Breast Intensity-modulated Radiotherapy Research Articles

Evaluation of robustness of optimization methods in breast intensity-modulated radiation therapy using TomoTherapy.

Intensity-modulated radiation therapy (IMRT) has become a popular choice for breast cancer treatment. We aimed to evaluate and compare the robustness of each optimization method used for breast IMRT using TomoTherapy. A retrospective analysis was performed on 10 patients with left breast cancer. For each optimization method (clipping, virtual bolus, and skin flash), a corresponding 50Gy/25 fr plan was created in the helical and direct TomoTherapy modes. The dose-volume histogram parameters were compared after shifting the patients anteriorly and posteriorly. In the helical mode, when the patient was not shifted, the median D1cc (minimum dose delivered to 1cc of the organ volume) of the breast skin for the clipping and virtual bolus plans was 52.2 (interquartile range: 51.9-52.6) and 50.4 (50.1-50.8) Gy, respectively. After an anterior shift, D1cc of the breast skin for the clipping and virtual bolus plans was 56.0 (55.6-56.8) and 50.9 (50.5-51.3) Gy, respectively. When the direct mode was used without shifting the patient, D1cc of the breast skin for the clipping, virtual bolus, and skin flash plans was 52.6 (51.9-53.1), 53.4 (52.6-53.9), and 52.3 (51.7-53.0) Gy, respectively. After shifting anteriorly, D1cc of the breast skin for the clipping, virtual bolus, and skin flash plans was 55.6 (54.1-56.4), 52.4 (52.0-53.0), and 53.6 (52.6-54.6) Gy, respectively. The clipping method is not sufficient for breast IMRT. The virtual bolus and skin flash methods were more robust optimization methods according to our analyses.

The Effect of Respiratory Motion in Breast Intensity-modulated Radiation Therapy: 3D-Printed Dynamic Phantom Study.

This study evaluated the dosimetric effect of respiratory motion in intensity-modulated radiation therapy (IMRT) for breast cancer using a three-dimensional (3D)-printed dynamic phantom. Computed tomography (CT) data from breast cancer patients were used to create a 3D-printed breast phantom. Various types of treatment plans were generated using CT images acquired at the exhalation phase. Different infill densities in the 3D-printed phantom were tested to validate their effect on simulating the average human breast tissue density. Plans were delivered to the 3D-printed dynamic phantom in the exhalation position and free-breathing motion. Dosimetric verification was performed using Gafchromic EBT3 films. After changing the infill density to obtain Hounsfield Unit values similar to those of human breast tissue, a realistic patient-specific breast phantom was fabricated using a 3D printer at 80% infill density. The gamma passing rates of the dose distribution delivered in the exhalation phase and free-breathing motion were 92% or more. In addition, the dynamic phantom doses with free-breathing motion were directly compared with the static phantom dose in terms of sagittal dose profiles. Gamma passing rates of >93% and 90% were achieved at 3%/3 mm and 3%/2 mm, respectively. Despite a blurred dose distribution, the dose map of the film measurement with respiratory motion could be delivered without significantly increasing the dose heterogeneity of the tumor bed or loss of target coverage. Our findings demonstrate that the impact of respiration on breast IMRT for whole-breast irradiation was not significant, even in the tumor bed.

Improvement in plan quality after Implementation of clinical goals in a large network of cancer centers.

