Robust optimization in lung treatment plans accounting for geometric uncertainty

Multiple brain metastases patients are typically treated by stereotactic radiosurgery (SRS) or whole brain radiation therapy (WBRT). In addition, there are advanced techniques for treating multiple brain metastases such as 3-dimensional Conformal Radiation Therapy (3D-CRT), Intensity Modulated Radiation Therapy (IMRT), and Volumetric Modulated Arc Therapy (VMAT). A new isocentric VMAT technique called HyperArc was developed for non-coplanar, it is an automated setting for couch angle and collimator angle. This study aims to compare the dosimetric effect for a single isocenter among Intensity Modulated Radiation Therapy, Volumetric Modulated Arc Therapy, and HyperArc for multiple brain metastases stereotactic radiosurgery. For 25 patients with multiple brain metastases (2-4 targets). IMRT, Coplanar VMAT (co-VMAT), Non-coplanar VMAT (non-co VMAT), and HyperArc plans with a prescription dose of 18 Gy in single-fraction were generated. All plans used 6 MV flattening filter-free energy. IMRT plans consisted of 9 coplanar fields. The co-VMAT plan used 2 full coplanar arcs, while non-co VMAT and HyperArc plans consisted of 1 full coplanar arc and 3 half arcs with non-coplanar planes at 45, 90, and 135 couch angles. The organs at risk (OARs) dose constraints at Dmax of the brainstem was 8 Gy, while Dmax of the eye lens, optic nerve, and optic chiasm should be less than 5 Gy. Paddick gradient index (GI), Paddick conformity index (CI), homogeneity index (HI), total number of monitor units, delivery time and normal brain tissue volume (V2-V16) were used to evaluate the plan quality. Showed that OAR doses were lower than the dose limits for all plans. HyperArc presented good results with the lowest GI (5.18± 1.15), and the highest CI (0.63±0.14) values compared with other techniques. For HI all techniques are hardly different (0.19±0.02). For the HyperArc the beam on time was significantly reduced from other techniques around 4 minutes. Also, MUs and the normal brain's moderate to low dose spreads (V2-V16) were reduced considerably in the HyperArc plan (5226.50±650.88, 10.08±3.84, respectively). Eventually, HyperArc plans led to a significant reduction in both the total number of monitor units and delivery time. We can conclude that the HyperArc plans provided a significantly better rapid dose falloff and higher conform the dose distribution to the targets with respect to the other plans. This is consistent with the computed reduction in V12 to the normal brain. Ultimately, HyperArc treatments were accomplished within around 4 minutes, signifying a noteworthy reduction in time compared to the other plans.

