Dmean Difference Research Articles

Deep learning and atlas-based models to streamline the segmentation workflow of total marrow and lymphoid irradiation.

To improve the workflow of total marrow and lymphoid irradiation (TMLI) by enhancing the delineation of organs at risk (OARs) and clinical target volume (CTV) using deep learning (DL) and atlas-based (AB) segmentation models. Ninety-five TMLI plans optimized in our institute were analyzed. Two commercial DL software were tested for segmenting 18 OARs. An AB model for lymph node CTV (CTV_LN) delineation was built using 20 TMLI patients. The AB model was evaluated on 20 independent patients, and a semiautomatic approach was tested by correcting the automatic contours. The generated OARs and CTV_LN contours were compared to manual contours in terms of topological agreement, dose statistics, and time workload. A clinical decision tree was developed to define a specific contouring strategy for each OAR. The two DL models achieved a median [interquartile range] dice similarity coefficient (DSC) of 0.84 [0.71;0.93] and 0.85 [0.70;0.93] across the OARs. The absolute median Dmean difference between manual and the two DL models was 2.0 [0.7;6.6]% and 2.4 [0.9;7.1]%. The AB model achieved a median DSC of 0.70 [0.66;0.74] for CTV_LN delineation, increasing to 0.94 [0.94;0.95] after manual revision, with minimal Dmean differences. Since September 2022, our institution has implemented DL and AB models for all TMLI patients, reducing from 5 to 2h the time required to complete the entire segmentation process. DL models can streamline the TMLI contouring process of OARs. Manual revision is still necessary for lymph node delineation using AB models.

An Observational Dosimetric Study in Definitively Treated Primary Head and Neck Cancers: To Assess the Effect of Weight Loss and Change in Lateral Neck Dimensions on the Difference Between Dose Planned and Received by the Parotid(s) and Correlation with Adaptive Radiation Therapy

The head and neck cancer (HNC) literature is rife with reports of differences in planned versus actual radiation doses to the parotid gland (PG) due to changes in anatomy during the course of radiation therapy. We prospectively studied and quantified changes in planned and delivered doses due to weight loss and changes in lateral neck dimensions. Sixty patients were enrolled in this prospective non-randomized observational study. The inclusion criterion was having a newly diagnosed, histologically proven squamous cell carcinoma of HNC. Weight loss (WL) and change in lateral neck dimensions (LND) were assessed weekly, and new hybrid plans were generated using interval replanning CT scans. Dose variations were monitored and extrapolated for replanning CT scans and correlated with WL and change in LND. The Pearson correlation coefficients for WL and difference in Dmean of ipsilateral and contralateral PG was 0.3292 (P = .0124) and 0.4232 (P = .0010), respectively. There was significantly higher change in the Dmean of bilateral PG (Ipsilateral(I) > contralateral(C)) in patients who experienced WL of >5%. Change in LND correlated with difference in Dmean of ipsilateral PG at 0.4829 (P = .0001) and difference in D50 at 0.4146 (P < .0013). Contralateral PG correlated with difference in Dmean at 0.5952 (P < .0001). The difference in Dmean for ipsilateral PG was 1.8535 Gy for those showing reduction in LND of >1 cm compared with 0.8596 Gy (P = .0091) for those who had ≤1 cm reduction in LND. Either WL of >5% or reduction in LND of >1 cm can be used as an external parameter to help select patients who might benefit most from replanning and adaptive radiation therapy.

Analysis of Individualized Silicone Rubber Bolus Using Fan Beam Computed Tomography in Postmastectomy Radiotherapy: A Dosimetric Evaluation and Skin Acute Radiation Dermatitis Survey.

Objective: To investigate the dosimetric effects of using individualized silicone rubber (SR) bolus on the target area and organs at risk (OARs) during postmastectomy radiotherapy (PMRT), as well as evaluate skin acute radiation dermatitis (ARD). Methods: A retrospective study was performed on 30 patients with breast cancer. Each patient was prepared with an individualized SR bolus of 3 mm thickness. Fan-beam computed tomography (FBCT) was performed at the first and second fractions, and then once a week for a total of 5 times. Dosimetric metrics such as homogeneity index (HI), conformity index (CI), skin dose (SD), and OARs including the heart, lungs, and spinal cord were compared between the original plan and the FBCTs. The acute side effects were recorded. Results: In targets' dosimetric metrics, there were no significant differences in Dmean and V105% between planning computed tomography (CT) and actual treatments (P > .05), while the differences in D95%, V95%, HI, and CI were statistically significant (P < .05). In OARs, there were no significant differences between the Dmean, V5, and V20 of the affected lung, V5 of the heart and Dmax of the spinal cord (P > .05) except the V30 of affected lung, which was slightly lower than the planning CT (P < .05). In SD, both Dmax and Dmean in actual treatments were increased than plan A, and the difference was statistically significant (P < .05), while the skin-V20 and skin-V30 has no difference. Among the 30 patients, only one patient had no skin ARD, and 5 patients developed ARD of grade 2, while the remaining 24 patients were grade 1. Conclusion: The OR bolus showed good anastomoses and high interfraction reproducibility with the chest wall, and did not cause deformation during irradiation. It ensured accurate dose delivery of the target and OARs during the treatment, which may increase SD by over 101%. In this study, no cases of grade 3 skin ARD were observed. However, the potential of using OR bolus to reduce grade 1 and 2 skin ARD warrants further investigation with a larger sample size.

