Abstract
Prostate stereotactic body radiation therapy (SBRT) delivers large fractional dosesthrough steep dose gradients and tight planning target volume (PTV) margins, placing
stringent demands on geometric accuracy, dosimetric precision, and workflow reliability.
Because each fraction carries a large share of the prescribed dose, a prostate SBRT
program cannot be introduced on equipment specifications alone; the full treatment chain
must be shown to perform within stereotactic tolerances at the specific center where
patients will be treated. This thesis supports the safe clinical implementation of such a
program by tailoring commissioning to the capabilities and constraints of one clinical
center. It pursues two objectives: comprehensive verification of the treatment
chain---reference dosimetry, machine performance, the treatment planning system (TPS)
beam model, and integrated patient-specific and end-to-end (E2E) testing---against
stereotactic tolerances, and an investigation of the attenuation introduced by the
treatment couch and a newly implemented immobilization board, which includes determining
the board's effective CT number for dose calculation.
All measurements were performed on a Varian TrueBeam linear accelerator with aMillennium~120 multileaf collimator (MLC) and kilovoltage cone-beam CT, with treatment
planning in the Eclipse TPS using the analytical anisotropic algorithm (AAA). Verification
spanned reference dosimetry (TG-51), machine performance (Winston--Lutz isocenter
coincidence and MLC checks), TPS beam-model parameters, and integrated patient-specific
and end-to-end (E2E) testing, each verified against its relevant tolerance before clinical
implementation. Couch-and-board attenuation was quantified with ion-chamber measurements
in solid water across a range of posterior gantry angles. Patient-specific QA used a
high-resolution diode array with gamma analysis, and E2E dose accuracy was verified by ion
chamber in a static anthropomorphic phantom.
Across the verification program, reference dosimetry, machine performance, the TPS beammodel, and the integrated patient-specific and end-to-end checks each met the geometric
and dosimetric tolerances required for high-dose hypofractionated delivery, which establishes
the site-specific baselines needed for ongoing quality assurance. Alongside these, the couch-and-board investigation confirmed that these support structures attenuate
posterior beams by a clinically meaningful margin and therefore cannot be neglected in the
dose calculation.
From these findings the thesis derives practical recommendations for clinical policy atthis center: the full set of commissioning tests should be verified against stereotactic
tolerances before any patient is treated and retained as the reference baselines for
routine periodic quality assurance and trending; and the treatment couch and immobilization
board should be represented in the dose calculation for every plan, with the board
assigned a CT number of approximately $-200$~HU.