3-dimensional Conformal Radiotherapy Research Articles

Physical and biological dosimetric margin according to prescription method for stereotactic body radiation therapy.

This study aimed to expand the biological conversion factor (BCF) model, which converts the physical dosimetric margin (PDM) to the biological dosimetric margin (BDM) for point prescription with 3-dimensional conformal radiation therapy (3DCRT) and the marginal prescription method with volumetric-modulated arc radiotherapy (VMAT). The VMAT of the marginal prescription and the 3DCRT of the point prescription with lung stereotactic body radiation therapy (SBRT) by using RayStation were planned. The biological equivalent dose (BED) for a dose per fraction (DPF) of 3-20Gy was calculated from these plans. The dose was perturbed with the calculation using a 1-mm step isocenter shift. The dose covering 95% of the target was greater than or equal to 90% of the prescribed physical dose, and the BED were defined as the PDM and BDM, respectively. The BCF was created as a function of the DPF. The PDM and BDM for all DPFs were larger with the point prescription method than with the marginal prescription method. The marginal prescription method with a 60% isodose line had a larger PDM and BDM. The BCF with the point prescription was smaller than that with the marginal prescription in the left-right (LR), anterior-posterior (AP) and cranio-caudal (CC) directions. In the marginal prescription method, the 60% isodose line had a higher BCF. In conclusion, the improved BCF method could be converted to BDM for point prescription with 3DCRT and marginal prescription method with VMAT, which is required for stereotactic radiation therapy in radiobiology-based treatment planning.

Dosimetric and Radiobiological Comparison of Three- Dimensional Conformal Radiotherapy and Helical Tomotherapy in Whole Pelvic Radiotherapy of Prostate Cancer Patients

Dosimetric and Radiobiological Comparison of Three- Dimensional Conformal Radiotherapy and Helical Tomotherapy in Whole Pelvic Radiotherapy of Prostate Cancer Patients

Optimal radiotherapy modality sparing for cardiac valves in left-sided breast cancer.

The cardiotoxicity caused by radiotherapy is a critical problem in the treatment of patients with breast cancer. The appropriate radiotherapy modality sparing for cardiac valves in left-sided breast cancer has not been well defined. The aim of this study was thus to compare the dosimetric differences in heart and cardiac valves of 3-dimensional conformal radiotherapy (3D-CRT), fixed-field intensity-modulated radiation therapy (IMRT), and volumetric-modulated arc therapy (VMAT) to find the optimal radiotherapy modality sparing for cardiac valves in patients with left breast cancer. From January 5, 2021, to March 15, 2021, 21 patients with left-sided breast cancer postmastectomy were included in this study, and 3 different plans for adjuvant radiation were created using 3D-CRT, IMRT, and VMAT for each patient. All patients received 50 Gy in 25 fractions. The mean dose (Dmean) of the heart; percentage volume of the heart receiving ≥5 Gy (V5), ≥30 Gy (V30), and ≥40 Gy (V40); and the Dmean and the near-maximum dose (D0.03cc) of cardiac valves were extracted from dose-volume histograms (DVHs) and compared. The correlations in dosimetric factors between cardiac valves and the whole heart were analyzed. IMRT significantly decreased the values of V5, V30, V40, and Dmean in the whole heart compared to 3D-CRT and VMAT (P<0.001). Among the 3 different plans, IMRT had the lowest radiation dose to the Dmean and the D0.03cc of the aortic valve (1.27 Gy/1.75 Gy), pulmonary valve (3.44 Gy/6.89 Gy), tricuspid valve (1.02 Gy/1.14 Gy), and mitral valve (0.93 Gy/1.00 Gy). Pearson correlation analysis found that local parameters (Dmean and D0.03cc) within valves were strongly correlated to the global parameters (V5, V30, V40, and Dmean) of the heart. This study revealed that IMRT showed the lowest cardiac valves dose compared with 3D-CRT and VMAT in left-sided breast cancer radiotherapy. IMRT might be the optimal modality sparing for cardiac valves in this group of patients. Further studies need to be carried out in order to validate the protective role of IMRT on the cardiac valves.

Risk evaluation of secondary malignancies after radiotherapy of breast cancer in light of the continuous development of planning techniques.

