Couch modeling optimization for tomotherapy planning and delivery.

We sought to validate new couch modeling optimization for tomotherapy planning and delivery. We constructed simplified virtual structures just above a default setting couch through a planning support system (MIM Maestro, version 8.2, MIM Software Inc, Cleveland, OH, USA). Based on ionization chamber measurements, we performed interactive optimization and determined the most appropriate physical density of these virtual structures in a treatment planning system (TPS). To validate this couch optimization, Gamma analysis and these statistical analyses between a three-dimensional diode array QA system (ArcCHECK, Sun Nuclear, Melbourne, FL, USA) results and calculations from ionization chamber measurements were performed at 3%/2 mm criteria with a threshold of 10% in clinical QA plans. Using a virtual model consisting of a center slab density of 4.2 g/cm3 and both side slabs density of 1.9 g/cm3 , we demonstrated close agreement between measured dose and the TPS calculated dose. Agreement was within 1% for all gantry angles at the isocenter and within 2% in off-axis plans. In validation of the couch modeling in a clinical QA plan, the average gamma passing rate improved approximately 0.6%-5.1%. It was statistically significant (P < 0.05) for all treatment sites. We successfully generated an accurate couch model for a TomoTherapy TPS by interactively optimizing the physical density of the couch using a planning support system. This modeling proved to be an efficient way of correcting the dosimetric effects of the treatment couch in tomotherapy planning and delivery.

Minimizing dose variation from the interplay effect in stereotactic radiation therapy using volumetric modulated arc therapy for lung cancer.

It is important to improve the magnitude of dose variation that is caused by the interplay effect. The aim of this study was to investigate the impact of the number of breaths (NBs) to the dose variation for VMAT-SBRT to lung cancer. Data on respiratory motion and multileaf collimator (MLC) sequence were collected from the cases of 30 patients who underwent radiotherapy with VMAT-SBRT for lung cancer. The NBs in the total irradiation time with VMAT and the maximum craniocaudal amplitude of the target were calculated. The MLC sequence complexity was evaluated using the modulation complexity score for VMAT (MCSv). Static and dynamic measurements were performed using a cylindrical respiratory motion phantom and a micro ionization chamber. The 1 standard deviation which were obtained from 10 dynamic measurements for each patient were defined as dose variation caused by the interplay effect. The dose distributions were also verified with radiochromic film to detect undesired hot and cold dose spot. Dose measurements were also performed with different NBs in the same plan for 16 patients in 30 patients. The correlations between dose variations and parameters assessed for each treatment plan including NBs, MCSv, the MCSv/amplitude quotient (TMMCSv), and the MCSv/amplitude quotient × NBs product (IVS) were evaluated. Dose variation was decreased with increasing NBs, and NBs of >40 times maintained the dose variation within 3% in 15 cases. The correlation between dose variation and IVS which were considered NBs was shown stronger (R2  = 0.43, P < 0.05) than TMMCSv (R2  = 0.32, P < 0.05). The NBs is an important factor to reduce the dose variation. The patient who breathes >40 times during irradiation of two partial arcs VMAT (i.e., NBs = 16 breaths per minute) may be suitable for VMAT-SBRT for lung cancer.

Error Detectability of Isodose Volumes as ROIs in Prostate Intensity-modulated RT QA.

BACKGROUND/AIM: To evaluate the quality of error detectability with a three-dimensional verification system using isodose volumes as regions of interest (ROIs) in quality assurance (QA) of intensity-modulated radiation therapy. PATIENTS AND METHODS: Treatment plans with four types of intentional errors were created from the data of 20 patients with localized prostate cancer. These plans underwent QA using the three-dimensional verification system. The datasets of another 30 cases without inserted errors were assessed as controls. The ROIs used in the evaluations were those used in our conventional method (planning target volume, rectum, and bladder). The isodose volume method (5%, 50% and 95% isodose volume) and the error detection rates (measurement above the tolerance values, as set from the other 30 cases) were assessed and compared. RESULTS: There was significantly higher multileaf collimator systematic closed error detectability with the isodose volume method compared to the conventional method (A-side 0.2 mm: p=0.005, A-side 0.35 mm: p=0.002, B-side 0.2 mm: p=0.001 and B-side 0.35 mm: p=0.010). There were no error types for which the error detection rate of the isodose volume method was lower than that of the conventional method. CONCLUSION: The isodose volume method was able to evaluate the irradiated ROIs that could be delineated, and improved error detectability. This method has the potential to provide a wider margin of safety in intensity-modulated radiation therapy.

Oesophageal Cancer: Conformal Radiotherapy vs. Hybrid-VMAT Technique With Two Different Treatment Planning Systems.

BACKGROUND/AIM: Traditionally, the radiotherapy of oesophageal cancer has been conformal radiotherapy (CRT). We sought to compare dosimetric parameters of conformal radiotherapy (CRT) with those of two treatment planning systems for hybrid-volumetric modulated arc therapy (h-VMAT) for the treatment of oesophageal cancer. PATIENTS AND METHODS: In 11 patients, we compared: i) planning target volume coverage, ii) dose to organs at risk, and iii) the dose rate (DR) of the three techniques. We evaluated two treatment planning systems: i) Eclipse and ii) RayStation. RESULTS: The Conformity Index of the CRT plan was significantly higher for the h-VMAT plans, compared to all other parameters. Normal lung tissue volumes receiving >5, 13, or 20 Gy were lower with the RayStation plan compared to Eclipse. The volume of cardiac tissue receiving >40 Gy was highest with the CRT plan. The minimum DR in VMAT was lowest for the RayStation plan (49.5 MU/min). CONCLUSION: The h-VMAT plan using RayStation is the appropriate choice for reducing lung dose.

