Purpose: To evaluate the dosimetric effects of the custom dose iteration function in the Monaco 6.0 planning system on stereotactic radiotherapy for lung cancer.Methods: Using the custom dose iterative function segment shape optimization (SSO) times in the Monaco 6.0 treatment planning system, the iterative times were set as 3, 5, 8, 10, and 12, respectively. Five volumetric modulated arc stereotactic body radiation therapy (SBRT) plans were made for each patient, and other opti-mization parameters and optimization functions were kept consistent. The dose volume histogram (DVH) sta-tistical table was used to evaluate the dose of the target area and organs at risk (OAR). Statistical analysis was performed using SPSS 25 software, and the results were statistically different when p < 0.05.Results: For the target area dose analysis, SSO8, SSO10, and SSO12 groups showed similar results, significantly better than both SSO3 and SSO5 groups (p < 0.05). With the increase in the times of SSO, the protection of the heart was better, except for SSO3, the maximum dose of the esophagus and V47Gy of great vessels were signif-icantly lower than SSO5 in all groups. The mean dose of heart was significantly lower in SSO10 and SSO12 than SSO5 (p < 0.05). There was no significant difference in other OAR among the groups. The optimization time (OT) of each group was statistically different, the maximum OT exceeded 1000s, the maximum deviation between groups exceeded 600s, and the OT increased significantly with the times of SSO (p < 0.05). There was no sta-tistically significant difference between the 5 groups of monitor unit (MU), and segment was not significantly different between the groups except SSO3 which was significantly higher than SSO5 (p < 0.05). The delivery time (DT) was statistically different between the groups except for SSO3.Conclusions: In the treatment of left-sided lung cancer patients with volumetric modulated arc SBRT, considering both calculation accuracy and clinical treatment efficiency, SSO times of 8 is recommended for designing SBRT for lung cancer with the Monaco treatment planning system.

Purpose: The purpose of this work is to present a practical, structured process allowing for consistent, safe radiation therapy delivery in the re-treatment environment. Methods and materials: A process for reirradiation is described with documentation in the form of a special physics consultation. Data acquisition associated with previous treatment is described from highest to lowest quality. Methods are presented for conversion to equieffective dose, as well as our departmental assumptions for tissue repair. The generation of organ-at-risk available physical dose for use in treatment planning is discussed. Results using our methods are compared with published values after conversion to biologically effective dose. Utilization of pulsed-low-dose-rate delivery is described, and data for reirradiation using these methods over the previous 5 years are presented. Results: Between 2015 and 2019, the number of patients in our department requiring equieffective dose calculation has doubled. We have developed guidelines for estimation of sublethal damage repair as a function of time between treatment courses ranging from 0% for <6 months to 50% for >1 year. These guidelines were developed based on available spinal cord data because we found that 84% of organs at risk involved nerve-like tissues. The average percent repair used increased from 32% to 37% over this time period. When comparing the results obtained using our methods with published values, 99% of patients had a cumulative biologically effective dose below the limits established for acceptable myelopathy rates. Pulsed-low-dose-rate use over this period tripled with an average prescription dose of 49 Gy. Conclusions: The methods described result in safe, effective treatment in the reirradiation setting. Further correlation with patient outcomes and side effects is warranted.

The purpose of this study is to evaluate the treatment plan adequacy and delivery efficiency among volumetric-modulated arc therapy (VMAT) with one or two arcs and the conventional static-field dynamic multileaf collimator (dMLC) intensity-modulated radiation therapy (IMRT) in patients undergoing oropharyngeal carcinoma. Fifteen patient cases were included in this investigation. Each of the cases was planned using step-and-shoot IMRT, VMAT with a single arc (Arc1) and VMAT with double arcs (Arc2). A two-dose level prescription for planning target volumes (PTVs) was delivered with 70 Gy/56 Gy in 30 fractions. Comparisons were performed of the dose-volume histograms (DVH) for PTVs, the DVH for organs at risk (OARs), the monitor units per fraction (MU/fx), and delivery time. IMRT and Arc2 achieved similar target coverage, but superior to Arc1. Apart from the oral cavity, Arc1 showed no advantage in sparing of OARs compared with IMRT, while Arc2 obtained equivalent or better sparing of OARs among the three techniques. VMAT reduced MU/fx and shortened delivery time remarkably compared with IMRT. Our results demonstrated that for oropharyngeal cases, Arc2 can achieve superior target coverage and normal tissue sparing, as well as a significant reduction in treatment time.

Patients (pts) diagnosed with malignant spinal cord compression (MSCC) have been shown to have a poor life expectancy in the order of 4 months (mo) and treatment strategy consists of radiation therapy with or without surgery. With increased availability of MRI scans, and improved patient education and awareness, the diagnosis of radiological or subclinical MSCC is increasing. The prognosis and optimal management of these pts is not well defined. We describe the prevalence of subclinical diagnoses of MSCC at a tertiary radiation oncology department, and the clinical characteristics, management patterns and survival outcomes of pts presenting with subclinical versus clinical MSCC. Patients with a diagnosis of MSCC between June 2004 and February 2011 were eligible for analysis. Clinical characteristics (American Spinal Injury Score [ASIA], gender, ECOG performance status, primary site, pain score and previous MSCC), management patterns (time from imaging to appointment with a specialist and the treatment modality) and survival data were extracted from our prospectively maintained database, cancer registry and radiation therapy treatment records. An ASIA score of E (normal sensory and motor function) was classified as subclinical and an ASIA score of A-D was classified as clinical MSCC. Between June 2004 and February 2011, 342 patients were eligible for analysis. ASIA score was available for 336 pts. The prevalence of patients with ASIA score E was 43%. This was stable over time. Men represented 52% ASIA E and 62% of ASIA A-D. The primary cancer diagnosis was similar between the groups with the most common diagnosis being lung cancer (21%) followed by breast (13%) and prostate (12%). Mean pain score (scale 0-10) was 5.4 and 5.7 for the ASIA E and A-D respectively. ECOG PS ≤2 was observed in 104 (71%) of ASIA E and 67 (35%) of ASIA A-D (p < 0.05). Treatment modality between the two groups was similar with 82% and 81% receiving radiation therapy alone and 12% and 16 % receiving combined treatment with surgery and radiation therapy for each group. The median time from diagnostic imaging to being seen in clinic was 2 and 1 day, respectively. The median overall survival (OS) between the two groups was significantly different, ASIA E 7.9 months (95% CI = 5.7 - 12.4), ASIA A-D 3.3 months (95% CI = 2.2-3.6) p < 0.0001. The median OS for the whole group was 4.7 months (95% CI = 3.5-5.9). The prevalence of ASIA E (subclinical MSCC) was relatively high at 43% throughout the study period. ASIA E and ASIA A-D pts are predominantly managed by radiation therapy alone; however, ASIA E pts enjoy a significantly more favorable survival. Consideration of different management strategies may need to be given for these two different scenarios. Distinction between patients with subclinical and clinical disease should be considered for future studies and reporting of treatment outcomes.