Secondary cancer risk is a significant concern for women treated with breast radiation therapy due to improved long-term survival rates. We evaluated the potential of new advanced automated planning algorithms together with hybrid techniques to minimize the excess absolute risk (EAR) for secondary cancer in various organs after radiation treatment for early staged breast cancer. Using CT data set of 25 patients, we generated 4 different radiation treatment plans of different complexity, including 3-dimensional conformal radiotherapy (3D-CRT), field-in-field (FinF), hybrid-IMRT (HMRT) and automated hybrid-VMAT (HVMAT) techniques. The organ-equivalent dose (OED) was calculated from differential dose-volume histograms on the basis of the "linear-exponential," "plateau," and "full mechanistic" dose-response models and was used to evaluate the EAR for secondary cancer in the contralateral breast (CB), contralateral lung (CL), and ipsilateral lung (IL). Statistical comparisons of data were performed by a Kruskal-Wallis analysis of variance. The planning objectives were fulfilled with all the planning techniques for both target coverage and organs-at-risk sparing. The differences in EAR for CB, CL and IL secondary tumor induction were not significant among the 4 techniques. For the CB and CL, the mean absolute difference did not reach 1 case of 10000 patient-years. For the IL, the mean absolute difference was up to 5 cases of 10,000 patient-years. In conclusion, the automated HVMAT technique allows an EAR reduction at the level of well-consolidated tangential 3D-CRT or FinF techniques, keeping all the HVMAT dosimetric improvements unchanged. On the basis of this analysis, the adoption of the HVMAT technique poses no increase in EAR and could be considered safe also for younger patients.

Impact of upgraded radiotherapy system on outcomes in postoperative head and neck squamous cell carcinoma patients.

This study was performed to evaluate the impact of upgrade of radiotherapy system, including launch of intensity-modulated radiation therapy (IMRT), on the therapeutic outcomes. Patients with head and neck (H&N) squamous cell carcinoma (SCC) who underwent postoperative radiotherapy at our hospital between June 2009 and July 2019 were retrospectively reviewed. In July 2014, we converted the radiotherapy technique for these patients from a 3-dimensional conformal radiotherapy (3D-CRT) to IMRT, along with the adoption of a meticulous planning policy and a few advanced procedures, including online imaging guidance. A total of 136 patients (57 treated with the previous system and 79 treated with the upgraded system) were reviewed. There were significantly more patients with extracapsular extension in the upgraded-system group than the previous-system group (p = 0.0021). There were significantly fewer patients with ≥ Grade 2 acute and late adverse events in the upgraded-system group than the previous-system group. The differences in progression-free survival (PFS), distant metastasis-free survival (DFFS), locoregional progression-free survival (LRPFS), and overall survival (OS) between the two groups were not statistically significant (p = 0.8962, 0.9926, 0.6244, and 0.4827, respectively). Multivariate analysis revealed that the upgrade had neither positive nor negative impact on survival outcomes. Extracapsular extension was independently associated with decreased LRPFS and OS (p = 0.0499 and 0.0392, respectively). The IMRT-centered upgrade was beneficial for the postoperative patients with H&N SCC, because survival outcomes were sustained with less toxicities.

Hypofractionated radiotherapy in postmastectomy locally advanced breast cancer: an interim report on acute toxicities and dosimetry.

There is a growing interest in the use of hypofractionation in the setting of post-mastectomy radiation therapy (PMRT). Here, we present an interim report on the acute toxicities and the dosimetry of a 15-day hypofractionated regimen. Patients aged 18-75 years who underwent mastectomy and had pathological stage IIB-IIIC or any clinical stage who had received neoadjuvant chemotherapy were treated with PMRT at a dose of 43.5 Gy in 15 fractions. Acute toxicities were scored using Common Terminology Criteria for Adverse Events (CTCAE) version 4.0. Between September 2020 and September 2021, 92 patients were enrolled in the study. Majority experienced grade 1 dermatitis during the course of treatment. Skin toxicities peaked two weeks after PMRT in which 57 patients (62%) had grade 2 dermatitis and 6 patients (7%) had grade 3 dermatitis. Most resolved one month after treatment, with all resolving at three months. Grade 2 fatigue occurred in 4 patients (4%). There were no grade 3 fatigue or pneumonitis of any grade. The average V95% for the chest wall, axilla, and supraclavicular fossa were 91.5%, 99.3%, and 97.5%, respectively. Average ipsilateral lung V17 was 43.6%, while the mean heart dose averaged at 3.46 Gy. This interim report showed that hypofractionated PMRT is associated with a low incidence of clinically significant acute toxicities. With the use of the 3-dimensional conformal radiotherapy technique and volume-based planning, adequate target volume coverage and acceptable heart doses were achieved, although with a slightly higher ipsilateral lung dose.

