Megavoltage versus kilovoltage image guidance for efficiency and accuracy in head and neck IMRT

Analysis of Online and Offline Head and Neck Image-guided Radiation Therapy

PURPOSE

The introduction of a daily image-guided radiation therapy (IGRT) program is an important step. It has implications for the radiation therapy team in terms of accuracy, workflow, and decision making. This study assesses how successful a radiation therapy department has been in using this technology and the accuracy of individual decision making when comparing online and offline image match data.

METHODS

Twenty intensity-modulated radiation therapy head and neck patients had their IGRT data assessed retrospectively. Online analysis was completed based on a 0-mm action threshold. Offline analysis was then conducted on the same data. Any discrepancies in decision making were then assessed.

RESULTS

Results indicated that the treating radiation therapy team was able to image match consistently when benchmarked against their colleagues in the offline environment. Analysis of online versus offline corrections in each of the three orthogonal directions showed strong agreement. Further analysis revealed no statistically significant differences for systematic errors, whereas a statistically significant but small difference was present for random error.

CONCLUSION

In this age of sophisticated equipment, daily IGRT is a valuable modality. However, the introduction of daily online IGRT inclusive of a 0-mm action threshold for head and neck IGRT requires careful consideration and evidence that such accuracy can be achieved. Ultimately, it is still the radiation therapist who must make the decision, which places great importance on the competency of the treating radiation therapy team.

Quality Improvement Investigation for Head and Neck Stabilization in Radiotherapy Using Setup Tattoos

PURPOSE

Highly complex planning techniques and delivery methods in the treatment of head and neck cancer require an advanced level of accuracy and reproducibility.

AIM

To determine if the addition of tattoos placed on the chest inferior to the CIVCO Vac-Lok stabilization system improves accuracy and reproducibility of patient set up.

METHODS

Eighteen patients with head and neck cancer were studied. Nine underwent radical treatment using the routine CIVCO stabilization system. The second group of nine used the same stabilization device but were positioned daily with the use of tattoos. Daily orthogonal kilovoltage setup images were used to calculate setup errors. Displacements in the left/right (Lt/Rt), superior/inferior (Sup/Inf), and anterior/posterior (Ant/Post) directions were determined as well as pitch and yaw rotational errors.

RESULTS

Five hundred and twenty-three image pairs were analysed. Clinically significant differences were found in yaw error, Lt/Rt displacement, and Sup/Inf displacement in the tattooed patients. The median (interquartile range) absolute yaw error was larger for patients without tattoos: 1.4° (1.4° to 2.1°) compared to 0.8° (0.8° to 1.4°) for patients with tattoos. The percentage of both Sup/Inf and Lt/Rt errors >3 mm was also greater for patients without tattoos: 23.7% of Sup/Inf errors were >3 mm compared with 17.3% for patients with tattoos, and 22.3% of Lt/Rt errors were >3 mm compared with 10.0% for patients with tattoos.

CONCLUSION

The addition of chest tattoos resulted in clinically relevant improvements in Lt/Rt and Sup/Inf translational displacements and variations in yaw for head and neck cancer patients.