Incidental Dose Research Articles

848: Treatment laterality and incidental dose to internal mammary nodes and axilla in breast radiotherapy

848: Treatment laterality and incidental dose to internal mammary nodes and axilla in breast radiotherapy

685: Incidental dose distribution to contralateral internal mammary nodes in breast cancer patients

685: Incidental dose distribution to contralateral internal mammary nodes in breast cancer patients

Incidental dose distribution to contralateral internal mammary nodes in breast cancer patients undergoing adjuvant radiotherapy

Background and purposeIn a relevant number of primary breast cancer patients, lymphatic drainage to the contralateral internal mammary nodes (cIMN) is being observed. Nevertheless, so far lymphatic drainage pathway to the cIMN is largely neglected during adjuvant radiotherapy. Materials and methodsThis study evaluated the incidental dose to the cIMN for 120 volumetric modulated arc therapy (VMAT) treatment plans for node positive breast in dependence of internal mammary node irradiation (IMNI) and deep inspiration breath hold (DIBH). Additionally, incidental dose distribution to the cIMN based on the field design in the MA20, EORTC22922/10925 and AMAROS trials was assessed. ResultsThe incidental dose (Dmean ± SD) to the cIMN-CTV was 13.0 (±4.7) Gy with a maximum dose of < 30 Gy in 113/120 cases. If IMNI was included (n = 80), the Dmean to the cIMN-CTV was significantly higher compared to no IMNI, but still comparably low (n = 40; 14.3 Gy vs. 9.6 Gy; p = 0.0001). Furthermore, the dose in the cIMN during free breathing (n = 80) was higher compared to DIBH (n = 40; 13.9 Gy vs. 11.2 Gy; p = 0.002).Simulated treatment plans based on the randomized RNI trials revealed neglectable dose coverage of the cIMN (Dmean 1.0–1.8 Gy) for all protocols. ConclusionNeither in the randomized RNI trials nor during contemporary treatment techniques clinically relevant dose distribution to the cIMN was observed. Further studies are warranted to assess the potential impact of intended irradiation of cIMN in high-risk patients.

The effect of incidental dose to pelvic nodes in bladder-only irradiation in the era of IMRT: adosimetric study.

While three-dimensional radiotherapy (RT) causes high incidental nodal doses in bladder-only irradiation for muscle-invasive bladder cancer (MIBC), the impact on pelvic lymphatics is unclear in the era of intensity-modulated RT (IMRT). This study evaluates incidental doses to pelvic lymphatics in MIBC patients treated with IMRT. The data of 40MIBC patients treated with bladder-only IMRT and concurrent chemotherapy were retrospectively evaluated. The pelvic lymphatics were contoured on initial simulation images and incidental nodal doses were evaluated. The Statistical Package for the Social Sciences (SPSS) version23.0 (IBM, Armonk, NY, USA) was used for statistics. Median RT dose to the bladder was 60 Gy in 30fractions. In dosimetric analysis, median values of mean dose (Dmean) of the obturator, presacral, external iliac, internal iliac, and distal common iliac lymphatics were 33 Gy (range 4-50 Gy), 3 Gy (range 1-28 Gy), 9.5 Gy (range 3-41 Gy), 7.5 Gy (range 2-14 Gy), and 1 Gy (range 0-15 Gy), respectively. The Dmean of the obturator lymphatics was significantly higher (p < 0.001) and the Dmean of the distal common iliac lymphatics was significantly lower (p < 0.001) than all remaining lymphatic stations. The Dmean of the external iliac lymphatics was significantly higher than that of the presacral lymphatics (p < 0.001), but the difference with the internal iliac lymphatics was not statistically significant (p = 0.563). The incidental nodal doses with bladder-only IMRT are heterogeneous and remain below the generally accepted doses for microscopic disease eradication for bladder cancer.

474: Unknown primary head & neck SCC: Involved neck only radiotherapy and incidental dose to oropharynx

474: Unknown primary head & neck SCC: Involved neck only radiotherapy and incidental dose to oropharynx

Does Breast Surgery Type Alter Incidental Axillary Irradiation? A Dosimetric Analysis of the "Sentinel Envahi et Randomisation du Curage" SERC Trial.

