Quantifying target-specific motion in anal cancer patients treated with intensity modulated radiotherapy (IMRT).
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.
['Durrant|Lisa|L|', 'Robinson|Maxwell|M|', 'Hawkins|Maria A|MA|', 'Van den Heuvel|Frank|F|', 'Muirhead|Rebecca|R|']
D000328:Adult D000368:Aged D001005:Anus Neoplasms D002294:Carcinoma, Squamous Cell D005260:Female D006801:Humans D008198:Lymph Nodes D008297:Male D008875:Middle Aged D009038:Motion D010388:Pelvis D011879:Radiotherapy Dosage D011880:Radiotherapy Planning, Computer-Assisted D050397:Radiotherapy, Intensity-Modulated D012189:Retrospective Studies
Inguinal node Anal cancer IMRT Elective irradiation Margin reduction