Toxicities and Deaths From Intercurrent Disease Following Contemporary Postoperative Radiotherapy in Resected Non-Small-Cell Lung Cancer

IntroductionThe role of postoperative radiotherapy (PORT) in patients with resected locally advanced non-small-cell lung cancer (NSCLC) remains controversial due to the radiation techniques used in randomized trials. We conducted a retrospective cohort study evaluating contemporary PORT techniques to evaluate the safety of PORT and risk of death from intercurrent disease . Materials and MethodsWe analyzed consecutive patients with NSCLC treated in a single center that underwent PORT for pN2 disease and/or positive margin, with 3-dimensional conformal radiotherapy (3DRT), intensity modulated radiotherapy , or proton RT (PRT), between 2008 and 2019. Clinical details were collected including intercurrent deaths, defined as death without cancer recurrence. Kaplan-Meier and Cox-Proportional Hazards Models were used. ResultsOf 119 patients, 21 (17.6%) received 3DRT, 47 (39.5%) intensity modulated radiotherapy, and 51 (42.9%) PRT. Median follow-up was 40 months (range 8-136) and median RT dose was 5040cGy. Most patients (65.5%) received sequential adjuvant chemoRT; 18.5% received concurrent chemoRT. The rate of grade 3 toxicities was 9.2%. There were 13 (10.9%) deaths from intercurrent diseases, including 6 from second primary cancers and 2 from cardiopulmonary diseases. There were 2 additional deaths from cardiopulmonary disease in patients with cancer progression at time of death. Mean, V5Gy, V30Gy heart doses and mean lung doses were significantly lower with PRT. Three-year OS and disease-free-survival were 70.1% and 49.9%. ConclusionPORT using contemporary techniques was well tolerated with acceptable toxicity and low rates of intercurrent deaths. Proton therapy significantly reduced heart and lung doses, but radiotherapy modality was not associated with differences in intercurrent disease.

Advanced stage cutaneous T-cell lymphoma treated with high-dose external beam radiation therapy: A case report.

The treatment for advanced-stage or refractory cutaneous T-cell lymphoma (CTCL) is largely palliative. Due to the rarity of the disease, there are few randomized controlled trials and large-scale prospective studies. Therefore, the treatment of advanced-stage CTCL remains challenging. A 64-years-old man who had received narrowband UVB phototherapy for several years presented with a generalized rash with widespread polycyclic erosions and painful ulcers on his hands and feet. We restaged him as stage III CTCL. He was treated with high-dose radiation for curative purposes and 3-dimensional conformal radiation therapy to both hands and feet. At the 2-year follow-up after the end of radiotherapy, the irradiated skin had recovered to normal soft, smooth skin with localized fibrosis and hypopigmented skin. He reported an excellent quality of life, and his hands and feet were free to move. CTCL at an advanced stage could require dose escalation with local radiotherapy for curative purposes. High-dose 3-dementional conformal radiation therapy could be effective and has tolerable toxicities.

Radiation-induced cancer after treatment for nasopharyngeal carcinoma: a study from a high prevalence area.