Technical note: Evaluation of deep learning based synthetic CTs clinical readiness for dose and NTCP driven head and neck adaptive proton therapy.

Adaptive proton therapy workflows rely on accurate imaging throughout the treatment course. Our centre currently utilizes weekly repeat CTs (rCTs) for treatment monitoring and plan adaptations. However, deep learning-based methods have recently shown to successfully correct CBCT images, which suffer from severe imaging artifacts, and generate high quality synthetic CT (sCT) images which enable CBCT-based proton dose calculations. To compare daily CBCT-based sCT images to planning CTs (pCT) and rCTs of head and neck (HN) cancer patients to investigate the dosimetric accuracy of CBCT-based sCTs in a scenario mimicking actual clinical practice. Data of 56 HN cancer patients, previously treated with proton therapy was used to generate 1.962 sCT images, using a previously developed and trained deep convolutional neural network. Clinical IMPT treatment plans were recalculated on the pCT, weekly rCTs and daily sCTs. The dosimetric accuracy of sCTs was compared to same day rCTs and the initial planning CT. As a reference, rCTs were also compared to pCTs. The dose difference between sCTs and rCTs/pCT was quantified by calculating the D98 difference for target volumes and Dmean difference for organs-at-risk. To investigate the clinical relevancy of possible dose differences, NTCP values were calculated for dysphagia and xerostomia. For target volumes, only minor dose differences were found for sCT versus rCT and sCT versus pCT, with dose differences mostly within ±1.5%. Larger dose differences were observed in OARs, where a general shift towards positive differences was found, with the largest difference in the left parotid gland. Delta NTCP values for grade 2 dysphagia and xerostomia were within ±2.5% for 90% of the sCTs. Target doses showed high similarity between rCTs and sCTs. Further investigations are required to identify the origin of the dose differences at OAR levels and its relevance in clinical decision making.

Comparison of Dynamic Trajectory Radiotherapy and Volumetric Modulated Arc Therapy for Loco-Regionally Advanced Oropharyngeal Cancer

Dynamic trajectory radiotherapy (DTRT) extends volumetric modulated arc therapy (VMAT) with dynamic table and collimator rotation. We investigate the potential benefit of DTRT over VMAT with respect to organ-at-risk (OAR) sparing for patients with loco-regionally advanced oropharyngeal cancer (OPC). We created DTRT and VMAT plans for 46 cases with prescribed doses of 50-70 Gy (2 Gy fractions, sequential boost) using 6 MV flattened beam on c-arm Linacs. For DTRT: case-specific collision avoidance maps were created and gantry-table paths were determined based on contoured structures to minimize fractional target/OAR overlap in beam's eye view. Gantry-collimator paths minimized field width in the leaf-travel direction. DTRT paths were imported in a research version of a commercial treatment planning system for intensity modulation optimization using the same optimizer and dose calculation algorithms as for VMAT. Plans at each dose level were normalized with 100% of the prescribed dose to 95% of the planning target volume (PTV). PTV coverage and OAR sparing for DTRT and VMAT were compared using Wilcoxon matched-pair signed rank test (5% significance level). The correlation between the fractional OAR/PTV50Gy volume overlap and difference in OAR Dmean between the two techniques was evaluated using Spearman's correlation coefficient. Plans at each dose level were all acceptable and had D0.03cc<110% prescription dose (difference between DTRT and VMAT were not statistically significant). In the combined plans, PTV50Gy D95% and D98% and PTV70Gy D95% were significantly higher with DTRT compared to VMAT. Differences in PTV66Gy coverage and PTV70Gy D5% were not statistically significant. Mean Dmean to the contralateral (CL) parotid gland was 13.99 / 15.28 Gy for DTRT / VMAT respectively, it was 25.75 / 28.05 Gy for the CL submandibular gland, 44.88 / 45.82 Gy for the pharynx and 30.90 / 33.93 Gy for the oral cavity (all with p<.001). Mean Dmean to the ipsilateral (IL) parotid gland was 29.00 / 29.28 Gy for DTRT / VMAT respectively (p = .77) and 57.71 / 57.91 Gy for the IL submandibular gland (p = .99). Significantly higher doses were observed with DTRT than with VMAT for the optical and auditory OARs and for the brain, but well below the clinical goals. The difference in Dmean (VMAT-DTRT) was negatively correlated to the fractional OAR/PTV50Gy overlap for the CL parotid and submandibular gland and the IL submandibular gland (r = -0.55 to -0.51, p<.001) but not for IL parotid gland (r = -0.17, p = .26), oral cavity (r = -0.13, p = .41) or pharynx (r = -011, p = .47). For at least the same target coverage, DTRT statistically significantly improves sparing for OARs related to salivary and swallowing functions compared to state-of-the-art VMAT. The advantage of DTRT decreases with increasing fractional OAR/PTV50Gy volume overlap for some salivary glands but not for pharynx or oral cavity. DTRT is promising to reduce treatment-related toxicity for patients with OPC.