The comparative study of dosimetric parameters for craniospinal irradiation (CSI) in medulloblastoma cancer patients has been conducted using three different radiation treatment modalities, such as helical intensity-modulated radiation therapy (RT) (HIMRT), helical three-dimensional (3D) conformal RT (H3DCRT), and volumetric modulated arc therapy (VMAT). Evaluation based on dosimetric parameters has been performed to check the better clinical outcomes of recent treatment techniques over one another. In this retrospective study, twenty patients have been taken who were suffering from average-risk medulloblastoma. For these patients, phase 1 and phase 2 treatment plans were generated with HIMRT, H3DCRT, and VMAT using Accuray Precision version 2.0.1.1 and Monaco version 5.51.10 treatment planning software (TPS). For dose calculation, the convolution superposition algorithm is used for HIMRT and H3DCRT and the Monte Carlo algorithm is used for VMAT. Homogeneity index (HI), conformity index (CI), heterogeneity index (HT), total treatment time (TT), and doses to organs at risk (OARs) have been calculated. Statistical analysis has been performed with a paired-samples test in Statistical Package for the Social Sciences (SPSS) software version 22. For target volume PTV_Brain, Conformity index in different treatment techniques are mentioned (HIMRT = 1.02 ± 0.016, H3DCRT = 1.04 ± 0.015, VMAT = 1.11 ± 0.090), homogeneity indexes is (HIMRT = 0.73 ± 0.088, H3DCRT = 0.39 ± 0.208, VMAT = 0.43 ± 0.102), and Heterogeneity index is (HIMRT = 1.51 ± 0.013, H3DCRT = 1.50 ± 0.017, VMAT = 1.09 ± 0.018). For target volume PTV_Spine Conformity index in different treatment techniques are mentioned (HIMRT = 1.00 ± 0.004, H3DCRT = 1.01 ± 0.013, VMAT = 1.07 ± 0.039), homogeneity indexes is (HIMRT=0.07 ± 0.043, H3DCRT =0.06 ± 0.070, VMAT = 0.23 ± 0.183), and Heterogeneity index is (HIMRT = 1.10 ± 0.12, H3DCRT = 1.11 ± 0.121, VMAT = 1.06 ± 0.007). For target volume Boost_GTV Conformity index in different treatment techniques are mentioned (HIMRT = 1.035 ± 0.016, H3DCRT = 1.04 ± 0.016, VMAT = 1.08 ± 0.05), homogeneity indexes is (HIMRT = 0.80 ± 0.090, H3DCRT = 0.44 ± 0.223, VMAT = 0.56 ± 0.105), and Heterogeneity index is (HIMRT = 1.27 ± 0.006, H3DCRT = 1.26 ± 0.009, VMAT = 1.07 ± 0.009). Total Treatment time (minutes) for phase 1 in different techniques (HIMRT = 17.77 ± 3.974, H3DCRT = 14.83 ± 3.750, VMAT = 9.72 ± 0.713) and for phase 2 treatment time (HIMRT = 1.99 ± 0.306, H3DCRT = 1.68 ± 0.326, VMAT = 3.39 ± 0.918). All techniques, such as HIMRT, H3DCRT, and VMAT, give a uniform and conformal target coverage, but HIMRT shows the best conformal and homogeneous dose distribution and better OAR sparing. In this study, CSI patients treated with HIMRT showed better results in terms of conformity, homogeneity, and doses to organs at risk.

Introduction: Radiotherapy plays a pivotal role in the treatment of carcinoma of the oral cavity. However, associated toxicities like xerostomia and dysphagia significantly affect patient quality of life. Advancements in radiotherapy techniques, including Intensity-Modulated Radiotherapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT), have aimed to improve dosimetric outcomes and reduce toxicity to organs at risk (OARs). Aims: To compare acute and late toxicity in patients of well lateralized carcinoma of oral cavity treated with two different radiotherapy techniques: Intensity modulated Radiotherapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT) with special interest in xerostomia and dysphagia Materials and Methods: It was a Prospective Observational Study this study was conducted 2 years at the Department of Radiotherapy, Medical College Kolkata. 36 Patients were included in this study Results: Target coverage was comparable in both groups with no significant differences in D95%, D50%, D2%, or D98%. VMAT demonstrated a significantly better conformity index (p < 0.002) and reduced doses to the parotid glands and pharyngeal constrictors (p < 0.001). Treatment time and MUs were significantly lower in the VMAT group (p < 0.0001). Although not statistically significant, VMAT showed a trend toward lower incidences of Grade 2 dysphagia and xerostomia at all-time points. No Grade 3 toxicities were reported in either group. Conclusion: VMAT provides superior conformity and reduced dose to critical OARs, along with shorter treatment times and fewer monitor units compared to IMRT. Clinically, VMAT is associated with a trend toward lower rates of xerostomia and dysphagia, supporting its potential as the preferred technique in well-lateralized oral cavity cancers.

Dosimetric Implication of Neural Planning Organ at Risk Volumes in Stereotactic BodyRadiation Therapy of the Spine

