Background: This study evaluated whether IMRT using fewer beams and segments could reduce delivery time without compromising plan quality in gastric cancer adjuvant radiotherapy. Materials and Methods: Fifteen patients with advanced gastric cancer who underwent D2, R0 surgery were included in this study. IMRT plans for each patient were designed as 7 equal beams with 40 segments, 5 beams with 25 segments and 4 beams with 20 segments. The dosimetric parameters were compared for the planned target volume (PTV). The dose of normal organs at risk (OARs) was also assessed. The monitor units and treatment times of the different IMRT plans were calculated. Results: The 20-segment IMRT plan significantly reduced the PTV maximum dose compared to the 40-segment IMRT plan. The 20-segment IMRT plan improved left kidney and liver dose sparing in V20 and V30 as well as the 40-segment IMRT plan did and provided better protection for the V20 (13.86±7.78) of the right kidney, the V30 (9.25±4.04) of the left kidney, the D mean (19.68±2.47) of liver and D max (38.79±3.57) of the spinal cord. Irradiation times in the         20-segment and 25-segment plans decreased by 2.5 and 1.9 min, respectively, compared to the 40-segment IMRT plan. Conclusion: IMRT using fewer beams and segments reduced delivery time without compromising plan quality in gastric cancer adjuvant radiotherapy. Fewer segments IMRT plans lowered the monitor units and the treatment time.

 

Background: The aim was to evaluate the benefit of technical advances for treatment planning: introduction of a hydrogel spacer, VMAT (volumetric modulated arc therapy) and a single biological organ at risk objective for the rectum and bladder. Initial standard was a step-and-shoot IMRT (intensity modulated radiotherapy) without a spacer and conventional organ at risk objectives.  Materials and Methods: Treatment plans were calculated using IMRT and VMAT techniques before and after spacer injection in 27 patients, respectively. Conventional organ at risk objectives have been used for the optimization of IMRT plans, only a single biological organ at risk objective for VMAT plans. VMAT vs. IMRT plans and plans before vs. after spacer injection were compared. Results: VMAT plans and independently the spacer demonstrated improved dose homogeneity, whereas VMAT additionally displayed improved dose conformity. The dose to the bladder and rectum could be significantly decreased applying the VMAT technique (mean rectum volumes of 14%/10%/5% in VMAT vs. 36%/24%/12% in IMRT within the 50Gy/60Gy/70Gy isodoses; p<0.01). NTCP for ≥grade 3 rectum toxicity could be accordingly decreased with the VMAT technique (3.6 vs. 0.9% for IMRT vs. VMAT; p<0.01) and the spacer gel (3.3 vs. 1.2% for plans without vs. with spacer gel; p<0.01) – only 0.3% with VMAT and spacer gel. Conclusion: In addition to the decreased rectal dose following spacer injection, VMAT with single biological organ at risk optimization resulted in further dose reduction to the organs at risk and improved dose homogeneity and conformity in comparison to the step-and-shoot IMRT technique with conventional objectives.
 

Background and Aim: The incidence of internal lymph node (IMN) involvement was 4- 65% in breast cancer patients. Despite studies indicating the positive effects of IMNRT on the oncological results, most of the clinicians avoided IMNRT because of the toxicity related to the increased dose of organs at risk (OAR). We aimed to compare the dosimetric results of RT plans with and without IMN containing planning target volumes (PTVs) using helical tomotherapy (HT) in obese patients. Materials and Methods: The PMRT data of 23 obese patients were evaluated retrospectively / dosimetrically. Two PTVs with and without IMN were defined and two separate plans were made with HT. Dose received by IMN and OAR were compared. Results: The untargeted IMN V₄₀ were calculated between 0% to 99%. When the plans are evaluated in terms of critical organs, the inclusion of the IMN into the target volume, the most significant adverse effect was observed in heart doses in the left chest wall (CW) irradiation. The significant increases in cardiac V₅ (%62.6 vs %48.6 p=0.007), V₁₀ (%38.2 vs %23.2 p=0.011), V₂₀ (%14.15 vs %9.06 p=0.045) and maximum heart dose (48.04 vs 43.2 p=0.043) were observed in the left-side CW irradiations that involving the IMN. In CW irradiation on the right side with IMN, only a significant increase in mean heart dose (5.44 vs 4.52 p=0.036) was observed. Lung V₅ doses were increased by inclusion with IMN in both sides. There was no difference in the contralateral breast doses in both plans for both sides. Conclusions: If the IMN is not targeted, some of the patients are getting appropriate doses in obese patients.

