Quantifying target-specific motion in anal cancer patients treated with intensity modulated radiotherapy (IMRT)

Abstract

Background and purposeIntensity 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 methodsTwenty 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.ResultsThe 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 1.5 mm, 2.7 mm and 2.8 mm; and the primary tumour were, 4.6 mm, 8.9 mm and 5.2 mm respectively.ConclusionsTarget-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.

Target volume motion during anal cancer image guided radiotherapy using cone-beam computed tomography

“…However, there are data demonstrating GTVa movement independent of bony anatomy. 9 We observed large volume changes in CTVa, which varied from the planning CT and between sequential CBCT images. This volume change did not appear to follow a trend, however, the greatest changes in CTVa were present in patients with a T-location involving the anorectum junction.…”

“…In ACC, only two studies are published that investigate the required CTV to PTV margins or describe the internal motion of the anus during anal cancer radiotherapy. 8,9 Despite high uptake of IGRT, there is a paucity of literature regarding the optimum IGRT protocol in ACC, in terms of imaging modality, normal tissue matching or frequency of data acquisition. 10 In preparation for the next UK anal cancer trial (PLATO ISRCTN88455282), the consensus document National objective: Literature regarding image-guidance and interfractional motion of the anal canal (AC) during anal cancer radiotherapy is sparse.…”

Image-Guided Radiotherapy for Pelvic Cancers: A Review of Current Evidence and Clinical Utilisation

“…The main cause of primary tumour movement appears to be a combination of bowel gas & filling variation (high tumours) and buttock displacement (low tumours). Finally, a single paper [33] reported on differential movement of primary tumour and involved (inguinal) node targets, and found considerable independent movement, highlighting the need for a target-specific match strategy in this patient group. There are no published studies on adaptive treatment strategies.…”

“…Margins in the region of 5-8 mm (depending on local setup and imaging policy) are typically adequate to ensure dose coverage in this case [29,30]. However, some volumes do exhibit more motion relative to pelvic bony structures, in particular rectal and mesorectal nodal volumes [31,32], and (to a smaller extent) inguinal nodes [33].…”

Management of locally advanced anal canal carcinoma with intensity-modulated radiotherapy and concurrent chemotherapy

“…Durrant et al assessed the motion around the inguinal nodes and the local tumor region using an online CBCT protocol. The estimated 3D margins needed to compensate for random displacements in the lateral, longitudinal, and vertical axes around the inguinal nodes and the primary tumor were, respectively, 1.5 mm, 2.7 mm, and 2.8 mm and 4.6 mm, 8.9 mm, and 5.2 mm [86]. Indeed, the ongoing PLATO trial (ISRCTN88455282) will assess the safety of individualized radiotherapy doses considering reduced margins around the targets.…”