Quality Assurance of Protocol Compliance in a Multicenter Randomized Trial Investigating the Role of Hypofractionated Comprehensive Reginal Nodal Irradiation in Node-Positive Breast Cancer (HARVEST)

The HARVEST trial (NCT03829553) is a phase III, multicenter, randomized clinical trial to explore efficacy and safety of hypofractionated irradiation (HFI) involving regional nodal irradiation (RNI, including internal mammary nodes, IMN) in N+ breast cancer patients treated with mastectomy or breast conserving surgery (BCS). Current study aims to analyze the dosimetric quality assurance so as to evaluate the compliance to the trial protocol. Eligible patients were randomly assigned (1:1) to receive conventional fractionated irradiation (CFI: 50 Gy/25Fx) or HFI (40.05 Gy/15Fx), which is delivered to ipsilateral chest wall or whole breast (CW/WB) with tumor bed boost (HFI: 10.68 Gy/4Fx; CFI: 10 Gy/5Fx) and comprehensive RNI (supra/infraclavicular nodes and IMN in each patient, lower axilla if indicated) by using IMRT technique. The plan quality was evaluated based on dose distribution, dose volume histogram (DVH) and field parameters. The target coverage, including planning target volume of CW/WB (PTV1) and tumor bed (PTV2) and doses of the organs at risk (OARs) were evaluated. The LQ model was used to convert doses of OARs in HFI group using α/β = 3 Gy (EQD23) for comparison. Between Feb 21, 2019 and Feb 14, 2022, 801 patients were enrolled at 8 centers with 401 and 400 in CFI and HFI group, respectively. There were 182 patients received BCS and 387 patients were with more than three positive lymph nodes. In the CFI group, the D90 and V45 of PTV1 reached the prescribed dose in 70.6% and 96.0% of the patients, respectively. In the HFI group, the D90 and V36 of PTV1 reached the prescribed dose in 87.8% and 95.5% of the patients, respectively. When the tumor bed was irradiated, the D90 of PTV2 reached the prescribed dose in 95.6% in the CFI group and 100% in the HFI group, respectively. The mean D90 of PTV1 and PTV2 were 50.09±0.65 Gy and 60.63±0.91 Gy in CFI group while 40.11±0.56 Gy and 50.79±2.03 Gy in HFI group. For OARs constraints, protocol compliance was all above 95% (heart: 95.3%; ipsilateral lung: 95.5%; contralateral lung: 97.1%; humeral head: 98.2% and spinal cord: 100%) with no significant difference between CFI and HFI groups. For patients with left-sided breast cancer, the Dmean of the heart was 5.10±1.75 Gy vs. 4.59±1.86 Gy (EQD23) in CFI and HFI groups (p = 0.51), respectively. No significant differences in Dmean of the heart (1.45±0.71 Gy vs. 1.33±0.77 Gy (EQD23), p = 0.40) was found either between two groups in right-sided patients. The differences were significant in the Dmean of the ipsilateral lung (13.37±1.99 Gy vs. 11.17±3.50 Gy (EQD23), p<0.01), contralateral lung (0.88±0.73 Gy vs. 0.74±0.61 Gy (EQD23), p<0.01) and the ipsilateral humeral head (15.27±7.62 Gy vs. 13.05±6.19 Gy (EQD23), p<0.01) and the Dmax of spinal cord (21.40±8.82 Gy vs. 19.47±7.99 Gy (EQD23), p = 0.05) between CFI and HFI groups. A high degree of compliance with protocol dose constraints was found for treatment plans in the HARVEST trial and doses to the most of OARs decreased in HFI group.

Clinical feasibility of a commercially available MRI-only method for radiotherapy treatment planning of the brain.

Advancements in deep-learning based synthetic computed tomography (sCT) image conversion methods have enabled the development of magnetic resonance imaging (MRI)-only based radiotherapy treatment planning (RTP) of the brain. This study evaluates the clinical feasibility of a commercial, deep-learning based MRI-only RTP method with respect to dose calculation and patient positioning verification performance in RTP of the brain. Clinical validation of dose calculation accuracy was performed by a retrospective evaluation for 25 glioma and 25 brain metastasis patients. Dosimetric and image quality of the studied MRI-only RTP method was evaluated by a direct comparison of the sCT-based and computed tomography (CT)-based external beam radiation therapy (EBRT) images and treatment plans. Patient positioning verification accuracy of sCT images was evaluated retrospectively for 10 glioma and 10 brain metastasis patients based on clinical cone-beam computed tomography (CBCT) imaging. An average mean dose difference of Dmean = 0.1% for planning target volume (PTV) and 0.6% for normal tissue (NT) structures were obtained for glioma patients. Respective results for brain metastasis patients were Dmean = 0.5% for PTVs and Dmean =1.0% for NTs. Global three-dimensional (3D) gamma pass rates using 2%/2 mm dose difference and distance-to-agreement (DTA) criterion were 98.0% for the glioma subgroup, and 95.2% for the brain metastasis subgroup using 1%/1 mm criterion. Mean distance differences of <1.0 mm were observed in all Cartesian directions between CT-based and sCT-based CBCT patient positioning in both subgroups. In terms of dose calculation and patient positioning accuracy, the studied MRI-only method demonstrated its clinical feasibility for RTP of the brain. The results encourage the use of the studied method as part of a routine clinical workflow.