An incidental axillary dose of adjuvant radiotherapy using tangential beams is usually given after breast-conserving surgery for breast cancer. The goal of this sub-study was to evaluate this incidental dose in the setting of post-mastectomy radiotherapy (PMRT) according to two different radiotherapy techniques. Patients participating in a randomized SERC trial who received PMRT in a single center were included. We collected the incidental axillary dose delivered to the Berg level 1 using different dosimetric parameters and compared two techniques using Student's t-test: three-dimensional conformal radiotherapy (3D-CRT) and volumetric arc therapy (VMAT). We analyzed radiotherapy plans from 52 patients who received PMRT from 2012 to 2021. The mean dose delivered to the Berg level 1 was 37.2 Gy. It was significantly higher with VMAT than with 3D-CRT-43.6 Gy (SD = 3.1 Gy) versus 34.8 Gy (SD = 8.6 Gy) p < 0.001. Eighty-four percent of the Berg level 1 was covered by 40 Gy isodose in the VMAT group versus 55.5% in the 3D-CRT group p < 0.001. On the Berg level 1, PMRT gives a dose at least equivalent to the one given by post-breast-conserving surgery radiotherapy, making it possible to limit completion axillary lymph node dissections in select pN1a patients treated with a mastectomy. Modern radiotherapy techniques like VMAT tend to increase this incidental dose.

Pulmonary vein dose and risk of atrial fibrillation in patients with non-small cell lung cancer following definitive radiotherapy: An NI-HEART analysis

Background and purposeSymptomatic arrhythmia is common following radiotherapy for non-small cell lung cancer (NSCLC), frequently resulting in morbidity and hospitalization. Modern treatment planning technology theoretically allows sparing of cardiac substructures. Atrial fibrillation (AF) comprises the majority of post-radiotherapy arrhythmias, but efforts to prevent this cardiotoxicity have been limited as the causative cardiac substructure is not known. In this study we investigated if incidental radiation dose to the pulmonary veins (PVs) is associated with AF. Material and methodsA single-centre study of patients completing contemporary (chemo)radiation for NSCLC, with modern planning techniques. Oncology, cardiology and death records were examined, and AF events were verified by a cardiologist. Cardiac substructures were contoured on planning scans for retrospective dose analysis. ResultsIn 420 eligible patients with NSCLC treated with intensity-modulated (70%) or 3D-conformal (30%) radiotherapy with a median OS of 21.8 months (IQR 10.8–35.1), there were 26 cases of new AF (6%). All cases were grade 3 except two cases of grade 4. Dose metrics for both the left (V55) and right (V10) PVs were associated with the incidence of new AF. Metrics remained statistically significant after accounting for the competing risk of death and cardiovascular covariables for both the left (HR 1.02, 95%CI 1.00–1.03, p = 0.005) and right (HR 1.01 (95%CI 1.00–1.02, p = 0.033) PVs. ConclusionRadiation dose to the PVs during treatment of NSCLC was associated with the onset of AF. Actively sparing the PVs during treatment planning could reduce the incidence of AF during follow-up, and screening for AF may be warranted for select cases.

Quality assurance of radiation therapy after breast-conserving surgery among patients in the BOOG 2013-08 trial

Background and purposeIn the BOOG 2013-08 trial (NCT02271828), cT1-2N0 breast cancer patients were randomized between breast conserving surgery with or without sentinel lymph node biopsy (SLNB) followed by whole breast radiotherapy (WBRT). While awaiting primary endpoint results (axillary recurrence rate), this study aims to perform a quality assurance analysis on protocol adherence and (incidental) axillary radiation therapy (RT) dose. Materials and methodsPatients were enrolled between 2015 and 2022. Data on prescribed RT and (in 25% of included patients) planning target volumes (PTV) parameters were recorded for axillary levels I-IV and compared between treatment arms. Multivariable linear regression analysis was performed to determine prognostic variables for incidental axillary RT dose. Results1,439/1,461 included patients (98.5%) were treated according to protocol and 87 patients (5.9%) received regional RT (SLNB 10.9%, no-SLNB 1.5 %). In 326 patients included in the subgroup analysis, the mean incidental PTV dose at axilla level I was 59.5% of the prescribed breast RT dose. In 5 patients (1.5%) the mean PTV dose at level I was ≥95% of the prescribed breast dose. No statistically or clinically significant differences regarding incidental axillary RT dose were found between treatment arms. Tumour bed boost (yes/no) was associated with a higher incidental mean dose in level I (R2 = 0.035, F(6, 263) = 1.532, p 0.168). ConclusionThe results indicate that RT-protocol adherence was high, and that incidental axillary RT dose was low in the BOOG 2013-08 trial. Potential differences between treatmentarms regarding the primary endpoint can thus not be attributed to different axillary radiation doses.