Clinical Goals (CG) is a tool available in the Varian Eclipse planning system to objectively and visually evaluate the quality of treatment plans based upon user-defined dose-volume parameters. We defined a set of CG for Stereotactic Radiosurgery (SRS) and Intensity-Modulated Radiotherapy (IMRT) based on published data and guidelines and implemented this in a network of cancer centers in India (American Institute of Oncology). A dosimetric study was performed to compare brain SRS and breast IMRT plan quality before and after CG implementation.The CG defined for SRS plans were target V100% ≥ 98%, dose gradient measure (GM) ≤ 0.5 cm, conformity index (CI) 1.0 to 1.2. For breast IMRT plans, CG defined target V100% ≥ 97%, V95% ≥ 95%, V107% ≤ 2%, V105% ≤ 10%, and Dmax ≤ 2.4 Gy. Dose limits to organs-at-risk (OAR) were summarize in supplemental materials. Twenty brain SRS and 10 breast IMRT treatment plans that were previously delivered on patients were selected and re-planned using CG. The pre and postoptimized plan parameters were compared using student t-tests.For brain SRS plans, the V100, GM, and CI for the pre- and post-Clinical-Goals plans were 93.22% ± 7.2% vs 97.96% ± 0.29% (p = 0.009), 0.63 ± 0.16 vs 0.42 ± 0.05 (p < 0.001) and 1.07 ± 0.18 vs 1.06 ± 0.06 (p = 0.79), respectively. There were no differences in max dose to OARs. In breast IMRT plans, the target V107% for pre and postimplemented plans were 16.50% ± 10.98% vs 0.32% ± 0.32%, respectively (p = 0.001). The average target V105% were 44.00% ± 15.72% and 8.69% ± 4.53%, respectively (p < 0.001). No differences were found in the average target V100% (p = 0.128) and V95% (p = 0.205). The average target Dmax were 112.28% ± 1.59% and 109.14% ± 0.73%, respectively (p < 0.001). There were only minor differences in doses to OARs.The implementation of CG in Varian Eclipse significantly improved SRS and IMRT plan quality with enhanced coverage, dose GM, and CI without increased dose to OARs.

Comparison of Dose Calculation Algorithms for Accelerated Partial Breast Intensity Modulated Radiation Therapy

<h3>Purpose/Objective(s)</h3> Accelerated partial breast irradiation (APBI) using intensity modulated radiation therapy (IMRT) has been introduced recently as an alternative treatment to whole breast irradiation for early-stage breast cancer after lumpectomy. Plan dose volume constraints for IMRT APBI are complex, requiring a more conformal and homogenous dose distribution compared to traditional tangential beam based whole breast planning. Anisotropic Analytical Algorithm (AAA) has been widely used for photon dose calculation. An Advanced Dose Calculation algorithm (AXB) is known to achieve comparable accuracy to Monte Carlo (MC) algorithm, the golden standard dose calculation, in heterogeneous media. However, the clinical assessment of AXB has been lacking. As a preliminary study, we investigated the dosimetric differences between the AAA, AXB and MC calculations on APBI IMRT. <h3>Materials/Methods</h3> Six patients with left breast cancer who previously received APBI IMRT were analyzed for this study. All patients received 30 Gy in 5 fractions with a multi beam IMRT technique using AAA 15.6 in the planning system. The following dose volume constraints were used for acceptable plan criteria based on the APBI IMRT Florence trial and all 6 cases previously treated met these criteria: For target (lumpectomy PTV), V28.5 Gy=100%, maximum dose to target < = 105% and V105% <= 2%. For critical organs, uninvolved breast with V15 Gy < 25%, ipsilateral lung volume with V10 Gy < 20%, contralateral breast maximal dose < 1 Gy, heart with V3 Gy < 10%. For a dosimetric comparison, plans were generated with AXB 15.6, reporting dose to medium, for each corresponding AAA plan by re-optimizing with the same dose constraints. After that, AXB plans were re-calculated with MC algorithm using XVMC and compared to AXB. <h3>Results</h3> The re-calculated plans using AXB for the same monitor units with an identical beam setup from AAA plans did not meet the acceptable dose volume criteria. For re-optimized plans with AXB, target conformity index, V28.5Gy and critical organs met the criteria but maximum dose and V105% were still higher than AAA plans (107-110% vs. 104-105.5% for max dose; <i>p</i>=0.02, 2.5- 5.0% vs. 0-2% for V105; <i>p</i> <0.001). The plan comparison between AXB and MC calculations showed similarity in dose distributions and hotspot area, and minimum difference in dose volume histogram. <h3>Conclusion</h3> The present data is the first report to assess the AXB for APBI IMRT. All 6 plans needed the re-optimization for AXB from plans with AAA to comply with the dose volume constraints. However hot spot size was better with AAA plans. MC calculation confirmed the dose distribution and hot spot area produced by AXB. Therefore, the clinical use of AXB for APBI IMRT will need careful evaluation due to a discrepancy in dose distributions and hot spot sizes between AAA and AXB calculations.

