PV QA 3 - Poster Viewing Q&A 3
Purpose/Objective(s): Helical tomotherapy is suitable for irradiating multiple targets at once. However, treatment time becomes long when the targets are separated in craniocaudal direction, since the couch moves slowly at a uniform pace. The dynamic-jaw and dynamic-couch (DJDC) mode offers dynamic jaw alignment throughout the treatment and variable couch speeds allowing faster movement in unirradiated parts of the body, but it is not yet available for clinical use. To solve the problem of long treatment time, we invented a new technique using multiple static-port tomotherapy with the dynamic-jaw mode and named it pseudo-DJDC (pDJDC) technique. We compared the pDJDC plans and helical tomotherapy plans using the dynamic-jaw mode (HDJ) for multiple targets.
Materials/Methods: In pDJDC plans, we use a beam set with 4-6 ports to the targets at the same level in the craniocaudal direction and employ another beam set for other targets using different port angles (9-12 angles in total). The couch moves fast during the intervals between the different beam sets. In 7 patients, 2 plans using the pDJDC and HDJ techniques were compared. Four of the 7 patients had multiple (n=2-6) distant metastases including those to the rib and lymph node and peritoneal dissemination. Two patients had esophageal cancer with 3 targets including a primary tumor and regional metastases. The other patient had 2 pleural disseminations from a thymic tumor. For multiple distant metastases, 25-40 Gy in 2- to 5-Gy fractions were prescribed for the planning target volumes at D50%. For esophageal cancer, 20-22 Gy in 2-Gy fractions were prescribed as boost plans. For thymic tumor, 60 Gy in 7.5-Gy fractions were prescribed. Conformity index, uniformity index (D5%/D95%), dose distribution in the lung, and beam-on time were evaluated using Wilcoxon signed-rank test.
Results: The median conformity index of all 7 patients was 3.0 for the pDJDC plans and 2.4 for the HDJ plans (P = .031). The median uniformity index of the planning target volume (n=25) for the 2 plans was 1.048 and 1.057, respectively (P = .10). For 5 patients with thoracic targets, the median of the mean lung dose was 2.6 Gy and 2.4 Gy, respectively (P = .63). The median V5Gy and V20Gy of the lung in the 5 patients were 11.8% and 8.5% (P = .63) and 1.6% and 2.1% (P = .32), respectively. The pDJDC plans reduced the beam-on time by 52% compared to the HDJ plans (median; 421 and 883 seconds, respectively, P = .016)
Conclusion: The pDJDC technique enables treatment of multiple targets in half time compared to the HDJ technique. The pDJDC plans were comparable to the HDJ plans in dose distribution except the conformity index.
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