Skin Dmax Research Articles

Abstract P1-10-11: Optical stimulated luminescence dosimeters for skin dose measurements during accelerated partial breast brachytherapy: In vivo dosimetric validation and clinical outcomes

Abstract BACKGROUND: The role of multi-lumen catheter devices in the delivery of high dose rate (HDR) brachytherapy for adjuvant accelerated partial breast irradiation (APBI) for women with DCIS or early-stage breast cancer has been well established. In vivo dosimetry (IVD) using optically stimulating luminescence dosimeters (OSLD) is a feasible way to detect applicator instability that may cause translational and rotational inaccuracies during HDR brachytherapy delivery. Herein, we evaluate the accuracy and effectiveness of IVD to improve patient outcomes following APBI brachytherapy using the Strut Adjusted Volume Irradiation (SAVI) device. METHODS: Single-institution cohort study piloting the use of OSLD on the patient’s skin during HDR brachytherapy APBI to assess the estimated maximum skin dose (skin Dmax) and the achievable accuracy of OSLD for skin Dmax measurements. Women treated with SAVI-based APBI between November 1, 2018 and October 1, 2021 were eligible to enroll in our study. All patients met the American Society for Radiation Oncology “suitable” or “cautionary” criteria and were treated according to the American Brachytherapy Society consensus treatment planning guidelines. A SAVI preplan was created to estimate the probable point of skin Dmax. During CT simulation, a radiopaque marker was placed on the skin for visualization during treatment planning. Correction factors were applied to account for the OSLD tissue-air interface that is not present in the TG-43 expected dose calculations. Measured and calculated IVD doses were analyzed to assess agreement and cause for discrepancies found. Breast phantom IVD measurements repeated seven times with two independent dose points were analyzed to assess the best accuracy achievable under ideal conditions. RESULTS: We enrolled 41 patients with an average age of 68 years. Table 1 details the brachytherapy treatment delivery and dosimetry data. Higher skin Dmax as a percentage of the radiation prescription was associated with the occurrence of breast volume loss noted on subsequent clinical breast exams (OR 1.84 per each 5% increase in skin Dmax; 95% CI 1.21 – 3.32; p=0.016). The graphically estimated skin Dmax threshold was 80% with all cases of noted breast volume loss occurring above this threshold. The overall level of achievable IVD accuracy was ±3.32% based on breast phantom measurements. Under ideal conditions, all measurements were in the ±7% range. Three of 14 phantom measurement exceeded the 6% discrepancy range. Clinical IVD measurements detected 5 true positive cases (12.2% of cohort) that required intervention due to rotations in the SAVI applicator. For a ±7% tolerance criteria, 90.2% of the patients tested passed IVD. Of the eight patients that failed at the 7% level, IVD detected 3 OSLD placement errors, 2 rotational discrepancy cases, and 1 large air-gap at the point of measurement. CONCLUSIONS: Accuracy and reproducibility are imperative tenets of HDR brachytherapy APBI. IVD utilizing OSLD is an effective method for detecting treatment set-up and delivery errors for patients receiving SAVI-based APBI with dose accuracy within ±3.32%. Errors requiring intervention due to SAVI device rotation were detected in 12.2% of our cohort, and these errors would have likely gone undetected without IVD. Using OSLD as IVD to measure skin Dmax doses that may increase the risk of breast cosmetic defects should be investigated further. Table 1. Brachytherapy treatment delivery and dosimetry data. *PTV-Eval is a uniform 10 mm expansion on the CTV with exclusion of PTV within 5 mm of skin or chest wall. +Percent dose discrepancy refers to difference in dose between APBI plan calculations and IVD measurements. Citation Format: Tyler Gutschenritter, Afua Yorke, Nayak Polissar, Nirnaya Miljacic, Janice Kim, Lori Young. Optical stimulated luminescence dosimeters for skin dose measurements during accelerated partial breast brachytherapy: In vivo dosimetric validation and clinical outcomes [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-10-11.

Real-Time Online Adaptation for Accelerated Partial Breast Irradiation Significantly Improves Target Coverage without Compromising Organs at Risk