Most Appropriate Radiation Therapy Techniques for The Breast Cancer Treatment: Dosimetric Analysis of Three Different Radiation Therapy Methods

Background: Radiation-induced cardiac events and pneumonitis are the major late radiotherapy side effects. Methods: We explored the differences in dose distribution between 3D CRT, IMRT and VMAT in 125 women with unilateral breast cancer. The various dose distribution to the tumor and OARs were studied for left and right sided irradiation. Results: Upon using 3D CRT breasts with lymph nodes, we observed a significant dose increase in the ipsilateral lung. Having irradiated only the right breast, there was a negligible Dmean difference to the adjacent lung between three methods, likewise for the myocardium in left breast cases. For right-sided cases 3D CRT showed the lowest doses in myocardium. Conclusion: Radiation oncologists should consider VMAT if conditions do not allow devising three plans with different methods. This in turn will reduce cardio and pneumotoxicity of left breast cancer treatment. In the treatment of right breast cancer, physicians should focus on 3D CRT.

A comparative study of volumetric modulated arc therapy plans based on the equivalent uniform dose optimization for left-sided breast cancer

PurposeTo investigate the effect of equivalent uniform dose (EUD)-based optimization on radiotherapy planning for left-sided breast cancer after mastectomy. MethodsTwelve patients treated with left-sided breast cancer using volumetric modulated arc therapy (VMAT) were retrospectively enrolled in this study. Four plans were generated for each patient. Plan A was optimized based on only physical parameters. EUD with α > 0 to organ at risk (OARs) was added in Plan B on the basis of Plan A; EUD with α < 0 to planning tumor volume (PTV) was added in Plan C on the basis of Plan A; EUD constraints were added for both OARs and PTV in Plan D. The quality of plans was evaluated in terms of Vx (volume percent of PTV or OARs received xGy dose), Dx (dose received by volume above x% of PTV or OARs), conformity index (CI), mean dose (Dmean), maximum dose (Dmax) and minimum dose (Dmin). ResultsFor PTV: Plan A vs. Plan B, the difference of D2 and CI was statistically significant (P < 0.05); Plan A vs. Plan C, the differences in D98, Dmean and HI were statistically significant (P < 0.05); Plan A vs. Plan D, differences in D2, Dmean and HI were statistically significant (P < 0.05). For OARs: Plan A vs. Plan B, and Plan A vs. Plan D, the differences in V5, V10, V20, V30, Dmean of the left lung and V10, V20, V30, Dmean of the heart were statistically significant (P < 0.05), the differences in Dmean of the thyroid and contralateral breast and the D2 and Dmax of spinal cord and spinal cord planning risk volume (PRV) were statistically significant (P < 0.05); Plan A vs. Plan C, only the difference in Dmax of spinal cord was statistically significant (P < 0.05). ConclusionCompared with DV condition, the dosimetric data with EUD-based optimization for OARs and PTV confer advantages in terms of the mean dose region of the left lung, heart, thyroid and contralateral (right) breast and the maximum dose of the spinal cord, and the improvement of the conformity and homogeneity of the target.

Quality Assurance of a Multicenter Prospective Phase III Randomized Controlled Trial Investigating the Role of Internal Mammary Lymph Node (IMN) in Node-Positive Breast Cancer: Individual Case Review

<h3>Purpose/Objective(s)</h3> Postmastectomy radiotherapy in Node-positive breast cancer with or without Internal mammary nodal irradiation (POTENTIAL) study is an ongoing study investigates the role of IMN irradiation in breast cancer patients. This study reported the result of the dosimetric quality assurance regarding individual case review of target coverage and doses to heart and lungs. <h3>Materials/Methods</h3> Real-time central reviews were performed for the first ten enrolled patients in each center regarding contouring and planning. The target coverage, including planning target volume of all targets and IMN (PTVall, PTVim), clinical target volume of IMN (CTVim), and doses to heart and lungs were evaluated. <h3>Results</h3> Among the 117 patients who were enrolled at 14 centers, 62 (53.0%) patients were randomly assigned to the IMN irradiation group (IMNI) and 55 (47.0%) patients to no IMN group (no IMNI group). Sixty (51.3%) patients received HFRT at dose of 43.5 Gy/15f/2.9 Gy, and 57 (48.7%) patients received CFRT at dose of 50 Gy/25f/2 Gy. A total of 108 (92.3%) patients were irradiated with intensity-modulated radiotherapy (IMRT) technique to the supra/infraclavicular nodal region (SNR) and chest wall (CW) +/- IMN. In 9 (7.6%) patients, the CW +/-IMN were irradiated by electrons, and the SNR was irradiated with IMRT technique. The D95 and D90 of PTVall reached the prescribed dose in 36.8% and 81.2% of the patients, respectively. In the IMN group who were irradiated with IMRT technique, the D95 and D90 of PTVim reached the prescribed dose in 29.8% and 78.9% of the patients, respectively. When the IMN was irradiated with electrons, the mean D95 and D90 of CTVim was 31.1 Gy and 37.1 Gy, significantly lower than that of patients treated with IMRT (P = 0.008). In the no IMNI group, the mean D95 of PTVim was 12.6 Gy and 20.2 Gy for patients treated with HFRT and CFRT, respectively, which was both significantly lower than that of the IMNI group (P < 0.001). For patients treated with HFRT, the Dmean and V5 of the heart was significantly higher in IMNI group compared to those in no IMNI group (5.2 vs 3.4 Gy, p = 0.001; 26.2% vs 14.4%, p< 0.001). The differences were significant in Dmean (12.9 vs 11.3 Gy, p = 0.001), V20 (26.0% vs 22.4%, p = 0.002), and V5 (50.2% vs 46.6%, p=0.009) of the ipsilateral lung, but not in V5 (6.2% vs 4.8%, p = 0.367) of contralateral lung, between IMN and no IMN group. For patients treated with CFRT, there were no significant differences in Dmean (5.4 vs 4.8 Gy, p = 0.366) and V5 (32.1% vs 26.7%, p = 0.169) of the heart between IMNI and no IMNI group. There were significant differences in Dmean (15.1 vs 14.0 Gy, p = 0.004), V20 (28.7% vs 26.0%, p=0.002), and V5 (56.9% vs 52.5%, p=0.001) of the ipsilateral lung, and V5 (12.7% vs 5.5%, p < 0.001) of contralateral lung between IMN and no IMN group. <h3>Conclusion</h3> Individual case review of POTENTIAL study showed that the target coverage was acceptable, and doses to the heart and lung increased in IMNI group compared to no IMNI group.

