Knowledge-based automatic optimization of adaptive early-regression-guided VMAT for rectal cancer

PurposeTo implement a knowledge-based (KB) optimization strategy to our adaptive (ART) early-regression guided boosting technique in neo-adjuvant radio-chemotherapy for rectal cancer.Material and methodsThe protocol consists of a first phase delivering 27.6 Gy to tumor/lymph-nodes (2.3 Gy/fr-PTV₁), followed by the ART phase concomitantly delivering 18.6 Gy (3.1 Gy/fr) and 13.8 Gy (2.3 Gy/fr) to the residual tumor (PTV_ART) and to PTV₁ respectively. PTV_ART is obtained by expanding the residual GTV, as visible on MRI at fraction 9. Forty plans were used to generate a KB-model for the first phase using the RapidPlan tool. Instead of building a new model, a robust strategy scaling the KB-model to the ART phase was applied. Both internal and external validation were performed for both phases: all automatic plans (RP) were compared in terms of OARs/PTVs parameters against the original plans (RA).ResultsThe resulting automatic plans were generally better than or equivalent to clinical plans. Of note, V_30Gy and V_40Gy were significantly improved in RP plans for bladder and bowel; gEUD analysis showed improvement for KB-modality for all OARs, up to 3 Gy for the bowel.ConclusionsThe KB-model generated for the first phase was robust and it was also efficiently adapted to the ART phase. The performance of automatically generated plans were slightly better than the corresponding manual plans for both phases.     

Dosimetric comparison of RapidPlan and manually optimized plans in volumetric modulated arc therapy for prostate cancer

PurposeThis study evaluated whether RapidPlan based plans (RP plans) created by a single optimization, are usable in volumetric modulated arc therapy (VMAT) for patients with prostate cancer.MethodsWe used 51 previously administered VMAT plans to train a RP model. Thirty RP plans were created by a single optimization without planner intervention during optimization. Differences between RP plans and clinical manual optimization (CMO) plans created by an experienced planner for the same patients were analyzed (Wilcoxon tests) in terms of homogeneity index (HI), conformation number (CN), D_95%, and D_2% to planning target volume (PTV), mean dose, V_50Gy, V_70Gy, V_75Gy, and V_78Gy to rectum and bladder, monitor unit (MU), and multi-leaf collimator (MLC) sequence complexity.ResultsRP and CMO values for PTV D_95%, PTV D_2%, HI, and CN were significantly similar (p < 0.05 for all). RP mean dose, V_50Gy, and V_70Gy to rectum were superior or comparable to CMO values; RP V_75Gy and V_78Gy were higher than in CMO plans (p < 0.05). RP bladder dose-volume parameter values (except V_78Gy) were lower than in CMO plans (p < 0.05). MU values were RP: 730 ± 55 MU and CMO: 580 ± 37 MU (p < 0.05); and MLC sequence complexity scores were RP: 0.25 ± 0.02 and CMO: 0.35 ± 0.03 (p < 0.05).ConclusionsRP plans created by a single optimization were clinically acceptable in VMAT for patient with prostate cancer. Our simple model could reduce optimization time, independently of planner’s skill and knowledge.     

Automatic VMAT planning for post-operative prostate cancer cases using particle swarm optimization: A proof of concept study

ObjectiveTo investigate the potential of Particle Swarm Optimization (PSO) for fully automatic VMAT radiotherapy (RT) treatment planning.Material and MethodsIn PSO a solution space of planning constraints is searched for the best possible RT plan in an iterative, statistical method, optimizing a population of candidate solutions. To identify the best candidate solution and for final evaluation a plan quality score (PQS), based on dose volume histogram (DVH) parameters, was introduced.Automatic PSO-based RT planning was used for N = 10 postoperative prostate cancer cases, retrospectively taken from our clinical database, with a prescribed dose of EUD = 66 Gy in addition to two constraints for rectum and one for bladder. Resulting PSO-based plans were compared dosimetrically to manually generated VMAT plans.ResultsPSO successfully proposed treatment plans comparable to manually optimized ones in 9/10 cases. The median (range) PTV EUD was 65.4 Gy (64.7–66.0) for manual and 65.3 Gy (62.5–65.5) for PSO plans, respectively. However PSO plans achieved significantly lower doses in rectum D_2% 67.0 Gy (66.5–67.5) vs. 66.1 Gy (64.7–66.5, p = 0.016). All other evaluated parameters (PTV D_98% and D_2%, rectum V_40Gy and V_60Gy, bladder D_2% and V_60Gy) were comparable in both plans. Manual plans had lower PQS compared to PSO plans with −0.82 (−16.43–1.08) vs. 0.91 (−5.98–6.25).ConclusionPSO allows for fully automatic generation of VMAT plans with plan quality comparable to manually optimized plans. However, before clinical implementation further research is needed concerning further adaptation of PSO-specific parameters and the refinement of the PQS.     

