Quantification of Dosimetry Improvement With or Without Patient Surface Guidance

Ke Sheng; Minsong Cao; Andrew Godley; Mu-Han Lin; Lukas Henze; Laura Hammond; Laurence Delombaerde; Kirsten Hierholz; Jana Kouptsidis

doi:10.1016/j.adro.2024.101570

Quantification of Dosimetry Improvement With or Without Patient Surface Guidance

Adv Radiat Oncol. 2024 Jul 14;9(9):101570. doi: 10.1016/j.adro.2024.101570. eCollection 2024 Sep.

Authors

Ke Sheng¹, Minsong Cao², Andrew Godley³, Mu-Han Lin³, Lukas Henze⁴, Laura Hammond⁵, Laurence Delombaerde⁶, Kirsten Hierholz⁷, Jana Kouptsidis⁷

Affiliations

¹ Department of Radiation Oncology, University of California, San Francisco, California.
² Department of Radiation Oncology, University of California, Los Angeles, California.
³ Department of Radiation Oncology, The University of Texas Southwestern Medical Center, Dallas, Texas.
⁴ Cancer Center Berlin-Neukölln, Vivantes Klinikum Neukölln, Berlin, Germany.
⁵ Radiotherapy Department, Raigmore Hospital, Inverness, United Kingdom.
⁶ Department of Oncology, UZ Leuven, Leuven, Belgium.
⁷ Klinikum Darmstadt GmbH, Institut für Radionkologie und Strahlentherapie, Darmstadt, Germany.

Abstract

Purpose: Noncoplanar beams and arcs are routinely used to improve dosimetry for intracranial cases, but their application for extracranial cases has been hampered by the risk of collision. This has led to conservative beam selection whose impact on plan dosimetry has not been previously studied.

Methods and materials: A full-body 3-dimensional patient surface was acquired using optical cameras for a single lung patient at the time of computed tomography simulation. Eight stereotactic body radiation therapy (SBRT) plans were created for the patient, with varying degrees of noncoplanarity and deliverability. The plans included volumetric modulated arc therapy and intensity modulated radiation therapy (IMRT) plans ranging from simple, coplanar arcs to multiple noncoplanar arcs and IMRT beams. A total of 70 fields were created across the 8 plans, of which 21 fields were undeliverable with a 5-cm buffer. Organs-at-risk (OARs) metrics including R50, Dmax 2 cm from the PTV, lung V20, and chest wall V30 were evaluated. Five expert SBRT dosimetrists from 5 institutions evaluated field deliverability, with or without the guidance of the clearance map.

Results: In the dosimetry evaluation, a clear trend in increasing dosimetric compactness and OAR sparing is observed with increasing plan noncoplanarity. R50, Dmax 2 cm, lung V20, and chest wall V30 decreased 41%, 39%, 43%, and 57%, respectively, from plan 1 (2 coplanar partial arcs) to plan 8 (19 noncoplanar IMRT beams). In the observer tests, the expert dosimetrists' ability to accurately discern beam deliverability because of collision significantly increases with the clearance map. The errors in predicting colliding fields were eliminated using the whole-body surface and clearance map, and the user was able to select fields based on plan quality and patient comfort instead of being overly conservative.

Conclusion: The study shows that incorporating a personalized, whole-body clearance map in the treatment planning workflow can facilitate the adoption of noncoplanar beams or arcs that benefit the SBRT plan dosimetry.