Abstract
BackgroundThis is the final report of a prospective phase I study which evaluated the feasibility, toxicities, and biochemical control in prostate cancer patients treated with a hypofractionated boost utilizing a fiducial marker-based daily image guidance strategy and small patient-specific PTV margins.MethodsLow- and intermediate-risk prostate cancer patients underwent transperineal ultrasound-guided implantation of three gold fiducial markers and were treated with three-dimensional conformal radiotherapy to 42 Gy (2 Gy/day). During the first nine fractions of treatment, pre- and post-treatment electronic portal imaging was performed to calculate intrafraction prostate motion. Patient-specific PTV margins were derived and a 30 Gy (3 Gy/day) intensity modulated radiotherapy boost was delivered (Total dose = 72 Gy in 31 fractions; EQD2 = 81 Gy, α/β = 1.4).ResultsThirty-three patients completed treatment and were followed for a median of 7.2 years (range, 1.2 – 9.5). Seven patients (21%) developed Radiation Therapy Oncology Group (RTOG) late grade 2 GI toxicity and 1 patient (3%) developed late grade 2 GU toxicity. No patients developed late grade 3 GI or GU toxicity. To date, nine patients developed PSA relapse according to the Phoenix criteria. The actuarial five, seven and nine year biochemical control (BC) rates were 87% (95% confidence interval: 69–95), 77% (95% confidence interval: 56–89) and 66% (95% confidence interval: 42–82).ConclusionsOur study demonstrates that the use of prostate fiducial markers in combination with a daily online image guidance protocol permits reduced, patient-specific PTV margins in a hypofractionated treatment scheme. This treatment planning and delivery strategy was well tolerated in the intermediate time frame. The use of very small PTV margins did not result in excessive failures when compared to other radiation regimens of similar radiobiological intensity.
Highlights
This is the final report of a prospective phase I study which evaluated the feasibility, toxicities, and biochemical control in prostate cancer patients treated with a hypofractionated boost utilizing a fiducial marker-based daily image guidance strategy and small patient-specific planning target volume (PTV) margins
The essential elements to safely deliver hypofractionated radiotherapy include the utilization of a daily image-guidance strategy and quantifying the geometric uncertainties associated with the treatment technique to derive the optimal planning target volume (PTV) margins to maximize tumour control while limiting late normal tissue toxicity. For this prospective phase I study, we previously presented the feasibility of a fiducial marker-based daily image guidance strategy to deliver a hypofractionated boost to low and intermediate risk prostate cancer patients
The average PTV margin used during the intensity modulated radiation (IMRT) hypofractionated boost was 4 mm in the AP direction, 3 mm in SI direction, and 3 mm in the RL direction [21]
Summary
This is the final report of a prospective phase I study which evaluated the feasibility, toxicities, and biochemical control in prostate cancer patients treated with a hypofractionated boost utilizing a fiducial marker-based daily image guidance strategy and small patient-specific PTV margins. Randomized trials with dose-escalated radiotherapy (74 – 80 Gy) demonstrate an improvement in biochemical control compared to conventional treatment regimens (64 – 70 Gy) [1,2,3,4,5,6,7,8,9]. There has been rising interest in using hypofractionated radiotherapy (higher doses per fraction with fewer fractions) to capitalize on the sensitivity of prostate tumours to high fraction sizes while maintaining similar or lowering rates of late normal tissue toxicity. There is the potential for lower costs and improved patient convenience with a shorter course of treatment [17]
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