Hypofractionated whole breast IMRT with HDR brachytherapy boost in early-stage breast cancer: Long-term results from a single-center.

INTRODUCTION/OBJECTIVES: The addition of a boost to the lumpectomy bed after whole-breast (WB) radiotherapy plays a key role in the treatment of patients with breast cancer (BC). The clinical benefits of a boost with high-dose-rate brachytherapy (HDR-BT) after conventional fractionation is supported by a large body of evidence. However, few studies have described its outcomes after a hypofractionated scheme. MATERIALS AND METHODS: We included all patients treated with adjuvant WB-IMRT in 15 sessions followed by a single-session HDR-BT boost with local anesthesia on an outpatient basis. RESULTS: Between 2009 and 2017, 638 patients with early-stage BC were treated according to the aforementioned protocol after breast-conserving surgery. Median follow-up was 6 years (4-11). Despite the low incidence of side effects and their slightness, we did identify an impact of breast volume on the risk of acute radiodermatitis, fibrosis, pain and edema. However, we did not identify any relationship between the volume in cubic centimeters of the BT-implant with acute or long-term side effects. 2.2% patients had an actual local relapse, 2.4% a 2nd primary in the same breast and 2.39% were diagnosed with contralateral BC. Event-free survival at 11 years was 85.5% with an overall survival of 95.7%. CONCLUSION: Adjuvant hypofractionated whole-breast IMRT followed by a single dose HDR-BT boost has a low incidence of acute and chronic toxicity and excellent oncological outcomes. However, it may be worthwhile to intensify self-care protocols and surveillance in women with large breasts who may be at increased risk of side effects.

MLC performance prognosis using a degradation model based on trajectory log data from a daily test.

PURPOSE: This paper investigates the feasibility of implementing a predictive maintenance program for a multileaf collimator (MLC) based on data collected in trajectory logs (TLs) obtained by conducting a simple daily test, with the aim of minimizing unscheduled downtime. METHODS: A dynamic field test was designed, and the TLs generated in the course of daily administration in a linear accelerator were collected to evaluate trajectory deviations of the MLC leaves as well as interlocks (COL 420219/20, COL 420207/08) reported by the machine. During this evaluation, we observed that the trajectory deviations of some leaves increased up to a threshold value beyond which certain interlocks began to appear in treatment fields in those leaves. An exponential degradation model was therefore developed to predict this drift and determine each leaf's remaining useful life (RUL). Once the applicability of the model was confirmed, we added a second accelerator equipped with an MLC with the same configuration to validate the model. RESULTS: The model was able to predict certain COL 420219/20 interlocks resulting from primary readout/expected position discrepancies and to estimate each leaf's RUL. In total, 11 cases (8 interlocks + 3 potential interlocks avoided due to service interventions [27.3% of the total]) were detected over 7 days in advance, with no false positive results. Scheduling of service interventions several days prior to MLC failure would therefore be possible. When these types of interlocks were not predicted by the model, they were always generated by leaf motor failure. Consequently, intervention time could also be optimized by directly replacing the motor. During the study period, for these types of interlocks, our approach would have reduced downtime from 35.25 to 4.00 h (88.7%) and from 34.75 to 22.83 h (34.3%) for each accelerator, respectively. For COL 420207/08 interlocks, which are generated by primary/secondary readout discrepancies, no correlation with leaf trajectory deviation increases recorded in the TLs was found. Throughout the study period, these types of interlocks requiring service intervention, also mainly for motor replacement, represented a downtime of 9.50 h for the first accelerator (21.2% of total downtime) and by 4.33 h (11.1% of total downtime) for the second accelerator. CONCLUSION: This study demonstrates that by applying a predictive MLC maintenance program based on information collected in TLs, it is possible to predict certain interlocks and therefore schedule preemptive interventions to avoid their occurrence. This could optimize health-care delivery performance and minimize the loss of treatment sessions.

On flattening filter-free portal dosimetry.

Varian introduced (in 2010) the option of removing the flattening filter (FF) in their C-Arm linacs for intensity-modulated treatments. This mode, called flattening filter-free (FFF), offers the advantage of a greater dose rate. Varian's "Portal Dosimetry" is an electronic portal imager device (EPID)-based tool for IMRT verification. This tool lacks the capability of verifying flattening filter-free (FFF) modes due to saturation and lack of an image prediction algorithm. (Note: the latest versions of this software and EPID correct these issues.) The objective of the present study is to research the feasibility of said verifications (with the older versions of the software and EPID). By placing the EPID at a greater distance, the images can be acquired without saturation, yielding a linearity similar to the flattened mode. For the image prediction, a method was optimized based on the clinically used algorithm (analytical anisotropic algorithm (AAA)) over a homogeneous phantom. The depth inside the phantom and its electronic density were tailored. An application was developed to allow the conversion of a dose plane (in DICOM format) to Varian's custom format for Portal Dosimetry. The proposed method was used for the verification of test and clinical fields for the three qualities used in our institution for IMRT: 6X, 6FFF and 10FFF. The method developed yielded a positive verification (more than 95% of the points pass a 2%/2 mm gamma) for both the clinical and test fields. This method was also capable of "predicting" static and wedged fields. A workflow for the verification of FFF fields was developed. This method relies on the clinical algorithm used for dose calculation and is able to verify the FFF modes, as well as being useful for machine quality assurance. The procedure described does not require new hardware. This method could be used as a verification of Varian's Portal Dose Image Prediction.