Radiation-induced cancer (RIC) is a late complication in patients who have been treated for nasopharyngeal carcinoma (NPC). The comparison of index anatomic location, index histological type, and survival of RIC in patients with NPC after different radiotherapy modalities (intensity-modulated radiotherapy [IMRT], 3-dimensional conformal radiotherapy [3D-CRT], and conventional 2D radiotherapy) is currently unavailable. A total of 38,565 patients with NPC who received curative-intent radiotherapy at Sun Yat-sen University Cancer Center between January 1986 and December 2017 were reviewed. A total of 141 patients who developed RIC and fulfilled the study criteria were included. Categorical variables were compared by the χ2 test or Fisher's exact test. Kaplan-Meier curves were used to evaluate overall survival. Cox proportional hazards models were used to examine the independent significance of RIC treatment. Among IMRT, 3D-CRT, and conventional 2D radiotherapy, the incidence of mandible RIC was higher in patients who received 3D-CRT (0.07%) than in those who received IMRT (0%). The proportion of mandible RICs was higher in patients who received 3D-CRT (16.667%) than in those who received IMRT (0%) and conventional 2D radiotherapy (3.529%). Regarding the histological type, the incidence of squamous cell carcinoma (SCC) was higher in patients who received conventional 2D radiotherapy (0.266%) than in those who received 3D-CRT (0.175%); patients who received IMRT had a higher proportion of SCC than those who received 3D-CRT/conventional 2D radiotherapy (86.4% vs. 41.7% vs. 74.2%); the incidence of sarcoma was higher in patients who received 3D-CRT (0.175%) than in those who received IMRT (0.025%); and the proportion of sarcoma was higher in patients who received 3D-CRT (41.667%) than in those who received IMRT (6.818%) and conventional 2D radiotherapy (17.647%). Patients who received surgery for RICs had better survival than those who received no surgery (64.49 vs. 12.42 months). In the univariate and multivariate analyses, surgery was an independent prognostic factor for overall survival. Our results have implications for long-term follow-up of RIC, multidisciplinary management, and patient counseling of RIC after nasopharyngeal carcinoma treatment by treating clinicians.

Planning issues on linac-based stereotactic radiotherapy.

This work aims to summarize and evaluate the current planning progress based on the linear accelerator in stereotactic radiotherapy (SRT). The specific techniques include 3-dimensional conformal radiotherapy, dynamic conformal arc therapy, intensity-modulated radiotherapy, and volumetric-modulated arc therapy (VMAT). They are all designed to deliver higher doses to the target volume while reducing damage to normal tissues; among them, VMAT shows better prospects for application. This paper reviews and summarizes several issues on the planning of SRT to provide a reference for clinical application.

Quality Assurance in Clinical Trials Requiring Radiation Therapy in Sub-Saharan Africa

Given the increasing availability of radiation therapy in sub-Saharan Africa, clinical trials that include radiation therapy are likely to grow. Ensuring appropriate delivery of radiation therapy through rigorous quality assurance is an important component of clinical trial execution. We reviewed the process for credentialing radiation therapy sites and radiation therapy quality assurance through the Imaging and Radiation Oncology Core (IROC) Houston Quality Assurance Center for AIDS Malignancy Consortium (AMC)-081, a multicenter study of cisplatin and radiation therapy for women with locally advanced cervical cancer living with HIV, conducted by the AIDS Malignancy Consortium at 2 sites in South Africa and Zimbabwe. Women living with HIV with newly diagnosed stage IB2, IIA (>4 cm), IIB-IVA cervical carcinoma (per the 2009 International Federation of Gynecology and Obstetrics [FIGO] staging classifications) were enrolled in AMC-081. They received 3-dimensional conformal external beam radiation therapy (EBRT) to the pelvis (41.4-45 Gy) using a linear accelerator, high-dose-rate brachytherapy (6-9 Gy to point A with each fraction and up to 4 fractions), and concurrent weekly cisplatin (40 mg/m2). IROC reviewed EBRT and brachytherapy quality assurance records after treatment. All of the 38 women enrolled in AMC-081 received ±5% of the protocol-specified prescribed dose of EBRT. Geometry of brachytherapy applicator placement was scored as per protocol in all implants. Doses to points A and B, International Commission on Radiation Units and Measurements (ICRU) bladder, or ICRU rectum required correction by IROC in >50% of the implants. In the final evaluation, 58% of participants (n=22) were treated per protocol, 40% (n=15) had minor protocol deviations, and 3% (n=1) had major protocol deviations. No records were received within 60 days of treatment completion as requested in the protocol. Major radiation therapy deviations were low, but timely submission of radiation therapy data did not occur. Future studies, especially those that include specialized radiation therapy techniques such as stereotactic or intensity-modulated radiation therapy, will require pathways to ensure timely and adequate quality assurance.

