Inter-fractional variations in the dosimetric parameters of accelerated partial breast irradiation using a strut-adjusted volume implant.

Akihisa Wakita,Akimoto Sugawara,Ako Aikawa,Etsuo Kunieda,Hiroyuki Okamoto,Jun Itami,Kana Takahashi,Ken Harada,Kotaro Iijima,Ryoichi Notake,Ryoichi Yoshimura,Satoshi Nakamura,Shie Nishioka

doi:10.1093/jrr/rrz061

Abstract

The aim of the study was to evaluate inter-fractional dosimetric variations for high-dose rate breast brachytherapy using a strut-adjusted volume implant (SAVI). For the nine patients included, dosimetric constraints for treatment were as follows: for the planning target volume for evaluation (PTV_Eval), the volume receiving 90, 150 and 200% of the prescribed dose (V90%,150%,200%) should be >90%, ≤50 cm3 and ≤20 cm3, respectively; the dose covering 1 cm3 (D1cc) of the organs at risk should be ≤110% of the prescribed dose; and the air volume should be ≤10% of PTV_Eval. Differences in V90%,150%,200%, D1cc and air volume (n}{}Delta V and n}{}Delta D) as inter-fractional dosimetric variations and SAVI displacements were measured with pretreatment and planning computed tomography (CT) images. Inter-fractional dosimetric variations were analyzed for correlations with the SAVI displacements. The patients were divided into two groups based on the distance of the SAVI from the surface skin to assess the relationship between the insertion position of the SAVI and dosimetric parameters. The median ΔV90%,150%,200% for the PTV_Eval in all patients was −0.3%, 0.2 cm3 and 0.2 cm3, respectively. The median (range) ΔD1cc for the chest wall and surface skin was −0.8% (−18.9 to 9.4%) and 0.3% (−7.6 to 5.3%), respectively. SAVI displacement did not correlate with inter-fractional dosimetric variations. In conclusion, the dose constraints were satisfied in most cases. However, there were inter-fractional dosimetric changes due to SAVI displacement.

Highlights

Postoperative external-beam radiation therapy (EBRT) to the whole breast with 42.56 Gy in 16 fractions is currently the standard of care after lumpectomy for early breast cancer
For the surface skin and chest wall, inter-fractional variations in D1cc with reference to the CTplan image were calculated as: D1cc [%] = Dt1rcecat − Dp1clacn, Figure 5 illustrates the three-dimensional vector of strutadjusted volume implant (SAVI) displacement
The rate of SAVI displacement ≥10 mm was 19.3%, and the rate of Sx,y,z displacement ≥5 to ≤−5 mm was 5.7, 5.7 and 26.4%, respectively. These findings show that the SAVI moves in the anterior–posterior direction

Summary

Introduction

Postoperative external-beam radiation therapy (EBRT) to the whole breast with 42.56 Gy in 16 fractions is currently the standard of care after lumpectomy for early breast cancer. It is conducted within 4–5 weeks and places a significant burden on the patient [1,2,3,4,5,6,7]. Because of its limited irradiated volume, APBI can be completed in a shorter period of time, even less than 1 week [8,9,10,11,12,13,14]. By manipulating the source dwell points and times in multiple catheters, optimized dose distribution is achieved while minimizing the dose to organs at

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Conclusion