Evaluation of External Margin Generation Techniques for Robust Breast Intensity-Modulated Radiation Therapy Planning

Underdosing of treatment targets can occur in radiation therapy due to electronic disequilibrium around air-tissue interfaces when tumors are situated near natural air cavities. These effects have been shown to increase with the beam energy and decrease with the field size. Intensity modulated radiation therapy (IMRT) and tomotherapy techniques employ combinations of multiple small radiation beamlets of varying intensities to deliver highly conformal radiation therapy. The use of small beamlets in these techniques may therefore result in underdosing of treatment target in the air-tissue interfaces region surrounding an air cavity. This work was undertaken to investigate dose reductions near the air-water interfaces of 1×1×1 and 3×3×3 cm3 air cavities, typically encountered in the treatment of head and neck cancer utilizing radiation therapy techniques such as IMRT and tomotherapy using small fields of Co-60, 6 MV and 15 MV photons. Additional investigations were performed for larger photon field sizes encompassing the entire air-cavity, such as encountered in conventional three dimensional conformal radiation therapy (3DCRT) techniques. The EGSnrc/DOSXYZnrc Monte Carlo code was used to calculate the dose reductions (in water) in air-water interface region for single, parallel opposed and four field irradiations with 2×2 cm2 (beamlet), 10×2 cm2 (fan beam), 5×5 and 7×7 cm2 field sizes. The magnitude of dose reduction in water near air-water interface increases with photon energy; decreases with distance from the interface as well as decreases as the number of beams are increased. No dose reductions were observed for large field sizes encompassing the air cavities. The results demonstrate that Co-60 beams may provide significantly smaller interface dose reductions than 6 MV and 15 MV irradiations for small field irradiations such as used in IMRT and tomotherapy.

Radiation Dose, Technique and Use of Brain Radiation on Overall Survival in Patients with Limited-Stage Small Cell Lung Cancer

Prone Breast Intensity Modulated Radiation Therapy: 5-Year Results

Executive Summary of the American Radium Society Appropriate Use Criteria for Radiation Treatment of Node-Negative Muscle Invasive Bladder Cancer

A multileaf collimator phantom for the quality assurance of radiation therapy planning systems and CT simulators

Correlation of Integral Dose, White Blood Cell Counts, and Radiation Therapy Techniques for Head and Neck Cancer Patients Under Radiation Therapy

Curative treatment for base-of-tongue squamous cell carcinoma (BOT SCC) has evolved over time; however, comparative outcomes analysis for various treatment strategies is lacking. The authors reviewed the evolution of treatment modality and radiotherapy (RT) technique for 231 consecutive BOT SCC patients at our institution between 1981 and 2011. Treatment modalities included definitive chemoradiotherapy (chemoRT) (42%), definitive RT (33%), surgery followed by RT (20%), and surgery alone (5%). RT techniques included external beam plus interstitial brachytherapy (EBRT + IB) (37%), conventional EBRT (29%), intensity-modulated radiation therapy ± simultaneous integrated boost (IMRT ± SIB) (34%). Clinical characteristics and outcomes were stratified by modality or RT technique. Treatment modality evolved from definitive RT (1980s–1990s) to definitive chemoRT (1990s–2000s). RT technique evolved from EBRT + IB (1980s–1990s) to conventional EBRT (1990s–2000s) to IMRT + SIB (2000s). With median alive follow-up of 6 years (0.3–28 years), the 5-year LC, LRC, and OS rates were 80%, 73%, and 51%. There was no difference in distribution of gender, age, stage among treatment modalities. Definitive chemoRT had improved LRC (HR 1.6) and OS (HR 1.7) compared to definitive RT. IMRT + SIB had improved LRC (HR 3.2), DFS (HR 3.4), and OS (HR 3.0) compared to conventional EBRT. Over the past 30 years, BOT SCC treatment has undergone major paradigm shifts that incorporate nonsurgical functional preservation, concurrent chemotherapy, and advanced RT techniques. Excellent locoregional control and survival outcomes are associated with accelerated IMRT with chemotherapy.

Complementary Relation Between the Improvement of Dose Delivery Technique and PTV Margin Reduction in Dose-Escalated Radiation Therapy for Prostate Cancer

The paper considers the intensity modulated radiation therapy (inverse) treatment planning. An approach to determine the trajectories of the leaves of the multileaf collimator (MLC) in order to produce the prescribed intensity distribution is developed. The paper concentrates on the multiple static delivery technique. A mathematical model for calculating the intensity distribution with the help of locations of the leafheads of subsequent subfields is constructed. Furthermore, an optimization model in which the decision variables are the locations of leafheads is developed. The relevant constraints are considered as well. The optimization problem is a large dimensional constrained nonlinear global extremum problem. It is solved by the LGO (Lipschitz (Continuous) Global Optimizer) program system. Comparisons with other optimization method (Hooke–Jeeves iteration) are included. Numerical experiments are presented to confirm the functionality of the method.

