The accuracy of three-dimensional dose delivery from linear accelerators has significant effects on the planning target volume margins used in intracranial stereotactic radiosurgery.
Researchers have long acknowledged the importance of precision when it involves administering radiation therapy for brain tumors. A recent multi-institutional study has taken significant strides to explore how the spatial accuracy of dose delivery impacts the planning target volume (PTV) margins necessary for effective treatment regimens.
This investigation focused on non-coplanar intracranial stereotactic radiosurgery (SRS), where small tumor sizes necessitate high precision. The study involved the assessment of 3D dose delivery accuracy across 22 institutions using Varian and Elekta linear accelerators (linacs). Utilizing advanced imaging techniques, researchers employed the three-dimensional starshot (3D-SS) test using polymer gel dosimeters to measure the spatial dose discrepancies effectively.
The findings revealed notable variability among institutions, with the distance between the imaging isocenter and beam exceeding 1 mm at one Varian facility and nine Elekta locations. Such inaccuracies can significantly influence the calculated PTV margins required to cover the gross tumor volume with high confidence.
Traditionally, depending on the linac used, the necessary PTV margins could reach up to 3.5 mm. Nevertheless, through careful systemic management—such as rigorous linac quality assurance and enhanced patient immobilization strategies—researchers indicated potential reductions. The margins determined were 2.3 mm for the Varian systems and 3.5 mm for Elekta systems. Yet, by ensuring optimal 3D dose delivery practices, these margins could be reduced to 1.0 mm and 1.5 mm respectively.
A prominent takeaway from the study stresses ensuring high-accuracy operations for linacs, as it became evident how fierce variation exists depending on the institution and manufacturer. The research substantiated the fact, confirming, "Maximizing a linac’s 3D dose delivery accuracy is necessary to achieve the required PTV margin in intracranial SRS." This highlights the need for the implementation of advanced imaging systems and strict QA protocols to improve outcomes.
This multi-institutional inquiry marks the first to assess the spatial accuracy of linacs comprehensively, and it provides relevant conclusions surrounding the management of PTV margins. Various hospitals will greatly benefit from adopting enhanced strategies to mitigate discrepancies associated with dose delivery accuracy.
Conclusively, as the field of radiation oncology experiences rapid advancements, the importance of solidifying protocols around accurate SRS delivery remains priority one. The results indicate the necessity of addressing the existing variability to minimize risks and optimize treatment strategies for patients battling brain tenacities.