Utilizing a diagnostic kV imaging system for x-ray psoralen activated cancer therapy (X-PACT)

Abstract

X-ray psoralen activated cancer therapy (X-PACT) is a new therapeutic approach that has been shown to induce tumor cell apoptosis and cytotoxicity in vitro, and slow tumor growth in BALB/c mice with syngeneic 4T1 tumors. X-PACT is accomplished by injection of co-incubated psoralen and phosphors; the phosphors emit UV to activate psoralen, and are activated by an external kV source. Here we describe application of a kV x-ray source mounted on board a medical linear accelerator for X-PACT in preparation for a phase I clinical trial of X-PACT for spontaneous tumors in pet dogs. We commissioned a 80 kVp beam at 50-80 cm from the source with varied blade settings to achieve rectangular collimated beams. Commissioning included dosimetry measurements, developing a formalism for absolute dose calculation in water, FLUKA Monte Carlo based planning and evaluation, and verification measurements. Dosimetry measurements included AAPM TG-61 absolute dose calibration, depth dose curves, backscatter and collimator scatter factors, heel effect, and leakage. Reasonable agreement was achieved between measurement and Monte Carlo, and between calculated dose and verification measurements. Finally, we demonstrate the X-PACT treatment process for an example dog with a 3-5 cc left hip sarcoma located at a 2 cm depth. The absolute dose formalism indicated 21 pulses of 160 mAs were required to deliver the prescription dose of 0.6 Gy to 2.8 cm depth. The dose distribution was calculated with the Monte Carlo planning tool and visualized at 1×1×2 mm 3 spatial resolution. A dose enhancement in the hip bone of up to 4.5 Gy was observed. This work demonstrates that X-PACT is feasible utilizing diagnostic kV sources such as those mounted on a clinical linear accelerator, and reports commissioning and treatment planning data and formalism respectively.