An analysis of plan robustness for oesophageal tumours: comparing volumetric modulated arctherapy plans and spot scanning proton planning

Publication date: Available online 30 January 2016
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Samantha Warren, Mike Partridge, Alessandra Bolsi, Anthony J. Lomax, Chris Hurt, Thomas Crosby, Maria A. Hawkins
PurposePlanning studies to compare x-ray and proton techniques and to select the most suitable technique for each patient are hampered by the non-equivalence of several aspects of treatment planning and delivery. A fair comparison should compare similarly advanced delivery techniques from current clinical practice, and also assess the robustness of each technique. This study therefore seeks to compare volumetric modulated arc therapy (VMAT) and single-field optimisation (SFO) spot scanning proton therapy plans created using with simultaneous integrated boost (SIB) for dose escalation in mid-oesophageal cancer, and to analyse the effect of set-up and range uncertainties on these plans.Methods and MaterialsFor 21 patients, SIB plans with a physical dose prescription of 2 Gy / 2.5 Gy per fraction (in 25 fractions) to PTV50Gy / PTV62.5Gy (primary tumour with 0.5cm margins) were created and evaluated for robustness to random set-up errors and proton range errors. Dose-volume metrics were compared for the optimal and uncertainty plans with p< 0.05 (Wilcoxon) taken as significant.ResultsSFO reduced mean lung dose by 51.4% (range: 35.1 – 76.1%) and mean heart dose by 40.9% (15.0 – 57.4%) compared to VMAT. Proton plan robustness to 3.5% range error was acceptable: across all patients CTV D98 was 95.0-100.4% of prescribed dose (PD) and GTV D98 was 98.8-101%. Set-up error robustness was patient anatomy dependant and potential minimum dose per fraction was always lower with SFO than VMAT: CTV D98 was lower by 0.6-7.8% PD and GTV D98 lower by 0.3 - 2.2% of prescribed GTV dose.ConclusionsSFO plans achieve significant sparing of normal tissue compared to VMAT for mid-oesophageal cancer. Target dose coverage in SIB proton plans was less robust to random set-up errors, and may be unacceptable for certain patients. Robust optimisation to ensure adequate target coverage of SIB proton plans may be beneficial.

Teaser

Comparing spot-scanning proton therapy single-field optimisation plans (SFO) with arctherapy (VMAT) plans indicates that SFO can achieve significant sparing of normal tissue for mid-oesophageal cancer compared to VMAT. However, the boost volume dose coverage in SIB proton plans appears less robust to set-up errors. Robust optimisation to ensure adequate target coverage of SIB proton plans may be beneficial.


from Cancer via ola Kala on Inoreader http://ift.tt/1Q0t15o
via IFTTT