The effect of material assignment in nasal cavity on dose calculation for nasopharyngeal carcinoma (NPC) using Acuros XB.

PurposeTo evaluate the effect of material assignment in nasal cavity on dose calculation for the volumetric modulated arc therapy (VMAT) of nasopharyngeal carcinoma (NPC) using Acuros XB (AXB) algorithm.MethodsThe VMAT plans of 30 patients with NPC were calculated using AXB with material auto‐assignment of nasal cavity to lung and reassignment to air respectively. The doses to the planning target volumes (PTVs) overlapping with nasal cavity with material auto‐assignment of lung (AXB_Lung) were compared to the values obtained when nasal cavity was reassigned to air (AXB_Air) under the dose‐to‐medium (D m) reporting mode of AXB.ResultsFor dose calculated under AXB_Lung, the D 98%, D 2%, and D mean of the PTV69.96_Air Cavity (PTV of prescription dose 69.96 Gy overlapping with nasal cavity) were on average 16.1%, 1.6%, and 8.6% larger than that calculated under AXB_Air, respectively. Up to 19.5% difference in D 98%, 3% difference in D 2%, and 11.2% difference in D mean were observed in the worst cases for PTV69.96. Similar trend was observed for the PTV5940_Air Cavity, in which the D 98%, D 2%, and D mean calculated under AXB_Lung were on average 14.7%, 2.5%, and 10.2% larger than that calculated under AXB_Air, respectively. In the worst cases, the difference observed in D 98%, D 2%, and D mean could be up to 17.7%, 4.5%, and 12.7%, respectively.ConclusionsSignificant dose difference calculated by AXB between the material assignment of lung and air in nasal cavity for NPC cases might imply the possibility of underdosage to the PTVs that overlap with inhomogeneity. Therefore, attention should be put to ensure that accurate material assignment for dose calculation under AXB such that optimal dosage was given for tumor control.

Cone beam CT-based dose accumulation and analysis of delivered dose to the dominant intraprostatic lesion in primary radiotherapy of prostate cancer

BackgroundEvaluation of delivered dose to the dominant intraprostatic lesion (DIL) for moderately hypofractionated radiotherapy of prostate cancer by cone beam computed tomography (CBCT)-based dose accumulation and target coverage analysis.MethodsTwenty-three patients with localized prostate cancer treated with moderately hypofractionated prostate radiotherapy with simultaneous integrated boost (SIB) between December 2016 and February 2020 were retrospectively analyzed. Included patients were required to have an identifiable DIL on bi-parametric planning magnetic resonance imaging (MRI). After import into the RayStation treatment planning system and application of a step-wise density override, the fractional doses were computed on each CBCT and were consecutively mapped onto the planning CT via a deformation vector field derived from deformable image registration. Fractional doses were accumulated for all CBCTs and interpolated for missing CBCTs, resulting in the delivered dose for PTVDIL, PTVBoost, PTV, and the organs at risk. The location of the index lesions was recorded according to the sector map of the Prostate Imaging Reporting and Data System (PIRADS) Version 2.1. Target coverage of the index lesions was evaluated and stratified for location.ResultsIn total, 338 CBCTs were available for analysis. Dose accumulation target coverage of PTVDIL, PTVBoost, and PTV was excellent and no cases of underdosage in DMean, D95%, D02%, and D98% could be detected. Delivered rectum DMean did not significantly differ from the planned dose. Bladder mean DMean was higher than planned with 19.4 ± 7.4 Gy versus 18.8 ± 7.5 Gy, p < 0.001. The penile bulb showed a decreased delivered mean DMean with 29.1 ± 14.0 Gy versus 29.8 ± 14.4 Gy, p < 0.001. Dorsal DILs, defined as DILs in the posterior medial peripheral zone of the prostate, showed a significantly lower delivered dose with a mean DMean difference of 2.2 Gy (95% CI 1.3–3.1 Gy, p < 0.001) compared to ventral lesions.ConclusionsCBCT-based dose accumulation showed an adequate delivered dose to the dominant intraprostatic lesion and organs at risk within planning limits. Cautious evaluation of the target coverage for index lesions adjacent to the rectum is warranted to avoid underdosage.

