A topology-based method to mitigate the dosimetric uncertainty caused by the positional variation of the boost volume in breast conservative radiotherapy

Abstract

BackgroundTo improve local control rate in patients with breast cancer receiving adjuvant radiotherapy after breast conservative surgery, additional boost dose to the tumor bed could be delivered simultaneously via the simultaneous integrated boost (SIB) modulated technique. However, the position of tumor bed kept changing during the treatment course as the treatment position was aligned to bony anatomy. This study aimed to analyze the positional uncertainties between bony anatomy and tumor bed, and a topology-based approach was derived to stratify patients with high variation in tumor bed localization.MethodsSixty patients with early-stage breast cancer or ductal carcinoma in situ were enrolled. All received adjuvant whole breast radiotherapy with or without local boost via SIB technique. The delineation of tumor bed was defined by incorporating the anatomy of seroma, adjacent surgical clips, and any architectural distortion on computed tomography simulation. A total of 1740 on-board images were retrospectively analyzed. Positional uncertainty of tumor bed was assessed by four components: namely systematic error (SE), and random error (RE), through anterior-posterior (AP), cranial-caudal (CC), left-right (LR) directions and couch rotation (CR). Age, tumor location, and body-mass factors including volume of breast, volume of tumor bed, breast thickness, and body mass index (BMI) were analyzed for their predictive role. The appropriate margin to accommodate the positional uncertainty of the boost volume was assessed, and the new plans with this margin for the tumor bed was designed as the high risk planning target volume (PTV-H) were created retrospectively to evaluate the impact on organs at risk.ResultsIn univariate analysis, a larger breast thickness, larger breast volume, higher BMI, and different tumor locations correlated with a greater positional uncertainty of tumor bed. However, BMI was the only factor associated with displacements of surgical clips in the multivariate analysis and patients with higher BMI were stratified as high variation group. When image guidance was aligned to bony structures, the SE and RE of clip displacement were consistently larger in the high variation group. The corresponding PTV-H margins for the high- and low-variation groups were 7, 10, 10 mm and 4, 9, 6 mm in AP, CC, LR directions, respectively. The heart dose between the two plans was not significantly different, whereas the dosimetric parameters for the ipsilateral lung were generally higher in the new plans.ConclusionsIn patients with breast cancer receiving adjuvant radiotherapy, a higher BMI is associated with a greater positional uncertainty of the boost tumor volume. More generous margin should be considered and it can be safely applied through proper design of beam arrangement with advanced treatment techniques.

A novel, adaptable, radiographically opaque, multi-plane continuous filament marker for optimizing tissue identification, radiation planning, and radiographic follow-up

“…The exact recommended placement and number of surgical clips for tumor bed identification with radiation planning varies (2,18,(21)(22)(23)(24)28,29). Clips have been reported to move or 'migrate' from their initial placement location (9,24,25,(30)(31)(32). Clip migration was noted to be similar between groups of patients' XRT 100 days (median 53 days) from surgery to group starting afterward (median 163 days) (31).…”

“…Clip migration after conventional breast surgery (closing the breast superficially) in comparison to lumpectomy with partial breast reconstruction techniques (sutured cavity) may not differ significantly (31). A potential relationship to body mass index and clip migration may has also been reported (30). Surgical techniques to decrease potential for displacement has been described (16).…”

The Factors of Fiducial Marker Motion and Individual Margin Assessment in Postoperative Breast Cancer Radiotherapy

“…However, the breast position and deformation are susceptible to respiratory motion, setup error and patient immobilization [3,4] . Previous studies have shown that surgical clips implanted in lumpectomy cavity during surgery can improve the accuracy of the target volume delineation and localization [5,6,7,8] . So, for improving the radiation accuracy, surgical clips inserted in are often used to mark the tumor bed.…”

Accelerated Partial Breast Irradiation

“…27 The position of the tumor bed can change in a subset of patients (eg, larger breast volume) during the course of treatment (ie, in distinction to changes in the volume of the cavity discussed above). 28 In 2015, Glide-Hurst et al 29 assessed changes in the lumpectomy cavity during external beam radiation treatment (intrafraction variability) using deformable registration. In this study, 16 left-sided and 1 bilateral breast cancer cases were simulated using both a free-breathing CT as well as a 10-phase 4DCT.…”

“…Finally, 1 consideration is to record and account for 3D pathologic margins with anisotropic margin expansion of the clinical target volume from the tumor bed to reduce the volume of irradiated volume or to reduce the overall margin due to increased precision of the technology; however, this too can increase the risk of interobserver variation or target misses 27. The position of the tumor bed can change in a subset of patients (eg, larger breast volume) during the course of treatment (ie, in distinction to changes in the volume of the cavity discussed above) 28. In 2015, Glide-Hurst et al29 assessed changes in the lumpectomy cavity during external beam radiation treatment (intrafraction variability) using deformable registration.…”