Assessment of Dosimetric Changes and Adaptive Replanning for Intraoperatively Placed Brachytherapy Applicators during Accelerated Partial Breast Irradiation

Abstract

PurposeAt our institution, the low false negative rate of frozen pathology margin assessment has enabled intraoperative brachytherapy catheter placement and completion of adjuvant APBI in less than one and half weeks from breast conserving surgery (BCS). It is unclear how immediate postoperative tissue changes related to inflammation and seroma formation affect radiation delivery compared to delayed catheter placement. The purpose of this study was to assess daily postoperative changes in the lumpectomy cavity and the corresponding dosimetric consequences during APBI.Materials and MethodsTwenty consecutive patients undergoing BCS for either ductal carcinoma in-situ or invasive breast cancer had intraoperative placement of the strut-adjusted volume implant (SAVI) brachytherapy device. CT simulation was performed on the next weekday following surgery, and 3-D treatment planning was accomplished on Eclipse BrachyVision per RTOG guidelines. On the subsequent weekday, brachytherapy treatments commenced to deliver a total dose of 34 Gy in 10 (n=17) or 32 Gy in 8 fractions (n=3) to the PTVEval. Limited field of view verification CT scans were obtained prior to each morning fraction. Adaptive replanning was utilized during the course of treatment at the discretion of the treating physician due to concerns about anatomical changes or changes in catheter position. Retrospective analysis of daily dosimetric changes was performed by propagating the original treatment plan to each daily verification CT scan and scaling dwell positions to account for radioisotope decay.ResultsOne hundred ninety-four fractions were delivered and 113 CT images were obtained from 20 patients. The mean initial lumpectomy cavity and PTVEval volumes were 25.7±13.0 cc and 74.2±22.4 cc, respectively. Lumpectomy cavity and PTVEval volumes exhibited a mean daily change of -2.5±3.8 cc and -2.3±7.2 cc, respectively. The mean V90 and V95 for the PTVEval on the initial plans were 96.9±1.1% and 94.2±1.2%, respectively. Corresponding values for the mean V150 and V200 were 32.1±7.4 cc and 15.4±2.9 cc. Six (30%) of the patients had adaptive replanning during APBI and all replans were completed during the first three days of APBI. Adaptive replans were more likely to be performed in patients with higher lumpectomy cavity air volumes and with lumpectomy cavities in close proximity to the chest wall on the planning CT. Retrospective analysis demonstrated that 4 out of 6 (67%) replans were dosimetrically necessary in order to achieve adequate PTVEval coverage (n=2) and avoid excessive chest wall doses (n=2).ConclusionsOur study demonstrates the feasibility of APBI delivery employing an intraoperatively placed applicator, which allows patients to complete their breast conserving therapy within one and a half weeks. Adaptive replanning was utilized in 30% of patients based on the treating physicians' discretion; however, 20% actually required replans based on retrospective dosimetric analyses. Potential dosimetric changes and adaptive replanning should be considered in APBI patients with an intraoperatively placed applicator, especially when increased air volume and close lumpectomy cavity proximity to the chest wall are noted on initial planning CT. Further analyses are ongoing to better identify which patients are most likely to require adaptive replanning. PurposeAt our institution, the low false negative rate of frozen pathology margin assessment has enabled intraoperative brachytherapy catheter placement and completion of adjuvant APBI in less than one and half weeks from breast conserving surgery (BCS). It is unclear how immediate postoperative tissue changes related to inflammation and seroma formation affect radiation delivery compared to delayed catheter placement. The purpose of this study was to assess daily postoperative changes in the lumpectomy cavity and the corresponding dosimetric consequences during APBI. At our institution, the low false negative rate of frozen pathology margin assessment has enabled intraoperative brachytherapy catheter placement and completion of adjuvant APBI in less than one and half weeks from breast conserving surgery (BCS). It is unclear how immediate postoperative tissue changes related to inflammation and seroma formation affect radiation delivery compared to delayed catheter placement. The purpose of this study was to assess daily postoperative changes in the lumpectomy cavity and the corresponding dosimetric consequences during APBI. Materials and MethodsTwenty consecutive patients undergoing BCS for either ductal carcinoma in-situ or invasive breast cancer had intraoperative placement of the strut-adjusted volume implant (SAVI) brachytherapy device. CT simulation was performed on the next weekday following surgery, and 3-D treatment planning was accomplished on Eclipse BrachyVision per RTOG guidelines. On the subsequent weekday, brachytherapy treatments commenced