Abstract
Purpose: To study the difference of physical dose of target volume and lungs among actual irregular arrangement multi-needle interstitial brachytherapy plan (AIBP), virtual regular arrangement multi-needle interstitial brachytherapy plan (VRBP) and virtual single needle center point interstitial brachytherapy plan (VSBP). Methods: According to the inclusion criteria: the CTV shape was approximately spherical and multiply needles arrangement was irregular. Thirteen lung cancer patients underwent interstitial brachytherapy were collected. Based on the thirteen CT data sets, the AIBP, VRBP and VSBP were respectively designed, then we collected the dose metrics involving: the minimum dosage received by 95% of the CTV (D95), D90, D80, D50 and D30; the percentage of lung volume receiving a dose of ≥ 5 Gy (V5), V20, V30 and the mean lung dose (MLD); D50 of heart; the maximum dose (Dmax) of spinal cord and the Dmax of ribs. The differences were tested by the two-sample paired (Wilcoxon) signed rank test, a P value less than 0.05 was considered statistically significant. Result: The differences of D95, D90, D80, D50 and D30 of CTV, D50 of heart, Dmax of spinal and Dmax of ribs were not statistical significant (P>0.05) and the V5, V20, V30 and MLD of lungs and ipsilateral lung were statistical significant (P 0.05) except for D30 of CTV (P<0.05) between AIBP and VRBP. Conclusion: In interstitial brachytherapy for lung tumor, the arrangement of implantation needles could influenced the dose distribution in target and lungs. If the CTV shape could be approximately considered to be a spherical and a regular arrangement of multiply needles was difficult to achieve; the lung dose of the AIBP might have no obvious advantage over the VSBP and the VSBP should be worth a try.
Highlights
A basic principle of radiotherapy planning is to maximize the target dose, as much as possible to reduce the amount of normal tissue [1]
All the dose metrics expect for D30 were not statistical significant (P>0.05) between arrangement multi-needle interstitial brachytherapy plan (AIBP) and VSBP (Table 3)
VRBP: virtual regular arrangement multi-needle interstitial brachytherapy plan; AIPB: actual irregular arrangement multi-needle interstitial brachytherapy plan; Dx: the the minimum dosage received by x% of the CTV; Vx: the percentage of lung volume received x Gy; MLD: the mean lung dose
Summary
A basic principle of radiotherapy planning is to maximize the target dose, as much as possible to reduce the amount of normal tissue [1]. In order to meet this principle, a parallel arrangement of the multiple implantation needles with uniformly-spaced was recommend [2]. If the tumor was located in the chest and surrounded by ribs, the route of implantation needles were greatly restricted. It becomes difficult to achieve a regular arrangement of multiple implantation needles. In most of clinical cases, multiple implantation needles arrangement was non parallel nor uniformly-spaced (Figure 1g). This might lead to an increasing of lung dose comparing with the regular arrangement of multiple implantation needles
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