Intensity modulated proton therapy: A clinical example

Abstract

In this paper, we report on the clinical application of fully automated three-dimensional intensity modulated proton therapy, as applied to a 34-year-old patient presenting with a thoracic chordoma. Due to the anatomically challenging position of the lesion, a three-field technique was adopted in which fields incident through the lungs and heart, as well as beams directed directly at the spinal cord, could be avoided. A homogeneous target dose and sparing of the spinal cord was achieved through field patching and computer optimization of the 3D fluence of each field. Sensitivity of the resultant plan to delivery and calculational errors was determined through both the assessment of the potential effects of range and patient setup errors, and by the application of Monte Carlo dose calculation methods. Ionization chamber profile measurements and 2D dosimetry using a scintillator/CCD camera arrangement were performed to verify the calculated fields in water. Modeling of a 10% overshoot of proton range showed that the maximum dose to the spinal cord remained unchanged, but setup error analysis showed that dose homogeneity in the target volume could be sensitive to offsets in the AP direction. No significant difference between the MC and analytic dose calculations was found and the measured dosimetry for all fields was accurate to 3% for all measured points. Over the course of the treatment, a setup accuracy of +/-4 mm (2 s.d.) could be achieved, with a mean offset in the AP direction of 0.1 mm. Inhalation/exhalation CT scans indicated that organ motion in the region of the target volume was negligible. We conclude that 3D IMPT plans can be applied clinically and safely without modification to our existing delivery system. However, analysis of the calculated intensity matrices should be performed to assess the practicality, or otherwise, of the plan.

Three‐dimensional gamma criterion for patient‐specific quality assurance of spot scanning proton beams

“…This physical difference in depth‐dose distributions between proton and photon radiation also presents new challenges, such as range uncertainty and increased dose gradients along the beam direction. The accuracy of proton dose calculation under range uncertainty 6 , 7 , 8 and the robustness of plan quality with increased dose gradients 9 , 10 , 11 , 12 have both been shown to be important factors in patient treatment. In this study, we report the effect of dose gradients along the beam direction on the patient‐specific quality assurance of dose distribution.…”

A scintillating gas detector for 2D dose measurements in clinical carbon beams

“…Stacks of ionization chambers with strip-segmented cathodes for 2D readout have a better spatial response in a plane perpendicular to the beam, but they do not provide full 2D dose information in that plane (only two projections of the beam profile in that plane) (Bonazzola et al 1998, Brusasco et al 2000. The use of stacks of films (Lomax et al 2001) gives dose information with very high spatial resolution, but the film measurement evaluation is time consuming. Scintillating screens (Boon et al 1998, Safai et al 2004 coupled to a CCD camera allow online measurements of dose distributions with a 2D spatial resolution nearly as good as the film in a plane perpendicular to the beam.…”

Redefine the role of range shifter in treating bilateral head and neck cancer in the era of Intensity Modulated Proton Therapy

“…As the Pencil Beam Scanning (PBS) technology has become commercially available in the recent 10 years,1 nearly all the new proton centers under the contract or constructions are now configured with only PBS technique. Compared to passive‐scattering technique, Intensity Modulated Proton Therapy (IMPT) based on PBS technique allows for creating a more conformal dose distribution to target volume while resulting in a less body integral dose and ultimately less neutron dose 1, 2. For a majority of the current commercial proton beam systems, the minimum proton beam energy ranges from 70 to 100 MeV which is about 4.1–7.5 cm in water‐equivalent thickness (WET).…”