<h3>Purpose/Objective(s)</h3> Adaptive online radiotherapy (AORT) is an emerging technology that re-optimizes treatment plans based on cone-beam CT (CBCT) for accurate delivery of prescription and avoidance of critical organs at risk (OARs). Women with breast cancer who qualify for accelerated partial breast irradiation (APBI) are ideal patients for AORT as plans can adapt to daily positional and shape changes. Here we report the dosimetry benefit and the efficiency of patients receiving AORT APBI within the last year in our department. <h3>Materials/Methods</h3> We retrospectively reviewed 18 patients who received AORT APBI, with a total of 84 evaluable fractions. Two plans are made after OARs and targets are contoured on CBCT: a "scheduled" plan, the simulated plan overlaid on CBCT, and an "adapted" plan, where dose delivery is re-optimized to new contours. PTV and CTV volumes, PTV V30 Gy, CTV V30 Gy, ipsilateral breast V50% and V100%, skin Dmax, ipsilateral lung V9Gy, and heart V150cGy (if left sided disease) were collected for both the scheduled and adapted plans per fraction. CTV volume was created from GTV, defined as cavity delineated by surgical clips, plus a 1 cm radial margin limited from musculature of chest wall and 5 mm from skin. PTV was a 0-5 mm radial expansion of CTV volume. Time for adaptive planning was collected prospectively by radiation therapists. Three fractions were excluded from analysis due to setup error or pre-planned lack of adaptation. Paired t-test was used for parametric data and Wilcoxon rank sum test for nonparametric data; analyses were done in R v4.1.2 (www.r-project.org). <h3>Results</h3> Mean patient age was 66.4 years (range 42-80). All patients met ASTRO APBI "suitable" or "cautionary" category. 15 patients had pathologic T1-2N0M0 invasive ductal carcinoma and 3 patients had ductal carcinoma in situ (1/3 grade 2 and 2/3 grade 3). 82% (69/84) of fractions were delivered adapted. CTV and PTV volumes ranged from 15.7-197 cm³ (mean 80.7 cm³) and 33.4-227 cm³ (mean 119.8 cm³). Scheduled PTV V30 was <95% in 60 fractions (71%) and <90% in 30 fractions (36%). On adapted fractions, PTV V30Gy and CTV V30Gy coverage were significantly improved comparing scheduled versus adaptive plans, median (IQR) 91.4 (85.9-94.4%) v 95% (95-95%) and 98 (93.4-99%) v 99.7% (98.8-99.8%), respectively, p < 0.0001. There were no differences in PTV/CTV coverage when scheduled plans were chosen over adapted plans. Only skin Dmax was statistically decreased among the OARs (635.3 vs 629.1 cGy per fraction, p = 0.018); all other OAR coverages were not statistically different. Contouring and plan generation took on average (IQR) 9.4 minutes (6-12 min) and 5 min (4-6 min) respectively. <h3>Conclusion</h3> Adaptation with AORT significantly improved PTV/CTV prescription coverage and skin dose in APBI with <15 min added treatment time. AORT may improve outcomes for ABPI due to improved PTV/CTV prescription delivery.

Minimizing the Risk of Acute Skin Toxicity Due to Hip Prosthesis Avoidance in Prostate Radiation Therapy

Limiting the entrance dose through hip prostheses to improve dosimetric accuracy can result in unfavorable skin toxicity. We propose a volumetric modulated arc therapy solution that strikes a better balance between dose accuracy and skin dosimetry. Our current planning strategy limits the entrance dose through hip prostheses using stringent optimization objectives on an avoidance structure. Avoidance efficiency is evaluated by recalculating the plan with prosthesis density set at 20 g/cc, and evaluating the loss of target coverage from increased attenuation. We require this loss to be ≤5% of the original values. This approach has resulted in an uncommon skin toxicity for a prostate-bed patient with bilateral hip prostheses. Thus, the dosimetric tradeoffs between skin dose and prosthesis avoidance were investigated by incrementally reducing prosthesis avoidance to achieve maximum skin doses (Dmax) between 30 and 50 Gy. When prosthesis avoidance is prioritized, the skin dose increases and the target dose coverage and conformity decrease. A large degradation in target coverage for plans with the lowest skin Dmax of 30 to 35 Gy indicates that a significant proportion of the target dose arises from beams entering the prostheses. The plan with a skin Dmax of 40 Gy provides a better compromise between skin and prosthesis entrance doses, with a <20% reduction in target coverage at an increased prosthesis density of 20 g/cm3. Skin dose needs to be considered when using prosthesis avoidance planning strategies. Allowing for a minimal dose through the prosthesis may be required to restrict skin dose and reduce the risk of toxicity.

Five Day Accelerated Partial Breast Irradiation (APBI) Using Stereotactic Body Radiation Therapy (SBRT) in Stage 0-II Breast Cancer: A Report of 218 Cases With Up to 39 Month Follow-Up

