Matched linac stereotactic radiotherapy: An assessment of delivery similarity and distributive patient‐specific quality assurance feasibility

Abstract

Matching multiple linacs to common baseline data allows patients to be treated, and patient‐specific quality assurance (PSQA) to be completed on any linac. Stereotactic body radiotherapy (SBRT) requires higher levels of accuracy and quality assurance than routine radiotherapy. The achieved linac matching must therefore be evaluated before distributive treatment or PSQA models can be implemented safely. This investigation aimed to propose metrics for defining linacs to be matched for SBRT deliveries, assess 12 linacs against these criteria, and determine if a distributive PSQA model could be implemented by reviewing the rates of false PSQA results. Ten SBRT spine plans were delivered by 12 matched Elekta linacs and measured using one of seven SRS MapCHECK devices. For gamma criteria of (3%, 2 mm), 96.9% of equivalent location detectors, showed a range of gamma ≤ 1.0 and 99.9% showed a standard deviation of ≤ 0.5. For criteria of (3%,1 mm) and (2%,1 mm), these ranges decreased to 92.1% and 80.2% while the standard deviations decreased to 99.3% and 95.7%, respectively. The dose differences showed that 43.6%, 82.7%, and 91.4% of detectors had a dose range of ≤ 3.0%, ≤ 5.0%, and ≤ 6.0%, respectively. Standard deviations of dose differences were 1.5%, 2.5%, and 3.0% for 94.1%, 98.3%, and 99.5% of detectors, respectively. For the fleet of linacs, distributive PSQA yielded false results for 0.0%, 17.7%, and 33.0% of plans, equivalent to 1.2%, 3.5%, and 9.4% of detectors when using gamma criteria of (3%,2 mm), (3%,1 mm), or (2%,1 mm), respectively. These linacs could be considered matched for SBRT treatments and implement a distributive PSQA model when gamma analysis was completed with a criterion of (3%, 2 mm). For stricter criterion of (3%,1 mm) or (2%,1 mm), they did not meet the proposed metrics.

Patient specific quality assurance in SBRT: a systematic review of measurement-based methods

“…Goodall et al have proposed an analysis to determine the feasibility of implementing a distributive PSQA approach when matched linacs are available (Goodall et al 2022). They concluded that discrepancies in linac performance translate into inconsistencies in PSQA measurements and assess the level of linac matching accuracy needed to obtain consistent PSQA results.…”

Correction factors for commissioning and patient specific quality assurance of stereotactic fields in a Monte Carlo based treatment planning system

“…All linacs have previously been shown to be well matched to a single beam model within the Monaco TPS and to each other. [18] A total of 82 cranial SRS treatment plans with either single or multiple targets per isocentre, using between 3 and 6 non coplanar VMAT arcs and a 6FFF energy, were measured using a CC01 ionisation chamber in a solid water phantom. A total of 28 SBRT prostate, bone or lung plans using coplanar dual VMAT arcs and a 6FFF energy were measured using a CC04 ionisation chamber in either a solid water phantom or the CIRS thorax phantom (Sun Nuclear Corporation, Norfolk, VA, USA).…”

Correction factors for commissioning and patient specific quality assurance of stereotactic fields in a Monte Carlo based treatment planning system

“…All linacs had previously been shown to be well matched to a single beam model within the Monaco TPS and to each other. 17 A total of 82 cranial SRS treatment plans with either single or multiple targets per isocentre, using between 3 and 6 non coplanar VMAT arcs and a 6FFF energy, were measured using a cc01 ionisation chamber in a solid water phantom. A total of 28 SBRT prostate, bone or lung plans using coplanar dual VMAT arcs and a 6FFF energy were measured using a cc04 ionisation chamber in either a solid water phantom or the CIRS thorax phantom (Sun Nuclear Corporation, Norfolk, VA, USA).…”