Abstract
BackgroundOptimal alignment is of utmost importance when treating pediatric patients with craniospinal irradiation (CSI), especially with regards to field junctions and multiple isocenters and techniques applying high dose gradients. Here, we investigated the setup errors and uncertainties for pediatric CSI using different setup verification protocols.MethodsA total of 38 pediatric patients treated with CSI were identified for whom treatment records and setup images were available. The setup images were registered retrospectively to the reference image using an automated tool and matching on bony anatomy, subsequently, the impact of different correction protocols was simulated.ResultsFor an action-level (AL)-protocol and a non-action level (NAL)-protocol, the translational residual setup error can be as large as 24 mm for an individual patient during a single fraction, and the rotational error as large as 6.1°. With daily IGRT, the maximum setup errors were reduced to 1 mm translational and 5.4° rotational versus 1 mm translational and 2.4° rotational for 3- and 6- degrees of freedom (DoF) couch shifts, respectively. With a daily 6-DoF IGRT protocol for a wide field junction irradiation technique, the residual positioning uncertainty was below 1 mm and 1° for translational and rotational directions, respectively. The largest rotational uncertainty was found for the patients’ roll even though this was the least common type of rotational error, while the largest translational uncertainty was found in the patients’ anterior-posterior-axis.ConclusionsThese results allow for informed margin calculation and robust optimization of treatments. Daily IGRT is the superior choice for setup of pediatric patients treated with CSI, although centers that do not have this option could use the results presented here to improve their margins and uncertainty estimates for a more accurate treatment alignment.
Highlights
Optimal alignment is of utmost importance when treating pediatric patients with craniospinal irradiation (CSI), especially with regards to field junctions and multiple isocenters and techniques applying high dose gradients
Residual setup errors The residual errors should only include rotational deviation since translational errors were corrected at treatment
Translational positioning deviations greater than 1 cm occurred in 6% of all fractions and 33% of the patients had at least one such correction while rotational deviations greater than 1° occurred in 34% of all fractions and 80% of the patients had at least one such correction
Summary
Optimal alignment is of utmost importance when treating pediatric patients with craniospinal irradiation (CSI), especially with regards to field junctions and multiple isocenters and techniques applying high dose gradients. We investigated the setup errors and uncertainties for pediatric CSI using different setup verification protocols. When treating pediatric patients with CNS tumors it is of utmost importance that the patients are optimally aligned since this anatomical region contains many organs-at-risk (OARs) and since the developing brain is vulnerable to the long-term toxicities of radiotherapy. Studies investigating hippocampal-sparing cranial irradiation including craniospinal irradiation (CSI) for patients with medulloblastoma have emerged in order to minimize the common, treatment related, neurocognitive side effects [2, 3]. Setup correction decisions have changed from being based on AL/NAL-protocols to daily pre-treatment image-guided radiotherapy (IGRT) [6]
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