Premium
SU‐F‐J‐63: Abdominal Diameter Changes in Children During Volumetric Modulated Arc Therapy (VMAT): Is Re‐Planning Needed?
Author(s) -
Guerreiro F,
Janssens G,
Seravalli E,
Raaymakers B
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4955971
Subject(s) - medicine , nuclear medicine , radiation treatment planning , cumulative dose , dosimetry , radiation therapy , wilms' tumor , cone beam computed tomography , computed tomography , radiology
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 softtissue contrast on CBCT, MRI‐guidance is required to obtain a better assessment of the accumulated dose on the remaining OARs.