Efficacy and workload analysis of a fixed vertical couch position technique and a fixed-action-level protocol in whole-breast radiotherapy

Is intensive training with a time interval between instruction and planning CT necessary for deep inspiration breath-hold radiotherapy in breast cancer?

BACKGROUND

Breathing instruction and exercises and a time gap between training and planning CT scans (pCT) is recommended as part of deep inspiration breath-hold (DIBH) assisted radiotherapy (RT). However, this is associated with additional time expenditure.

MATERIALS AND METHODS

In two of the authors' treatment centers (TC), patient training took place before the planning CT of DIBH-assisted therapy. In TC 1, a further appointment was made with a minimum interval of 2 days to perform the planning CT. At TC 2, the planning CT was performed immediately after the first patient instruction. A retrospective evaluation of the clinical parameters of the therapy was carried out to investigate the relevance of the time gap between DIBH exercises and pCT.

RESULTS

A total of 72 patients were included, 35 of whom were treated in TC 1 and 37 in TC 2. In TC 1, an average interval of ~4 days was observed between patient training and planning CT, while in TC 2, training and CT were performed immediately after each other. No significant differences in radiation dose exposure of the lung on the treated side, the whole lung, or the heart were found between the two centers. Furthermore, there was no significant difference in the application of the daily RT fraction. The requirement for daily positioning checks was also the same at both treatment centers.

CONCLUSION

This study does not show any advantages for a time gap between instruction/training and pCT. Skipping the time break does not deteriorate any clinically relevant endpoints.

A study of the dosimetric impact of daily setup variations measured with cone-beam CT on three-dimensional conformal radiotherapy for early-stage breast cancer delivered in the prone position

PURPOSE

To evaluate the dosimetric impact of daily positioning variations measured with cone-beam computed tomography (CBCT) on whole-breast radiotherapy patients treated in the prone position.

METHODS

Daily CBCT was prospectively acquired for 30 consecutive patients positioned prone. Treatment for early-stage (≤II) breast cancer was prescribed with standard dose (50 Gy/25 fractions) or hypofractionation (42.56 Gy/16 fractions) for 13 and 17 patients, respectively. Systematic and random errors were calculated from the translational CBCT shifts and used to determine population-based setup margins. Mean translations (±one standard deviation) for each patient were used to simulate the dosimetric impact on targets (PTV_eval and lumpectomy cavity), heart, and lung. Paired Student's t tests at α = 0.01 were used to compare dose metrics after correction for multiple testing (P < 0.002). Significant correlation coefficients were used to identify associations (P < 0.01).

RESULTS

Of 597 total fractions, 20 ± 13% required patient rotation. Mean translations were 0.29 ± 0.27 cm, 0.41 ± 0.34 cm, and 0.48 ± 0.33 cm in the anterior-posterior, superior-inferior, and lateral directions leading to calculated setup margins of 0.63, 0.88, and 1.10 cm, respectively. Average three-dimensional (3D) shifts correlated with the maximum distance of breast tissue from the sternum (r = 0.62) but not with body-mass index. Simulated shifts showed significant, but minor, changes in dose metrics for PTV_eval, lung, and heart. For left-sided treatments (n = 18), mean heart dose increased from 109 ± 75 cGy to 148 ± 115 cGy. Shifts from the original plan caused PTV_eval hotspots (V105%) to increase by 5.2% ± 3.8%, which correlated with the total MU of wedged fields (r = 0.59). No significant change in V95% to the cavity was found.

CONCLUSIONS

Large translational variations that occur when positioning prone breast patients had small but significant dosimetric effects on 3DCRT plans. Daily CBCT may still be necessary to correct for rotational variations that occur in 20% of treatments. To maintain planned dose metrics, unintended beam shifts toward the heart and the contribution of wedged fields should be minimized.

Technical note: improved positioning protocol for patient setup accuracy in conventional radiotherapy for lung cancer

This study aimed to investigate an improved setup protocol for maintaining patient setup accuracy, with minimal or no use of image-guided radiation therapy in conventional radiotherapy for lung cancer. A coordinate value for the treatment couch in the anterior-posterior (AP) direction was obtained from the first fraction using bony anatomy image guidance. The coordinate value was invariably used for patient positioning in the second and subsequent treatment fractions. The errors of 2410 setup image sets (anterior and lateral) from 105 patients with lung cancer were analyzed. The systematic and random patient positioning errors in the AP direction were 0.6 ± 1.0 mm. Such errors accounted for 97% of all fractions within ± 2 mm. The protocol resulted in minimal patient setup errors in the AP direction using only one image for guidance; therefore, it may be applied to conventional radiotherapy for lung cancer in case of insufficient image guidance.