Retrospective Analysis for Dose Reduction to Organs at Risk with New Personalized Breast Holder (PERSBRA) in Left Breast IMRT.

This study evaluated dose differences in normal organs at risk, such as the lungs, heart, left anterior descending artery (LAD), right coronary artery, left ventricle, and right breast under personalized breast holder (PERSBRA), when using intensity-modulated radiation therapy (IMRT). This study evaluated the radiation protection offered by PERSBRA in left breast cancer radiation therapy. Here, we retrospectively collected data from 24 patients with left breast cancer who underwent breast-conserving surgery as well as IMRT radiotherapy. We compared the dose differences in target coverage and organs at risk with and without PERSBRA. For target coverage, tumor prescribed dose 95% coverage, conformity index, and homogeneity index were evaluated. For organs at risk, we compared the mean heart dose, mean left ventricle dose, LAD maximum and mean dose, mean left lung receiving 20 Gy, 10 Gy, and 5 Gy of left lung volume, maximum and mean coronary artery of the right, maximum of right breast, and mean dose. Good target coverage was achieved with and without PERSBRA. When PERSBRA was used with IMRT, the mean dose of the heart decreased by 42%, the maximum dose of LAD decreased by 26.4%, and the mean dose of LAD decreased by 47.0%. The mean dose of the left ventricle decreased by 54.1%, the volume (V20) of the left lung that received 20 Gy decreased by 22.8%, the volume (V10) of the left lung that received 10 Gy decreased by 19.8%, the volume (V5) of the left lung that received 5 Gy decreased by 15.7%, and the mean dose of the left lung decreased by 23.3%. Using PERSBRA with IMRT greatly decreases the dose to organs at risk (left lung, heart, left ventricle, and LAD). This study found that PERSBRA with IMRT can achieve results similar to deep inspiration breath-hold radiotherapy (DIBH) in terms of reducing the heart radiation dose and the risk of developing heart disease in patients with left breast cancer who cannot undergo DIBH.

PROshot: Internal Mammary Coverage, Dose-Reduced Radiation After Transoral Surgery, Sequencing of Total Neoadjuvant Therapy for Rectal Cancer, Hypofractionated Whole Breast Intensity Modulated Radiation Therapy, Hypofractionated Prostate Fossa Radiation Therapy, and Stereotactic Body Radiation Therapy for Oligoprogressive Cancer

PROshot: Internal Mammary Coverage, Dose-Reduced Radiation After Transoral Surgery, Sequencing of Total Neoadjuvant Therapy for Rectal Cancer, Hypofractionated Whole Breast Intensity Modulated Radiation Therapy, Hypofractionated Prostate Fossa Radiation Therapy, and Stereotactic Body Radiation Therapy for Oligoprogressive Cancer

Intensity Modulated Radiotherapy and Volumetric Modulated Arc Therapy in the Treatment of Breast Cancer: An Updated Review.

Radiation therapy (RT) plays a critical role in breast cancer treatment. In the modern technological era, innovations and progress in breast RT and delivery techniques have greatly improved the clinical outcomes. Intensity-modulated RT (IMRT) is a modern RT technology that permits the modulation of RT beams, ensuring a more uniform dose distribution through the target tissue and better avoidance of underlying critical structures. Recently, several studies have been published on breast IMRT. However, the interpretation of these results can be challenging because of the wide diversity of patients and treatment. The purpose of this study was to review these studies, focusing on the impact of IMRT on reducing toxicity and increasing convenience, as well as addressing concerns regarding breast IMRT.