Image-guided volumetric arc radiotherapy of pancreatic cancer with simultaneous integrated boost: Optimization strategies and dosimetric results

PurposeTo introduce volumetric modulated arc therapy treatments (VMAT) with simultaneous integrated boost (SIB) for pancreatic cancer and describe dosimetric results on a large patient series.Methods and materials45 patients with pancreatic malignancies were treated with 18 MV single-arc VMAT. Image guidance was performed with daily online kilo-volt cone-beam computed tomography (CBCT). The conformity index (CI) and homogeneity index (HI) to the target volumes, PTV_45Gy and PTV_54Gy, and dose–volume indices to OARs from the QUANTEC task group were reported. The risk of clinical nephritis was evaluated using normal tissue complication probability (NTCP). Treatments were verified in-phantom with the Delta4 system.ResultsAverage CI was 1.06 with 95% confidence intervals (95% CI) of 0.97–1.22 for PTV_45Gy and 1.17 (0.66–1.61) for PTV_54Gy. HI of PTV_54Gy was 1.06 (1.04–1.10). OAR constraints were achieved in all patients, except for kidneys V_12Gy of 48 (35.4–72.3)%. NTCP of the kidneys was 0.98 (0.6–1.7)%. Kidneys V_12Gy and V_20Gy were inversely related to PTV_54Gy CI and maximum dose. All in-phantom tests had gamma pass rates exceeding 95% with global 3% dose difference and 3 mm distance to agreement. Patient shifts measured with CBCT had 95% CI of −0.8, +0.8 in the RL, −0.7, +0.8 in the SI, and −0.8, +0.7 cm in the AP directions.ConclusionsDosimetric results of VMAT were excellent on PTVs and organs at risk. The kidneys represent the dose-limiting organ at risk for this technique. NTCP indicates that this technique is safe from radiation-induced side effects to the kidneys.     

Assessment of monitor unit limiting strategy using volumetric modulated arc therapy for cancer of hypopharynx

PurposeTo quantify relative merit of MU deprived plans against freely optimized plans in terms of plan quality and report changes induced by progressive resolution optimizer algorithm (PRO3) to the dynamic parameters of RapidArc.Materials and methodsTen cases of carcinoma hypopharynx were retrospectively planned in three phases without using MU tool. Replicas of these baseline plans were reoptimized using “Intermediate dose” feature and “MU tool” to reduce MUs by 20%, 35%, and 50%. Overall quality indices for target and OAR, integral dose, dose-volume spread were assessed. All plans were appraised for changes induced in RapidArc dynamic parameters and pre-treatment quality assurance (QA).ResultsWith increasing MU reduction strength (MURS), MU/Gy values reduced, for all phases with an overall range of 8.6–34.7%; mean dose rate decreased among plans of each phase, phase3 plans recorded greater reductions. MURS20% showed good trade-off between MUs and plan quality. Dose-volume spread below 5 Gy was higher for baseline plans while lower between 20 and 35 Gy. Integral dose was lower for MURS0%, not exceeding 1.0%, compared against restrained plans. Mean leaf aperture and control point areas increased systematically, correlated negatively with increasing MURS. Absolute delta dose rate variations were least for MURS0%. MU deprived plans exhibited GAI (>93%), better than MURS0% plans.ConclusionBaseline plans are superior to MU restrained plans. However, MURS20% offers equivalent and acceptable plan quality with mileage of MUs, improved GAI for complex cases. MU tool may be adopted to tailor treatment plans using PRO3.     