Randomized trials in selected early-stage breast cancer patients with up to 10-year follow-up have proven that Accelerated Partial Breast Irradiation (APBI) given via High Dose Rate (HDR) implant bid in 5 days is equivalent to whole breast irradiation (WBI) given q.d. in 5-6 weeks in regard to breast tumor local recurrence (LR). However, complications with APBI implant in a Medicare database review have been significant, with 3.95% of women requiring Mastectomy, 16.2% developing infections, and another 16.3% experiencing non-infection complications including rib fractures, fat necrosis, and breast pain. Recently APBI using non-invasive Intensity Modulated Radiation Therapy (IMRT) or SBRT given q.d. in 5 fractions has been shown in another randomized trial with 10-year follow-up to be equivalent to q.d. WBI in 6 weeks, with respect to LR. IMRT/SBRT was superior in regard to acute effects, late effects, and cosmesis. In the randomized clinical trial of APBI IMRT/SBRT, the Clinical Target Volume (CTV) was defined by the injection of individual fiducial markers bordering the surgical cavity. At our institution, we have used a bioabsorbable fiducial marker system to localize the CTV for SBRT. We sought to confirm the APBI IMRT/SBRT results with this simpler less labor-intensive fiducial placement system.Between 2017 and 2021, 218 patients have undergone SBRT targeted to a bioabsorbable fiducial marker defined CTV with the walls of the surgical cavity sewn to the fiducial marker. Eligible patients were older than age 40, had tumor sizes ≤ 3 cm, negative surgical margins, and negative sentinel node dissections. SBRT dose was 30 Gy given in 5 fractions. Dose Constraints were as follows: V-30 Gy < 105%, Ipsilateral Breast V-15 Gy < 50%, Ipsilateral Lung V-10 Gy < 20%, Contralateral Lung V-5 Gy < 10%, Heart V-3 Gy < 20%, Contralateral Breast Dmax < 2 Gy and Skin Dmax < 27 Gy. The Planning Target Volume (PTV) ranged from 27 to 355 cc with a median of 80 cc. PTV = CTV + 1-2 cm.Follow-up ranged from 1-39 months with a median of 20 months. LR has been 0% (0/218). There have been no skin reactions, seromas, or infections. Four (2.1%) patients developed pain around the fiducial marker site. This resolved within 2 days on a short course of steroids in all cases. Cosmetic results as rated by the Surgeon, Radiation Oncologist, and Nurse, were rated excellent in 99.0% (216/218) of cases.Non-invasive APBI with SBRT given q.d. over 5 days targeted to bioabsorbable fiducial marker has resulted in LR, complications, and cosmetic results which compare favorably to invasive APBI given bid with HDR implant. At last follow-up, there have been no LR, skin reactions, or significant complications. Cosmesis has been excellent in 99.0% of patients.

SBRT Treatment Planning Study for the First Clinical Biology-Guided Radiotherapy System

<h3>Purpose/Objective(s)</h3> The first clinical biology-guided radiation therapy (BgRT) system – RefleXion X1 - is installed and is being commissioned for clinical use at our institution. The system delivers 6MV-FFF beam via 50 firing positions at 850 cGy/min dose rate on 60 rpm rotating gantry with the couch advancing in 2.1 mm increments. Collimation is achieved through a binary multi-leaf collimator system composed of 64 (6.25 mm width at 850 cm SAD) leaves and 10mm or 20mm jaws. The purpose of this study was to compare the treatment plan quality and delivery efficiency for SBRT cases without PET-guidance. <h3>Materials/Methods</h3> Five lung cancer patients (50 Gy/4fx) with motion-inclusive PTV previously treated with VMAT SBRT were selected for this retrospective study. For each VMAT plan a corresponding plan was generated on the RefleXion treatment planning system (TPS) using our institutional planning constraints. VMAT SBRT plans used 1-2 partial arcs with 10MV-FFF energy and 2400 MU/min dose rate. RefleXion SBRT plans used all 50 firing positions and 1 cm jaw collimation. As plan normalization option does not yet exist in the RefleXion TPS, the plans were optimized to achieve PTV D95% coverage with 100% of prescription dose to the best of planner's ability. All clinically relevant metrics in this study, including plan PTV D95%, PTV D1%, 50% isodose volume (I50%), Conformity Index (CI), organs at risk constraints, and treatment time were analyzed and compared between VMAT and RefleXion plans using paired t-tests. <h3>Results</h3> Clinically acceptable plans were obtained with both techniques. The average PTV volume was 14.1 ± 6.4cc. For VMAT and RefleXion plans, no statistically significant difference was observed in PTV D95%, PTV D1%, CI or I50%. Ipsilateral lung volume spared at 12.4 Gy (VS12.4) was slightly greater (31.6cc increase, <i>P</i> < 0.035) and skin Dmax was slightly lower (1.4 Gy decrease, <i>P</i> < 0.038) for RefleXion plans. Treatment beam-on time was significantly longer for RefleXion plans (23.4min increase, <i>P</i> < 0.0002). <h3>Conclusion</h3> RefleXion TPS provided comparable plan quality to lung SBRT VMAT plans. Treatment beam-on time is significantly longer for the RefleXion system.