A novel semi auto-segmentation method for accurate dose and NTCP evaluation in adaptive head and neck radiotherapy

Background and purposeAccurate segmentation of organs-at-risk (OARs) is crucial but tedious and time-consuming in adaptive radiotherapy (ART). The purpose of this work was to automate head and neck OAR-segmentation on repeat CT (rCT) by an optimal combination of human and auto-segmentation for accurate prediction of Normal Tissue Complication Probability (NTCP). Materials and methodsHuman segmentation (HS) of 3 observers, deformable image registration (DIR) based contour propagation and deep learning contouring (DLC) were carried out to segment 15 OARs on 15 rCTs. The original treatment plan was re-calculated on rCT to obtain mean dose (Dmean) and consequent NTCP-predictions. The average Dmean and NTCP-predictions of the three observers were referred to as the gold standard to calculate the absolute difference of Dmean and NTCP-predictions (|ΔDmean| and |ΔNTCP|). ResultsThe average |ΔDmean| of parotid glands in HS was 1.40 Gy, lower than that obtained with DIR and DLC (3.64 Gy, p < 0.001 and 3.72 Gy, p < 0.001, respectively). DLC showed the highest |ΔDmean| in middle Pharyngeal Constrictor Muscle (PCM) (5.13 Gy, p = 0.01). DIR showed second highest |ΔDmean| in the cricopharyngeal inlet (2.85 Gy, p = 0.01). The semi auto-segmentation (SAS) adopted HS, DIR and DLC for segmentation of parotid glands, PCM and all other OARs, respectively. The 90th percentile |ΔNTCP|was 2.19%, 2.24%, 1.10% and 1.50% for DIR, DLC, HS and SAS respectively. ConclusionsHuman segmentation of the parotid glands remains necessary for accurate interpretation of mean dose and NTCP during ART. Proposed semi auto-segmentation allows NTCP-predictions within 1.5% accuracy for 90% of the cases.

Deep learning prediction of proton and photon dose distributions for paediatric abdominal tumours

ObjectiveDose prediction using deep learning networks prior to radiotherapy might lead tomore efficient modality selections. The study goal was to predict proton and photon dose distributions based on the patient-specific anatomy and to assess their clinical usage for paediatric abdominal tumours. Material and methodsData from 80 patients with neuroblastoma or Wilms’ tumour was included. Pencil beam scanning (PBS) (5 mm/ 3%) and volumetric-modulated arc therapy (VMAT) plans (5 mm) were robustly optimized on the internal target volume (ITV). Separate 3-dimensional patch-based U-net networks were trained to predict PBS and VMAT dose distributions. Doses, planning-computed tomography images and relevant optimization masks (ITV, vertebra and organs-at-risk) of 60 patients were used for training with a 5-fold cross validation.The networks’ performance was evaluated by computing the relative error between planned and predicted dose-volume histogram (DVH) parameters for 20 inference patients. In addition, the organs-at-risk mean dose difference between modalities was calculated using planned and predicted dose distributions (ΔDmean = DVMAT-DPBS). Two radiation oncologists performed a blind PBS/VMAT modality selection based on either planned or predicted ΔDmean. ResultsAverage DVH differences between planned and predicted dose distributions were ≤ |6%| for both modalities. The networks classified the organs-at-risk Dmean difference as a gain (ΔDmean > 0) with 98% precision. An identical modality selection based on planned compared to predicted ΔDmean was made for 18/20 patients. ConclusionDeep learning networks for accurate prediction of proton and photon dose distributions for abdominal paediatric tumours were established. These networks allowing fast dose visualisation might aid in identifying the optimal radiotherapy technique when experience and/or resources are unavailable.

Dosimetric comparison of level II lymph nodes between mono-isocentric and dual-isocentric approaches in 3D-CRT and IMRT techniques in breast radiotherapy of mastectomy patients

AbstractAim:To evaluate the dosimetric parameters of level II lymph nodes in chest wall three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT) of mastectomy patients using dual-isocentric (DIT) and mono-isocentric techniques (MIT).Materials and methods:Computed tomography (CT) images of 20 mastectomy patients undergoing chest wall external radiotherapy were used as the input data for the abovementioned techniques. Selected dosimetric parameters were calculated for the axillary level I–III lymph nodes, chest wall, heart and lung. Paired t-test statistical analysis was used for comparing the results of MIT and DIT in both 3D-CRT and IMRT methods.Results:There were significant differences in Dmin (minimum dose), Dmax (maximum dose) and maximum–minimum dose between MIT and DIT techniques (13, −8·6, −52·2% differences for Dmin, Dmax and maximum–minimum, respectively) in IMRT. There were also significant differences for Dmean (mean dose), Dmax and maximum–minimum dose (7·8, −11·4, −44·6% differences in Dmean, Dmax and maximum–minimum, respectively) in 3D-CRT (p &lt; 0·05). In addition, there were not any differences in the dosimetric parameters for heart, lung and level I and III lymph nodes.Conclusion:In both 3D-CRT and IMRT methods, level II lymph node dose distribution in MIT was closer to the prescribed dose compared with DIT due to the position of these nodes in the field junction area. To achieve a better dose homogeneity, it could be recommended to use MIT instead of DIT in 3D-CRT and IMRT for mastectomy patients.