Inter-institutional Variation in Intensity-modulated Radiotherapy for Breast Cancer in Korea (KROG 19-01).

To present the variations in the target delineation and the planning results of intensity-modulated radiation therapy (IMRT) for breast cancers. We requested the target volumes and organs at risk delineation for two cases of left breast cancers, and evaluated the IMRT plans including the supraclavicular and internal mammary node irradiation. Twenty-one institutions participated in this study. Differences in the planning target volume among institutions reached up to three-times for breast-conserving surgery (BCS) case and five-times for mastectomy case. Mean heart doses ranged from 3.3 to 24.1 Gy for BCS case and from 5.0 to 26.5 Gy for mastectomy case. Ipsilateral lung volumes receiving more than 20 Gy ranged from 4.7 to 57.4% for BCS case and from 16.4 to 55.5% for mastectomy case. There were large variations in the target delineation and planning results of IMRT for breast cancers among institutions. Considering the increased use of breast IMRT, more standardized protocols are needed.

Dosimetric Impact of Respiratory Motion During Breast Intensity-modulated Radiation Therapy Using Four-dimensional Dose Calculations.

The use of intensity-modulated radiation therapy (IMRT) in the treatment of breast cancer is increasing worldwide. Despite clear benefits concerning normal tissue sparing and dose homogeneity, the effects of breathing motion and setup error during breast IMRT should be considered. This study aimed to assess the dosimetric impact of respiratory motion on breast IMRT using four-dimensional (4D) dose calculations. Multiple computed tomography datasets acquired in three representative respiratory amplitudes, were retrospectively re-planned. Based on the reference dose distribution (RDD), motion-adjusted dose distributions (MDD) were recalculated. All 4D dose distributions were calculated by the voxel-based accumulation of RDD and MDD using five temporal probabilities. The dosimetric parameters of the 4D plans were compared to those of RDD. The dosimetric parameters of the planning target volume (PTV) were not significantly different between the RDD and 4D plans. Of the parameters of tumor bed (TB) simultaneous-integrated boost (SIB), the mean dose and V95% for the 4D plans were significantly reduced compared to those of RDD, and the percentage difference in the TB V95% ranged from -1.1% to -5.7% (p<0.05). The breast IMRT plan was robust against respiratory motion during tidal breathing. However, special considerations should be made when designing the TB SIB.

Low dose exposure evaluation for hypofractionated breast intensity modulated radiation therapy – taking into account the fraction-size effect with the linear quadratic model

Low dose exposure evaluation for hypofractionated breast intensity modulated radiation therapy – taking into account the fraction-size effect with the linear quadratic model

Three-Dimensional Versus Four-Dimensional Dose Calculation for Breast Intensity-Modulated Radiation Therapy

Objective:To analyze the effect of intra- and interfractional motion during breast intensity modulated radiation therapy (IMRT) by calculating dose distribution based on four-dimensional computed t...

Skin Toxicity in Early Breast Cancer Patients Treated with Field-In-Field Breast Intensity-Modulated Radiotherapy versus Helical Inverse Breast Intensity-Modulated Radiotherapy: Results of a Phase III Randomised Controlled Trial