Performance of the eclipse monitor unit objective tool utilizing volumetric modulated arc therapy for rectal cancer

AimTo assess the performance of the monitor unit (MU) Objective tool in Eclipse treatment planning system (TPS) utilizing volumetric modulated arc therapy (VMAT) for rectal cancer.BackgroundEclipse VMAT planning module includes a tool to control the number of MUs delivered: the MU Objective tool. This tool could be utilized to reduce the total number of MUs in rectal cancer treatments.Materials and methods20 rectal cancer patients were retrospectively studied using VMAT and the MU Objective tool. The baseline plan for each patient was selected as the one with no usage of the MU Objective tool. The number of MUs of this plan was set to be the reference number of MUs (MU_ref). Five plans were re-optimized for each patient only varying the Max MU parameter. The selected values were 30%, 60%, 90%, 120% and 150% of MU_ref for each patient. Differences with respect to the baseline plan were evaluated regarding MU number and parameters for PTVs coverage evaluation, PTVs homogeneity and OARs doses assessment. A two-tailed, paired-samples t-test was used to quantify these differences.ResultsAverage relative differences in MU number obtained was 10% for Max MU values of 30% and 60% of MU_ref, respectively (p < 0.03). PTVs coverage and homogeneity were not compromised and discrepancies obtained with respect to baseline plans were not significant. Furthermore, maximum OARs doses deviations were also not significant.ConclusionsA 10% reduction in the MU number could be obtained without an alteration of PTV coverage and OARs doses for rectal cancer.     

Dosimetric study of a hybrid plan technique for external beam radiotherapy in patients with cervical cancer

The aim of this study was to investigate the effect of a hybrid technique which results from combining intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) for the treatment of cervical cancer patients. Plans made with the hybrid technique and pure IMRT and VMAT were retrospectively compared in 20 patients with cervical cancer at different stages. All plans were made using the same contours based on the original computed tomography (CT) scans. Conformity (CI) and homogeneity (HI) indices of the planning target volumes (PTVs) were calculated for each technique in order to evaluate plan quality. All techniques were compared in terms of dose to organs at risk (OARs), number of monitor units (MUs) and treatment time. It turned out that plans made with the hybrid technique had improved dose conformity and homogeneity compared to plans made only with IMRT and VMAT (p < 0.001). Regarding the OARs, the maximum dose (D_max) delivered to the bladder, rectum and femoral heads was lower for the hybrid plans compared to the IMRT and VMAT plans (p < 0.001). The volumes irradiated to doses of 50 Gy (V_50Gy) for rectum, bladder and bowel were lower for the hybrid plans (p < 0.001, p = 0.002). Furthermore, the treatment time and MU values for the hybrid plans were found to be between of the values for the IMRT and VMAT plans. It is concluded that, as compared to IMRT and VMAT plans, the hybrid plan technique allowed a better conformity and homogeneity for the dose distribution in the PTV and a dose reduction to the OARs.

     

Efficacy of tangential irradiation with volumetric modulated arc therapy on scalp angiosarcoma using medical linac

PurposeTo increase the superficial dose and reduce the brain dose for radiotherapy of scalp angiosarcoma, we propose a novel irradiation technique of tangential irradiation volumetric modulated arc therapy (TI-VMAT).MethodsTI-VMAT and the conventional VMAT treatment plans for thirteen scalp angiosarcoma patients were created with a prescribed dose of 70 Gy. Each treatment was normalized to cover 95% of the planning target volume (PTV) with its prescribed dose. To realize TI-VMAT, an avoidance structure (AS) function was applied. AS was defined as a contour subtracted PTV by a certain space from the brain contour. TI-VMAT treatment plans for six different spaces between PTV and AS were developed and compared with the conventional VMAT treatment plan with respect to the following dosimetric parameters: homogeneity index (HI) and conformity index (CI) of the PTV, mean brain dose, and brain volume irradiated with 20% (V_20% [cc]), 40% (V_40% [cc]), 60% (V_60% [cc]), 80% (V_80% [cc]), and 100% (V_100% [cc]) of the prescribed dose.ResultsHI and CI were comparable between TI-VMAT and the conventional VMAT, the mean brain dose for TI-VMAT with AS defined by a space of 2.0 cm and jaw tracking was 14.27 Gy, which was significantly lower than that for the conventional VMAT (21.20 Gy). In addition, dosimetric parameters such as V_20% [cc] were significantly suppressed compared to those for high doses.ConclusionOur proposed irradiation technique TI-VMAT shows the potential to reduce radiation doses in the brain with maintaining higher dose coverage on the PTV.     