Deep inspiration breath-hold for left-sided breast irradiation: Analysis of dose-mass histograms and the impact of lung expansion

BackgroundThe aim of this study was to compare dose-volume histogram (DVH) with dose-mass histogram (DMH) parameters for treatment of left-sided breast cancer in deep inspiration breath-hold (DIBH) and free breathing (FB). Additionally, lung expansion and anatomical factors were analyzed and correlated to dose differences.MethodsFor 31 patients 3D conformal radiation therapy plans were retrospectively calculated on FB and DIBH CTs in the treatment planning system. The calculated doses, structures and CT data were transferred into MATLAB and DVHs and DMHs were calculated. Mean doses (Dmean), volumes and masses receiving certain doses (Vx, Mx) were determined for the left lung and the heart. Additionally, expansion of the left lung was evaluated using deformable image registration. Differences in DVH and DMH dose parameters between FB and DIBH were statistically analyzed and correlated to lung expansion and anatomical factors.ResultsDIBH reduced Dmean (DVH) and relative V20 (V20 [%]) of the left lung in all patients, on average by − 19 ± 9% (mean ± standard deviation) and − 24 ± 10%. Dmean (DMH) and M20 [%] were also significantly reduced (− 12 ± 11%, − 16 ± 13%), however 4 patients had higher DMH values in DIBH than in FB. Linear regression showed good correlations between DVH and DMH parameters, e.g. a dosimetric benefit smaller than 8.4% for Dmean (DVH) in DIBH indicated more irradiated lung mass in DIBH than in FB. The mean expansion of the left lung between FB and DIBH was 1.5 ± 2.4 mm (left), 16.0 ± 4.0 mm (anterior) and 12.2 ± 4.6 mm (caudal). No significant correlations were found between expansions and differences in Dmean for the left lung. The heart dose in DIBH was reduced in all patients by 53% (Dmean) and this dosimetric benefit correlated to lung expansion in anterior.ConclusionsTreatment of left-sided breast cancer in DIBH reduced dose to the heart and in most cases the lung dose, relative irradiated lung volume and lung mass. A mass related dosimetric benefit in DIBH can be achieved as long as the volume related benefit is about ≥8–9%. The lung expansion (breathing pattern) showed no impact on lung dose, but on heart dose. A stronger chest breathing (anterior expansion) for DIBH seems to be more beneficial than abdominal breathing.

51. A novel algorithm (DirectDensity™) for reconstruction of simulation CT images used in radiotherapy treatment planning: dosimetric evaluation

Purpose CT imaging in radiotherapy represents the standard for treatment planning. The calculation of dose distribution requires appropriate energy-dependent calibration curves to convert Hounsfield Units (HU) into electronic densities relative to water (rEDs). To obtain optimal image quality and reduce dose, it could be useful to modulate X-ray tube potential based on patient size, but in radiotherapy treatment planning this practice requires the use of several calibration curves. A novel algorithm (DirectDensity™, DD™ recently developed by Siemens Healthcare, uses CT projection data to reconstruct images directly proportional to rEDs, independently of kVp used, thus removing the need of different curves. The purpose of the study is to evaluate this algorithm for clinical use. Methods The CIRS Density Phantom with different tissue equivalent inserts was scanned at 70, 80, 100, 120 and 140 kVp with the new Siemens Confidence CT scanner. Images were reconstructed with the DD™ algorithm to assess the correspondence of rEDs obtained from imaging with those certified. Afterwards the images of 7 patients scanned at 120 kVp were reconstructed with standard filtered backprojection (FBP) and DD™ algorithm. Treatment plans were calculated on both FBP and DD™ images by using standard HU-rEDs curve and linear CTvalue-rEDs relationship respectively (Fig. 1). Dose differences were evaluated through γ -analysis (1 mm, 1%). Results The rEDs measured from images (by reversing the linear relationship between CTvalue and rED) in regions corresponding to phantom inserts were compared to certified rEDs: differences were reported in Table 1 . Minimal dosimetric differences were found between treatment plans calculated on both FBP and DD™ images. DVHs showed differences in Dmean, D98, D2 and V95 for PTVs and OARs smaller than 1%. γ -analysis indicated negligible differences between dose distributions, with lowest passing rate at 97%. Conclusions This study proved the equivalence between DD™ and FBP, including the possibility to modulate kVp during CT acquisition, thus reducing patient dose without complicating treatment planning workflow.

