Automated IMRT planning with regional optimization using planning scripts

Abstract

Intensity-modulated radiation therapy (IMRT) has become a standard technique in radiation therapy for treating different types of cancers. Various class solutions have been developed for simple cases (e.g., localized prostate, whole breast) to generate IMRT plans efficiently. However, for more complex cases (e.g., head and neck, pelvic nodes), it can be time-consuming for a planner to generate optimized IMRT plans. To generate optimal plans in these more complex cases which generally have multiple target volumes and organs at risk, it is often required to have additional IMRT optimization structures such as dose limiting ring structures, adjust beam geometry, select inverse planning objectives and associated weights, and additional IMRT objectives to reduce cold and hot spots in the dose distribution. These parameters are generally manually adjusted with a repeated trial and error approach during the optimization process. To improve IMRT planning efficiency in these more complex cases, an iterative method that incorporates some of these adjustment processes automatically in a planning script is designed, implemented, and validated. In particular, regional optimization has been implemented in an iterative way to reduce various hot or cold spots during the optimization process that begins with defining and automatic segmentation of hot and cold spots, introducing new objectives and their relative weights into inverse planning, and turn this into an iterative process with termination criteria. The method has been applied to three clinical sites: prostate with pelvic nodes, head and neck, and anal canal cancers, and has shown to reduce IMRT planning time significantly for clinical applications with improved plan quality. The IMRT planning scripts have been used for more than 500 clinical cases.

Figure 1

An overview of the steps completed by each script for a clinical site.

Figure 2

Jaw positions for IMRT fields are fixed in the script to reduce probability of local minimum to avoid beam splitting for more accurate and efficient radiation delivery.

Figure 3

DVH comparison for a head and neck case between manually (dashed line) and automatically generated plans (solid line).

Figure 4

Comparison of dose distribution on a transverse slice for a head and neck case between manually generated IMRT plan and automatically generated IMRT plan using the iterative method. Red shaded volume is PTV70 covered by 70 Gy isodose line in blue, and green shaded volume is PTV63 covered by 63 Gy isodose line in black.

Figure 5

DVH comparison for a prostate case with pelvic nodes irradiation between manually (dashed line) and automatically generated IMRT plans (solid line).

Figure 6

Comparison of dose distribution on a coronal slice for a prostate case with pelvic nodes between manually and automatically generated IMRT plans. Red shaded volume is PTV76 for prostate covered by 76 Gy isodose line shown in dark blue and purple shaded volume is PTV45 for pelvic nodes covered by 45 Gy isodose line shown in light blue.

Figure 7

DVH comparison for an anal canal irradiation between manually (dashed line) and automatically generated IMRT plans (solid line).

Figure 8

Comparison of dose distributions on a transverse and a sagittal slice for anal canal case between manually and automatically generated IMRT plans. Red, pink, and blue shaded volumes are PTV36, PTV45, and PTV54, respectively, covered by the isodose line 36 Gy shown in green, 45 Gy shown in purple, and 54 Gy shown in blue, respectively.

Figure 9

Comparison of dose distribution on the coronal slice for a head and neck case before (left) and after (right) automated regional optimization. Shaded volumes are PTV70 (blue), PTV63 (green), and PTV56 (red), respectively.