to deliver a total dose of 34 Gy in 10 (n=17) or 32 Gy in 8 fractions (n=3) to the PTVEval. Limited field of view verification CT scans were obtained prior to each morning fraction. Adaptive replanning was utilized during the course of treatment at the discretion of the treating physician due to concerns about anatomical changes or changes in catheter position. Retrospective analysis of daily dosimetric changes was performed by propagating the original treatment plan to each daily verification CT scan and scaling dwell positions to account for radioisotope decay. Twenty consecutive patients undergoing BCS for either ductal carcinoma in-situ or invasive breast cancer had intraoperative placement of the strut-adjusted volume implant (SAVI) brachytherapy device. CT simulation was performed on the next weekday following surgery, and 3-D treatment planning was accomplished on Eclipse BrachyVision per RTOG guidelines. On the subsequent weekday, brachytherapy treatments commenced to deliver a total dose of 34 Gy in 10 (n=17) or 32 Gy in 8 fractions (n=3) to the PTVEval. Limited field of view verification CT scans were obtained prior to each morning fraction. Adaptive replanning was utilized during the course of treatment at the discretion of the treating physician due to concerns about anatomical changes or changes in catheter position. Retrospective analysis of daily dosimetric changes was performed by propagating the original treatment plan to each daily verification CT scan and scaling dwell positions to account for radioisotope decay. ResultsOne hundred ninety-four fractions were delivered and 113 CT images were obtained from 20 patients. The mean initial lumpectomy cavity and PTVEval volumes were 25.7±13.0 cc and 74.2±22.4 cc, respectively. Lumpectomy cavity and PTVEval volumes exhibited a mean daily change of -2.5±3.8 cc and -2.3±7.2 cc, respectively. The mean V90 and V95 for the PTVEval on the initial plans were 96.9±1.1% and 94.2±1.2%, respectively. Corresponding values for the mean V150 and V200 were 32.1±7.4 cc and 15.4±2.9 cc. Six (30%) of the patients had adaptive replanning during APBI and all replans were completed during the first three days of APBI. Adaptive replans were more likely to be performed in patients with higher lumpectomy cavity air volumes and with lumpectomy cavities in close proximity to the chest wall on the planning CT. Retrospective analysis demonstrated that 4 out of 6 (67%) replans were dosimetrically necessary in order to achieve adequate PTVEval coverage (n=2) and avoid excessive chest wall doses (n=2). One hundred ninety-four fractions were delivered and 113 CT images were obtained from 20 patients. The mean initial lumpectomy cavity and PTVEval volumes were 25.7±13.0 cc and 74.2±22.4 cc, respectively. Lumpectomy cavity and PTVEval volumes exhibited a mean daily change of -2.5±3.8 cc and -2.3±7.2 cc, respectively. The mean V90 and V95 for the PTVEval on the initial plans were 96.9±1.1% and 94.2±1.2%, respectively. Corresponding values for the mean V150 and V200 were 32.1±7.4 cc and 15.4±2.9 cc. Six (30%) of the patients had adaptive replanning during APBI and all replans were completed during the first three days of APBI. Adaptive replans were more likely to be performed in patients with higher lumpectomy cavity air volumes and with lumpectomy cavities in close proximity to the chest wall on the planning CT. Retrospective analysis demonstrated that 4 out of 6 (67%) replans were dosimetrically necessary in order to achieve adequate PTVEval coverage (n=2) and avoid excessive chest wall doses (n=2). ConclusionsOur study demonstrates the feasibility of APBI delivery employing an intraoperatively placed applicator, which allows patients to complete their breast conserving therapy within one and a half weeks. Adaptive replanning was utilized in 30% of patients based on the treating physicians' discretion; however, 20% actually required replans based on retrospective dosimetric analyses. Potential dosimetric changes and adaptive replanning should be considered in APBI patients with an intraoperatively placed applicator, especially when increased air volume and close lumpectomy cavity proximity to the chest wall are noted on initial planning CT. Further analyses are ongoing to better identify which patients are most likely to require adaptive replanning. Our study demonstrates the feasibility of APBI delivery employing an intraoperatively placed applicator, which allows patients to complete their breast conserving therapy within one and a half weeks. Adaptive replanning was utilized in 30% of patients based on the treating physicians' discretion; however, 20% actually required replans based on retrospective dosimetric analyses. Potential dosimetric changes and adaptive replanning should be considered in APBI patients with an intraoperatively placed applicator, especially when increased air volume and close lumpectomy cavity proximity to the chest wall are noted on initial planning CT. Further analyses are ongoing to better identify which patients are most likely to require adaptive replanning.