Five-day accelerated partial breast irradiation (APBI) using intensity modulated radiation therapy (IMRT) in stage 0-II breast cancer: A report of 214 cases with up to 39 month follow-up.

e12508 Background: Randomized trials in stage 0-II breast cancer have proven that APBI given via HDR implant in 5 days is equivalent to whole breast irradiation (WBI) given in 5-6 weeks in regard to breast tumor local recurrence (LR). However, complications have been significant. Recently APBI using non-invasive IMRT given in 5 fractions has been shown in another randomized trial with 10 year follow-up to be equivalent to WBI in 6 weeks, with respect to LR. IMRT was superior in regard to acute effects, late effects, and cosmesis. In the randomized clinical trial of APBI IMRT, the Clinical Target Volume (CTV) was defined by the injection of individual fiducial markers bordering the surgical cavity. We have used the Biozorb fiducial system to localize the CTV for IMRT. We sought to confirm the APBI IMRT results with this simpler less labor intensive fiducial placement system. Methods: Between 2017 and 2021, 214 patients have undergone IMRT targeted to a Biozorb defined CTV with the walls of the surgical cavity sewn to the Biozorb device. Eligible patients were older than age 40, had tumor sizes &lt; 3 cm, negative surgical margins, and negative sentinel node dissections. IMRT dose was 30 Gy given in 5 fractions. Dose Constraints were as follows : V-30 Gy &lt; 105%, Ipsilateral Breast V-15 Gy &lt; 50%, Ipsilateral Lung V-10 Gy &lt; 20%, Contralateral Lung V-5 Gy &lt; 10%, Heart V-3 Gy &lt; 20%, Contralateral Breast Dmax &lt; 2 Gy and Skin Dmax &lt; 27 Gy. The Planning Target Volume (PTV) ranged from 27 to 355 cc with a median of 80 cc. PTV = CTV + 1-2 cm. Results: Follow-up ranged from 1-39 months with a median of 20 months. LR has been 0% (0/214). There have been no skin reactions or seromas. Infection has occurred in one patient (0.5%). Four (1.9%) patients developed pain around the Biozorb site. This resolved on a short courses of steroids in all cases. Cosmetic results as rated by the Surgeon, Radiation Oncologist, and Nurse, were rated excellent in 99.0% (212/214) of cases. Conclusions: Non-invasive APBI with IMRT given qd over 5 days targeted to Biozorb has resulted in LR, complications, and cosmetic results which compare favorably to invasive APBI given bid with HDR implant. At last follow-up, there have been no LR, skin reactions, or significant complications. Cosmesis has been excellent in 99.0% of patients.

Using flattening filter free beams in electronic tissue compensation whole breast irradiation with deep inspiration breath hold.

PurposeIn order to reduce heart dose, DIBH has become a common practice in left‐sided whole breast irradiation. This technique involves a significant strain on patients due to the breath‐hold requirements. We hereby investigate the dosimetric and delivery feasibility of using flattening filter free (FFF) energies with electronic tissue compensation (ECOMP) planning technique to reduce the required breath‐hold lengths and increase patient compatibility.MethodsFifteen left‐sided, postlumpectomy patients previously receiving DIBH whole‐breast radiotherapy (266cGy x 16fx) were retrospectively planned using ECOMP for both 6X and 6X‐FFF. A dosimetric comparison was made between the two plans for each patient using various dosimetric constraints. Delivery feasibility was analyzed by recalculating the 6X ECOMP plan with 6X‐FFF without replanning (6X‐FFF QA) and delivering both plans for a one‐to‐one comparison using Gamma analysis. Beam‐on times for the 6X and 6X‐FFF plans were measured. For all tests, Wilcoxon signed‐rank test was used with P < 0.05 as significant.ResultsNo statistical difference was observed between 6X and 6X‐FFF plans for most dosimetric endpoints except contralateral breast Dmax (P = 0.0008) and skin Dmax (p = 0.03) and Dmin (P = 0.01) for which 6X‐FFF showed favorable results when compared with 6X. 6X‐FFF significantly reduced beam‐on times for all patients by 22%–42% (average 32%). All plan QAs passed departmental gamma criteria (10% low‐dose threshold, 3%/3mm, >95% passing).ConclusionECOMP planning with FFF was found feasible for left‐sided breast patients with DIBH. Plan quality is comparable, if not better, than plans using flattened beams. FFF ECOMP could significantly reduce beam‐on time and required breath‐hold lengths thereby increasing patient compatibility for this treatment while offering satisfactory plan quality and delivery accuracy.

Five day accelerated partial breast irradiation (APBI) using stereotactic body radiation therapy (SBRT) in stage 0-II breast cancer: A report of 135 cases with up to two-year follow-up.

