Intensity and energy modulated radiotherapy with proton beams: Variables affecting optimal prostate plan

Abstract

Inverse planning for intensity- and energy-modulated radiotherapy (IEMRT) with proton beams involves the selection of (i) the relative importance factors to control the relative importance of the target and sensitive structures, (ii) an appropriate energy resolution to achieve an acceptable depth modulation, (iii) an appropriate beamlet width to modulate the beam laterally, and (iv) a sufficient number of beams and their orientations. In this article we investigate the influence of these variables on the optimized dose distribution of a simulated prostate cancer IEMRT treatment. Good dose conformation for this prostate case was achieved using a constellation of I factors for the target, rectum, bladder, and normal tissues of 500, 50, 15, and 1, respectively. It was found that for an active beam delivery system, the energy resolution should be selected on the basis of the incident beams' energy spread (sigmaE) and the appropriate energy resolution varied from 1 MeV at sigmaE = 0.0 to 5 MeV at sigmaE= 2.0 MeV. For a passive beam delivery system the value of the appropriate depth resolution for inverse planning may not be critical as long as the value chosen is at least equal to one-half the FWHM of the primary beam Bragg peak. Results indicate that the dose grid element dimension should be equal to or no less than 70% of the beamlet width. For this prostate case, we found that a maximum of three to four beam ports is required since there was no significant advantage to using a larger number of beams. However for a small number (< or = 4) of beams the selection of beam orientations, while having only a minor effect on target coverage, strongly influenced the sensitive structure sparing and normal tissue integral dose.

Optimized treatment planning using intensity and energy modulated proton and very high energy electron beams

“…In the case of prostate cancer Model V, it was observed that a maximum of eleven beam ports was sufficient for IMXT and VHEET, and that the best plan for each modality resulted from the beam arrangement for which the first beam was incident at a gantry angle of approximately 7°. For IMPT the fourfield configuration from {0°, 90°, 180°, 270°} gave the "best" dose distribution for Model V among the set of one to nine-field plans, as reported in chapter 4 (Yeboah et al 2002). TABLE 6.1 summarizes the beam and optimization parameters used for designing the "best" plans for the three modalities under consideration for each prostate cancer model.…”

“…Model IV is an even more complex target problem that comprises of a butterfly-shaped target overlapping with both sensitive structures where the regions of overlap are taken to be target regions. Finally, Model V is similar to Model IV, however, unlike the latter, the target does not overlap with the rectum or bladder (Yeboah et al 2002). Instead, it is in direct contact with these sensitive structures in the anterior and posterior concavities.…”

“…Dose kernels for individual beamlets of size 5 mm 2 were pre-calculated using the proton loss model pencil beam algorithm (Sandison and Chvetsov 2000). To implement depth modulation the Bragg peak location of the 200 MeV beam was chosen as the greatest depth and then Bragg peaks were selected to occur at progressively shallower depths corresponding to a depth resolution of 0.4 cm (Yeboah et al 2002).…”

Proposal for Comprehensive Quality Control of Heavy-Ion Medical Accelerator

“…6) Unlike proton therapy, all heavyion medical accelerators utilize synchrotron accelerators and a combination of scattering (or passive beam) and scanning (or pencil beam) beam for irradiation. [6][7][8][9][10] However, it is understood that IBA, which has previously operated cyclotron accelerators, is working in tandem with Russia's JINR to install a heavy-ion accelerator based [24][25][26][27] Thus, it is expected, based on the cancer treatment trends in local proton therapy treatment centers, that the proportion of patients opting for heavy-ion medical accelerator treatment would be significant should it be introduced formally. Furthermore, noting that a radiotherapy for cancer in certain organs such as the lung and the liver may potentially result in undesirable side effects on other healthy organs exposed to low doses of radiation, it is possible to predict that the demand for heavy-ion medical accelerator treatment will increase for lung and liver cancer patients, as studies attesting to the ability of heavy-ion accelerators to focus radiation doses on the tumor target and reduce radioactive exposure to the peripheral organs increase in number.…”

Particle selection for laser‐accelerated proton therapy feasibility study

“…Because of the possibility of giving a homogeneous dose distribution in the target's depth direction, 12,13 one can expect that energy-and intensity-modulated proton therapy ͑EIMPT͒ will further improve target coverage and normal tissue sparing effects. In recent years, the planning and delivery of x rays has improved considerably so that the gap between the conventional proton techniques and x-ray methods has decreased dramatically.…”