The Association of Incidental Radiation Dose to the Heart Base with Overall Survival and Cardiac Events after Curative-intent Radiotherapy for Non-small Cell Lung Cancer: Results from the NI-HEART Study

AimsCardiac disease is a dose-limiting toxicity in non-small cell lung cancer radiotherapy. The dose to the heart base has been associated with poor survival in multiple institutional and clinical trial datasets using unsupervised, voxel-based analysis. Validation has not been undertaken in a cohort with individual patient delineations of the cardiac base or for the endpoint of cardiac events. The purpose of this study was to assess the association of heart base radiation dose with overall survival and the risk of cardiac events with individual heart base contours. Materials and methodsPatients treated between 2015 and 2020 were reviewed for baseline patient, tumour and cardiac details and both cancer and cardiac outcomes as part of the NI-HEART study. Three cardiologists verified cardiac events including atrial fibrillation, heart failure and acute coronary syndrome. Cardiac substructure delineations were completed using a validated deep learning-based autosegmentation tool and a composite cardiac base structure was generated. Cox and Fine–Gray regressions were undertaken for the risk of death and cardiac events. ResultsOf 478 eligible patients, most received 55 Gy/20 fractions (96%) without chemotherapy (58%), planned with intensity-modulated radiotherapy (71%). Pre-existing cardiovascular morbidity was common (78% two or more risk factors, 46% one or more established disease). The median follow-up was 21.1 months. Dichotomised at the median, a higher heart base Dmax was associated with poorer survival on Kaplan–Meier analysis (20.2 months versus 28.3 months; hazard ratio 1.40, 95% confidence interval 1.14–1.75, P = 0.0017) and statistical significance was retained in multivariate analyses. Furthermore, heart base Dmax was associated with pooled cardiac events in a multivariate analysis (hazard ratio 1.75, 95% confidence interval 1.03–2.97, P = 0.04). ConclusionsHeart base Dmax was associated with the rate of death and cardiac events after adjusting for patient, tumour and cardiovascular factors in the NI-HEART study. This validates the findings from previous unsupervised analytical approaches. The heart base could be considered as a potential sub-organ at risk towards reducing radiation cardiotoxicity.

Delivery of re-irradiation and complex palliative radiotherapy using proton therapy in pediatric cancer patients.

The intent of this study is to characterize indications for pediatric palliative-intent proton radiation therapy (PIPRT). We retrospectively reviewed patients 21years and younger who received PIPRT. We defined PIPRT as radiotherapy (RT) aimed to improve cancer-related symptoms/provide durable local control in the non-curative setting. Mixed proton/photon plans were included. Adjacent re-irradiation (reRT) was defined as a reRT volume within the incidental dose cloud of a prior RT target, whereas direct reRT was defined as in-field overlap with prior RT target. Acute toxicity during RT until first inspection visit was graded according to the Common Terminology Criteria for Adverse Events. The Kaplan-Meier method, measured from last PIPRT fraction, was used to assess progression-free survival (PFS) and overall survival (OS). Eighteen patients underwent PIPRT between 2014 and 2020. Median age at treatment start was 10years [2-21]. Median follow-up was 8.2months [0-48]. Treatment sites included: brain/spine [10], abdomen/pelvis [3], thorax [3], and head/neck [2]. Indications for palliation included: durable tumor control [18], neurologic symptoms [4], pain [3], airway compromise [2], and great vessel compression [1]. Indications for protons included: reRT [15] (three adjacent, 12 direct), craniospinal irradiation [4], reduction of dose to normal tissues [3]. Sixteen experienced grade (G) 1-2 toxicity; two G3. There were no reports of radionecrosis. Median PFS was 5.3months [95% confidence interval (CI): 2.7-16.3]. Median OS was 8.3months [95% CI: 5.5-26.3]. The most common indication for PIPRT was reRT to provide durable tumor control. PIPRT appears to be safe, with no cases of high-grade toxicity.