AimsSkin toxicity is a common adverse effect of breast radiotherapy. We investigated whether inverse-planned intensity-modulated radiotherapy (IMRT) would reduce the incidence of skin toxicity compared with forward field-in-field breast IMRT (FiF-IMRT) in early stage breast cancer. Materials and methodsThis phase III randomised controlled trial compared whole-breast irradiation with either FiF-IMRT or helical tomotherapy IMRT (HT-IMRT), with skin toxicity as the primary end point. Patients received 50 Gy in 25 fractions and were assessed to compare skin toxicity between treatment arms. ResultsIn total, 177 patients were available for assessment and the median follow-up was 73.1 months. Inverse IMRT achieved more homogeneous coverage than FiF-IMRT; erythema and moist desquamation were higher with FiF-IMRT compared with HT-IMRT (61% versus 34%; P < 0.001; 33% versus 11%; P < 0.001, respectively). Multivariate analysis showed large breast volume, FiF-IMRT and chemotherapy were independent factors associated with worse acute toxicity. There was no difference between treatment arms in the incidence of late toxicities. The 5-year recurrence-free survival was 96.3% for both FiF-IMRT and HT-IMRT and the 5-year overall survival was 96.3% for FiF-IMRT and 97.4% for HT-IMRT. ConclusionsOur study showed significant reduction in acute skin toxicity using HT-IMRT compared with FiF-IMRT, without significant reduction in late skin toxicities. On the basis of these findings, inverse-planned IMRT could be used in routine practice for whole-breast irradiation with careful plan optimisation to achieve the required dose constraints for organs at risk.

Long-term outcomes of patients with conserved breast cancer treated with adjuvant hypofractionated prone breast intensity-modulated radiation therapy.

New techniques for adjuvant radiation therapy after breast conservation include prone positioning, hypofractionation and intensity-modulated radiation therapy (IMRT). Long-term evaluations of this combination are lacking, and we report our own experience. Patients with invasive breast cancer followed for a minimum 36months post-IMRT were eligible. Dose used was 40 Gray in 15 fractions over 3weeks to the whole breast via forward-planned prone, whole breast IMRT. A 10Gy in 5 fraction supine boost was offered. Between January 2012 and January 2020, 2199 patients had breast conservation and adjuvant radiation: 489 received hypofractionated prone breast IMRT, with 155 eligible for our evaluation. Median follow-up was 52months. Median age was 62 (range 36-80), 78.7% were T1, 20.6% were T2, and 12.3% were node-positive. Grade was 1 in 26.5%, 2 in 43.9% and 3 in 29.7%; 87.1% were oestrogen receptor positive, 3.2% were HER2 positive, and 11.0% were triple negative. 58.6% received a boost, 74.8% endocrine therapy and 32.3% chemotherapy. No patient developed local recurrence. One regional recurrence was successfully salvaged. Six patients (3.9%) developed metastases, and 1.9% died. Five-year actuarial local recurrence-free, regional recurrence-free and breast cancer-specific survival rates were 100.0%, 98.2% and 94.8%. Late grade 1 and 2 breast pain occurred in 20.0% and 1.3% of patients. Only 11.0% had new pain compared to pre-radiation. No patient developed radiation-induced pneumonitis, pulmonary fibrosis, rib fracture or cardiac toxicity. All patients scored cosmesis as 'good' or better. Adjuvant hypofractionated prone breast IMRT has excellent locoregional control and minimal toxicity.

Application of Two-Dimensional Detector Arrays to the Delivery Quality Assurance in Breast IMRT

Most two-dimensional (2D) detector arrays used for the verification of the intensity-modulated radiotherapy (IMRT) dose distribution comprise diode detectors or ion chamber detectors. These detectors show different sensitivities depending on the angle of incidence of the IMRT beam on the detector. In this study, the effect of the radiation beam’s angle of incidence onto the detector was analyzed in order to find an optimal 2D detector array setup position for delivery quality assurance in breast IMRT. For breast IMRT plans, comprising mostly tangential fields, the dose distribution produced with true composite beams was measured by arranging 2D detector array devices at various angles. The change in dosimetric accuracy was then assessed as a function of the radiation beam’s angle of incidence. A total of 72 dose distributions were measured and analyzed for 12 breast IMRT plans. Both the diode detector array and the ion chamber array showed a higher gamma passing ratio in the sagittal dose distribution measurement, where the beam’s angle of incidence was relatively larger. This study indicates that using a 2D detector array placed at a relatively large angle of incidence offers a more accurate verification of the IMRT dose distribution.

