Determining whether multiple needles are necessary in interstitial brachytherapy for thoracic tumors: A dosimetry analysis.

BACKGROUND

In interstitial brachytherapy, needles must be inserted in a regular, parallel arrangement to ensure a uniform target dose distribution and conformal distribution to the target. It is generally difficult to achieve this in thoracic tumors because of obstruction by the ribs. Furthermore, insertion of multiple needles may cause the patient considerable harm and could expose him/her to additional risks. Thus, we propose the single-dwell-position method, discuss its applicability, and compare it with the actual multiple-needle method using dosimetry. The aim of this study was to evaluate the necessity for multiple needles with irregular alignment in interstitial brachytherapy for thoracic tumors.

METHODS

Twelve patients' interstitial brachytherapy plans were reviewed. The single-dwell-position interstitial brachytherapy plans, wherein one needle was hypothetically inserted, were compared with the actual multiple-needle plans. Dose parameters, including clinical target volume (CTV) and volumes of the lung, spinal cord, heart, and ribs, were compared. We also evaluated the correlation between CTV size and dose difference in the lungs. The nonparametric Wilcoxon test was used.

RESULTS

There were no statistically significant differences in the doses achieved with the single-dwell-position plans and actual multiple-needle plans. The correlation between the CTV size and dose difference in the lungs was weak.

CONCLUSIONS

Irregularly arranged multiple-needle interstitial brachytherapy does not provide superior doses to the lung, heart, spinal cord, or ribs compared with single-dwell-position plans. If regular arrangement of multiple needles is difficult to achieve, the multiple-needle scheme is not the only viable option.