Pancreas: An Organ-at-Risk to Consider in Future Pediatric Abdominal Radiotherapy

Irradiation to the pancreas during pediatric radiotherapy is associated with secondary late effects, yet the pancreas is not typically considered an organ-at-risk (OAR) during radiotherapy planning. This audit investigated incidental pancreatic doses to estimate the relative risk (RR) of developing diabetes in later life. Incidental pancreas doses were audited from 92 patients aged 2 to 19 historically treated with photons for craniospinal irradiation (CSI, N = 73) and for abdominal neuroblastoma (N = 19). Prescription doses ranged 21-36 Gy and 21-39 Gy (with boost to spine up to 50 Gy) for neuroblastoma and CSI patients, respectively. The pancreas was segmented on all planning CT scans following RTOG guidelines. Furthermore, the pancreas was split into its sub-volumes (head, body and tail) for abdominal cases only, since these scans were acquired with contrast enhancement. The RR of developing subsequent diabetes was estimated as a function of dose (D): RR = 1+0.65 × D × exp(-0.3 × D). Dose to the pancreas tail was used for neuroblastoma cases, whereas dose to the whole pancreas was used for CSI patients given that the pancreas could not be split in non-contrast scans. The mean dose delivered to the whole pancreas was 15.4±7.5 Gy for all patients, 12.7±4.7 Gy for CSI patients and 25.9±7.4 Gy for abdominal patients. Pancreas V10Gy was 61.2% for all patients, 51.5% for CSI, and 98.6% for abdominal patients; V30Gy = 0% in all cases. These doses represented an estimated diabetes RR of 7.3±1.5, 6.6±1.3, and 8.7±0.6, respectively; RR>5 in 88%, 85% and 100% of all patients, CSI and abdominal patients audited, respectively. Current incidental doses were associated with a diabetes RR>5 in all patients treated for abdominal neuroblastoma and the majority who received CSI. These findings suggest the pancreas should be routinely delineated and considered as an OAR in radiotherapy planning. This may help to identify higher risk patients and inform late-effect monitoring during survivorship. Further work in underway to assess if proton therapy could reduce the RR of diabetes particularly in abdominal cases. Improved availability of high-quality imaging during radiotherapy planning, such as contrast administration or planning MRI, is becoming more necessary to accurately delineate subsegments of the pancreas for improved RR estimations.

Simulation CT Features and Radiation Cardiotoxicity in Non-Small Cell Lung Cancer