Dosimetric analysis of 3 dimensional conformal radiotherapy with volumetric modulated arc therapy in patients with carcinoma oesophagus – Prospective study

: To study the dosimetry and treatment plan of Volumetric Modulated Arc Therapy and 3 Dimensional Conformal Radiotherapy in patients with carcinoma oesophagus. : A prospective study was taken up in Department of Radiotherapy, from October 2017 to June 2019. A total 20 patients who achieved eligibility criteria was taken into study and both 3D CRT (3D Conformal Radiation Therapy)and VMAT(Volumetric Modulated Arc Therapy ) plans was done in all patients. Dosimetric comparison is done between these two techniques. Dose to spinal cord is significantly reduced with VMAT technique when compared to 3D CRT. VMAT plans in this study showed significantly reduced doses to heart, when compared to 3D CRT plans. VMAT plans decrease volume of lung receiving high dose(v20,dmean,v30,v40) compared to 3D CRT but at a cost of delivering low dose to more volume of lung (v5, v10, v15) resulting in serious complications like radiation pneumonitis. VMAT plans are advisable in carcinoma oesophagus patients to achieve reduced doses to OARs(Organs at Risk) like Spinal Cord, Heart &amp; Lung and better target coverage particularly in cervical esophagus where higher doses are planned.

Dosimetric comparison study of intensity modulated radiotherapy technique (IMRT/VMAT) with three dimensional field-in-field tangents for left breast cancer irradiation

Purpose: To retrospectively compare dosimetrically three dimensional field-in-field tangents (3D F-in-F), Intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) left breast irradiation plans. Materials and Methods: A total of 30 patients were included in this study. All patients diagnosed with early–stage malignant neoplasm of the breast prior to treatment. Patients were contoured with three main PTV-Chest wall (PTVCW), PTV-Axilla (PTVAX), and PTV-IMC (PTVIMC). Monaco treatment planning system was used to create the plans. For each patient, three treatment plans were created; three dimensional conformal radiotherapy (3D-CRT), intensity modulated radiotherapy (IMRT), and volumetric modulated arc therapy (VMAT). The dose coverage of PTVs and the dose constraints of Organ-at-Risks (OARs) were compared and analyzed. Results: The dose objective to cover the PTVs; PTVCW, PTVAX, and PTVIMC were V40.43Gy (95%) ≥ 95%, V38.3Gy (90%) ≥ 95%, and V34.05Gy (80%) ≥ 95% respectively. Comparing the dose coverage of PTVCW between 3D-CRT and VMAT, resulted in a significant difference (P= 0.003) and the VMAT was superior for the coverage of target than 3D-CRT. For PTVAX, the coverage was 45.80±0.55, 45.96±0.73, and 45.58±0.63 for 3D-CRT, IMRT, and VMAT respectively. For PTVIMC, the coverage was 45.80±0.55, 45.96±0.73, and 45.58±0.63 for 3D-CRT, IMRT, and VMAT respectively.

PO46 Presentation Time: 4:45 PM: MRI-Guided Adaptive External Beam Radiotherapy for Cervical Cancer

Cervical cancer is the fourth most common cancer in women worldwide. Traditionally, bulky cervical tumors or those with clinical nodal involvement are treated with definitive chemoradiation therapy. Pelvic or extended field radiation has traditionally been delivered using 3-dimensional conformal radiotherapy with fields that are not altered during treatment. However, there is an emerging role for intensity modulated radiotherapy as well as adaptive planning. Although MRI-based linear accelerators have recently been used for image guidance during brachytherapy, to our knowledge, there are no reports of adaptive planning for cervical cancer cases using MRI-based linear accelerators. We present a case of a postpartum patient with a bulky cervical adenocarcinoma who underwent replanning twice during treatment due to uterine and tumor shrinkage. The use of a MRI-based linear accelerator facilitated both replanning and tumor assessment.

