Primary renal cell cancer SBRT: a dosimetric evaluation of VMAT, Cyberknife and proton beam therapy
Harshani Green,
United Kingdom
PO-1970
Abstract
Primary renal cell cancer SBRT: a dosimetric evaluation of VMAT, Cyberknife and proton beam therapy
Authors: Harshani Green1, Orla Byrne2, Julia Henderson2, Pravesh Bhudia3, Vasilis Rompokos4, Anita Mitra5, Vincent Khoo1
1Royal Marsden Hospital NHS Foundation Trust, Urology, Radiotherapy, London, United Kingdom; 2Royal Marsden NHS Foundation Trust, Radiotherapy Physics, London, United Kingdom; 3University College London Hospitals NHS Foundation Trust, Radiotherapy and Proton Beam Therapy Dosimetry, London, United Kingdom; 4University College London Hospitals NHS Foundation Trust, Proton Beam Therapy Physics, London, United Kingdom; 5University College London Hospitals NHS Foundation Trust, Urology. Radiotherapy, London, United Kingdom
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Purpose or Objective
Stereotactic body radiotherapy (SBRT) for primary renal cell carcinoma (RCC) has increasing clinical data to support its use; however, the optimal dose regimes and delivery techniques are not known.
RCC five-year net survival ranges from >85% and >70% for stage I and stage III respectively. However, mortality is higher in the older population. Many patients who require the use of radiotherapy are older, frail or have comorbidities that preclude them from invasive intervention. Radiotherapy is becoming an increasingly important treatment option to optimise in this underserved cohort. We carried out a retrospective observational analysis of primary RCC SBRT comparing linear accelerator (LINAC)-based volumetric modulated arc therapy (VMAT), Cyberknife (CK) and pencil-beam scanning (PBS) proton beam therapy (PBT).
Material and Methods
Adult patients from two institutions with a primary RCC underwent renal SBRT planning using VMAT, CK and PBS PBT platforms. For VMAT and CK, a PTV margin of 5mm from ITV and CTV respectively was used. For PBS, the plans were evaluated under robustness for uncertainties of 5mm (geometric) and 3.5% (range) using ITV. A dose prescription of 42Gy in 3 fractions for tumours >4cm was used in line with FASTTRACK II (NCT02613819) clinical protocol. Cases were stratified to left and right-sided tumours. Dose constraints were in line with national clinical guidance. The aim was to achieve 95% coverage of the target volume with 42Gy, with a GTV Dmax of between 123-143%. Benefits and challenges of each technique in minimising dose to organs at risk were evaluated. Doses to skin, spinal cord, cauda equina, small bowel, duodenum, large bowel, stomach, liver, pancreas, spleen, ipsilateral normal and contralateral kidney were recorded. Means, range and SDs were calculated.
Results
Mean target volumes were 388.48cm3, 268.11cm3 and 388.73cm3 for VMAT, CK and PBT respectively. CK volumes were smaller, as it required a PTV expansion from CTV only. There was equivalent target coverage using all 3 platforms. However, regardless of technique, limitations were noted in achieving adequate dose to the target volume when bowel loops are immediately adjacent. PBT was able to achieve most sparing of the large bowel; mean D0.1cc of 14.03Gy (0-28.06) and 16.27Gy (5.04-27.5) for PBT and VMAT respectively. An overall trend towards superior OAR sparing was seen with PBT, but with higher skin doses.
Conclusion
Clinically acceptable target volume coverage was achievable and comparable with VMAT, CK and PBT. Bowel within or immediately adjacent to the target volume is a major limitation to achieving the prescription dose. Strategies that include an adaptive approach can be explored. Using PBT as a modality offers potential to decrease mean dose to OARs and may permit treatment in cases where the OAR constraints are challenging to meet. Further work will explore its utility with different patient cohorts in primary RCC.