Radiation cardiotoxicity is a significant clinical dilemma in non-small cell lung cancer (NSCLC) radiation therapy (RT). Baseline cardiovascular (CV) status may influence the risk of cardiotoxicity, and may be ascertainable from the appearance of the heart on simulation computed tomography (CT). We examined the association of CT features with incidental heart dose and risk of cardiac events in NSCLC. Patients treated with curative-intent RT between 2015 and 2020 at a regional center were identified. Clinical notes were interrogated for baseline patient and CV health details, and follow-up CV events. Cardiac events were verified by a cardiologist. A deep learning-based auto-segmentation tool was applied, allowing extraction of a pre-specified list of volume parameters in a programming environment. CAC was graded as none, mild, moderate and severe in patients with a non-contrast scan. The craniocaudal relationship of the PTV and heart (Feng atlas) were annotated. A total of 478 patients were included, with a median age of 70 and Charlson Index of 5. The median mean heart dose was 6.3 Gy (IQR 2.7-11.4). The median lung V20 was 20.0% (IQR 14.8-27.1). Cardiovascular risk factors were common, with most patients having 2 (39%) or 3 (31%). A history of previous cardiac events was common, including myocardial infarction (14%), arrhythmia (11%) or heart failure (9%). A total of 6.9% and 7.1% patients developed a new atrial arrhythmia (AA) or heart failure (HF) after completing RT. The volume metrics with the highest AUC for AA and HF events were the left atrium (LA) (AUC 0.67, p = 0.0002) and left ventricle:right ventricle (LV:RV) ratio (AUC 0.66, p = 0.0021). Kaplan-Meier analysis for cardiac events dichotomizing at the optimal cut-point for maximum sensitivity and specificity demonstrated significantly different rates for both AA (LA 109cc, HR 3.35, 95% CI 1.64-6.83, p = 0.0009) and HF (LV:RV ratio 1.61, HR 2.37, 95% CI 1.19-4.74, p = 0.0143). Only 2 patients with non-contrast scans developed a myocardial infarction, both had mild CAC. The incidence of pooled cardiac events was not significantly different between patients with no (n = 2/21, 9.5%), mild (n = 10/38, 26.3%), moderate (n = 8/53, 15.1%) and severe (n = 7/24, 29.2%) CAC (p = 0.3916). Where the inferior border of the PTV was above the superior border of the heart, mean heart dose was significantly lower than compared with overlap of levels (1.9 Gy v 9.7 Gy, p<0.0001), and this was true for 3DCRT (n = 139, p<0.001), IMRT (n = 94, p<0.001) and VMAT (n = 145, p<0.001) patients. LA volume and LV:RV volume ratio are predictive for the development of AA and HF respectively. CAC grade did not differentiate patients by risk of cardiac events. Where the craniocaudal level of the PTV doesn't overlap with the level of the heart, the cardiac dose is likely to be very low. Several simulation CT features are associated with cardiac events following treatment for NSCLC and prospective evidence of cardiac risk could enable medical optimization prior to RT.

Dosimetry Comparison of Incidental Irradiation to the Low Axilla in Whole Breast Irradiation Using IMRT and IMPT Therapy

It has been hypothesized that incidental dose to low axilla contributes to regional control in patients receiving whole breast irradiation (WBI), especially in patients with limited metastatic sentinel nodes who were spared from subsequent axillary dissection. We aimed to compare axillary dose between intensity-modulated radiotherapy (IMRT) and intensity-modulated proton radiotherapy (IMPT). Dosimetric comparisons between IMRT and IMPT were conducted in 15 patients treated with WBI without planned regional node irradiation (RNI). The prescribed dose was 40.05 Gy (RBE)/15 Fx. Axillary lymph nodes levels I, II (ALN I, ALN II) and rotter's lymph nodes (RN) were contoured and evaluated. The dose to the axilla was generally low for IMPT, with mean dose to ALN I, ALN II, and RN of 896.31, 194.64, and 2111.58 cGy (RBE), respectively. The mean V90% and V50% of ALN I was higher for IMRT (11.5 cm3, 22.9% of structure volume, p < 0.0001; 36.1 cm3, 66.6%, p < 0.0001) compared to IMPT (1.1 cm3, 2.0%; 8.1cm3, 15.9%). Similar finding was found in other low axilla. Mean dose to total ALN caudal to axillary vein was 936.6 cGy (RBE) in IMPT compared to 2407.3 cGy in IMRT (p < 0.0001). Within all substructures of axilla, mean dose to RN was the highest, but it remains lower in IMPT than in IMRT [2111.58 cGy (RBE) versus 3510.88 cGy, p < 0.0001]. WBI treated with IMPT leads to a significant reduction of axilla dose compared to IMRT. In clinical scenarios like Z0011 or likewise requiring incidental irradiation to the low axilla without additional RNI, contouring should be modified based on individual risk.