A study on conventional IMRT and RapidArc treatment planning techniques for head and neck cancers

AimTo evaluate the performance of volumetric arc modulation with RapidArc against conventional IMRT for head and neck cancers.BackgroundRapidArc is a novel technique that has recently been made available for clinical use. Planning study was done for volumetric arc modulation with RapidArc against conventional IMRT for head and neck cancers.Materials and methodsTen patients with advanced tumors of the nasopharynx, oropharynx, and hypopharynx were selected for the planning comparison study. PTV was delineated for two different dose levels and planning was done by means of simultaneously integrated boost technique. A total dose of 70 Gy was delivered to the boost volume (PTV boost) and 57.7 Gy to the elective PTV (PTV elective) in 35 equal treatment fractions. PTV boost consisted of the gross tumor volume and lymph nodes containing visible macroscopic tumor or biopsy-proven positive lymph nodes, whereas the PTV elective consisted of elective nodal regions. Planning was done for IMRT using 9 fields and RapidArc with single arc, double arc. Beam was equally placed for IMRT plans. Single arc RapidArc plan utilizes full 360° gantry rotation and double arc consists of 2 co-planar arcs of 360° in clockwise and counter clockwise direction. Collimator was rotated from 35 to 45° to cover the entire tumor, which reduced the tongue and groove effect during gantry rotation. All plans were generated with 6 MV X-rays for CLINAC 2100 Linear Accelerator. Calculations were done in the Eclipse treatment planning system (version 8.6) using the AAA algorithm.ResultsDouble arc plans show superior dose homogeneity in PTV compared to a single arc and IMRT 9 field technique. Target coverage was almost similar in all the techniques. The sparing of spinal cord in terms of the maximum dose was better in the double arc technique by 4.5% when compared to the IMRT 9 field and single arc techniques. For healthy tissue, no significant changes were observed between the plans in terms of the mean dose and integral dose. But RapidArc plans showed a reduction in the volume of the healthy tissue irradiated at V_15 Gy (5.81% for single arc and 4.69% for double arc) and V_20 Gy (7.55% for single arc and 5.89% for double arc) dose levels when compared to the 9-Field IMRT technique. For brain stem, maximum dose was similar in all the techniques. The average MU (±SD) needed to deliver the dose of 200 cGy per fraction was 474 ± 80 MU and 447 ± 45 MU for double arc and single arc as against 948 ± 162 MU for the 9-Field IMRT plan. A considerable reduction in maximum dose to the mandible by 6.05% was observed with double arc plan. Double arc shows a reduction in the parotid mean dose when compared with single arc and IMRT plans.ConclusionRapidArc using double arc provided a significant sparing of OARs and healthy tissue without compromising target coverage compared to IMRT. The main disadvantage with IMRT observed was higher monitor units and longer treatment time.     

Dosimetric accuracy of three dose calculation algorithms for radiation therapy of in situ non-small cell lung carcinoma

BackgroundStudy determines differences in calculated dose distributions for non-small cell lung carcinoma (NSC LC) patients. NSC LC cases were investigated, being the most common lung cancer treated by radiotherapy in our clinical practice.Materials and methodsA retrospective study of 15 NSCLC patient dose distributions originally calculated using standard superposition (SS) and recalculated using collapsed cone (CC ) and Monte Carlo (MC) based algorithm expressed as dose to medium in medium (MCD_m) and dose to water in medium (MCD_w,) was performed so that prescribed dose covers at least 99% of the gross target volume (GTV). Statistical analysis was performed for differences of conformity index (CI), heterogeneity index (HI), gradient index (GI), dose delivered to 2% of the volume (D_2%), mean dose (D_mean) and percentage of volumes covered by prescribed dose (V_70Gy). For organs at risk (OARs), D_mean and percentage of volume receiving 20 Gy and 5Gy (V_20Gy, V_5Gy) were analysed.ResultsStatistically significant difference for GTVs was observed between MCD_w and SS algorithm in mean dose only. For planning target volumes (PTVs), statistically significant differences were observed in prescribed dose coverage for CC, MCD_m and MCD_w. The differences in mean CI value for the CC algorithm and mean HI value for MCD_m and MCD_w were statistically significant. There is a statistically significant difference in the number of MUs for MCD_m and MCD_w compared to SS.ConclusionAll investigated algorithms succeed in managing the restrictive conditions of the clinical goals. This study shows the drawbacks of the CC algorithm compared to other algorithms used.     