A meta-analysis comparing Dosimetric between volumetric-modulated arc therapy and intensity-modulated radiotherapy for left sided breast cancer after breast-conserving surgery

Objective To compare the dosimetric parameters of target volumes and organs at risk between volumetric-modulated arc therapy (VMAT) and intensity-modulated radiotherapy (IMRT) for left sided breast cancer after breast-conserving surgery by a meta-analysis. Methods Literature search was performed to include related studies to analyze the dosimetric parameters of target volumes and organs at risk. Results A total of 11 studies involving 154 patients were included in meta-analysis. There were no significant differences in Dmean, HI of PTV-Whole breast and PTV-Boost. Comparing to IMRT, VMAT increased the conformity index (CI) of PTV-Whole breast (P=0.000) and PTV-Boost (P=0.002). When the mean volume of target volumes was≤634 cm3, there were no significant differences in Dmean, V5, V20 of the heart and left sided lung, V30 of the heart, Dmean of the right sided lung and breast between VMAT and IMRT.When the mean volume of target volumes was>634 cm3, the Dmean(P=0.037), V5(P=0.005) and V20(P=0.030) of the heart in IMRT was lower than VMAT, but the V30(P=0.001) of heart in VMAT was lower than IMRT.IMRT showed significantly lower Dmean(P=0.013), V5(P=0.000), V20(P=0.000) of the left sided lung, and Dmean(P=0.001) of the right sided lung than VMAT.There were no significant differences in Dmean of the right sided breast. Conclusions There were no significant differences in dosimetric parameters of target volumes between VMAT and IMRT.When the mean volume of target volumes was≤634 cm3, there were no significant differences in dosimetric parameters of organs at risk. When the mean volume of target volumes was>634 cm3, IMRT has some advantages in protection of the heart and lung. Key words: Breast neoplasms/breast-conserving surgery; Breast neoplasms/volumetric-modulated arc therapy; Breast neoplasms/intensity-modulated radiotherapy; Meta-analysis

Parotid gland radiation dose-xerostomia relationships based on actual delivered dose for nasopharyngeal carcinoma.

Xerostomia induced by radiotherapy is a common toxicity for head and neck carcinoma patients. In this study, the deformable image registration of planning computed tomography (CT) and weekly cone‐beam CT (CBCT) was used to override the Hounsfield unit value of CBCT, and the modified CBCT was introduced to estimate the radiation dose delivered during the course of treatment. Herein, the beams from each patient's treatment plan were applied to the modified CBCT to construct the weekly delivered dose. Then, weekly doses were summed together to obtain the accumulated dose. A total of 42 parotid glands (PGs) of 21 nasopharyngeal carcinoma patients were analyzed. Doses delivered to the parotid glands significantly increased compared with the planning doses. V20, V30, V40, Dmean, and D50 increased by 11.3%, 28.6%, 44.4%, 9.5%, and 8.4% respectively. Of the 21 patients included in the study, eight developed xerostomia and the remaining 13 did not. Both planning and delivered PG Dmean for all patients exceeded tolerance (26 Gy). Among the 21 patients, the planning dose and delivered dose of Dmean were 30.6 Gy and 33.6 Gy, respectively, for patients with xerostomia, and 26.3 Gy and 28.0 Gy, respectively, for patients without xerostomia. The D50 of the planning and delivered dose for patients was below tolerance (30 Gy). The results demonstrated that the p‐value of V20, V30, D50, and Dmean difference of the delivery dose between patients with xerostomia and patients without xerostomia was less than 0.05. However, for the planning dose, the significant dosimetric difference between the two groups only existed in D50 and Dmean. Xerostomia is closely related to V20, V30, D50, and Dmean.

Comparison of incidental irradiation dose to the internal mammary nodes among I-IMRT, F-IMRT, and 3DCRT after breast-conserving surgery

Objective To explore the dosimetric variance in incidental irradiation to the internal mammary nodes among inverse intensity-modulated radiotherapy (I-IMRT), forward intensity-modulated radiotherapy (F-IMRT), and three-dimensional conformal radiotherapy (3DCRT) after breast-conserving surgery, and to provide a basis for deciding whether to spare the internal mammary nodes in clinical treatment. Methods A total of 84 patients undergoing breast-conserving surgery were enrolled as subjects. The internal mammary nodes in the first three intercostal spaces were contoured. Three radiotherapy plans were designed for each patient. The internal mammary nodes were not included in the planning target volume. Comparison was made among the three plans. The results were compared using Wilcoxon signed rank test. Results The I-IMRT, F-IMRT, and 3DCRT plans had similar median Dmean values for the internal mammary nodes, which were 2740.2, 2973.9, and 2951.4 cGy, respectively. The analyses of the three individual intercostal spaces showed that there was no difference in Dmean for the first intercostal space or the second intercostal space between the three plans; For the third intercostal space, however, I-IMRT had a significantly higher Dmean than 3DCRT and F-IMRT. The analyses of the three individual plans showed that for each plan, the Dmean was the highest in the third intercostal space, followed by the second intercostal space and the first intercostal space. Conclusions All the three plans fail to attain an adequate prescribed dose to cure subclinical disease, and there is no significant difference among the three plans. Therefore, it is risky to exclude the internal mammary nodes using any one of the three radiotherapy techniques for patients with clinical indications for internal mammary nodes radiation. In the combination therapy including chemotherapy, endocrine therapy, and targeted therapy, however, further follow-up is needed to determine whether the incidental irradiation dose to the internal mammary nodes could meet clinical requirement. Key words: Breast-conserving postoperative radiotherapy; Internal mammary lymph node region; Incidental irradiated dose; Treatment planning comparison