Toward planning target volume margin reduction for the prostate using intrafraction motion correction with online kV imaging and automatic detection of implanted gold seeds.

PURPOSE: The imaging application Auto Beam Hold (ABH) allows for the online analysis of 2-dimensional kV images acquired during treatment. ABH can automatically detect fiducial markers and initiate a beam interrupt. In this study, we investigate the practical use and results of this intrafraction monitoring tool for patients with prostate cancer who have implanted gold seeds treated with a RapidArc technique. METHODS AND MATERIALS: A total of 105 patients were included. For setup, the seeds were lined up using 2 orthogonal 2-dimensional kV images. After the setup procedure, ABH was applied at an interval of 3 seconds. The software requires a maximum-allowed deviation to be defined for each seed, which is referred to as a deviation limit (DL). Online, the ABH application evaluates the position of the seeds and indicates for each seed whether or not it exceeds the DL. Patients were divided in 3 groups. For the first group ABH was used with the DL at 6 mm, which corresponds to the planning target volume (PTV) margin. For the second group, the DL was set at 5 mm with an unchanged PTV margin of 6 mm. For the third group, the PTV margin was reduced to 5 mm with a DL of 5 mm. Offline, we performed an analysis of the number of beam stops and resulting re-setups. RESULTS: ABH initiated a beam interrupt 223 times (13%) during a total of 1736 sessions. By decreasing the DL from 6 mm to 5 mm, the amount of workload for re-setups increased from 6% (group 1) to 14% (groups 2 and 3). Re-setup, 3-dimensional shifts larger than the PTV margin were found in 44%, 35%, and 45% for groups 1,2, and 3, respectively. CONCLUSIONS: Intrafraction imaging of prostate position during treatment using automatic detection of implanted gold seeds was successfully implemented. PTV margins were safely reduced from 6mm to 5mm without a substantial increase in workload.

Prognostic Value of [18F]-Fluoromethylcholine Positron Emission Tomography/Computed Tomography Before Stereotactic Body Radiation Therapy for Oligometastatic Prostate Cancer.

PURPOSE: To investigate the predictive value of [18F]-fluoromethylcholine positron emission tomography/computed tomography (PET/CT)-derived parameters on progression-free survival (PFS) in oligometastatic prostate cancer patients treated with stereotactic body radiation therapy (SBRT). METHODS AND MATERIALS: In [18F]-fluoromethylcholine PET/CT scans of 40 consecutive patients with ≤4 metachronous metastases treated with SBRT we retrospectively measured the number of metastases, standardized uptake values (SUVmean, SUVmax, SUVpeak), metabolically active tumor volume (MATV), and total lesion choline uptake. Partial-volume correction was applied using the iterative deconvolution Lucy-Richardson algorithm. RESULTS: Thirty-seven lymph node and 13 bone metastases were treated with SBRT. Thirty-three patients (82.5%) had 1 lesion, 4 (10%) had 2 lesions, and 3 (7.5%) had 3 lesions. After a median follow-up of 32.6 months (interquartile range, 35.5 months), the median PFS was 11.5 months (95% confidence interval 8.4-14.6 months). Having more than a single metastasis was a significant prognostic factor (hazard ratio 2.74; P = .03), and there was a trend in risk of progression for large MATV (hazard ratio 1.86; P = .10). No SUV or total lesion choline uptake was significantly predictive for PFS, regardless of partial-volume correction. All PET semiquantitative parameters were significantly correlated with each other (P ≤ .013). CONCLUSIONS: The number of choline-avid metastases was a significant prognostic factor for progression after [18F]-fluormethylcholine PET/CT-guided SBRT for recurrent oligometastatic prostate cancer, and there seemed to be a trend in risk of progression for patients with large MATVs. The lesional level of [18F]-fluoromethylcholine uptake was not prognostic for progression.

Benefits of Using Stereotactic Body Radiotherapy in Patients With Metachronous Oligometastases of Hormone-Sensitive Prostate Cancer Detected by [18F]fluoromethylcholine PET/CT.

INTRODUCTION: For patients with oligometastatic recurrence of prostate cancer (PC), stereotactic body radiation therapy (SBRT) represents an attractive treatment option, as it is safe without major side effects. The aim of this study was to investigate the impact of SBRT in delaying the start of androgen deprivation therapy (ADT). PATIENTS AND METHODS: Forty-three patients treated with SBRT for oligometastatic recurrence (< 5 metastases) of hormone-sensitive PC, defined with [18F]fluoromethylcholine positron emission tomography/computed tomography were included. As a control group, 20 patients with oligometastatic disease not treated with SBRT were identified from another hospital. Data were collected retrospectively. RESULTS: A post-SBRT prostate-specific antigen (PSA) response was seen in 29 (67.4%) of 43 patients. Median ADT-free survival (ADT-FS) was 15.6 months (95% confidence interval [CI], 11.7-19.5) for the whole group, and 25.7 months (95% CI, 9.0-42.4) for patients with a PSA response. Seven patients were treated with a second course of SBRT because of oligometastatic disease recurrence; the ADT-FS in this group was 32.1 months (95% CI, 7.8-56.5). Compared with the control group, the ADT-FS from first diagnosis of metastasis was significantly longer, with 17.3 (95% CI, 13.7-20.9) months versus 4.19 months (95% CI, 0.0-9.0), P < .001. Also, time between diagnosis of the metastasis until progression of disease during ADT use (castration resistance) was longer for the SBRT-treated patients (mean 66.6, 95% CI, 53.5-79.8, vs. 36.41, 95% CI, 26.0-46.8 months, P = .020). There were no grade III or IV adverse events reported. CONCLUSION: SBRT can safely and effectively be used to postpone ADT in appropriately selected patients with oligometastatic recurrence of PC.