Adaptive volumetric modulated arc treatment planning for esophageal cancers using cone beam computed tomography

PurposeTo assess the potential of cone beam CT (CBCT) derived adaptive RapidArc treatment for esophageal cancers in reducing the dose to organs at risk (OAR).Methods and materialsTen patients with esophageal cancer were CT scanned in free breathing pattern. The PTV is generated by adding a 3D margin of 1 cm to the CTV as per ICRU 62 recommendations. The double arc RapidArc plan (Clin_RA) was generated for the PTV. Patients were setup using kV orthogonal images and kV-CBCT scan was acquired daily during first week of therapy, then weekly. These images were exported to the Eclipse TPS. The adaptive CTV which includes tumor and involved nodes was delineated in each CBCT image set for the length of the PTV. The composite CTV from first week CBCT was generated using Boolean union operator and 5 mm margin was added circumferentially to generate adaptive PTV (PTV1). Adaptive RapidArc plan (Adap_RA) was generated. NTCP and DVH of the OARs of the two plans were compared. Similarly, PTV2 was generated from weekly CBCT. PTV2 was evaluated for the coverage of 95% isodose of Adap_RA plan.ResultsThe PTV1 and PTV2 volumes covered by 95% isodose in adaptive plans were 93.51 ± 1.17% and 94.59 ± 1.43% respectively. The lung V_10Gy, V_20Gy and mean dose in Adap_RA plan was reduced by 17.43% (p = 0.0012), 34.64% (p = 0.0019) and 16.50% (p = 0.0002) respectively compared to Clin_RA. The Adap_RA plan reduces the heart D_35% and mean dose by 17.35% (p = 0.0011) and 17.16% (p = 0.0012). No significant reduction in spinal cord and liver doses were observed. NTCP for the lung (0.42% vs. 0.08%) and heart (1.39% vs. 0.090%) was reduced significantly in adaptive plans.ConclusionThe adaptive re-planning strategy based on the first week CBCT dataset significantly reduces the doses and NTCP to OARs.     

Tracking,gating, free-breathing,which technique to use for lung stereotactic treatments? A dosimetric comparison

BackgroundThe management of breath-induced tumor motion is a major challenge for lung stereotactic body radiation therapy (SBRT). Three techniques are currently available for these treatments: tracking (T), gating (G) and free-breathing (FB).AimTo evaluate the dosimetric differences between these three treatment techniques for lung SBRT.Materials and methodsPretreatment 4DCT data were acquired for 10 patients and sorted into 10 phases of a breathing cycle, such as 0% and 50% phases defined respectively as the inhalation and exhalation maximum. GTV_ph, PTV_ph (=GTV_ph + 3 mm) and the ipsilateral lung were contoured on each phase.For the tracking technique, 9 fixed fields were adjusted to each PTV_ph for the 10 phases. The gating technique was studied with 3 exhalation phases (40%, 50% and 60%). For the free-breathing technique, ITV_FB was created from a sum of all GTV_ph and a 3 mm margin was added to define a PTV_FB. Fields were adjusted to PTV_FB and dose distributions were calculated on the average intensity projection (AIP) CT. Then, the beam arrangement with the same monitor units was planned on each CT phase.The 3 modalities were evaluated using DVHs of each GTV_ph, the homogeneity index and the volume of the ipsilateral lung receiving 20 Gy (V_20Gy).ResultsThe FB system improved the target coverage by increasing D_mean (75.87_(T)–76.08_(G)–77.49_(FB)Gy). Target coverage was slightly more homogeneous, too (HI: 0.17_{(T and G)}–0.15_(FB)). But the lung was better protected with the tracking system (V_20Gy: 3.82_(T)–4.96_(G)–6.34_(FB)%).ConclusionsEvery technique provides plans with a good target coverage and lung protection. While irradiation with free-breathing increases doses to GTV, irradiation with the tracking technique spares better the lung but can dramatically increase the treatment complexity.     