Outcomes Following SBRT vs. IMRT and 3DCRT for Older Patients with Stage IIA Node-Negative Non-Small Cell Lung Cancer > 5 cm

BackgroundTo describe outcomes and compare the effectiveness of stereotactic body radiotherapy (SBRT) versus 3-dimensional conformal radiotherapy (3DCRT) or intensity-modulated radiotherapy (IMRT) in patients with stage IIA lymph node-negative (N0) non-small cell lung cancer (NSCLC) tumors > 5 cm. MethodsWe used the SEER-Medicare database (2005-2015) to identify patients > 65 years with stage IIA (AJCC TNM7) N0 NSCLC > 5 cm tumors who were treated with SBRT, IMRT, and 3DCRT. We used propensity score methods with inverse probability weighting to compare lung cancer-specific survival (LCSS), overall survival (OS), and toxicity. ResultsOf 584 patients, 88 (15%), 140 (24%), and 356 (61%) underwent SBRT, IMRT, and 3DCRT, respectively. The SBRT group was older (P = .004), had more comorbidities (P = .02), smaller tumors (P = .03), and more adenocarcinomas (P < .0001). We found a trend towards higher median unadjusted OS with SBRT compared to IMRT and 3DCRT (19 vs. 13 and 14 months, respectively, P = .37). In our propensity score-adjusted analyses, SBRT was significantly associated with better OS and LCSS compared to IMRT (HROS: 0.78, 95% CI: 0.68-0.89, HRLCSS: 0.70, 95% CI: 0.60-0.81) and 3DCRT (HROS: 0.81, 95% CI: 0.72-0.93, HRLCSS: 0.80, 95% CI: 0.68-0.93). SBRT-treated patients also had lower overall adjusted complication rates compared to IMRT (OR: 0.74, 95% CI: 0.55-0.99) and 3DCRT (OR: 0.53, 95% CI: 0.40-0.71). ConclusionFor patients with NSCLC tumors > 5 cm, SBRT trends towards fewer toxicities and improved survival compared to other forms of radiotherapy. Our findings support SBRT as an appropriate treatment strategy for older patients with larger inoperable NSCLC tumors.

Measurement of Absorbed Dose in Water Using Co-60 gamma source Teletherapy Units According to IAEA Dosimetry Protocols

Modern radiotherapy facilities like 3-Dimensional conformal radio therapy (3DCRT), Intensity Modulated Radiotherapy (IMRT), were recently suggested in Co-60 machine with Multi-leaf Collimator (MLC). In this study, two reference chambers NE-2571#1205 and NE2581#537 were used for absolute dose measurement in Equinox accelerator. A comparison of dose measurement by two different IAEA protocols TRS-277 and TRS-398 has been studied. Analyzing TRS-398, a common shaped empirical formula was developed for the four Co-60 units of four Medical Colleges in Bangladesh with fitting parameters. It was found that an average discrepancy in the determination of absorbed dose in water among the two different protocols TRS-277 and TRS-398 were 1.33 % for the chamber NE-2571#1205 and 0.65 % for the chamber NE2581#537 with combined uncertainty ±1.59 % (k=1). A good convergence has been obtained in the concepts and methods in this study.

Left Anterior Descending Coronary Artery Radiation Dose Association with All-Cause Mortality in NRG Oncology Trial RTOG 0617

Left Anterior Descending Coronary Artery Radiation Dose Association with All-Cause Mortality in NRG Oncology Trial RTOG 0617

Correlation of Left Anterior Descending Coronary Artery Radiation Dose with Major Adverse Cardiac Events and Feasibility of Coronary Artery Sparing Treatment Planning in Lung Cancer