This study investigates the impact of convergence mode (CM) in Eclipse (Varian Medical Systems) on the quality and complexity of volumetric modulated arc therapy (VMAT) plans for nasopharyngeal carcinoma (NPC) patients. We retrospectively analyzed data from 21 NPC patients. For each patient, three VMAT plans with different CM settings (Off, On, and Extended) were created using identical optimization objectives. Plan quality was assessed using indices such as the conformity index (CI) and homogeneity index (HI), as well as evaluating target coverage and sparing of organs at risk (OARs). Complexity was measured by metrics including average leaf pair opening (ALPO), modulation complexity scores for VMAT (MCSv), monitor units (MUs), and optimization time. Dosimetric verification was performed based on the gamma pass rate. Different CM settings can generate treatment plans that meet clinical dose objectives for planning target volumes (PTVs) and OARs. The 'On' or 'Extended' CM settings improved CI and HI for the NPC target volume and reduced OAR doses, especially the mean dose, without compromising target coverage. The 'Extended' CM setting produced the most favorable outcomes. ALPO values for CM settings 'Off', 'On', and 'Extended' were 29.1 ± 4.3 mm, 28.6 ± 4.2 mm, and 28.4 ± 4. 2 mm, respectively. MCSv values for these settings were 0.1730 ± 0.0215, 0.1691 ± 0.0204, and 0.1693 ± 0.0208, respectively. MUs were 796.2 ± 110.8 for CM 'Off', 798.6 ± 106.1 for CM 'On', and 799.7 ± 103.6 for CM 'Extended', with no significant differences (p > 0.05). Gamma pass rates for all plans were above 99% (3%/3 and 2%/2 mm), with no significant differences among groups (p > 0.05). The average optimization times for CM settings 'Off', 'On', and 'Extended' were 14.4 ± 3.2, 35.9 ± 8.9, and 145.6 ± 50.3 min, respectively (p < 0.001). CM usage can improve the CI and HI of the target volume and decrease the dose to OARs in VMAT plans for NPC patients. This study suggests that CM can be a valuable tool in VMAT planning for nasopharyngeal carcinoma, given adequate planning time.

Hypofractionation for localized prostate cancer treatment is rapidly spreading in the medical community and it is supported by radiobiological evidences (lower α/β ratio compared with surrounding tissues). Stereotactic body radiation therapy (SBRT) is a technique to administer high doses with great precision, which is commonly performed with CyberKnife (CK) in prostate cancer treatment. Since the CyberKnife (CK) is not available at all radiotherapy center, alternative SBRT techniques are available such as Volumetric Modulated Arc Therapy (VMAT) and Helical Tomotherapy (HT). The aim of the present study was to compare the dosimetric differences between the CK, VMAT, and HT plans for localized prostate cancer treatment.Seventeenpatients have been recruited and replanned using VMAT and HT to this purpose: they received the treatment using the CK with a prescription of 36.25 Gy in 5 fractions; bladder, rectum and penis bulb were considered as organs at risk (OAR). In order to compare the techniques, we considered DVHs, PTV coverage, Conformity Index and new Conformity Index, Homogeneity Index, beam-on time and OARs received dose.The 3 treatments methods showed a comparable coverage of the lesion (PTV 95%: 99.8 ± 0.4% CK; 98.5 ± 0.8% VMAT; 99.4 ± 0.5% HT. P < .05) and good sparing of OARs. Nevertheless, the beam-on time showed a significant difference (37 ± 9 m CK; 7.1 ± 0.3 m VMAT; 17 ± 2 m HT. P < .05).Our results showed that, although CK is the best SBRT technique for prostate cancer treatment, in case this technology is not available, it can be replaced by a similar treatment delivered by VMAT technique. VMAT can be administrated only if it has an appropriate Image Guided Radiation Therapy (IGRT) tracking system.

IntroductionCutaneous squamous cell carcinoma with large nerve perineural (LNPN) infiltration of the base of skull is a radiotherapeutic challenge given the complex target volumes to nearby organs at risk (OAR). A comparative planning study was undertaken to evaluate dosimetric differences between volumetric modulated arc therapy (VMAT) versus intensity modulated radiation therapy (IMRT) in the treatment of LNPN.MethodsFive consecutive patients previously treated with IMRT for LNPN were selected. VMAT plans were generated for each case using the same planning target volumes (PTV), dose prescriptions and OAR constraints as IMRT. Comparative parameters used to assess target volume coverage, conformity and homogeneity included V95 of the PTV (volume encompassed by the 95% isodose), conformity index (CI) and homogeneity index (HI). In addition, OAR maximum point doses, V20, V30, non-target tissue (NTT) point max doses, NTT volume above reference dose, monitor units (MU) were compared.ResultsIMRT and VMAT plans generated were comparable for CI (P = 0.12) and HI (P = 0.89). VMAT plans achieved better V95 (P = < 0.001) and reduced V20 and V30 by 652 cubic centimetres (cc) (28.5%) and 425.7 cc (29.1%), respectively. VMAT increased MU delivered by 18% without a corresponding increase in NTT dose.ConclusionCompared with IMRT plans for LNPN, VMAT achieved comparable HI and CI.