e12596 Background: Randomized trials in stage 0-II breast cancer have proven that APBI given via HDR implant in 5 days is equivalent to whole breast External Radiation Therapy (XRT) given in 5-6 weeks in regard to breast tumor local recurrence (LR). However, complications have been significant. Recently APBI using non-invasive IMRT given in 5 fractions has been shown in another randomized trial to be equivalent to XRT in 6 weeks, with respect to LR. IMRT was superior in regard to acute effects, late effects, and cosmesis. In the randomized clinical trial of APBI IMRT, the Clinical Target Volume (CTV) was defined by the injection of individual fiducial markers bordering the surgical cavity. At our institution, we have used the Biozorb fiducial system to localize the CTV for IMRT. We sought to confirm the APBI IMRT results with this simpler less labor intensive fiducial placement system. Methods: Between 2017 and 2020, 135 patients have undergone SBRT targeted to a Biozorb defined CTV with the walls of the surgical cavity sewn to the Biozorb device. Eligible patients were older than age 40, had tumor sizes &lt; 3 cm, negative surgical margins, and negative sentinel node dissections. SBRT dose was 30 Gy given in 5 fractions. Dose Constraints were as follows: V-30 Gy &lt; 105%, Ipsilateral Breast V-15 Gy &lt; 50%, Ipsilateral Lung V-10 Gy &lt; 20%, Contralateral Lung V-5 Gy &lt; 10%, Heart V-3 Gy &lt; 20%, Contralateral Breast Dmax &lt; 2 Gy and Skin Dmax &lt; 27 Gy. The Planning Target Volume (PTV) ranged from 27 to 355 cc with a median of 80 cc. PTV = CTV + 1-2 cm. Results: Follow-up ranged from 1-26 months with a median of 12 months. LR has been 0% (0/135). There have been no skin reactions or seromas. Infection has occurred in one patient (0.7%). Three (2.2%) patients developed pain around the Biozorb site. This resolved within 2 days on a short course of steroids in all cases. Cosmetic results as rated by the Surgeon, Radiation Oncologist, and Nurse, were rated excellent in 98.5% (133/135) of cases. Conclusions: Non-invasive APBI with SBRT given qd over 5 days targeted to Biozorb has resulted in LR, complications, and cosmetic results which compare favorably to invasive APBI given bid with HDR implant. At last follow-up, there have been no LR, skin reactions, or significant complications. Cosmesis has been excellent in 98.5% of patients.

Abstract P4-13-08: Five day accelerated partial breast irradiation (APBI) using stereotactic body radiation therapy (SBRT) in stage 0-II breast cancer: A report of 86 patients with up to 2 year follow-up

Abstract Background: Randomized trials in selected early stage breast cancer patients with up to 10 year follow-up have proven that Accelerated Partial Breast Irradiation (APBI) given via High Dose Rate (HDR) implant bid in 5 days is equivalent to whole breast External Radiation Therapy (XRT) given qd in 5-6 weeks in regard to breast tumor local recurrence (LR) [1-2]. However, complications with APBI implant in a Medicare database review have been significant, with 3.95% of women requiring Mastectomy, 16.2% developing infections, and another 16.3% experiencing non-infection complications including rib fractures, fat necrosis, and breast pain [3]. Recently APBI using non-invasive Intensity Modulated Radiation Therapy (IMRT) or Stereotactic Body Radiation Therapy (SBRT) given qd in 5 fractions has been shown in another randomized trial with 5 year follow-up to be equivalent to qd XRT in 6 weeks, with respect to LR [4]. IMRT/SBRT was superior in regard to acute effects, late effects, and cosmesis. Objectives: In the randomized clinical trial of APBI IMRT/SBRT, the Clinical Target Volume (CTV) was defined by the injection of individual fiducial markers bordering the surgical cavity. At our institution, we have used the Biozorb fiducial system to localize the CTV for SBRT. We sought to confirm the APBI SBRT/IMRT results with a simpler fiducial system. Materials and Methods: Between 2017 and 2019, 86 patients have undergone SBRT targeted to a Biozorb defined CTV with the walls of the surgical cavity sewn to the Biozorb device. Eligible patients were older than age 40, had tumor sizes ≤ 3 cm, negative surgical margins, and negative sentinel node dissections. SBRT dose was 30 Gy given in 5 fractions. Dose Constraints were as follows: V-30 Gy &amp;lt; 105%, Ipsilateral Breast V-15 Gy &amp;lt; 50%, Ipsilateral Lung V-10 Gy &amp;lt; 20%, Contralateral Lung V-5 Gy &amp;lt; 10%, Heart V-3 Gy &amp;lt; 20%, Contralateral Breast Dmax &amp;lt; 2 Gy and Skin Dmax &amp;lt; 27 Gy. The Planning Target Volume (PTV) ranged from 27 to 355 cc with a median of 80 cc. PTV = CTV + 1-2 cm. Results: Follow-up ranged from 1-24 months with a median of 12 months. LR has been 0% (0/86). There were no skin reactions. One patient developed pain around the Biozorb site. This resolved within 2 days on a short course of steroids. Cosmetic results as rated by the Surgeon, Radiation Oncologist, and Nurse, were rated excellent in 100% (86/86) of cases. Conclusions:Non-invasive APBI with SBRT given qd over 5 days targeted to Biozorb has resulted in LR, complications, and cosmetic results which compare favorably to invasive APBI given bid with HDR implant. At last follow-up, there have been no LR, skin reactions, or complications. Cosmesis has been excellent in 100% of patients. Refernces:1. Polgar C, Fodor J, Major T, et al. Breast-conserving therapy with partial or whole breast irradiation: Ten-year results of the Budapest randomized trial. Radiother Oncol 2013; 108[2]: 197-202. 2. Strnad V, Ott O, Hildebrandt G, et al. 5-year results of accelerated partial breast irradiation using sole interstitial multicatheter brachytherapy versus whole-breast irradiation with boost after breast-conserving surgery for low-risk invasive and in-situ carcinoma of the female breast: a randomised, phase 3, non-inferiority trial. Lancet 2016; 387[10015]: 229-38. 3. Smith G, Xu Y, Bucholz T, et al. Association between treatment with brachytherapy vs whole-breast irradiation and subsequent mastectomy, complications, and survival among older women with invasive breast cancer. JAMA 2012; 307[17]: 1827-37. 4. Livi L, Meattini I, Marrazzo L, et al. Accelerated partial breast irradiation using intensity-modulated radiotherapy versus whole breast irradiation: 5-year survival analysis of a phase 3 randomised controlled trial. Eur J Cancer, 2015; 51 [4]: 451-63. Citation Format: Rufus Mark, Valerie Gorman, Steven McCullough. Five day accelerated partial breast irradiation (APBI) using stereotactic body radiation therapy (SBRT) in stage 0-II breast cancer: A report of 86 patients with up to 2 year follow-up [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-13-08.

