Detectors assessment for stereotactic radiosurgery with cones

Abstract

The purpose of this work is to assess eight detectors performance for output factor (OF), percent depth dose (PDD), and beam profiles in a 6‐MV Clinac stereotactic radiosurgery mode for cone irradiation using Monte Carlo simulation as reference. Cones with diameters comprised between 30 and 4 mm have been studied. The evaluated detectors were ionization chambers: pinpoint and pinpoint 3D, diodes: SRS, P and E, Edge, MicroDiamond and EBT3 radiochromic films. The results showed that pinpoints underestimate OF up to −2.3% for cone diameters ≥10 mm and down to −12% for smaller cones. Both nonshielded (SRS and E) and shielded diodes (P and Edge) overestimate the OF respectively up to 3.3% and 5.2% for cone diameters ≥10 mm and in both cases more than 7% for smaller cones. MicroDiamond slightly overestimates the OF, 3.7% for all the cones and EBT3 film is the closest to Monte Carlo with maximum difference of ±1% whatever the cone size is. For the profiles and the PDD, particularly for the small cones, the size of the detector predominates. All diodes and EBT3 agree with the simulation within ±0.2 mm for beam profiles determination. For PDD curve all the active detectors response agree with simulation up to 1% for all the cones. EBT3 is the more accurate detector for beam profiles and OF determinations of stereotactic cones but it is restrictive to use. Due to respectively inappropriate size of the sensitive volume and composition, pinpoints and diodes do not seem appropriate without OF corrective factors below 10 mm diameter cone. MicroDiamond appears to be the best detector for OF determination regardless all cones. For off‐axis measurements, the size of the detector predominates and for PDD all detectors give promising results.

Feasibility study of using Stereotactic Field Diode for field output factors measurement and evaluating three new detectors for small field relative dosimetry of 6 and 10 MV photon beams

“…Field output factors with EBT3 films were calculated employing method proposed by Garnier et al 33 Table 2. Advantages of this method include the irradiation of films in an ideal dose range and getting the same signal to noise ratio and hence the same uncertainty for all field sizes that would be compromised for smaller fields otherwise.…”

“…Field output factors with EBT3 films were calculated employing method proposed by Garnier et al 33 as described in Eq. (5).…”

“…Advantages of this method include the irradiation of films in an ideal dose range and getting the same signal to noise ratio and hence the same uncertainty for all field sizes that would be compromised for smaller fields otherwise. 33 Field output factors with EBT films were calculated using Eq. (5).…”

SciFi detector and associated method for real‐time determination of profile and output factor for small fields in stereotactic radiotherapy

“…3 To address these problems, there has been a very dynamic research activity over the last decade, in particular concerning the determination of the output factor (OF) which is a critical dosimetric parameter for the characterization of small fields used in radiotherapy. 4,[6][7][8][9] Correction factors have been proposed for small-field dosimetry based on solid-state detectors such as diodes and microdiamonds. 8,10,11 However, in the recent joint IAEA -AAPM publication of the International Code of Practice TRS-483, the use of detectors that exhibit output correction factors close to unity is recommended for the field output factor determination.…”

“…To address these problems, there has been a very dynamic research activity over the last decade, in particular concerning the determination of the output factor (OF) which is a critical dosimetric parameter for the characterization of small fields used in radiotherapy …”