2358: Establishment of Intensity-Modulated Radiation Therapy for Whole Pelvic Irradiation in Cervical Carcinoma Patients After Hysterectomy

Nasopharyngeal cancer (NPC) is more common in the Southern China region than the rest of the world. Radiation therapy (RT) is the contemporary and standard treatment for nasopharyngeal cancer. Chronic complications arise from RT including hearing loss, xerostomia, trismus and dysphagia. Previous research has shown that dysphagia is prevalent in irradiated NPC patients. Radiation therapy techniques have improved in the last decade with the emergence of Intensity Modulated Radiation Therapy (IMRT), which allows more precise radiation beams directed at the tumor. In turn, it should also allow greater sparing of surrounding structures that are vital for preservation of swallowing function. This study was designed to investigate the difference in the degree of swallowing function preservation in two groups of irradiated NPC patients: the conventional RT and the IMRT group.
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\nThirty patients with NPC who received RT from 1998 to 2006 in Queen Mary Hospital, Hong Kong were randomly recruited during the period from January to December 2011. Participant’s swallowing competence and its effect on the quality of life was assessed by videofluoroscopic swallowing study (VFSS) and by the MD Anderson Dysphagia Inventory, respectively.
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\nIn comparison of swallowing performance with VFSS between the two groups, only one measure (Duration of Laryngeal Elevation) out of 13 showed significant difference on thin liquid and congee diet. Results from the MDADI did not show significant difference between the two groups.
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\nFrom the results, it was concluded that IMRT only resulted in subtle improvement in preserving the swallowing function as compared to conventional RT. One possibility is the subject self-compensation of their swallowing impairments that led to functionally similar performance despite their differences in the anatomy and physiology. Swallowing is a highly complex body function and no single parameter can be used to accurately quantify and characterize one’s swallowing function. The interaction between the anatomical and physiological impairments resulted from radiation therapy and the compensatory mechanism could not be clearly explained with this study. Future research could adopt a longitudinal approach such that the changes in NPC patients who received radiation therapy can be better understood.

Anal canal squamous cell carcinoma (SCC) is managed definitively with chemoradiation, reserving surgery for salvage. The dosage of radiation has varied from 30 Gy to in excess of 60 Gy. RTOG 0529 established intensity modulated radiation therapy (IMRT) as standard of care for anal canal SCC with doses of 50.4 to 54 Gy. We sought to use the National Cancer Database to examine trends in dose selection and radiation technique over time. We queried the National Cancer Database from 2004 to 2015 for cases of anal cancer stage groups 1 to 3, treated with definitive doses of radiation with chemotherapy. Dose escalation was defined as >54 Gy. Univariable and multivariable analyses were performed to identify factors predictive of dose, IMRT, and overall survival. Propensity-adjusted Cox proportional hazard ratios for survival were used to account for indication bias. We identified 7792 patients meeting the eligibility criteria, with 4269 treated to doses of 45 to 54 Gy and 3163 treated to doses >54 Gy. Patients who were older, had government or private insurance, IMRT treatment, treatment at an academic center, or more recent years were less likely to get dose escalation. The use of dose escalation decreased over time, from 50% in 2005 to 30% in 2015. IMRT use increased over time from 2% to 63%. On multivariable analysis with propensity score included it was found that increased age, higher comorbidity score, lower income, shorter distance to facility, and male sex were predictive of decreased overall survival. In addition, escalated dose was associated with a lower survival (hazard ratio: 1.10, 95% confidence interval: 1.01-1.20, P=0.03). The results of this analysis show a steady increase in the use of IMRT, with corresponding decrease in dose escalation. These findings correlate with the results of RTOG 0529 establishing IMRT as standard of care for anal SCC, using doses of 50.4 to 54 Gy.

The present study compared the dosimetry of intensity‐modulated radiation therapy (IMRT) and three‐dimensional conformal radiation therapy (3D‐CRT) techniques in patients treated for high‐grade glioma. A total of 20 patients underwent computed tomography treatment planning in conjunction with magnetic resonance imaging fusion. Prescription dose and normal‐tissue constraints were identical for the 3D‐CRT and IMRT plans. The prescribed dose was 59.4 Gy delivered at 1.8 Gy per fraction using 4 – 10 MV photons. Normal‐tissue dose constraints were 50 – 54 Gy for the optic chiasm and nerves, and 55 – 60 Gy for the brainstem.The IMRT plan yielded superior target coverage as compared with the 3D‐CRT plan. Specifically, minimum and mean planning target volume cone down doses were 54.52 Gy and 61.74 Gy for IMRT and 50.56 Gy and 60.06 Gy for 3D‐CRT (p≤0.01). The IMRT plan reduced the percent volume of brainstem receiving a dose greater than 45 Gy by 31% (p=0.004) and the percent volume of brain receiving a dose greater than 18 Gy, 24 Gy, and 45 Gy by 10% (p=0.059), 14% (p=0.015), and 40% (p≤0.0001) respectively. With IMRT, the percent volume of optic chiasm receiving more than 45 Gy was also reduced by 30.40% (p=0.047). As compared with 3D‐CRT, IMRT significantly increased the tumor control probability (p≤0.005) and lowered the normal‐tissue complication probability for brain and brainstem (p<0.033).Intensity‐modulated radiation therapy improved target coverage and reduced radiation dose to the brain, brainstem, and optic chiasm. With the availability of new cancer imaging tools and more effective systemic agents, IMRT may be used to intensify tumor doses while minimizing toxicity, therefore potentially improving outcomes in patients with high‐grade glioma.PACs number: 87.53 Tf

Impact of Treatment Margins and Treatment Technique in Hippocampal Sparing Radiation Therapy for Pediatric Medulloblastoma

Comparison of two different VMAT radiotherapy TPSs for pancreatic cancer using flattening filter free photon beam energy