Feasibility of magnetic resonance-guided adaptive post-prostatectomy radiotherapy
Vikneswary Batumalai,
Australia
PO-1374
Abstract
Feasibility of magnetic resonance-guided adaptive post-prostatectomy radiotherapy
Authors: Sean Hassan1, Michael Jameson1,2, Vikneswary Batumalai1,2, David Crawford1, Zoe Moutrie1, Louise Hogan1, Conrad Loo1, Maddison Picton1, Claire Pagulayan3, Urszula Jelen3, Stacy Alvares1, Monique Heinke3, Sandy Sampaio1, Kathy Simon1, Tania Twentyman1, Neha Dwivedi4, Jeremiah de Leon1
1GenesisCare St Vincent's Sydney, Radiation Oncology, Sydney, Australia; 2University of New South Wales, St Vincent's Clinical School, Sydney, Australia; 3 GenesisCare St Vincent's Sydney, Radiation Oncology, Sydney, Australia; 4MIM Software Inc , Clinical Support Engineering , Cleveland , USA
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Purpose or Objective
Radiotherapy is a mainstay of treatment in locally recurrent prostate cancer following prostatectomy. However, target volumes are highly variable and anisotropic margins are often utilised with traditional linear accelerator treatment to account for inter- and intra-fraction organ changes. This in turn can lead to greater toxicity. The use of magnetic resonance imaging based adaptive radiotherapy (MRgART) endeavours to mitigate this variability to ensure adequate CTV coverage whilst minimising dose to adjacent Organs at Risk (OARs).
The purpose of this study was to assess the utility of MRgART in the post-prostatectomy setting and to analyse toxicity in patients receiving treatment.
Material and Methods
Nine patients were treated with MRgART utilising an Elekta Unity MR Linear Accelerator. Prescription used was 66-70Gy in 33-35 fractions with patients who had PSMA-detected local recurrences receiving a boost to the GTV. OAR doses were as per published guidelines. Daily adaptive plans were generated and clinically delivered. For each clinically delivered adaptive fraction, a comparative non-adaptive equivalent was generated from the pre-treatment reference plan. Acute toxicity was then assessed at three months following completion of treatment with EORTC Toxicity Criteria.
Results
A total of 313 fractions were clinically delivered to 9 patients. Pre-treatment reference plans met all CTV and OAR criteria. CTV coverage criteria of D98%>70Gy was met in 85.2% of MRgART fractions compared to 41.54% of non-adaptive fractions. Bladder V50Gy<50% was met in 85.16% of MRgART fractions compared to 76.18% for non-adaptive plans. Rectum V40Gy<60% was met in 98.13% of MRgART fractions compared to 85.78% of non-adaptive fractions. 3-month EORTC genitourinary and gastrointestinal acute toxicity was absent in most patients, and mild-to-moderate in a minority of patients (Grade 2 GI toxicity in 1 patient and Grade 1 GU toxicity in 1 patient).
Conclusion
Daily MRgART treatment consistently met planning criteria more often than non-adaptive comparison. Target volume variability in prostate bed treatment can be mitigated by using MRgART and delivers satisfactory coverage of CTV whilst minimising dose to adjacent OARs and reducing toxicity.