Multifield optimization intensity-modulated proton therapy (MFO-IMPT) for prostate cancer: Robustness analysis through simulation of rotational and translational alignment errors

Abstract

Purpose To evaluate the dosimetric consequences of rotational and translational alignment errors in patients receiving intensity-modulated proton therapy with multi-field optimization (MFO-IMPT) for prostate cancer. Materials and Methods Ten control patients with localized prostate cancer underwent treatment planning for MFO-IMPT. Rotational and translation errors were simulated along each of three axes: anterior–posterior (A-P), superior–inferior (S-I), and left–right. Results Clinical target volume (CTV) coverage remained high with all alignment errors simulated. Rotational errors did not result in significant rectum or bladder dose perturbations. Translational errors resulted in larger dose perturbations to the bladder and rectum. Perturbations in rectum and bladder doses were minimal for rotational errors and larger for translational errors. Rectum V45 and V70 increased most with A-P misalignment, whereas bladder V45 and V70 changed most with S-I misalignment. The bladder and rectum V45 and V70 remained acceptable even with extreme alignment errors. Even with S-I and A-P translational errors of up to 5 mm, the dosimetric profile of MFO-IMPT remained favorable. Conclusions MFO-IMPT for localized prostate cancer results in robust coverage of the CTV without clinically meaningful dose perturbations to normal tissue despite extreme rotational and translational alignment errors.

Proton energy optimization and reduction for intensity-modulated proton therapy

“…2010, Pugh et al , 2013; Liu et al , 2014; Li et al , 2014; Lomax et al , 2004; Stuschke et al , 2012). The demand for IMPT is rapidly increasing.…”

“…As pointed out by many other researchers (Albertini et al , 2007; Albertini et al , 2010; Oelfke and Bortfeld, 2000; Lomax, 1999), IMPT plans may be even more degenerate than intensity-modulated radiation therapy plan (Alber et al , 2002; Jorge et al , 2004; Webb, 2003), because IMPT has one more degree of freedom, i.e., the range of protons, than intensity-modulated radiation therapy. For IMPT plans with multi-field optimization (Pugh et al , 2013), intensities of scanning spots at different two-dimensional positions in different energy layers from different treatment beam angles are independently modulated and optimized. It is likely to find certain treatment plans to achieve desired dose distributions by specifically devising optimization models such as the energy-constrained model we implemented in this study.…”

Proton Beam Therapy for Localized Prostate Cancer: Results from a Prospective Quality-of-Life Trial

“…For IMPT, a scanning target volume margin was applied as follows: 12 mm laterally and 6 mm in all other dimensions, except 4 to 5 mm posteriorly to the CTV. The IMPT treatment-planning technique and robustness have been described previously [16][17][18][19][20]. The total prescribed dose was 75.6 to 78 Gy (RBE), delivered in equivalent 1.8 to 2 Gy (RBE) fractions.…”

Prospective MRI-based imaging study to assess feasibility of proton therapy for post-prostatectomy radiation

“…Several prior studies have examined the robustness of proton therapy plans for patients receiving radiotherapy to the prostate, seminal vesicles, and/or the pelvic lymph nodes [16][17][18][19][20]. The results of these studies have identified strategies to optimize proton therapy delivery through selection of beam angles less sensitive to patient setup error, modification of planning optimization techniques, or patient alignment strategies that minimize displacement of internal pelvic anatomy (e.g.…”