PurposeTo compare plan quality among photon volumetric modulated arc therapy (VMAT) and intensity‐modulated proton therapy (IMPT) with robustness using three different proton beam delivery systems with various spot size (σ) ranges: cyclotron‐generated proton beams (CPBs) (σ: 2.7–7.0 mm), linear accelerator proton beams (LPBs) (σ: 2.9–5.5 mm), and linear accelerator proton mini beams (LPMBs) (σ: 0.8–3.9 mm) for the treatment of head and neck (HN) cancer with bilateral neck irradiation.MethodsTen patients treated for oropharynx cancer with bilateral neck irradiation were planned using CPBs, LPBs, LPMBs, and VMAT. The homogeneity index (HI), mean body dose, and defined volumetric doses for selected critical organs‐at‐risk (OARs) were compared. Set‐up uncertainties of ±3 mm and ± 3.5% range uncertainties were included in robust evaluation using V95%Rx > 95% (Volume that covers 95% of the target volume at 95% of the prescription (Rx) dose) to high dose and low dose CTV volumes (CTV_70 Gy and CTV_56 Gy). VMAT and proton plans were compared in terms of OAR doses and mean body dose only. Homogeneity Indices were compared among IMPT plans in addition to OAR doses. The Wilcoxon signed‐rank test was used to evaluate statistical differences between evaluation metrics for VMAT plans and all proton plan types.ResultsOAR dose metrics were improved by 2% to 30% from CPB plans to LPB or LPMB plans. Compared to photon VMAT plans, all OAR doses except for mandible dose metrics were improved by 2% to 53% for all proton plans. The mean body dose was also improved by 7.5% from CPB to LPB and by 10.8% from CPB to LPMB. In addition, the mean body dose was also improved by 44% from VMAT to CPB, by 48% from VMAT to LPB, and by 50% from VMAT to LPMB plans. Compared to CPB plans, HI was significantly better (p < 0.05) for the LPB and LPMB plans. HI also improved considerably from VMAT to CPB, LPB, and LPMB. For both CTV_70 Gy and CTV_56 Gy, average robust evaluation across all worst‐case scenarios was slightly better for CPB plans, with an average of V95%Rx of the CTV_70 Gy of 97.6% ± 1.22%, followed by 97.2% ± 1.31% and 97.2% ± 1.35% for LPB and LPMB plans, respectively. Robustness for CTV_56 Gy showed comparable robustness across all proton plan types, with an average V95%Rx of 97.4% ± 0.87% for CPB, 97.4% ± 1.21%, and 97.5% ± 1.08% for CPB, LPB, and LPMB plans, respectively.ConclusionWith decreased spot size, the LPB and LPMB are excellent alternatives to VMAT and CPB therapy and can significantly reduce the dose to normal tissue.

Simple template-based optimization for pediatric total lymphoid irradiation (TLI) radiotherapy treatments

IntroductionDue to its spherical surface, scalp angiosarcoma requires careful consideration for radiation therapy planning and dose delivery. Herein, we investigated whether volumetric modulated arc therapy (VMAT) is superior to intensity modulated radiation therapy (IMRT) in terms of the plan quality and delivery time.MethodsThree different coplanar treatment plans were created for four patients, comprising a two‐arc VMAT plan as well as 5‐field and 9‐field IMRT plans with 6 MV beams. The X‐ray Voxel Monte Carlo algorithm was employed for dose calculation. A radiation therapy dose of 60 Gy was prescribed to the planning target volume (PTV) in 30 fractions. The homogeneity indexes (HIs) and conformity indexes (CIs) of the PTV, organs at risk (OARs) doses and delivery times were calculated and compared.ResultsFor the VMAT, 5‐field and 9‐field IMRT plans, the mean HIs were 0.14, 0.16 and 0.15; CIs100% were 0.63, 0.61 and 0.64; CIs98% were 0.72, 0.66 and 0.70 and CIs95% were 0.74, 0.67 and 0.71 respectively. All mean dose parameters of the VMAT and 9‐field IMRT plans for the brain were equal to or lower than those of the 5‐field IMRT plan. For the 5‐field IMRT plan, the dose constraints for the left lens were not satisfied in two patients. The mean delivery times were 3.3, 11.1 and 14.7 min for the VMAT, 5‐field and 9‐field IMRT plans respectively.ConclusionThe VMAT plan quality is comparable to that of 9‐field IMRT, with a reduced delivery time. Therefore, VMAT represents a valuable, sophisticated irradiation technique for treating scalp angiosarcoma.

Intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) are the main radiotherapy techniques for treating and managing rectal cancer. Collimator rotation is one of the crucial parameters in radiotherapy planning, and its alteration can cause dosimetric variations. This study assessed the effect of collimator rotation on the dosimetric results of various IMRT and VMAT plans for rectal cancer. Computed tomography (CT) images of 20 male patients with rectal cancer were utilized for IMRT and VMAT treatment planning with various collimator angles. Nine different IMRT techniques (5, 7, and 9 coplanar fields with collimator angles of 0°, 45°, and 90°) and six different VMAT techniques (1 and 2 full coplanar arcs with collimator angles of 0°, 45°, and 90°) were planned for each patient. The dosimetric results of various treatment techniques for target tissue (conformity index [CI] and homogeneity index [HI]) and organs at risk (OARs) sparing (parameters obtained from OARs dose-volume histograms [DVH]) as well as radiobiological findings were analyzed and compared. The 7-fields IMRT technique demonstrated lower bladder doses (V40Gy, V45Gy), unaffected by collimator rotation. The 9-fields IMRT and 2-arcs VMAT (excluding the 90-degree collimator) had the lowest V35Gy and V45Gy. A 90-degree collimator rotation in 2-arcs VMAT significantly increased small bowel and bladder V45Gy, femoral head doses, and HI values. Radiobiologically, the 90-degree rotation had adverse effects on small bowel NTCP (normal tissue complication probability). No superiority was found for a 45-degree collimator rotation over 0 or 30 degrees in VMAT techniques. Collimator rotation had minimal impact on dosimetric parameters in IMRT planning but is significant in VMAT techniques. A 90-degree rotation in VMAT, particularly in a 2-full arc technique, adversely affects PTV homogeneity index, bladder dose, and small bowel NTCP. Other evaluated collimator angles did not significantly affect VMAT dosimetrical or radiobiological outcomes.

This study investigated the dose-volume dependences of planning target volume (PTV) and organs-at-risk (OARs) on prostate volumetric modulated arc therapy (VMAT), when the collimator angle is varied. Single-arc VMAT plans at different collimator angles (0°, 15°, 30°, 45°, 60°, 75° and 90°) were created systematically based on a Harold pelvis phantom and the 6 MV photon beams. The conformity index (CI), homogeneity index (HI), gradient index (GI), machine monitor units (MUs), dose-volume histogram and mean and maximum dose of the PTV were calculated and analyzed (Table 1). The dose-volume histogram and mean and maximum doses of OARs such as bladder, rectum and femoral heads for different collimator angles were determined from the plans (Table 2). From our dosimetric results, there was no significant difference, according to the planned dose-volume evaluation criteria, found in the VMAT optimizations for all studied collimator angles. However, a higher CI (0.53) and lower HI (0.064) resulted from the 45° collimator angle. The 15° collimator angle provided a lower value of HI similar to the 45° angle while collimator angles of 75° and 90° were found to be good for rectum sparing. In addition, collimator angles of 75° and 30° worked well for sparing the right and left femur. The PTV dose coverage for each plan was comparatively independent of the collimator angle. The dosimetric results in this study provide support and guidance in the collimator angle selection for prostate VMAT to improve the PTV coverage and OARs sparing.