Matching between Clinical and Dosimetric Results in Comparing Intensity Modulated Radiotherapy with Three-Dimensional Conformal Radiotherapy in Locally Advanced Lung Cancer

Background Radiation therapy plays an essential role in the treatment of locally advanced lung cancer, but it inevitably leads to incidental and unnecessary dose to critical organs, including the lung, heart, and esophagus. Objective A dosimetric study to compare 3D CRT to IMRT in locally advanced lung cancer as regards normal tissue irradiation and target coverage using COSI &amp; modified COSI indices, DVH, homogeneity index, conformity index, target coverage index. Also to evaluate acute and late toxicity of esophagus, heart and lung in three-dimensional conformal radiotherapy and intensity modulated radiotherapy, in patients with locally advanced lung cancer who received definitive concurrent chemo-radiation or sequential chemo-radiation according to Common Terminology Criteria for Adverse Events (CTCAE) version 5.0. Patients and Methods 20 patients were selected to participate in our retrospective study from 2014 till 2019. They were recruited from bronchogenic cancer clinic, clinical oncology department in Ain Shams University Hospitals using a convenient sampling method. Diagnosis of NSCLC or SCLC was confirmed histologically and further radiological assessment for TNM staging was performed. All patients where 18 years old or older and were prescribed for either combined or sequential chemoradiotherapy for treatment of locally invasive lung cancer with ECOG PS equal or less than 2. They received 3D CRT of total 60 Gy. On the same CT contour defined for 3D CRT another plan was done for IMRT by computer based inverse planning with specific dose constrains to surrounding organs. Results In our study IMRT technique helped in sparing doses delivered to heart, lung &amp; esophagus in comparison with 3D CRT, but it was statistically significant for the lung only with p-value = 0.003. As regard the dosimetric indices IMRT showed better target coverage, dose homogenity &amp; dose conformity in comaparison with 3D CRT, but it was statistically significant for CI with p-value= 0.028. Using the COSI &amp; mCOSI also was in favor of IMRT but it was stastistically significant in mCOSI with pvalue=0.023 Conclusion IMRT showed superior outcomes as regards delivered doses (both to target and at-risk organs) compared to the conventional 3D CRT achieving the main purpose for patients with locally advanced lung cancer receiving chemoradiothrapy which is better target volume coverage and less unnecessary dose to at-risk nearby vital organs. As IMRT spares OAR it’s expected that clinical toxicity noticed with 3DCRT will be less thus, more tolerability to CCRT.

Predicting cancer relapse following lung stereotactic radiotherapy: an external validation study using real-world evidence.

For patients receiving lung stereotactic ablative radiotherapy (SABR), evidence suggests that high peritumor density predicts an increased risk of microscopic disease (MDE) and local-regional failure, but only if there is low or heterogenous incidental dose surrounding the tumor (GTV). A data-mining method (Cox-per-radius) has been developed to investigate this dose-density interaction. We apply the method to predict local relapse (LR) and regional failure (RF) in patients with non-small cell lung cancer. 199 patients treated in a routine setting were collated from a single institution for training, and 76 patients from an external institution for validation. Three density metrics (mean, 90th percentile, standard deviation (SD)) were studied in 1mm annuli between 0.5cm inside and 2cm outside the GTV boundary. Dose SD and fraction of volume receiving less than 30Gy were studied in annuli 0.5-2cm outside the GTV to describe incidental MDE dosage. Heat-maps were created that correlate with changes in LR and RF rates due to the interaction between dose heterogeneity and density at each distance combination. Regions of significant improvement were studied in Cox proportional hazards models, and explored with and without re-fitting in external data. Correlations between the dose component of the interaction and common dose metrics were reported. Local relapse occurred at a rate of 6.5% in the training cohort, and 18% in the validation cohort, which included larger and more centrally located tumors. High peritumor density in combination with high dose variability (0.5 - 1.6cm) predicts LR. No interactions predicted RF. The LR interaction improved the predictive ability compared to using clinical variables alone (optimism-adjusted C-index; 0.82 vs 0.76). Re-fitting model coefficients in external data confirmed the importance of this interaction (C-index; 0.86 vs 0.76). Dose variability in the 0.5-1.6cm annular region strongly correlates with heterogeneity inside the target volume (SD; ρ = 0.53 training, ρ = 0.65 validation). In these real-world cohorts, the combination of relatively high peritumor density and high dose variability predicts increase in LR, but not RF, following lung SABR. This external validation justifies potential use of the model to increase low-dose CTV margins for high-risk patients.