Dose-escalated volumetric modulated arc therapy for total marrow irradiation: A feasibility dosimetric study with 4DCT planning and simultaneous integrated boost

PurposeTo evaluate the planning feasibility of dose-escalated total marrow irradiation (TMI) with simultaneous integrated boost (SIB) to the active bone marrow (ABM) using volumetric modulated arc therapy (VMAT), and to assess the impact of using planning organs at risk (OAR) volumes (PRV) accounting for breathing motion in the optimization.MethodsFive patients underwent whole-body CT and thoraco-abdominal 4DCT. A planning target volume (PTV) including all bones and ABM was contoured on each whole-body CT. PRV of selected OAR (liver, heart, kidneys, lungs, spleen, stomach) were determined with 4DCT. Planning consisted of 9–10 full 6 MV photon VMAT arcs. Four plans were created for each patient with 12 Gy prescribed to the PTV, with or without an additional 4 Gy SIB to the ABM. Planning dose constraints were set on the OAR or on the PRV. Planning objective was a PTV D_mean < 110% of the prescribed dose, a PTV V_110% < 50%, and OAR D_mean ≤ 50–60%.ResultsPTV D_mean < 110% was accomplished for most plans (n = 18/20), while all achieved V_110%<50%. SIB plans succeeded to optimally cover the boost volume (median ABM D_mean = 16.3 Gy) and resulted in similar OAR sparing compared to plans without SIB (median OAR D_mean = 40–54% of the ABM prescribed dose). No statistically significant differences between plans optimized with constraints on OAR or PRV were found.ConclusionsAdding a 4 Gy SIB to the ABM for TMI is feasible with VMAT technique, and results in OAR sparing similar to plans without SIB. Setting dose constraints on PRV does not impair PTV dosimetric parameters.     

Patient-specific quality assurance and plan dose errors on breast intensity-modulated proton therapy

PurposeTo investigate, in proton therapy, whether the Gamma passing rate (GPR) is related to the patient dose error and whether MU scaling can improve dose accuracy.MethodsAmong 20 consecutively treated breast patients selected for analysis, two IMPT plans were retrospectively generated: (1) the pencil-beam (PB) plan and (2) the Monte Carlo (MC) plan. Patient-specific QA was performed. A 3%/3-mm Gamma analysis was conducted to compare the TPS-calculated PB algorithm dose distribution with the measured 2D dose. Dose errors were compared between the plans that passed the Gamma testing and those that failed. The MU was then scaled to obtain a better GPR. MU-scaled PB plan dose errors were compared to the original PB plan.ResultsOf the 20 PB plans, 8 were passed Gamma testing (G_pass_group) and 12 failed (G_fail_group). Surprisingly, the G_pass_group had a greater dose error than the G_fail_group. The median (range) of the PTV DVH RMSE and PTV ΔDmean were 1.36 (1.00–1.91) Gy vs 1.18 (1.02–1.80) Gy and 1.23 (0.92–1.71) Gy vs 1.10 (0.87–1.49) Gy for the G_pass_group and the G_fail_group, respectively. MU scaling reduced overall dose error. However, for PTV D99 and D95, MU scaling worsened some cases.ConclusionFor breast IMPT, the PB plans that passed the Gamma testing did not show smaller dose errors compared to the plans that failed. For individual plans, the MU scaling technique leads to overall smaller dose errors. However, we do not suggest use of the MU scaling technique to replace the MC plans when the MC algorithm is available.     

