Focal salvage treatment for radiorecurrent prostate cancer: A magnetic resonance-guided stereotactic body radiotherapy versus high-dose-rate brachytherapy planning study

Abstract

Background and Purpose: Magnetic resonance imaging (MRI)-guided focal salvage high-dose-rate brachytherapy (FS-HDR-BT) is one of the treatment options for radiorecurrent localized prostate cancer. However, due to the invasive nature of the treatment, not all patients are eligible. Magnetic resonance linear accelerator (MR-Linac) systems open up new treatment possibilities and could potentially replace FS-HDR-BT treatment. We conducted a planning study to investigate the feasibility of delivering a single 19 Gy dose to the recurrent lesion using a 1.5 Tesla MR-Linac system. Materials and Methods: Thirty patients who underwent FS-HDR-BT were included. The clinical target volume (CTV) encompassed the visible lesion plus a 5 mm margin. Treatment plans were created for a 1.5 Tesla MR-Linac system using a 1 mm planning target volume (PTV) margin. A dose of 19 Gy was prescribed to ≥ 95% of the PTV. In case this target could not be reached, i.e. when organs-at-risk (OAR) constraints were violated, a dose of ≥ 17 Gy to ≥ 90% of the PTV was accepted. MR-Linac plans were compared to clinical FS-HDR-BT plans. Results: Target dose coverage was achieved in 14/30 (47%) FS-HDR-BT plans and 17/30 (57%) MR-Linac plans, with comparable median D95% and D90%. In FS-HDR-BT plans, a larger volume reached ≥ 150% of the prescribed dose. Urethra D10%, rectum D1cm 3 , and rectum D2cm 3 were lower in the FS-HDR-BT plans, while bladder dose was comparable for both modalities. Conclusion: Single fraction treatment of recurrent prostate cancer lesions may be feasible using stereotactic body radiotherapy (SBRT) on a MR-Linac system.

The value of brachytherapy in the age of advanced external beam radiotherapy: a review of the literature in terms of dosimetry

“…In the CK plans with the synchrony tracking system, the CTV–PTV margin varied between 0 and 5 mm. MLC tracking on conventional linear accelerators was used in three studies [ 45 , 57 , 61 ]. A margin of 3 mm was added to the CTV for lung and 7 mm for prostate [ 45 , 57 ].…”

“…A margin of 3 mm was added to the CTV for lung and 7 mm for prostate [ 45 , 57 ]. Using an MR-linac with an online re-planning feature, only a 1‑mm margin around the CTV was applied [ 61 ].…”

“…The hips and sigmoid were best protected by HDR-BT. In a feasibility study, Willigenburg et al [61] created comparative SBRT treatment plans on an MR-linac system for 30 patients treated with focal salvage HDR-BT. Since intrafractional prostate motion detection and online replanning is available with the MR-linac, only a 1-mm CTV-PTV margin was used in the SBRT plans.…”

Intrafraction motion tracking for MR-Linac prostate radiotherapy

“…Furthermore, a planning study by Willigenburg et al [39] showed that single fraction 19 Gy treatment of recurrent prostate cancer may be feasible using the MR-Linac. In this study, 30 patients were included using a 1 mm PTV margin and target dose coverage on the MR-Linac plans was achieved in 57% of the patients.…”

“…MR-Linac is feasible if combined with real-time motion mitigation strategies. In addition, Willigenburg et al [39] has shown the feasibility of single fraction 19 Gy MR-Linac treatment for recurrent prostate cancer. The benefit of the MR-Linac in this case may be that ultra-hypofractionation can be delivered without any invasive procedure (fiducial markers, bladder catheter, rectal probe, balloon and/or rectal spacer).…”