<h3>Purpose/Objective(s)</h3> Radiation dose to the left anterior descending (LAD) coronary artery is associated with major adverse cardiac events (MACE) in patients with locally advanced non-small cell lung cancer (LA-NSCLC). However, the newly identified LAD metric (percent volume receiving 15 Gy [LAD V15Gy]) has not been independently validated and the extent to which modern radiotherapy (RT) planning techniques can reduce LAD V15Gy without exceeding dose tolerances to other critical organs at risk (OAR) remains uncertain. <h3>Materials/Methods</h3> This is a single institution retrospective study of 98 patients with LA-NSCLC treated with RT between 2005-2020. The LAD was manually delineated for each patient. MACE (unstable angina, myocardial infarction, heart failure, coronary revascularization, and cardiac death) cumulative incidence was estimated and Fine and Gray regressions were performed, adjusting for non-cardiac death as a competing risk. Patients who received LAD V15Gy ≥10% and experienced MACE were re-planned with volumetric-modulated arc therapy (VMAT) to optimize reduction of LAD V15Gy while maintaining target coverage and meeting standard OAR constraints. <h3>Results</h3> The median follow up was 23.2 months. The median age was 69 years, 30.6% of patients had pre-existing coronary heart disease (CHD) or a CHD risk-equivalent. The mean LAD V15Gy was 32% (standard deviation [SD] 27.8%). Ten patients developed at least one MACE, with a 2-year cumulative incidence of 10.2% (95% CI: 3.1-17.0%). Adjusting for pre-existing CHD there was an increased risk of MACE with LAD V15Gy (subdistribution hazard ratio 1.03; 95% CI 1.00-1.06; p=.034), with a significant interaction between LAD V15Gy and CHD (p=.005). Among the 10 patients who developed a MACE, 6 (60%) had an LAD V15Gy ≥ 10% (mean 52%, range 10-100%). The original planning techniques included: 3-dimensional conformal RT (3D-CRT; n=2), static intensity-modulated RT (IMRT; n=2), and VMAT (n=2). In 4 of these plans (n=2 IMRT, n=1 3D-CRT, n=1 VMAT), the re-planned LAD V15Gy was reduced to <10%, however all 6/6 plans achieved some degree of LAD V15Gy reduction (range, 9-100%). Specifically, optimization with LAD-sparing VMAT achieved a mean absolute decrease of 35.1% for LAD V15Gy (SD 32.4%) and 6.2 Gy mean heart dose (SD 10.9 Gy), with a concomitant mean increase of 0.8 Gy mean lung dose (SD 1.8 Gy), and mean lung V20Gy of 0.2% (SD 4.1%). All re-plans achieved similar target coverage and remained within national guideline OAR constraints. <h3>Conclusion</h3> LAD V15Gy is associated with an increased risk of MACE in this independent retrospective cohort. VMAT-based LAD-sparing RT plan optimization is feasible and can achieve meaningful reductions in LAD V15Gy with potentially clinically acceptable tradeoffs in lung dose. Together, these findings underscore the need for more aggressive LAD-sparing RT planning approaches.

Futility of the Third-Party Peer-to-Peer Review Process and Entailed Delays to Cancer-Directed Therapy

<h3>Purpose/Objective(s)</h3> The health plan management process of prior authorization (PA) ostensibly exists to control healthcare spending and to ensure evidence-based practice. However, the process of PA is cumbersome, creating de novo bureaucratic and operational costs, and entails delays to the initiation of treatment. This study investigates the rates of overturned PA denials for radiation services, radiotherapy (RT) prescription alterations, and the associated delays to treatment initiation at a high-volume academic radiation medicine department. <h3>Materials/Methods</h3> We queried de-identified departmental billing records for the 7-month period from 1/12/21 to 8/12/21. We obtained the cases referred for PA, and then obtained the subset for which prior authorization was denied and a peer-to-peer (P2P) review referral was made. The latter cases were subdivided into those in which the original denial was overturned, those in which the initial prescription was upheld but without requested image-guided radiation therapy (IGRT), those in which the initial prescription was denied but a downgraded modality (e.g., 3-dimensional conformal radiotherapy in place of intensity-modulated radiation therapy (IMRT)) was approved, and those in which RT was denied outright. We calculated the rates of each of the above categories, as well as the associated delays to initiation of treatment (mean, median, and range). <h3>Results</h3> Of the 1620 RT courses prescribed during the analyzed period, 697 cases (43%) were managed by insurance plans requiring PA, of which 123 (17.6%) were denied and referred for P2P review. 85 of the 123 (69.1%) had the denial overturned without altering the initial prescription. 5 cases (4.1%) were overturned but without requested IGRT. 26 cases (4.1%) were only approved for a downgraded modality. 5 cases (4.1%) were denied again on P2P review and RT abandoned, and in 2 cases (1.6%), the ultimate disposition was not available. For the cases ultimately approved without alteration, the mean delay to treatment initiation was 12.1 days (median 11, range 0-37). For the cases approved without IGRT, the delay was mean 6.8 days (median 6, range 5-9). For the downgraded treatment modalities, the delay was mean 9.8 days (median 9, range 1-23). Overall, in 15 cases (12.2%) the delay was > 20 days. <h3>Conclusion</h3> The majority of radiotherapy services initially denied were ultimately approved without alteration following P2P, but with resultant delays in patient care. Our analysis further suggests that the PA process is associated with treatment delays and added operational expense. Additional cross-departmental and cross-regional evaluations may further validate these findings.