Robotic Stereotactic Accelerated Partial-Breast Irradiation for Early-Stage Breast Cancer: 5-Year Results of a Single-Institution Pilot Study

Outcomes following adjuvant accelerated partial breast irradiation (APBI) in select women with early stage breast cancer are comparable to whole breast irradiation. Robotic stereotactic accelerated partial breast irradiation (SAPBI) with fiducial tracking is an attractive treatment option, but limited data are available regarding the feasibility of this approach and 5 year outcomes have not yet been published. We report our institutional experience treating select women with SAPBI. Women with DCIS and early stage breast cancer treated from November 2008 to September 2015 were evaluated. Treatments were delivered with a robotic radiosurgical system. At least 4 gold fiducials were implanted around the lumpectomy cavity prior to the start of treatment for target tracking. The CTV was delineated on contrast enhanced CT scans using surgical clips and the lumpectomy cavity. In 2014, following the publication of the University of Florence phase III trial, the protocol was amended after 13 patients and the CTV was defined as the lumpectomy cavity with a uniform 1 cm expansion confined to the breast tissue. The PTV, prescribed 30 Gy in 5 fractions, was defined as the CTV with a 3-5 mm uniform expansion. AAPM TG-101 skin dose constraints were respected. Clinical examination and mammography were completed at 6-12 month follow up intervals. Breast cosmesis was scored using The Harvard Breast Cosmesis Grading Scale. Twenty women (median age 65 years) were treated over a median 7 days (range 5-13). Fourteen women had DCIS and 50% of the tumors were located in the upper outer quadrant. The median treated PTV was 63 cm3 (range 15-142), the median PTV/breast volume ratio was 8.3% (range 4.1-25.6) and the median prescription isodose line was 83% (range 75-87). Three or 4 fiducials were successfully tracked in 90% of patients. At a median follow up of 60 months (range 33-108), locoregional control, distant control, and overall survival was 100%. Five women with skin Dmax > 33 Gy (skin = CT surface minus 2 mm) developed chronic grade 1 dermatitis (faint hyperpigmentation), one of whom developed focal grade 1 telangiectasia at 52 months. Three women developed grade 1 fibrosis, one of whom was later diagnosed with fat necrosis on mammography. Two additional asymptomatic women were diagnosed with fat necrosis on routine mammography. There were no rib fractures. One woman required stereotactic biopsy to confirm benign tumor bed calcifications at 66 months. Fifteen evaluable patients maintained Good-Excellent cosmesis. Robotic SAPBI with fiducial tracking is a feasible, well tolerated and highly effective technique for the adjuvant treatment of select early-stage breast cancer patients. Cosmetic outcomes may be improved further by decreasing the skin Dmax to < 33 Gy. A confirmatory multi-institutional registry is actively enrolling patients. Given these encouraging results, future research in this patient population will evaluate robotic SAPBI as a definitive treatment.