Retrospective analysis of portal dosimetry pre-treatment quality assurance of hybrid IMRT breast treatment plans

AbstractBackground:The purpose of this study is to evaluate the effectiveness and sensitivity of the Varian portal dosimetry (PD) system as a quality assurance (QA) tool for breast intensity-modulated radiation therapy (IMRT) treatment plans.Materials and methods:Four hundred portal dose images from 200 breast cancer patient IMRT treatment plans were analysed. The images were obtained using Varian PortalVision electronic portal imaging devices (EPIDs) on Varian TrueBeam Linacs. Three patient plans were selected, and the multi-leaf collimator (MLC) positions were randomly altered by a mean of 0·5, 1, 1·5 and 2 mm with a standard deviation of 0·1 mm on 50, 75 and 100% of control points. Using the improved/global gamma calculation algorithm with a low-dose threshold of 10% in the EPID, the change in gamma passing rates for 3%/3 mm, 2%/2 mm and 1%/1 mm criterion was analysed as a function of the introduced error. The changes in the dose distributions of clinical target volume and organ at risk due to MLC positioning errors were also analysed.Results:Symmetric and asymmetric breast or chest wall plan fields are different in delivery as well as in the QA. An average gamma passing rate of 99·8 ± 0·5 is presented for 3%/3 mm symmetric plans and 96·9 ± 4·5 is presented for 3%/3 mm asymmetric plans. An average gamma passing rate of 98·4 ± 4·3 is presented for 2%/2 mm symmetric plans and 89·7 ± 9·5 is presented for 2%/2 mm asymmetric plans. A large-induced error in MLC positioning (2·0 mm, 100% of control points) results in an insignificant change in dose that would be delivered to the patient. However, EPID portal dosimetry is sensitive enough to detect even the slightest change in MLC positioning error (0·5 mm, 50% of control points).Conclusions:Stricter pre-treatment QA action levels can be established for breast IMRT plans utilising EPID. For improved sensitivity, a multigamma criteria approach is recommended. The PD tool is sensitive enough to detect MLC positioning errors that contribute to even insignificant dose changes.

Using Robust Optimization for Skin Flashing in Intensity Modulated Radiation Therapy for Breast Cancer Treatment: A Feasibility Study

PurposeTo study the feasibility and the effectiveness of a novel implementation of robust optimization on 2 sets of computed tomography (CT) data simultaneously for skin flashing in intensity modulated radiation therapy for breast cancer. Method and MaterialsFive patients who received treatment to the breast and regional lymphatics were selected for this study. For each patient, 3 plans were generated using 3 different skin-flashing methods, including (1) a manual flash plan with optimization on the nominal planning target volume (PTV) not extending beyond the skin that required manually postplanning the opening of the multi-leaf collimator and jaw to obtain flash; (2) an expanded PTV plan with optimization on an expanded PTV that included the target in the air beyond the skin; and (3) a robust-optimized (RO) plan using robust optimization that simultaneously optimizes on the nominal CT data set and a simulated geometry error CT data set. The feasibility and the effectiveness of the robust optimization approach was investigated by comparing it with the 2 other methods. The robustness of the plan against target position variations was studied by simulating 0-, 5-, 10-, and 15-mm geometry errors. ResultsThe RO plans were the only ones able to meet acceptable criteria for all patients in both the nominal and simulated geometry error scenarios. The expanded PTV plans developed major deviation on the maximum dose to the PTV for 1 patient. For the manual flash plans, every patient developed major deviation either on 95% of the dose to the PTV or the maximum dose to the PTV in the simulated geometry error scenarios. The RO plan demonstrated the best robustness against the target position variation among the 3 methods of skin flashing. The doses to the lung and heart were comparable for all 3 planning techniques. ConclusionUsing robust optimization for skin flash in breast intensity modulated radiation therapy planning is feasible. Further investigation is warranted to confirm the clinical effectiveness of this novel approach.