BackgroundThe advent of volumetric modulated arc therapy (VMAT) in radiotherapy has made it one of the most commonly used techniques in clinical practice. VMAT is the delivery of intensity modulated radiation therapy (IMRT) while the gantry is in motion, and existing literature has shown it has decreased treatment delivery times and the number of monitor units without sacrificing coverage. It has previously been shown that for IMRT, multi‐leaf collimators (MLC) with narrower leaf widths produce demonstrably higher treatment plan quality. However, as VMAT is rapidly becoming the global standard, this needs to be re‐evaluated, especially in a global context. This study assesses the impact of MLC leaf width on VMAT treatment plans and asks whether reducing the number of leaves‐ and thus increasing leaf width‐ provides clinically acceptable treatment plans using VMAT delivery.Material & methodsUsing Varian Eclipse, 51 anonymised patients with prostate, lung, liver, colorectal, or cervical cancer had VMAT treatment plans generated. Treatment plans were generated for MLC leaf widths of 2.5, 5 and 10 mm. Plans were compared using D2[%], D50[%], and D98[%], homogeneity index (HI), conformity index (CI), average leaf pair opening (ALPO), modulation factor (MF) and Estimated Treatment Delivery Time.ResultsThe dose to the target structures showed little difference between 2.5 and 5 mm MLC leaves, however 10 mm MLC provided 5% more median dose than the narrower leaf widths for D2[%] (p < 0.05) and D50[%] (p < 0.05). The average HI per leaf width was 0.0777 for 2.5 mm, 0.0752 for 5 mm, and 0.0890 for 10 mm. Organs At Risk (OAR) sparing was consistent between all leaf widths except at low dose percentages, where 10 mm MLC delivered an extra dose to the bladder (p < 0.05) and the heart (p < 0.05). The average ALPO was 38.0 mm for 2.5 mm, 34.1 mm for 5 mm, and 32.7 mm for 10 mm leaf width. 10 mm MLC leaves traveled a shorter distance from the center (p < 0.05). The median MF was 336 MU/Gy for 2.5 mm, 344 MU/Gy for 5 mm, and 384 MU/Gy for 10 mm. There were no differences in estimated treatment delivery time between MLC leaf width.ConclusionThere is little difference in treatment quality between any of the investigated MLC leaf widths. This work demonstrates that for VMAT treatments, wider MLC leaf widths can still deliver acceptable treatment plans. This finding has potential implications for radiotherapy in low‐ and middle‐income countries and low socio‐economic or rural areas where a focus on MLC robustness and LINAC up‐time is paramount.

Pulmonary Toxicity of Chemotherapy

In the Treatment Planning System (TPS), when the patient is irradiated with one direction of radiation, the Organ At Risk (OAR) around the Planning Target Volume (PTV) receives a high dose and receives an uneven dose. By considering the dose distribution on the PTV and OAR, it is necessary to determine the appropriate radiation direction on the TPS. This study compares the radiation dose achieved by the PTV and OAR of breast cancer patients with radiation directions 3, 5, 7, and 9 on the TPS Intensity Modulated Radiation Therapy (IMRT). This study used 16 retrospective data sets of breast cancer patients consisting of 8 patient data without breast surgery and 8 post-breast surgery data. The data obtained in this study were V95, D2%, D50%, and D98% from the DVH graph. Data analysis was carried out by comparing the average values of the Conformity Index (CI) and Homogeneity Index (HI) and the average dose received by the OAR in four variations of radiation directions. In breast cancer patients without surgery, better CI values were obtained in 9 radiation directions with an average CI = 0.980424; the lowest CI value = 0.957054 and the highest CI value = 0.998541. While in post-operative breast cancer patients, better CI values were obtained in 7 radiation directions with an average CI = 0.983920; the lowest CI value = 0.928394 and the highest CI value = 0.999994. In breast cancer patients without surgery, better HI values were obtained in 9 radiation directions with an average HI = 0.153551; the lowest HI value = 0.086190, and the highest HI value = 0.209303. While in post-operative breast cancer patients, better HI values were obtained in 7 radiation directions with an average HI = 0.121777; the lowest HI value = 0.081539, and the highest HI value 0.158169. The mean dose received by OAR of breast cancer patients without surgery was achieved in 9 radiation directions. In contrast, in post-operative breast cancer patients, it was completed in 5, 7, and 9 radiation directions. Reviewed from the conformity factor (CI) and uniformity (HI), and the mean dose received by breast cancer patients, it can be concluded that planning using IMRT with 9 radiation directions is optimal for use in breast cancer patients without surgery. While radiation with 7 directions is optimal for use in post-operative breast cancer patients. With higher conformity, lower homogeneity, and PTV receiving the maximum dose, the dose received by OAR can be minimized.