NRG RTOG 1005: A Phase III Trial of Hypo Fractionated Whole Breast Irradiation with Concurrent Boost vs. Conventional Whole Breast Irradiation Plus Sequential Boost Following Lumpectomy for High Risk Early-Stage Breast Cancer

<h3>Purpose/Objective(s)</h3> Randomized trials support a supplemental radiation dose (Boost) to the lumpectomy (L) cavity region after whole breast irradiation (WBI), providing a 20-30% relative reduction of in-breast recurrence (IBR); with the disadvantage that it extends treatment duration ⁓ 1 week. Hypofractionated WBI (H-WBI) in ≤ 3 weeks is used after L to deliver adjuvant WBI with acceptable toxicity and comparable IBR as conventional WBI (C-WBI) 50 Gy in 2 Gy fractions (F). NRG RTOG 1005 sought to determine whether a boost delivered concomitantly with H-WBI over 15 F is non-inferior for IBR compared to boost delivered sequentially after C-WBI in patients (pts) considered at High Risk of IBR. <h3>Materials/Methods</h3> Protocol-specified High Risk pts post L with stages 0, I & II breast cancer were randomized to C-WBI 50 Gy in 25 F or 42.7 Gy in 16 F plus sequential boost of 12 Gy in 6 F or 14 Gy in 7 F (Arm I) or H-WBI 40 Gy in 15 F plus concomitant boost of 8 Gy in 15 F of 0.53 Gy per day (Arm II). Radiation was target based 3-dimensional conformal radiation therapy (3DCRT) or intensity modulated radiation therapy (IMRT) and quality review (QA) was required. Stratification was by age (<50 vs ≥ 50), adjuvant chemotherapy (Y vs N), ER status (+ vs -) and histologic grade (1, 2 v 3). The primary endpoint is IBR. Assuming Arm I 5‐year IBR of 1.59%, 90% CI upper bound hazard ratio (HR) of 2.12 and 1‐sided significance level = 0.05, 2150 pts with at least 46 IBR events provide >80% power to conclude non‐inferiority. IBR was analyzed comparing the cause-specific hazards. Adverse Events (AE) were graded with NCI CTCAE v4. Physician-reported NRG-RTOG Global Cosmetic Score (GCS) was grouped as excellent/good vs fair/poor, and arms compared with chi-square. <h3>Results</h3> 2262 of 2354 randomized pts were eligible (Arm I n=1124; Arm II n=1138). Median age 55 years, 34% Stage II, 52% grade 3, 30% ER-, 17% close/+ margins consistent with a "High Risk" population. Radiation was 3DCRT 81%, IMRT 19%, and the QA was per protocol 81% and 88% on Arm I vs II, respectively. With a median follow-up of 7.3 years and 56 IBR events, the 5 and 7-year IBR were 2.0% and 2.2% on Arm I and 1.9% and 2.6% on Arm II. The non-inferiority comparison (Arm I reference level) resulted in a HR (90% CI): 1.32 (0.84, 2.05) and p = 0.039, thus meeting non-inferiority. No differences in AEs noted between arms, with low rates of ≥ grade 3 treatment-related AEs, 3.3% vs 3.5% for Arm I vs II, respectively (p=0.79). No difference in 3-year excellent/good cosmesis by arm: 86% for Arm I vs 84% Arm II (p=0.61). <h3>Conclusion</h3> Concomitant boost with H-WBI results in non-inferior IBR compared to sequential boost after C-WBI in high-risk cases and reduces overall treatment time. Using target based 3DCRT or IMRT, there are no differences in toxicity or cosmetic outcome for concomitant v sequential boost or the WBI fractionation regimen.