ESTRO 2024 - Abstract Book

S2065

Clinical - Paediatric

ESTRO 2024

For patients aged 5 and below, administration of anesthesia during simulation and treatment phases was imperative to ascertain patient comfort and immobilization. The immobilization devices included the Portrait S Frame Device and a 3-Pt head mask (Q-Fix Systems, NJ, USA) with Moldcare® (Q-Fix Systems, NJ, USA). An adult size vaclok bag (Q-Fix Systems, NJ, USA) was preferred for the patient’s immobilization. Patients were laid supine without clothing on the chuck for reproducibility. Arms were positioned laterally adjacent to the torso, fingers extended along the thigh and secured using Microspore surgical adhesive tape. Legs were placed as straight and close together as possible and stabilized using the Vaclok. The reproducibility of the arms and the feet was ensured before scanning. An index bar was used to keep the vaclok in place on the S-frame. A 3mm CT scan of the patient was obtained with a few slices superior to the scalp and a few slices inferior to the feet. The bones, ribs, chestwall, lungs and all major organs were contoured. The Planning Target Volume (PTV) included the entire body with the lungs and 3mm skin rind cropped off. The skeletal structure contoured as “All bones” with and without ribs included was used for treatment planning. A 7mm virtual bolus rind with a density of 1 g/cc was contoured around the fingers. The virtual bolus was set to 1cm rind around the distal end of the feet in all directions and 2 cm inferiorly. This is to ensure adequate radiation coverage for the fingers and toes to accommodate variations in position. A 5mm virtual bolus rind around the external with a low density of 0.02g/cc optimized to very low importance was used to provide a flash to account for positioning uncertainties. The prescriptions used were either 13.2Gy or 12Gy in 8 fractions twice a day (BID). IMRT treatment plans were created on the Radixact (Accuray, Sunnyvale, CA). A suitable combination of pitch(P) and modulation factor (MF) with a field size of 5cm was used to obtain a homogenous dose distribution while minimizing thread effect and beam on-time (BOT). For three patients, the plans were optimized resulting in approximately 110% of the prescription dose to bones at a lower coverage while ensuring adequate coverage to ribs/chestwall. Multiple optimization structures obtained by shrinking the lungs by 3, 5, 8, and 10mm were used to carve optimal dose fall-off to minimize the dose to the lungs. Plans were optimized so that 95% of PTV received approximately 95% of the prescription dose while keeping the mean lungs dose below 8Gy.

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