Inter-planner variation in treatment-plan quality of plans created with a knowledge-based treatment planning system.

PURPOSE: This study aimed to clarify the inter-planner variation of plan quality in knowledge-based plans created by nine planners. METHODS: Five hypofractionated prostate-only (HPO) volumetric modulated arc therapy (VMAT) plans and five whole-pelvis (WP) VMAT plans were created by each planner using a knowledge-based planning (KBP) system. Nine planners were divided into three groups of three planners each: Senior, Junior, and Beginner. Single optimization with only priority modification for all objectives was performed to stay within the dose constraints. The coefficients of variation (CVs) for dosimetric parameters were evaluated, and a plan quality metric (PQM) was used to evaluate comprehensive plan quality. RESULTS: Lower CVs (<0.05) were observed at dosimetric parameters in the planning target volume for both HPO and WP plans, while the CVs in the rectum and bladder for WP plans (<0.91) were greater than those for HPO plans (<0.17). The PQM values of HPO plans for Cases1-5 (average ±â€¯standard deviation) were 41.2 ±â€¯7.1, 40.9 ±â€¯5.6, and 39.9 ±â€¯4.6 in the Senior, Junior, and Beginner groups, respectively. For the WP plans, the PQM values were 51.9 ±â€¯6.3, 47.5 ±â€¯4.3, and 40.0 ±â€¯6.6, respectively. The number of clinically acceptable HPO and WP plans were 13/15 and 11/15 in the Senior group, 13/15 and 10/15 plans in the Junior group, and 8/15 and 2/15 plans in the Beginner group, respectively. CONCLUSION: Inter-planner variation in the plan quality with RapidPlan remains, especially for the complicated VMAT plans, due to planners' heuristics.

Bowel and urinary quality of life after whole-pelvic versus prostate-only volumetric-modulated arc therapy for localized prostate cancer.

PURPOSE: This study aimed to compare bowel and urinary health-related quality of life (HRQOL) between prostate-only (PO) volumetric modulated arc therapy (VMAT) and whole-pelvis (WP) VMAT in patients with localized prostate cancer. METHODS AND MATERIALS: A total of 234 patients treated with definitive VMAT to 78 Gy in 39 fractions were enrolled. Of these, 108 patients received PO-VMAT and 126 patients received initial WP-VMAT to 46.8 Gy in 26 fractions using a simultaneous integrated boost technique. HRQOL was prospectively assessed before radiation therapy (baseline), and 3, 6, 12, and 24 months after treatment using the Expanded Prostate Cancer Index Composite (EPIC). RESULTS: Baseline HRQOL scores did not differ significantly between the 2 groups. No significant between-group differences in HRQOL change from baseline were observed for all bowel and urinary EPIC domains. The proportion of patients showing a clinically relevant decrease in bowel and urinary HRQOL scores from baseline was similar between the groups throughout the follow-up period. An analysis of individual HRQOL items showed that patients undergoing WP-VMAT were more likely to report moderate/big problems with bloody stools (P = .039) and overall bowel problems (P = .008) than those undergoing PO-VMAT at 12 months. There was no significant between-group difference in any individual items at 24 months, however. CONCLUSIONS: Bowel and urinary HRQOL is largely similar for patients receiving PO-VMAT and WP-VMAT during 24 months of follow-up, with the only differences seen in responses to specific bowel HRQOL items at 12 months.

A treatment-planning comparison of three beam arrangement strategies for stereotactic body radiation therapy for centrally located lung tumors using volumetric-modulated arc therapy.

The purpose of this study was to determine appropriate beam arrangement for volumetric-modulated arc therapy (VMAT)-based stereotactic body radiation therapy (SBRT) in the treatment of patients with centrally located lung tumors. Fifteen consecutive patients with centrally located lung tumors treated at our institution were enrolled. For each patient, three VMAT plans were generated using two coplanar partial arcs (CP VMAT), two non-coplanar partial arcs (NCP VMAT), and one coplanar full arc (Full VMAT). All plans were designed to deliver 70 Gy in 10 fractions. Target coverage and sparing of organs at risk (OARs) were compared across techniques. PTV coverage was almost identical for all approaches. The whole lung V10Gy was significantly lower with CP VMAT plans than with NCP VMAT plans, whereas no significant differences in the mean lung dose, V5Gy, V20Gy or V40Gy were observed. Full VMAT increased mean contralateral lung V5Gy by 12.57% and 9.15% when compared with NCP VMAT and CP VMAT, respectively. Although NCP VMAT plans best achieved the dose-volume constraints for mediastinal OARs, the absolute differences in dose were small when compared with CP VMAT. These results suggest that partial-arc VMAT may be preferable to minimize unnecessary exposure to the contralateral lung, and use of NCP VMAT should be considered when the dose-volume constraints are not achieved by CP VMAT.