Association between statin therapy dose intensity and radiation cardiotoxicity in non-small cell lung cancer: Results from the NI-HEART study

IntroductionRadiation cardiotoxicity is a dose-limiting toxicity and major survivorship issue for patients with non-small cell lung cancer (NSCLC) completing curative-intent radiotherapy, however patients’ cardiovascular baseline is not routinely optimised prior to treatment. In this study we examined the impact of statin therapy on overall survival and post-radiotherapy cardiac events. MethodsPatients treated between 2015–2020 at a regional center were identified. Clinical notes were interrogated for baseline patient, tumor and cardiac details, and both follow-up cancer control and cardiac events. Three cardiologists verified cardiac events. Radiotherapy planning scans were retrieved for application of validated deep learning-based autosegmentation. Pre-specified Cox regression analyses were generated with varying degrees of adjustment for overall survival. Fine and Gray regression for the risk of cardiac events, accounting for the competing risk of death and cardiac covariables was undertaken. ResultsStatin therapy was prescribed to 59% of the 478 included patients. The majority (88%) of patients not prescribed a statin had at least one indication for statin therapy according to cardiovascular guidelines. In total, 340 patients (71%) died and 79 patients (17%) experienced a cardiac event. High-intensity (HR 0.68, 95%CI 0.50–0.91, p = 0.012) and medium-intensity (HR 0.70, 95%CI 0.51–0.97, p = 0.033) statin therapy were associated with improved overall survival after adjustment for patient, cancer, treatment, response and cardiovascular clinical factors. There were no consistent differences in the rate or grade of cardiac events according to statin intensity. ConclusionsStatin therapy is associated with improved overall survival in patients receiving curative-intent radiotherapy for NSCLC, and there is evidence of a dose–response relationship. This study highlights the importance of a pre-treatment cardiovascular risk assessment in this cohort. Further studies are needed to examine if statin therapy is cardioprotective in patients undergoing treatment for NSCLC with considerable incidental cardiac radiation dose and a low baseline cardiac risk.

Incidental Axillary Dose of Tomotherapy in Hypofractionated Whole Breast Radiotherapy for Early Breast Cancer: A Dosimetrical Analysis.

Background and Objectives: Intensity-modulated radiation therapy (IMRT) is becoming a more common method of performing whole breast irradiation (WBI) for early breast cancer. This study aimed to examine the incidental dose to the axillary region using tomotherapy, a unique form of IMRT. Patients and Methods: This study included 30 patients with early-stage breast cancer who underwent adjuvant WBI using TomoDirect IMRT. A hypofractionation scheme of 42.4 Gy delivered in 16 fractions was prescribed. The plan comprised of two parallel-opposed beams, along with two additional beams positioned anteriorly at gantry angles of 20° and 40° from the medial beam. The incidental dose received at axillary levels I, II, and III was evaluated using several dose-volume parameters. Results: The study participants had a median age of 51 years, and 60% had left-sided breast cancer. The mean dose of the axilla for levels I, II, and III were 15.5 ± 4.8 Gy, 14.9 ± 4.2 Gy, and 1.5 ± 1.6 Gy, respectively. Adequate coverage of the axilla, defined as V95%[%], was achieved for 4.7 ± 3.9%, 4.8 ± 3.7%, and 0 ± 0% for levels I, II, and III, respectively. The results were compared with those of previously published studies, and the axillary mean dose and V95%[%] of TomoDirect IMRT were low, comparable to other IMRT techniques, and lower than those of traditional tangential therapy. Conclusions: While incidental axillary radiation during WBI has been proposed to assist in regional disease control, the TomoDirect plan was demonstrated to decrease this dose, and a hypofractionation scheme would further lower its biological effectiveness. Future clinical studies should incorporate dosimetrical analysis of incidental axillary dose, in order to facilitate hypofractionated IMRT planning with risk-adjusted axilla coverage in early breast cancer.