Background: The current study aimed to compare the tumor control probability (TCP) and normal tissue complication probability (NTCP) of three-dimensional conformal radiation therapy (3D-CRT) and intensity-modulated radiation therapy (IMRT) for left-sided breast cancer using radiobiological models. Methods: This study was conducted on 30 patients with left-sided breast cancer, who were planned for 3D-CRT and 6-9 fields IMRT treatments using the PROWESS treatment planning system.  The planning target volume (PTV) dose of 50 Gy was administered for the 3D-CRT and IMRT plans, respectively.  The Niemierko’s equivalent uniform dose (EUD) model was utilized for the estimation of tumor control probability (TCP) and normal tissue complication probability (NTCP). Results: According to the results, the mean TCP values for 3D-CRT, 6-fields IMRT, and 9-fields IMRT plans were 99.07 ±0.07, 99.24 ±0.05 and 99.28 ±0.04, respectively, showing no statistically significant difference. The NTCPs of the lung and heart were considerably lower in the IMRT plans, compared to those in the 3D-CRT plans.

Background: This study aims to investigate the effect of reference dose calculation grid size (RDCGS) on gamma passing rate (GPR) for patient-specific quality assurance of intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT). Materials and Methods: A total of 20 patients were retrospectively selected. Both IMRT and VMAT plans were generated for each patient. Reference dose distributions for gamma analysis were calculated with RDCGS of 1–5 mm at intervals of 1 mm. Dose distributions were measured using MapCHECK2 and ArcCHECK dosimeters. Both global and local gamma analyses with gamma criteria of 3%/3 mm, 2%/3 mm, 2%/2 mm, and 2%/1 mm were performed with various RDCGS. Results: As the RDCGS increased from 1 mm to 5 mm, the average global GPRs with 2%/2 mm for VMAT with MapCHECK2 and ArcCHECK decreased by 9.3% and 5.9%, respectively. The average local GPRs decreased by 14% and 11.7%, respectively. For IMRT, the global GPRs decreased by 4.8% and 6%, respectively, whereas the local GPRs decreased by 10.5% and 8.6%, respectively. The effect of the RDCGS on the GPRs became larger when performing local gamma analysis as well as when applying small distance-to-agreement (DTA). As the RDCGS increased, the average changes in the GPR per mm of DTA change increased regardless of the type of radiotherapy, detector, or gamma analysis. Conclusion: For an accurate verification of the IMRT and VMAT plans, it is recommended that the reference dose distribution must be calculated with the smallest possible RDCGS.

Background: The design of intensity modulated radiation therapy (IMRT) plans is difficult and time-consuming. The retrieval of similar IMRT plans from the IMRT plan dataset can effectively improve the quality and efficiency of IMRT plans and automate the design of IMRT planning. However, the large IMRT plans datasets will bring inefficient retrieval result. Materials and Methods: An intensity-modulated radiation therapy (IMRT) plan clustering method based on k-means algorithm and geometrical features is proposed to improve the retrieval efficiency from the IMRT plan dataset. The proposed method could benefit future automatic IMRT planning based on prior knowledge. In this study, a collection dataset including 100 cases of nasopharyngeal carcinoma IMRT plans was employed in the clustering experiment. The geometrical features of each cluster center were used to qualitatively predict the dosimetric characteristics of organs at risk (OARs) and compared with practical results. Results: Experimental results demonstrate that the tested dataset can be well clustered using the proposed method. The predicted dosimetric characteristics of OARs for each cluster agree well with their practical results, and the difficulty of IMRT planning for each cluster can be derived. Conclusion: The proposed IMRT plan clustering method can bring great benefit to the new cases of IMRT planning.

