Abstract
Background: Magnetic resonance (MR)-fusion contouring is the standard of care in prostate stereotactic body radiotherapy (SBRT) for target volume localisation. However, the planning computerised tomography (CT) scan continues to be used for dose calculation and treatment planning and verification. Discrepancies between the planning MR and CT scans may negate the benefits of MR-fusion contouring and it adds a significant resource burden. We aimed to determine whether CT-only contouring resulted in a dosimetric detriment compared with MR-fusion contouring in prostate SBRT planning. Methods: We retrospectively compared target volumes and SBRT plans for 20 patients treated clinically with MR-fusion contouring (standard of care) with those produced by re-contouring using CT data only. Dose was 36.25 Gy in 5 fractions. CT-only contouring was done on two occasions blind to MR data and reviewed by a separate observer. Primary outcome was the difference in rectal volume receiving 36 Gy or above. Results: Absolute target volumes were similar: 63.5 cc (SD ± 27.9) versus 63.2 (SD ± 26.5), Dice coefficient 0.86 (SD ± 0.04). Mean difference in apex superior-inferior position was 1.1 (SD ± 3.5; CI: −0.4–2.6). Small dosimetric differences in favour of CT-only contours were seen, with the mean rectal V36 Gy 0.3 cc (95% CI: 0.1–0.5) lower for CT-only contouring. Conclusions: Prostate SBRT can be successfully planned without MR-fusion contouring. Consideration can be given to omitting MR-fusion from the prostate SBRT workflow, provided reference to diagnostic MR imaging is available. Development of MR-only work flow is a key research priority to gain access to the anatomical fidelity of MR imaging.
Highlights
Stereotactic body radiotherapy (SBRT) is a treatment option for localised prostate cancer which uses highly conformal dose distributions and precise image guidance to deliver treatment in a few large fractions [1]
Magnetic resonance (MR)-fusion contouring describes the process by which planning MR and computerised tomography (CT) data are fused based on prostate position
We retrospectively compared prostate target volumes and stereotactic body radiotherapy (SBRT) plans for patients treated clinically with MR-fusion contouring with those produced by re-contouring using CT data only
Summary
Stereotactic body radiotherapy (SBRT) is a treatment option for localised prostate cancer which uses highly conformal dose distributions and precise image guidance to deliver treatment in a few large fractions [1]. MR-fusion contouring describes the process by which planning MR and CT data are fused based on prostate position. Physicians use information from both data sets to contour a target volume. Magnetic resonance (MR)-fusion contouring is the standard of care in prostate stereotactic body radiotherapy (SBRT) for target volume localisation. CT-only contouring resulted in a dosimetric detriment compared with MR-fusion contouring in prostate SBRT planning. Methods: We retrospectively compared target volumes and SBRT plans for 20 patients treated clinically with MR-fusion contouring (standard of care) with those produced by re-contouring using CT data only. Development of MR-only work flow is a key research priority to gain access to the anatomical fidelity of MR imaging
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