Accelerated partial breast irradiation (APBI) using intensity modulated radiation therapy (IMRT) in stage 0-II breast cancer: A preliminary report of 57 cases.

e12068 Background: Randomized trials in Stage 0-II breast cancer have proven that APBI given via HDR implant in 5 days is equivalent to whole breast External Radiation Therapy (XRT) given in 5-6 weeks in regard to breast tumor local recurrence (LR). However, complications have been significant. Recently APBI using non-invasive IMRT given in 5 fractions has been shown in another randomized trial to be equivalent to XRT in 6 weeks, with respect to LR. IMRT was superior in regard to acute effects, late effects, and cosmesis. In the randomized clinical trial of APBI IMRT, the Clinical Target Volume (CTV) was defined by the injection of individual fiducial markers bordering the surgical cavity. At our institution, we have used the Biozorb fiducial system to localize the CTV for IMRT. We sought to confirm the APBI IMRT results with this simpler less labor intensive fiducial placement system. Methods: Between 2017 and 2019, 57 patients have undergone IMRT targeted to a Biozorb defined CTV with the walls of the surgical cavity sewn to the Biozorb device. Eligible patients were older than age 40, had tumor sizes ≤ 3 cm, negative surgical margins, and negative sentinel node dissections. IMRT dose was 30 Gy given in 5 fractions. Dose Constraints were as follows : V-30 Gy &lt; 105%, Ipsilateral Breast V-15 Gy &lt; 50%, Ipsilateral Lung V-10 Gy &lt; 20%, Contralateral Lung V-5 Gy &lt; 10%, Heart V-3 Gy &lt; 20%, Contralateral Breast Dmax &lt; 2 Gy and Skin Dmax &lt; 27 Gy. The Planning Target Volume (PTV) ranged from 27 to 355 cc with a median of 80 cc. PTV = CTV + 1-2 cm. Results: Follow-up ranged from 1-14 months with a median of 7 months. LR has been 0% (0/57). There were no skin reactions. One patient developed pain around the Biozorb site. This resolved within 2 days on a short course of steroids. Cosmetic results as rated by the Surgeon, Radiation Oncologist, and Nurse, were rated excellent in 100% (57/57) of cases. Conclusions: Non-invasive APBI with IMRT targeted to Biozorb has resulted in LR, complications, and cosmetic results which compare favorably to invasive APBI given with HDR implant. At last follow-up, there have been no LR, skin reactions, or complications. Cosmesis has been excellent in 100% of patients.

Clinical implementation of a novel Double-Balloon single-entry breast brachytherapy applicator

PurposeThe purpose of the study was to describe the clinical utilization of a novel Double-Balloon applicator for accelerated partial breast irradiation (APBI). Methods and MaterialsThe Double-Balloon single-entry breast applicator contains a single central treatment catheter, as well as four peripheral catheters that can be differentially loaded to customize radiation dose coverage. An inner balloon is filled with up to 7–30 cm3 of saline to increase separation between the peripheral catheters, and an outer balloon is filled with up to 37–115 cm3 of saline to displace breast tissue from the peripheral catheters. Treatment planning objectives include coverage of the breast planning target volume to a minimum of V90 > 90%, limiting dose heterogeneity such that V200 < 10 cm3 and V150 < 50 cm3, and limiting maximum dose to skin (<100% of prescription dose) and ribs (<145% of prescription dose). ResultsHigh-dose-rate APBI was delivered to 11 women using this device (34 Gy in 10 twice daily fractions). The mean V90 was 98.2% (range 94.2–99.4%). The mean skin Dmax with the Double-Balloon applicator was 83.3% (range 75.6–99.5%). The mean breast V200 was 5.8 cm3 (range 2.3–10.2 cm3), and the mean breast V150 was 32.9 cm3 (range 25.0–41.7 cm3). Pretreatment quality assurance was performed using CT prior to each morning fraction and ultrasound prior to each afternoon fraction. ConclusionsThe Double-Balloon applicator can be easily introduced into a previously existing brachytherapy program. APBI plans created with this applicator achieve excellent planning target volume coverage, while limiting skin dose and maintaining breast V200 < 10 cm3.

SU‐E‐T‐487: Impact of Geometric Uncertainties in Accelerated Partial Breast Irradiation Using the Strut‐Adjusted Volume Implant (SAVI)

Purpose:Single‐entry multi‐catheter devices have been developed for accelerated partial breast irradiation (APBI). Rotational and translational uncertainties are usually mitigated by quality assurance, however its actual dosimetric impact has not been addressed, which is presented here for SAVI applicator.Methods:Under Institutional Review Board exemption status, we retrospectively analyzed 48 APBI treatment plans using SAVI applicator. For quick calculation of dose‐volume histogram (DVH) considering geometric uncertainties, the coordinate of each voxel of critical organs after rotation or translation along the central catheter was calculated using an in‐house software instead of rotating or translating the entire dose distribution.Results:For most cases, the skin doses increased with rotation to both directions. At 10 degree of rotation, the increase of Dmax (percent prescribed dose) at 50% (median), 75%, 90%, and 100% (maximum) percentile were 0.3%, 1.7%, 5.6% and 25.0%, respectively. The increase of chest wall Dmax at 50%, 75%, 90%, and 100% percentile were 0.1%, 1.0%, 10.3% and 38.8%, respectively. The increase of skin Dmax of the patients with the distance between skin surface and lumpectomy cavity surface ≤16 mm was significantly larger than those with the distance &gt;16 mm. Similarly, patients with the distance between lung and lumpectomy cavity surface ≤20 mm showed higher sensitivity of chest wall Dmax against rotation than patients with the distance &lt;20 mm. Translation of the applicator showed larger impact on the skin dose than rotation, although the effects on chest wall was less than 2% even at 10 mm displacement. At 5 mm of translation, increase of skin Dmax at 50%, 75%, 90%, and 100% percentile were 2.3%, 8.0%, 15.3% and 77.7%, respectively.Conclusion:The impacts of the geometric uncertainties (rotation and translation) of SAVI applicator were investigated. The skin‐lumpectomy cavity and lung‐lumpectomy cavity distances showed significant relationship with skin and chest wall doses, respectively.

