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Quantifying target-specific motion in anal cancer patients treated with intensity modulated radiotherapy (IMRT)
Lisa Durrant1, Maxwell Robinson1, Maria A Hawkins1
1CRUK/MRC Oxford Institute for Radiation Oncology, University of Oxford, UK.
Background And Purpose:
Intensity modulated radiotherapy requires all target areas to be treated by a single radiotherapy plan. In anal cancer, the pelvic nodes, inguinal nodes and primary tumour represent three different targets. We aim to calculate target-specific motion in anal cancer radiotherapy, when delivered using a single pelvic online auto-match.
Materials And Methods:
Twenty consecutive patients treated using IMRT at a single institution were studied. CBCTs were retrospectively re-matched around the inguinal nodes and primary tumour. Match values were recorded relative to origin, defined as pelvic CBCT auto-match. Systematic and random errors were quantified to determine target-specific motion and suggested margins calculated using van Herk formulae.
Results:
The suggested margins to cover the independent motion of the inguinal and anal targets for LR, CC and AP set up around the inguinal nodes were 1.5mm, 2.7mm and 2.8mm; and the primary tumour were, 4.6mm, 8.9mm and 5.2mm respectively.
Conclusions:
Target-specific set up will likely result in reduced treatment volumes and as such reduced toxicity. This is the first time a relationship has been described between pelvic bones, inguinal nodes and primary tumour. The PLATO study will prospectively assess the toxicity and outcomes of this target-specific margins strategy.