Dosimetric comparison of normal breathing and deep inspiration breath hold technique for synchronous bilateral breast cancer using 6MV flattened beam and flattening filter free beam

BackgroundThe present study was to investigate the usefulness of deep inspiration breath hold (DIBH) in bilateral breast patients using 6MV flattened beam (FB) and flattening filter free beam (FFFB).Materials and methodsTwenty bilateral breast cancer patients were simulated, using left breast patients treated with DIBH technique. CT scans were performed in the normal breathing (NB) and DIBH method. Three-dimensional conformal radiotherapy (3DCRT) and volumetric arc therapy (VMAT) plans were generated.ResultsIn our study the best organ at risk (OAR) sparing is achieved in the 3DCRT DIBH plan with adequate PTV coverage (V₉₅ ≥ 47.5 Gy) as compared to 6MV FB and FFFB VMAT DIBH plans. The DIBH scan plan reduces the heart mean dose significantly at the rate of 49% in 3DCRT (p = 0.00) and 22% in VMAT (p = 0.010). Similarly, the DIBH scan plan produces lesser common lung mean dose of 18% in 3DCRT (p = 0.011) and 8% in VMAT (0.007) as compared to the NB scan. The conformity index is much better in VMAT FB (1.04 ± 0.04 vs. 1.04 ± 0.05), p =1.00 and VMAT FFFB (1.04 ± 0.05 vs. 1 ± 0.24, p = 0.345) plans as compared to 3DCRT (1.63 ± 0.2 vs. 1.47 ± 0.28, p = 0.002). The homogeneity index of all the plans is less than 0.15. The global dmax is more in VMAT FFFB DIBH plan (113.7%). The maximum MU noted in the NB scan plan (478 vs. 477MU, 1366 vs. 1299 MU and 1853 vs. 1788 MU for 3DCRT, VMAT FB and VMAT FFFB technique as compared to DIBH scan.ConclusionWe recommend that the use of DIBH techniques for bilateral breast cancer patients significantly reduces the radiation doses to OARs in both 3DCRT and VMAT plans.     

Dosimetric impact of Acuros XB on cervix radiotherapy using RapidArc technique: a dosimetric study

BackgroundAcuros XB (AXB) may predict better rectal toxicities and treatment outcomes in cervix carcinoma. The aim of the study was to quantify the potential impact of AXB computations on the cervix radiotherapy using the RapidArc (RA ) technique as compared to anisotropic analytical algorithm (AA) computations.Materials and methodsA cohort of 30 patients previously cared for cervix carcinoma (stages II–IIIB) was selected for the present analysis. The RA plans were computed using AA and AXB dose computation engines under identical beam setup and MLC pattern.ResultsThere was no significant (p > 0.05) difference in D_95% and D_98% to the planning target volume (PTV); moreover, a significant (p < 0.05) rise was noticed for mean dose to the PTV (0.26%), D_50% (0.26%), D_2% (0.80%) and V_110% (44.24%) for AXB computation as compared to AA computations. Further, AXB estimated a significantly (p < 0.05) lower value for maximum and minimum dose to the PTV. Additionally, there was a significant (p < 0.05) reduction observed in mean dose to organs at risk (OARs) for AXB computation as compared to AA, though the reduction in mean dose was non-significant (p > 0.05) for the rectum. The maximum difference observed was 4.78% for the rectum V_50Gy, 1.72%, 1.15% in mean dose and 2.22%, 1.48% in D_2% of the left femur and right femur, respectively, between AA and AXB dose estimations.ConclusionFor similar target coverage, there were significant differences observed between the AAA and AXB computations. AA underestimates the V_50Gy of the rectum and overestimates the mean dose and D_2% for femoral heads as compared to AXB. Therefore, the use of AXB in the case of cervix carcinoma may predict better rectal toxicities and treatment outcomes in cervix carcinoma using the RA technique.     

Plan quality and robustness in field junction region for craniospinal irradiation with VMAT

PurposeTo propose a “staggered overlap” technique in volumetric modulated arc therapy (VMAT) for craniospinal irradiation (CSI) and compare the dose distribution and plan robustness with “overlap” technique and “gradient optimization” approach.Methods and Materials6 patients previously treated in our clinic were retrospectively selected. 9 VMAT plans of each patient were optimized with “staggered overlap”, “overlap” and “gradient optimization” in overlapping region of 3 cm, 6 cm, and 9 cm separately. For the “staggered overlap” plan, adjacent field sets were intentionally overlapped by staggering field edges in an appropriate step size to avoid sharp dose gradient. Evaluation metrics including V_95%, D_2%, D_98%, conformity number (CN) and homogeneity index (HI) were employed to evaluate the dose distribution. Moreover, shifts of the upper spinal field isocenter in each direction were performed to simulate junction errors for robustness analysis.ResultsThe CN and HI of VMAT plans with “staggered overlap” were 0.82 (0.811–0.822) and 0.113 (0.112–0.114), while they were 0.778 (0.776–0.782) and 0.131 (0.130–0.131) for plans with “gradient optimization”. In the robustness study, <3% dose deviations were found for 5 mm shifts in lateral and vertical directions with all techniques. In cranial-caudal direction, “overlap” technique created hot spots (D_2% > 170%) and cold spots (D_98% < 44%) in the junction region with 10 mm shifts. The dose deviations were decreased to 22% for plans with “staggered overlap” and 9 cm overlapping region.Conclusion“Staggered overlap” technique provides better plan quality as compared to “gradient optimization” approach and makes the plan more robust against junction errors as compared to “overlap” technique.     

