¹¹C-Choline PET/CT as a guide to radiation treatment planning of lymph-node relapses in prostate cancer patients

To evaluate, in prostate cancer (PCa) patients the potential of ¹¹C-choline PET/CT as a guide to helical tomotherapy (HTT) of lymph-node (LN) relapses with simultaneous integrated boost (SIB). The efficacy and feasibility of HTT in terms of acute toxicity were assessed.

We enrolled 83 PCa patients (mean age 68 years, range 51 – 82 years) with biochemical recurrence after radical primary treatment (mean serum PSA 7.61 ng/ml, range 0.37 – 187.00 ng/ml; PSA₀) who showed pathological findings on ¹¹C-choline PET/CT only at the LN site. ¹¹C-Choline PET/CT was performed for restaging and then for radiation treatment planning (PET/CT₀). Of the 83 patients, 8 experienced further LN relapse, of whom 5 were retreated once and 3 were retreated twice (total 94 radiotherapy treatments). All pelvic and/or abdominal LNs positive on PET/CT₀ were treated with high doses using SIB. Doses were in the range 36 – 74 Gy administered in 28 fractions. After the end of HTT (mean 83 days, range 16 – 365 days), serum PSA was measured in all patients (PSA₁) and compared with PSA₀ to evaluate early biochemical response. In 47 patients PET/CT was repeated (PET/CT₁) to assess metabolic responses at the treated areas. Toxicity criteria of the Radiation Therapy Oncology Group (RTOG) were used to assess acute toxicity.

PET/CT₀ revealed pathological LNs in the pelvis in 49 patients, pathological LNs in the abdomen in 15 patients pathological LNs in both the pelvis and abdomen in 18 patients, and pathological LNs in the pelvis or abdomen and other sites in 12 patients. All these sites were treated with HTT. With respect to PSA₀, PSA₁ (mean 6.28 ng/ml, range 0.00 – 220.46 ng/ml) showed a complete biochemical response after 66 of the 94 HTT treatments, a partial response after 12 treatments, stable disease after 1 treatment and progression of disease after 15 treatments. Of the 47 patients receiving PET/CT₁, 20 showed a complete metabolic response at the treated area, 22 a partial metabolic response, 3 progression of disease and 2 stable disease. HTT with SIB was well tolerated in all patients. Grade 3 acute toxicity in the genitourinary tract was observed in two patients.

¹¹C-Choline PET/CT is a valuable tool for planning and monitoring HTT in LN relapse after primary treatment. High-dose hypofractionated ¹¹C-choline PET/CT-guided HTT with SIB is well tolerated and is associated with a high early biochemical response rate.