The Role of Multiparametric Magnetic Resonance in Volumetric Modulated Arc Radiation Therapy Planning for Prostate Cancer Recurrence After Radical Prostatectomy: A Pilot Study

Abstract

Background and PurposeVolumetric modulated arc radiotherapy (RT) has become pivotal in the treatment of prostate cancer recurrence (RPC) to optimize dose distribution and minimize toxicity, thanks to the high-precision delineation of prostate bed contours and organs at risk (OARs) under multiparametric magnetic resonance (mpMRI) guidance. We aimed to assess the role of pre-treatment mpMRI in ensuring target volume coverage and normal tissue sparing.Material and MethodsPatients with post-prostatectomy RPC eligible for salvage RT were prospectively recruited to this pilot study. Image registration between planning CT scan and T2w pre-treatment mpMRI was performed. Two sets of volumes were outlined, and DWI images/ADC maps were used to facilitate precise gross tumor volume (GTV) delineation on morphological MRI scans. Two rival plans (mpMRI-based or not) were drawn up.ResultsTen patients with evidence of RPC after prostatectomy were eligible. Preliminary data showed lower mpMRI-based clinical target volumes than CT-based RT planning (p = 0.0003): median volume difference 17.5 cm3. There were no differences in the boost volume coverage nor the dose delivered to the femoral heads and penile bulb, but median rectal and bladder V70Gy was 4% less (p = 0.005 and p = 0.210, respectively) for mpMRI-based segmentation.ConclusionsmpMRI provides high-precision target delineation and improves the accuracy of RT planning for post-prostatectomy RPC, ensures better volume coverage with better OARs sparing and allows non-homogeneous dose distribution, with an aggressive dose escalation to the GTV. Randomized phase III trials and wider datasets are needed to fully assess the role of mpMRI in optimizing therapeutic strategies.

Linac-based stereotactic salvage reirradiation for intraprostatic prostate cancer recurrence: toxicity and outcomes

“…Second, the relatively small PTV size obtained with the help of pretreatment mpMRI for target volume delineation. A pilot study by Sardaro and colleagues in 10 patients with postprostatectomy recurrent PC recently showed significantly lower mpMRI-based clinical target volumes than CT-based RT planning (p = 0.0003), with better OAR sparing and contemporary nonhomogeneous dose distribution, leading to an eventually aggressive dose escalation to the GTV [70]. The better soft tissue contrast provided by MRI and the advent of functional MR sequences may improve the definition of the prostate boundaries and pelvic OAR anatomy, the precise location of intraprostatic lesions, and thus the accuracy and safety of ablative, high-precision radiation treatments with linac, even in the setting of reirradiation [71][72][73].…”

Quantitative ADC: An Additional Tool in the Evaluation of Prostate Cancer?

“…MRI is well-known to provide better soft tissue contrast than conventional morphological imaging techniques such as ultrasound or computed tomography (CT). For this reason, MRI may ensure a proper definition of the anatomy of the pelvic organs and of the prostate and prostate bed boundaries [ 35 ].…”

Targeting Local Recurrence After Surgery With MRI Imaging for Prostate Cancer in the Setting of Salvage Radiation Therapy

“…In the case of an identified recurrence, modification of the CTV could be necessary to avoid underdosage of the recurrence area ( 53 ). Image registration between mpMRI and planning CT scan helps to identify accurately the target and decreases the CTV and the doses delivered to organs at risk ( 54 ). Moreover, it allows intensification of radiotherapy: Zilli et al ( 55 ) treated 131 patients with a dose of 64 Gy on a surgical bed and added a 10-Gy boost on the recurrence site.…”