Program Information
Abdominal Diameter Changes in Children During Volumetric Modulated Arc Therapy (VMAT): Is Re-Planning Needed?
F Guerreiro1*, G Janssens1 , E Seravalli1 , B Raaymakers1 , (1) University Medical Center Utrecht, Department of Radiotherapy and Imaging Division, Utrecht
Presentations
SU-F-J-63 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To investigate the dosimetric impact of daily changes in patient's diameter, due to weight gain/loss and air in the bowel, based on CBCT information during radiotherapy treatment of pediatric abdominal tumors.
Methods: 10 pediatric patients with neuroblastoma (n=6) and Wilms' (n=4) tumors were included. Available CBCTs were affinely registered to the planning CT for daily set-up variations corrections. A density override approach assigning air-density to the random air pockets and water-density to the remaining anatomy was used to determine the CBCT and CT dose. Clinical VMAT plans, with a PTV prescribed dose ranging between (14.4-36) Gy, were re-optimized on the density override CT and re-calculated on each CBCT. Dose-volume statistics of the PTV and kidneys, delineated on each CBCT, were used to compare the daily and cumulative CBCT dose with the reference CT dose.
Results: The average patient diameter variation was (0.5 ± 0.7) cm (maximum daily difference of 2.3 cm). The average PTV mean dose difference (MDD) between the CT and the cumulative CBCT plans was (0.1 ± 1.1)% (maximum daily MDD of 2%). A reduction in target coverage up to 3% and 7% was observed for the cumulative and daily CBCT plans, respectively. The average kidneys’ cumulative MDD was (-2.7 ± 3.6)% (maximum daily MDD of -12%), corresponding to an overdosage.
Conclusion: Due to patient’s diameter changes, a target underdosage was assessed. Given the high local tumor control of neuroblastoma and Wilms’ diseases, the need of re-planning might be discarded. However, the assessed kidneys overdosage could represent a problem when the normal tissue tolerance is reached. The necessity of re-planning should then be considered to reduce the risk of long-term renal complications. Due to the poor soft-tissue contrast on CBCT, MRI-guidance is required to obtain a better assessment of the accumulated dose on the remaining OARs.
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