Dosimetric evaluation of multilumen intracavitary balloon applicator rotation in high‐dose‐rate brachytherapy for breast cancer

The objective of this work is to evaluate dosimetric impact of multilumen balloon applicator rotation in high‐dose‐rate (HDR) brachytherapy for breast cancer. Highly asymmetrical dose distribution was generated for patients A and B, depending upon applicator proximity to skin and rib. Both skin and rib spacing was ≤0.7 cm for A; only rib spacing was ≤0.7 cm for B. Thirty‐five rotation scenarios were simulated for each patient by rotating outer lumens every 10° over ±180∘ range with respect to central lumen using mathematically calculated rotational matrix. Thirty‐five rotated plans were compared with three plans: 1) original multidwell multilumen (MDML) plan, 2) multidwell single‐lumen (MDSL) plan, and 3) singledwell single‐lumen (SDSL) plan. For plan comparison, planning target volume for evaluation (PTV_EVAL) coverage (dose to 95% and 90% volume of PTV_EVAL) (D95 and D90), skin and rib maximal dose (Dmax), and normal breast tissue volume receiving 150% (V150) and 200% (V200) of prescribed dose (PD) were evaluated. Dose variation due to device rotation ranged from −5.6% to 0.8% (A) and −6.5% to 0.2% (B) for PTV_EVAL D95; −5.2% to 0.4% (A) and −4.1% to 0.7% (B) for PTV_EVAL D90; −2.0 to 18.4% (A) and −7.8 to 17.5% (B) for skin Dmax; −11.1 to 22.8% (A) and −4.7 to 55.1% (B) of PD for rib Dmax, respectively. Normal breast tissue V150 and V200 variation was <1.0 cc, except for −0.1 to 2.5 cc (B) of V200. Furthermore, 30° device rotation increased rib Dmax over 145% of PD: 152.9% (A) by clockwise 30° rotation and 152.5% (B) by counterclockwise 30° rotation. For a highly asymmetric dose distribution, device rotation can outweigh the potential benefit of improved dose shaping capability afforded by multilumen and make dosimetric data worse than single‐lumen plans unless it is properly corrected.PACS number: 87.53.Jw

The dosimetric effects of photon energy on the quality of prostate volumetric modulated arc therapy

PurposeStudies comparing the dosimetric effects of high- and low-energy photons to treat prostate cancer using 3-dimensional conformal and intensity modulated radiation therapy have yielded mixed results. With the advent of newer radiation delivery systems like volumetric modulated arc therapy (VMAT), the impact of changing photon energy is readdressed. Methods and MaterialsSixty-five patients treated for prostate cancer at our institution from 2011 to 2012 underwent CT simulation. A target volume encompassing the prostate and entire seminal vesicles was treated to 50.4 Gy, followed by a boost to the prostate and proximal seminal vesicles to a total dose of 81 Gy. The VMAT plans were generated for 6-MV and 10-MV photons under identical optimization conditions using the Eclipse system version 8.6 (Varian Medical Systems, Palo Alto, CA). The analytical anisotropic algorithm was used for all dose calculations. Plans were normalized such that 98% of the planning target volume (PTV) received 100% of the prescribed dose. Dose-volumetric data from the treatment planning system was recorded for both 6-MV and 10-MV plans, which were compared for both the entire cohort and subsets of patients stratified according to the anterior–posterior separation. ResultsPlans using 10-MV photons had statistically significantly lower relative integral dose (4.1%), gradient measure (4.1%), skin Dmax (16.9%), monitor units (13.0%), and bladder V30 (3.1%) than plans using 6-MV photons (P < .05). There was no difference in rectal dose, high-dose-region bladder dose, PTV coverage, or conformity index. The benefit of 10-MV photons was more pronounced for thicker patients (anterior–posterior separation >21 cm) for most parameters, with statistically significant differences in bladder V30, bladder V65, integral dose, conformity index, and monitor units. ConclusionsThe main dosimetric benefits of 10-MV as compared with 6-MV photons are seen in thicker patients, though for the entire cohort 10-MV plans resulted in a lower integral dose, gradient measure, skin Dmax, monitor units, and bladder V30, possibly at the expense of higher rectum V81.