Background: In head and neck radiotherapy, immobilization devices can affect dose delivery. In this study, a comprehensive end-to-end test was developed to evaluate the accuracy of radiotherapy treatment. Materials and Methods: An Alderson Radiation Therapy (ART) anthropomorphic phantom with EBT3 film was used to mimic the actual patient treatment process. Ten patients treated for nasopharyngeal carcinomas with IMRT were retrospectively selected. For each patient, the treatment plan, as well as the targets and OARs was transplanted onto the phantom, and the IMRT plan was subsequently recalculated to the phantom with EBT3 film. Two quality assurance (QA) plans were generated, namely “Plan-with” wherein the immobilization device was contoured and “Plan-without” wherein it was omitted. EBT3 measurements were compared with the results of the TPS calculation. Results: With different gamma calculation criteria applied, the results obtained for Plan-with were closer to the dose measured with the EBT3 film. Moreover, 1.8% deviation was observed in the posterior neck skin dose for Plan-with when compared to the film measurements while the value was 33.1% lower for Plan-without. When compared to Plan-without, each target volume in Plan-with exhibited a 1–4% reduction in the maximum dose (D_2%), minimum dose (D_98%) and mean dose (D_mean). Conclusion: Immobilization devices decrease the radiation dose to target volumes while increasing the skin dose and should be included within the body contour to ensure an accurate planning dose. The end-to-end IMRT test using an ART anthropomorphic phantom is a valuable tool to identify discrepancies between calculated and delivered radiation doses.

Background: This study aimed to compare high-grade gliomas radiation therapy methods (high energy three-dimensional conformal radiation therapy [3D-CRT] vs. low energy intensity-modulated radiation therapy [IMRT]). Materials and Methods: Out-of-field photons resulting from 15- and 18-MV 3D-CRT and 6-MV IMRT techniques were measured with thermo-luminescent dosimeters in a head and neck homogeneous phantom. Moreover, the dose to the left and right eye lenses, parotid glands, the thyroid gland, and the tongue was determined for each of the treatment techniques. Additionally, the risk of secondary thyroid cancer was estimated according to the biological effects of ionizing radiation BEIR VII model. Results: Errors in the treatment planning system (TPS) increased with increasing distance from the field edge and varied in different treatment techniques. The 6-MV IMRT technique increased the photon dose to all of the organs. Further, the excess relative risk for thyroid cancer was obtained higher in the 6-MV IMRT technique than in the 15- and 18-MV 3D-CRT techniques, as the photon dose to the thyroid gland was higher. Conclusion: Although 6-MV IMRT better improves local control and dose distribution than 3D-CRT, it increases the total dose equivalent in out-of-field organs independently of beam energy and exacerbates the risk of secondary thyroid cancer more significantly.

Background: Aim of this study was to evaluate the extent of the error that the gating system incorporates into an intensity-modulated radiation therapy (IMRT) delivery for the different duty cycles of beam gated treatments (beam-interruption) by comparing the gamma between the dose planes. Materials and Methods: Respiratory motion patterns was recorded in the real-time position management (RPM) software, which controls the triggering of the linear accelerator for the beam ON/OFF based on the predefined gating window. 10 IMRT plans consisting of 60 IMRT fields were delivered for three different duty cycles (20%DC, 30%DC and 40%DC) of gated and non-gated delivery. Planar dose measurements of IMRT delivery were performed with the commercially available two-dimensional ion chamber array and portal dosimetry. Gamma evaluation was carried out for the three different duty cycles of gated delivery with that of the reference of non-gated delivery, and the measured dose planes of gated and non-gated delivery were gamma analyzed with the treatment planning system (TPS) dose planes. Multileaf collimator (MLC) dynalog files were acquired and analyzed for the different duty cycles of gated and non-gated IMRT deliveries. Results: Gamma between the gated and non-gated dose planes were found within the 3% deviation.  Area gamma for the gated and non-gated delivery to the reference of TPS dose planes were found within the deviation of 6%. Conclusion: Gamma comparison of the gated delivery with the reference of non-gated delivery results demonstrated that increasing the duty cycle reduced the deviation between the gated and non-gated delivery.