Study of setup error in cone beam CT for whole breast intensity-modulated radiotherapy with breast board immobilization

Objective To investigate the setup errors and influencing factors of the whole breast intensity-modulated radiotherapy (IMRT) after breast-conserving surgery, and to identify the margins from clinical target volume (CTV) to planning target volume (PTV). Methods Thirty patients with left-sided (n=15) or right-sided breast cancer (n=15) receiving whole breast hypofractionated IMRT with breast board immobilization after breast-conserving surgery in Cancer Hospital from 2016 to 2017 were enrolled. The kilo-voltage cone-beam computed tomography (CBCT) was used to compare the errors of planning CT and treatment unit and determine the setup errors. The margins from CTV to PTV were calculated. The setup errors under different conditions were statistically compared by t-test. Results A total of 151 sets of CBCT images were taken in the whole cohort, (5.0±1.3) sets per patient on average. The setup errors in the x-axis (left-right direction), y-axis (cranial-caudal direction) and z-axis (anterior-posterior direction) were (2.2±1.7) mm, (3.1±2.5) mm and (3.3±2.3) mm, respectively. The margins from CTV to PTV were 6.39 mm, 10.00 mm and 8.57 mm, respectively. The setup error in anterior-posterior direction in the first week was (3.7±2.5) mm, significantly larger than (2.6±1.6) mm in the following week (P=0.002). The setup error of the patients with overweight or obesity was (3.9±2.6) mm, significantly higher than (2.9±2.0) mm in those with normal weight in the z-axis direction (P=0.033). Conclusion The margins from CTV to PTV are recommended to be ranged from 6 to 10 mm during hypofractionated whole breast IMRT with breast board immobilization after breast-conserving surgery. More frequent imaging verification should be applied in the first week of IMRT. Key words: Breast neoplasm/radiotherapy; Cone-beam CT; Setup error; Margin

Comparison of gamma index based on dosimetric error and clinically relevant dose\u2013volume index based on three-dimensional dose prediction in breast intensity-modulated radiation therapy

BackgroundMeasurement-guided dose reconstruction has lately attracted significant attention because it can predict the delivered patient dose distribution. Although the treatment planning system (TPS) uses sophisticated algorithm to calculate the dose distribution, the calculation accuracy depends on the particular TPS used. This study aimed to investigate the relationship between the gamma passing rate (GPR) and the clinically relevant dose–volume index based on the predicted 3D patient dose distribution derived from two TPSs (XiO, RayStation).MethodsTwenty-one breast intensity-modulated radiation therapy plans were inversely optimized using XiO. With the same plans, both TPSs calculated the planned dose distribution. We conducted per-beam measurements on the coronal plane using a 2D array detector and analyzed the difference in 2D GPRs between the measured and planned doses by commercial software. Using in-house software, we calculated the predicted 3D patient dose distribution and derived the predicted 3D GPR, the predicted per-organ 3D GPR, and the predicted clinically relevant dose–volume indices [dose–volume histogram metrics and the value of the tumor-control probability/normal tissue complication probability of the planning target volume and organs at risk]. The results derived from XiO were compared with those from RayStation.ResultsWhile the mean 2D GPRs derived from both TPSs were 98.1% (XiO) and 100% (RayStation), the mean predicted 3D GPRs of ipsilateral lung (73.3% [XiO] and 85.9% [RayStation]; p < 0.001) had no correlation with 2D GPRs under the 3% global/3 mm criterion. Besides, this significant difference in terms of referenced TPS between XiO and RayStation could be explained by the fact that the error of predicted V5Gy of ipsilateral lung derived from XiO (29.6%) was significantly larger than that derived from RayStation (− 0.2%; p < 0.001).ConclusionsGPR is useful as a patient quality assurance to detect dosimetric errors; however, it does not necessarily contain detailed information on errors. Using the predicted clinically relevant dose–volume indices, the clinical interpretation of dosimetric errors can be obtained. We conclude that a clinically relevant dose–volume index based on the predicted 3D patient dose distribution could add to the clinical and biological considerations in the GPR, if we can guarantee the dose calculation accuracy of referenced TPS.