PD-0235 Variation in incidental dose to the axilla in patients treated with whole breast radiotherapy alone

PD-0235 Variation in incidental dose to the axilla in patients treated with whole breast radiotherapy alone

Incidental nodal irradiation in patients with esophageal cancer undergoing (chemo)radiation with 3D-CRT or VMAT

The extent of elective nodal irradiation (ENI) in patients undergoing definitive chemoradiotherapy (dCRT) for esophageal squamous cell carcinoma (ESCC) remains unclear. The aim of this dosimetric study was to evaluate the extent of incidental nodal irradiation using modern radiation techniques. A planning target volume (PTV) was generated for 30 patients with node-negative esophageal carcinoma (13 cervical/upper third, 7 middle third, 10 lower third/abdomen). Thereby, no elective nodal irradiation (ENI) was intended. Both three-dimensional conformal radiotherapy (3D-CRT) and volumetric-modulated arc therapy (VMAT) treatment plans (50 Gy in 25 fractions) were calculated for all patients. Fifteen nodal stations were contoured according to the definitions of the AJCC and investigated in regard to dosimetric parameters. Compared to 3D-CRT, VMAT was associated with lower dose distribution to the organs at risk (lower Dmean, V20 and V30 for the lungs and lower Dmean and V30 for the heart). For both techniques, the median Dmean surpassed 40 Gy in 12 of 15 (80%) nodal stations. However, VMAT resulted in significantly lower Dmeans and equivalent uniform doses (EUD) compared to 3D-CRT for eight nodal stations (1L, 2L, 2R, 4L, 7, 8L, 10L, 15), while differences did not reach significance for seven nodal station (1R, 4R, 8U, 8M, 10R, 16). For dCRT of ESCC, the use of VMAT was associated with significantly lower median (incidental) doses to eight of 15 regional lymph node areas compared to 3D-CRT. However, given the small absolute differences, these differences probably do not impair (regional) tumor control rates.

DOSIMETRIC ANALYSIS OF INCIDENTALAXILLARY IRRADIATION IN BREAST CANCER USING TANGENTIAL FIELDS TREATED BY 3DCRT TECHNIQUE

Introduction Radiotherapy is an important aspect of treatment for multimodality approach in cancer breast. Inclusion of axillary nodes in radiotherapy tangential elds remains a long-standing controversial issue. It is considered that axillary nodes receive incidental radiation through tangential beams of chest-wall. The benet of decreasing regional recurrences with axillary nodal irradiation needs to be weighed against the risk of chronic lymphedema and its impact on quality of life. The following study was done to analyze the incidental dose received to axillary region and whether the addition of radiotherapy to axillary region will be useful. Material and methods Twenty post Modied Radical Mastectomy (MRM) patients who had received adjuvant radiotherapy from 2018-2021were retrospectively selected. Planning was a done with Field in Field–Forward planned–3DCRT with mono-isocentric technique. Dose prescribed was 50Gy/25 fractions. Axillary Lymph nodes were contoured according to RTOG guidelines. Various parameters of PTV(V95,D90, D95, Dmax, Dmean, Homogeneity Index(HI), Conformity Index (CI), Volume of PTV), Axillary Lymph nodes I, II, III and SCF (Dmean,V95, V90, Volume) and BMI were evaluated. Correlation was done among these parameters and Statistical analysis was done using Pearson-Correlation coefcient. Results The mean dose to axillary Lymph node level I, II, III were 45.75Gy, 31.80Gy and 25.83Gy respectively. The V90% and V95% of Axillary level–III also received a dose of 32.97Gy and 22.73Gy respectively. The combined volume of I and II received a mean dose of 40.85Gy and all three levels received 39.44.Gy. There is a weak correlation of SCF dosimetry with axillary nodal volumes although PTV volumes and BMI had positive correlation with axillary lymph nodal irradiation. ConclusionAxillary levels I and II received substantial amount of incidental radiation by the tangential eld 3DCRT technique. Our small sample size may have impacted a more detailed analysis of the correlation among variables. However more prospective clinical studies addressing this issue may help in understanding the risks versus benets of axillary lymph nodal irradiation.