Successful completion of an international dosimetry audit

Successful completion of an international dosimetry audit

17 September 2018

The international Imaging and Radiation Oncology Core (IROC), a Houston based quality assurance center, has completed their dosimetry audit of our proton therapy treatment beam. This audit was part of a certification process, allowing us to participate in international clinical trials.

The audit consisted of irradiating six thermoluminescent dosimeters (TLDs), positioned at three depths within a cubic phantom. Using our ‘RayStation’ treatment planning system we designed a spot-scanning dose distribution delivering a homogeneous dose to an 11x11x11 cm3 region, encompassing all TLDs (see figure). The TLDs were located at two different depths. The prescription was to deliver a dose of 300 cGy. 

Using the Monte Carlo dose calculation algorithm, available within Raystation, we determined the expected dose to each of the six TLDs. Varying between 298.7 and 301.6 cGy, these doses deviated less than one percent from the prescribed dose. The right hand pane of the figure shows the calculated dose distribution in a representative transversal plane.

Left: Spread-out Bragg peak (dose as a function of depth). Middle: proton spot distribution. Right: Calculated dose distribution and location of the TLDs, as indicated by the white arrow Left: Spread-out Bragg peak (dose as a function of depth). Middle: proton spot distribution. Right: Calculated dose distribution and location of the TLDs, as indicated by the white arrow

The IROC phantom and TLDs were irradiated on 19 January and subsequently shipped to Houston for the IROC team. They read-out the TLDs and determined the delivered dose to be 303 cGy. As this one percent deviation from the dose prescription is well within their tolerance level, we have successfully completed the audit.