Intensity-modulated radiotherapy and hypofractionated volumetric modulated arc therapy for elderly patients with breast cancer: comparison of acute and late toxicities.

To evaluate the differences between conventional fractionated intensity-modulated radiotherapy (IMRT) and hypofractionated (HypoRT) volumetric modulated arc therapy (VMAT) in elderly women affected by early-stage breast cancer (BC) in terms of RT-related acute/late side effect. Between October 2011 and July 2015, 80 consecutive elderly BC patients were treated with IMRT for 5weeks (40 patients) or HypoRT-VMAT for 3weeks (40 patients). Inclusion criteria were: age ≥ 70years, early BC (pT1-2 pN0-1), no prior neoadjuvant chemotherapy and non-metastatic disease. For patients receiving IMRT or HypoRT-VMAT, a total dose of 50Gy (25 fractions) or 40.5Gy (15 fractions) was prescribed to the whole ipsilateral breast, respectively. All patients received a simultaneously integrated boost up to a total dose of 60Gy for IMRT and 48Gy for HypoRT-VMAT. Acute and late side effects were evaluated using the RTOG/EORTC radiation morbidity scoring system. With a median follow-up of 45months, acute skin toxicity was overall very low, with grade 1 in 25 cases (62.5%) of the IMRT group and 21 cases (52.5%) of the HypoRT-VMAT group, while grade 2 toxicity was reported in 10 IMRT patients (25%) and 1 HypoRT-VMAT patient (2.5%) (p = 0.001). Regarding late adverse events, only grade 1 skin toxicity was recorded. The present study showed that whole breast IMRT and HypoRT-VMAT are feasible and well tolerated in early-stage BC elderly patients and that HypoRT-VMAT is affected by lower risk of acute and late RT-related side effects.

Use of electronic portal images to evaluate setup error and intra-fraction motion during free-breathing breast IMRT treatment

Before delivering of intensity-modulated radiotherapy, kilo-voltage image-guidance radiotherapy is widely used in setup error correction and monitoring intra-fraction motion effectively. Accordingly, this study proposes and tests an image integration technique for observing intra-fraction motion during beam delivery, with the wider objective of reducing both image-guidance time and the dose delivered to normal breast tissue. The study sample comprised 33 female patients with breast cancer, and 241 sets of portal images acquired using a VARIAN aSi-1000 electronic portal imaging device. Motion amplitudes and vectors were collected and calculated separately by two senior therapists. The setup error in 3 axes was computed for every fraction, with average shifting for lateral, longitudinal and vertical direction was −0.3-mm ± 0.5, −0.1-mm ± 0.5 and −0.6-mm ± 1.6, with the average vector of setup error being 2.9-mm ± 1.4. The average intra-fraction motion for vertical direction was (A: −0.1-mm ± 1.0; B: −0.0 ± 1.1), for longitudinal was (A: −0.4-mm ± 1.7; B: 2.0 ± 1.1), and for lateral direction was (A: 0.3-mm ± 1.3; B: 0.2 ± 1.8). The average intra-fraction vector was 2.9-mm ± 1.3 for therapist A, and 3.4-mm ± 1.8 for therapist B. Offline Review commercial software was utilized for setup error and motion analysis, and data analysis and reliability testing were conducted with statistical package of the social sciences. Pearson correlations between the two therapists was moderate (0.59, p << 0.01), and the Cohen's kappa value for inter rater agreement between different evaluators was fair in the anterior-posterior direction (0.25, p << 0.01), with slight agreement in other two directions and vectors. The study presented efficient and dose reduction method to evaluate setup error and intra-fraction motion during breast intensity-modulated radiotherapy treatment.