Multi-centre evaluation of variation in cumulative dose assessment in reirradiation scenarios.

BACKGROUND AND PURPOSE: Safe reirradiation relies on assessment of cumulative doses to organs at risk (OARs) across multiple treatments. Different clinical pathways can result in inconsistent estimates. Here, we quantified the consistency of cumulative dose to OARs across multi-centre clinical pathways. MATERIAL AND METHODS: We provided DICOM planning CT, structures and doses for two reirradiation cases: head & neck (HN) and lung. Participants followed their standard pathway to assess the cumulative physical and EQD2 doses (with provided α/ß values), and submitted DVH metrics and a description of their pathways. Participants could also submit physical dose distributions from Course 1 mapped onto the CT of Course 2 using their best available tools. To assess isolated impact of image registrations, a single observer accumulated each submitted spatially mapped physical dose for every participating centre. RESULTS: Cumulative dose assessment was performed by 24 participants. Pathways included rigid (n = 15), or deformable (n = 5) image registration-based 3D dose summation, visual inspection of isodose line contours (n = 1), or summation of dose metrics extracted from each course (n = 3). Largest variations were observed in near-maximum cumulative doses (25.4 - 41.8 Gy for HN, 2.4 - 33.8 Gy for lung OARs), with lower variations in volume/dose metrics to large organs. A standardised process involving spatial mapping of the first course dose to the second course CT followed by summation improved consistency for most near-maximum dose metrics in both cases. CONCLUSION: Large variations highlight the uncertainty in reporting cumulative doses in reirradiation scenarios, with implications for outcome analysis and understanding of published doses. Using a standardised workflow potentially including spatially mapped doses improves consistency in determination of accumulated dose in reirradiation scenarios.

Comparison of CT-volumed supraclavicular fossa radiotherapy planning and conventional simulator-planned defined by bony landmarks for early breast cancer.

AIM: A comparison of techniques, CT planning of the supraclavicular fossa and field based simulation. We highlight CT planned SCF radiotherapy which would be useful for a centre introducing the technique. BACKGROUND: Development of radiotherapy technique includes a move from field-based simulation to CT planning. MATERIALS AND METHODS: We conducted a retrospective review of the first 50 patients receiving radiotherapy according to the 3D CT planning protocol. Production of the previous field based technique, by virtual simulation methods on the same 50 patient CT data sets allowed both techniques to be compared for beam energy, field size, planning target volume (PTV) minimum and maximum, mean doses, depth dose normalisation, V40% lung volume and brachial plexus. RESULTS: 88% CT-volumed plans received mean dose within ICRU recommended limits compared with only 8% using previous conventional technique. 76% required 10 MV to improve coverage and one patient (2%) an opposed posterior field. The mean normalisation depth was 4.5 cm (range 1.9-7.7 cm) compared with pre-set 3 cm of the conventional technique. With CT-volumed technique the whole lung volume exposed to V40%, including the tangential fields, reduced from 10.79% to 9.64% (p < 0.001) but the mean maximum brachial plexus dose increased from 48.9 Gy to 51.6 Gy (p < 0.001). CONCLUSIONS: Dose coverage of the SCF PTV was greatly improved for plans produced from 3DCT volumes compared to field based techniques.