of prostate cancer (PCa) underestimates disease burden. Prostate-specific membrane antigen (PSMA) PET/CT detects PCa metastasis with superior accuracy, having a potential impact on the planning of definitive radiation therapy (RT) for nonmetastatic PCa. Our objectives were to determine how often definitive RT planning based on standard target volumes covers Ga-PSMA-11 PET/CT-defined disease and to assess the potential impact ofGa-PSMA-11 PET/CT on definitive RT planning. This was a post hoc analysis of an intention-to-treat population of 73 patients with localized PCa without prior local therapy who underwentGa-PSMA PET/CT for initial staging as part of an investigational new drug trial. Eleven of the 73 were intermediate-risk (15%), 33 were high-risk (45%), 22 were very-high-risk (30%), and 7 were N1 (9.5%). Clinical target volumes (CTVs), which included the prostate, seminal vesicles, and (in accord with the Radiation Therapy Oncology Group consensus guidelines) pelvic lymph nodes (LNs), were contoured on the CT portion of the PET/CT images by a radiation oncologist masked to the PET findings. Ga-PSMA-11 PET/CT images were analyzed by a nuclear medicine physician.Ga-PSMA-11-positive lesions not covered by planning volumes based on the CTVs were considered to have a major potential impact on treatment planning. All patients had one or moreGa-PSMA-11-positive primary prostate lesions. Twenty-five (34%) and 7 (9.5%) of the 73 patients had Ga-PSMA-11-positive pelvic LN and distant metastases, respectively. The sites of LN metastases in decreasing order of frequency were external iliac (20.5%), common iliac (13.5%), internal iliac (12.5%) obturator (12.5%), perirectal (4%), abdominal (4%), upper diaphragm (4%), and presacral (1.5%). The median size of the LN lesions was 6 mm (range, 4-24 mm). RT planning based on the CTVs covered 69 (94.5%) of the 73 primary lesions and 20 (80%) of the 25 pelvic LN lesions, on a per-patient analysis. Ga-PSMA-11 PET/CT had a major impact on intended definitive RT planning for PCa in 12 (16.5%) of the 73 patients whose RT fields covered the prostate, seminal vesicles, and pelvic LNs and in 25 (37%) of the 66 patients whose RT fields covered the prostate and seminal vesicles but not the pelvic LNs.

Prospective, Multisite, International Comparison of 18F-Fluoromethylcholine PET/CT, Multiparametric MRI, and 68Ga-HBED-CC PSMA-11 PET/CT in Men with High-Risk Features and Biochemical Failure After Radical Prostatectomy: Clinical Performance and Patient Outcomes

“…With the exception of the recent Australian guidelines (8), most currently published guidelines do not recommend imaging for BCR at PSA levels of less than 1.0 ng/mL (7). This stance has been challenged recently, with several studies reporting high detection rates for recurrent disease in men with BCR at low PSA levels using PSMA PET (9)(10)(11)(12)(13)(14).The present study confirmed the high detection rates for disease recurrence using PSMA both in the PF and distantly. Consistent with the previous comparisons of 18 F-FCH and PSMA PET, the number of extra fossa lesions visualized on PSMA was higher than that visualized on 18 F-FCH in men who underwent imaging with both modalities (15,16).…”

Impact of 68Ga-PSMA PET/CT on the Radiotherapeutic Approach to Prostate Cancer in Comparison to CT: A Retrospective Analysis

“…Although patients before definitive radiotherapy constituted the smallest subgroup of the present cohort, there was a modest change in management (36%) compared with postoperative patients. This finding is in accordance with the few existing analyses on 68 Ga-PSMA PET/CT in therapynaïve patients before radiotherapy (19)(20)(21). In a recent analysis by Calais et al based on 73 patients with localized untreated prostate cancer, a major impact of 68 Ga-PSMA PET/CT was noted for 16.5% (12/73) of patients with intended irradiation of prostate, seminal vesicles, and pelvic lymphatic pathways and 37% of patients when radiotherapy fields covered prostate and seminal vesicles only (19).…”

“…This finding is in accordance with the few existing analyses on 68 Ga-PSMA PET/CT in therapynaïve patients before radiotherapy (19)(20)(21). In a recent analysis by Calais et al based on 73 patients with localized untreated prostate cancer, a major impact of 68 Ga-PSMA PET/CT was noted for 16.5% (12/73) of patients with intended irradiation of prostate, seminal vesicles, and pelvic lymphatic pathways and 37% of patients when radiotherapy fields covered prostate and seminal vesicles only (19). Likewise, Koerber et al presented data on the impact of 68 Ga-PSMA PET/CT on radiotherapy planning in 50 otherwise untreated prostate cancer patients (21).…”

“…Therefore, 68 Ga-PSMA PET/CT might further improve oncologic outcome by modifying target volume delineation and intended overall doses. There is increasing evidence that 68 Ga-PSMA PET/CT might have a major impact on radiotherapy planning in the primary (19)(20)(21) and postoperative settings (21)(22)(23)(24)(25)(26)(27)(28)(29)(30).…”

Current and potential future role of PSMA-PET in patients with castration-resistant prostate cancer

“…Encouraging results of local or metastasis-directed therapy in patients with hormone-naïve oligometastatic recurrent PC [35,36] raise the question if oligoprogressive mCRPC patients may also benefit from local and/or metastasis-directed therapy [37][38][39]…”