Development of a modified head and neck quality assurance phantom for use in stereotactic radiosurgery trials

Abstract

An anthropomorphic head phantom, constructed from a water‐equivalent plastic shell with only a spherical target, was modified to include a nonspherical target (pituitary) and an adjacent organ at risk (OAR) (optic chiasm), within 2 mm, simulating the anatomy encountered when treating acromegaly. The target and OAR spatial proximity provided a more realistic treatment planning and dose delivery exercise. A separate dosimetry insert contained two TLD for absolute dosimetry and radiochromic film, in the sagittal and coronal planes, for relative dosimetry. The prescription was 25 Gy to 90% of the GTV, with ≤10% of the OAR volume receiving ≥8.2emGy for the phantom trial. The modified phantom was used to test the rigor of the treatment planning process and phantom reproducibility using a Gamma Knife, CyberKnife, and linear accelerator (linac)‐based radiosurgery system. Delivery reproducibility was tested by repeating each irradiation three times. TLD results from three irradiations on a CyberKnife and Gamma Knife agreed with the calculated target dose to within ± 4% with a maximum coefficient of variation of ±2.1%. Gamma analysis in the coronal and sagittal film planes showed an average passing rate of 99.4% and 99.5% using ±5%/3.2emmm criteria, respectively. Results from the linac irradiation were within ±6.2% for TLD with a coefficient of variation of ±0.1%. Distance to agreement was calculated to be 1.2 mm and 1.3 mm along the inferior and superior edges of the target in the sagittal film plane, and 1.2 mm for both superior and inferior edges in the coronal film plane. A modified, anatomically realistic SRS phantom was developed that provided a realistic clinical planning and delivery challenge that can be used to credential institutions wanting to participate in NCI‐funded clinical trials.PACS number: 87.55 ‐v

Adaptation and validation of a commercial head phantom for cranial radiosurgery dosimetry end-to-end audit

“…12 The results presented in this study also demonstrate similar levels of agreement with the TPS to other studies that also used anthropomorphic phantoms. 8,16,27 Most importantly, the film measurements show a high degree of consistency which is essential if the methodology is to be employed for audit purposes. The high agreement with the TPS and consistency in measurement suggests that this is an appropriate phantom design and film methodology to be used for an end-to-end audit.…”

“…6 There are numerous examples where anthropomorphic phantoms have been utilized for complex radiotherapy treatment quality assurance, audits and trials. [7][8][9][10] In this study, we present the adaptation of a commercial anthropomorphic phantom for the novel use of three simultaneous detectors, with the purpose of employing it for a radiosurgery dosimetry audit. The methodology utilized was guided by the results of a recent survey on the current practice for cranial SRS in the UK.…”

Quantifying isocenter measurements to establish clinically meaningful thresholds

“…Stereotactic radiosurgery (SRS), by definition, is the delivery of a large therapeutic dose of radiation to an accurately localized target 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 . This results in an ablative dose of radiation at the target with a steep dose gradient to minimize damage to tissues outside of the target 9 , 10 , 11 , 12 .…”

Technical Note: Construction of heterogeneous head phantom for quality control in stereotactic radiosurgery

“…The Leksell Gamma Knife consists of 201 collimated cobalt 60 sources arranged over a hemispherical surface . To implement Gamma Knife radiosurgery in clinical practice, some quality control and dosimetry should be performed . Several studies were performed to measure the dose delivered to the target with a homogenous head phantom and some dosimeters such as radichromic film, ion chamber, diode, etc .…”

“…3 Several studies were performed to measure the dose delivered to the target with a homogenous head phantom and some dosimeters such as radichromic film, ion chamber, diode, etc. [1][2][3] These studies used a modified head phantom similar to an adult human head with the actual size of a head. These phantoms were made from water or water-equivalent soft tissue, and no heterogeneity was considered.…”