Novel knowledge-based treatment planning model for hypofractionated radiotherapy of prostate cancer patients

PurposeTo demonstrate the strength of an innovative knowledge-based model-building method for radiotherapy planning using hypofractionated, multi-target prostate patients.Material and methodsAn initial RapidPlan model was trained using 48 patients who received 60 Gy to prostate (PTV60) and 44 Gy to pelvic nodes (PTV44) in 20 fractions. To improve the model's goodness-of-fit, an intermediate model was generated using the dose-volume histograms of best-spared organs-at-risk (OARs) of the initial model. Using the intermediate model and manual tweaking, all 48 cases were re-planned. The final model, trained using these re-plans, was validated on 50 additional patients. The validated final model was used to determine any planning advantage of using three arcs instead of two on 16 VMAT cases and tested on 25 additional cases to determine efficacy for single-PTV (PTV60-only) treatment planning.ResultsFor model validation, PTV V_95% of 99.9% was obtained by both clinical and knowledge-based planning. D_1% was lower for model plans: by 1.23 Gy (PTV60, CI = [1.00, 1.45]), and by 2.44 Gy (PTV44, CI = [1.72, 3.16]). OAR sparing was superior for knowledge-based planning: ΔD_mean = 3.70 Gy (bladder, CI = [2.83, 4.57]), and 3.22 Gy (rectum, CI = [2.48, 3.95]); ΔD_2% = 1.17 Gy (bowel bag, CI = [0.64, 1.69]), and 4.78 Gy (femoral heads, CI = [3.90, 5.66]). Using three arcs instead of two, improvements in OAR sparing and PTV coverage were statistically significant, but of magnitudes < 1 Gy. The model failed at reliable DVH predictions for single PTV plans.ConclusionsOur knowledge-based model delivers efficient, consistent plans with excellent PTV coverage and improved OAR sparing compared to clinical plans.     

The robustness of dual isocenter VMAT radiation therapy for bilateral lymph node positive breast cancer

PurposeTo investigate the use of dual isocenters for VMAT planning in patients with lymph node positive synchronous bilateral breast cancer (BBC) compared to a single isocenter option.MethodsTreatment plans of 11 patients with lymph node positive BBC were retrospectively analyzed using two different VMAT planning techniques: dual-isocenter split-arc VMAT plans (Iso2) were compared with mono-isocenter VMAT plans (Iso1). For Iso2 plans, PTV dose was investigated after introducing ±2 and ±5 mm couch shift errors between the two isocenters in the lateral, longitudinal and vertical direction.ResultsFor both techniques the planning aims for PTV coverage and OARs were met. The mean dose for the bilateral lungs and heart was reduced from 11.3 Gy and 3.8 Gy to 10.9 Gy (p < .05) and 3.6 Gy (p < .05), respectively, for Iso2 plans when compared to Iso1 plans. Positive statistically significant correlation (rho = 0.76, p = .006) was found between PTV volume and D2cc_PTV for Iso1 plans. No clinically significant change was seen in the D98_CTV or D2cc_PTV after the 2 and 5 mm errors were introduced between isocenters for Iso2 plans.ConclusionsThe split arc method was shown to be a feasible treatment technique in the case of synchronous BBC for both mono and dual isocenter techniques. The dose parameters were slightly favoring dual-isocenter option instead of mono-isocenter. The dual-isocenter method was shown to be a robust treatment option in the presence of ≤5 mm errors in the shifts between the two isocenters.