Helical Tomotherapy Plans Research Articles

Comparison of target volume and clinical effects of four radiotherapy plans for acute lymphoblastic leukemia prior to hematopoietic stem cell transplantation.

The present study aimed to investigate the variations in target volume, clinical reaction and transplantation effects of helical tomotherapy (HT)-total body irradiation (TBI), HT-total marrow and lymphatic irradiation (TMLI), intensity modulated radiotherapy (IMRT)-TBI and IMRT-TMLI within patients with acute lymphoblastic leukemia (ALL). A total of 18 patients with ALL were treated with the four aforementioned radiotherapy plans prior to hematopoietic stem cell transplantation. A planned prescribed dose of 12 Gy/6 Frequency was administered to determine planning target volume (PTV). Dosimetry evaluation indexes in PTV and organs at risk were analyzed. Comparison of clinical untoward effects and the results of transplantation among the four plans were performed. The conformity index of HT plans was significantly increased compared with those in IMRT plans. The mean dose (D) to the lung and volume ratio of target volume occupied by 5 Gy (V5) in TMLI plans were lower compared with TBI plans. Doses to organs were controlled within the normal range. Dmax, Dmean and V5 of bilateral lungs and Dmax and Dmean of bilateral crystalline lens in IMRT plans were significantly higher compared with HT plans. There were no significant differences in untoward effects among the four plans. Subsequent to symptomatic treatments with antiemetic, antidiarrheal and fluid infusion, untoward effects improved, and all patients demonstrated tolerance to these therapies. A total of six patients treated with HT-TBI revealed complete and successful transplantation; however, one patient following transplantation suffered from severe rejection and had succumbed to mortality due to severe infection. Patients treated with HT-TMLI, IMRT-TBI and IMRT-TMLI completed successful transplantation and no rejection responses were observed. Conformity of HT plans are higher than that of IMRT plans. The four radiotherapy plans exhibit similar clinical untoward effects and the same transplantation success rate. HT-TMLI is more feasible in dosimetry compared with HT-TBI, IMRT-TBI and IMRT-TMLI, which require further long-term observation.

Dosimetric comparison of TomoDirect, helical tomotherapy, VMAT, and ff-IMRT for upper thoracic esophageal carcinoma

The new TomoDirect (TD) modality offers a nonrotational option with discrete beam angles. We aim to compare dosimetric parameters of TD, helical tomotherapy (HT), volumetric-modulated arc therapy (VMAT), and fixed-field intensity-modulated radiotherapy (ff-IMRT) for upper thoracic esophageal carcinoma (EC). Twenty patients with cT2-4N0-1M0 upper thoracic esophageal squamous cell carcinoma (ESCC) were enrolled. Four plans were generated using the same dose objectives for each patient: TD, HT, VMAT with a single arc, and ff-IMRT with 5 fields (5F). The prescribed doses were used to deliver 50.4 Gy/28F to the planning target volume (PTV50.4) and then provided a 9 Gy/5F boost to PTV59.4. Dose-volume histogram (DVH) statistics, dose uniformity, and dose homogeneity were analyzed to compare treatment plans. For PTV59.4, the D2, D98, Dmean, and V100% values in HT were significantly lower than other plans (all p < 0.05), and those in TD were significantly lower than VMAT and ff-IMRT (all p < 0.05). However, there was no significant difference in the D2 and Dmean values between VMAT and ff-IMRT techniques (p > 0.05). The homogeneity index (HI) differed significantly for the 4 techniques of TD, HT, VMAT, and ff-IMRT (0.03 ± 0.01, 0.02 ± 0.01, 0.06 ± 0.02, and 0.05 ± 0.01, respectively; p < 0.001). The HI for TD was similar to HT (p = 0.166), and had statistically significant improvement compared to VMAT (p < 0.001) and ff-IMRT (p = 0.003). In comparison with the 4 conformity indices (CIs), there was no significant difference (p > 0.05). For PTV50.4, the D2 and Dmean values in HT were significantly lower than other plans (all p < 0.05), and those in TD were significantly lower than VMAT and ff-IMRT (all p < 0.05). However, there was no significant difference in the D2 and Dmean values between VMAT and ff-IMRT techniques (p > 0.05). No D98 and V100% parameters differed significantly among the 4 treatment types (p > 0.05). HT plans were provided for statistically significant improvement in HI (0.03 ± 0.01) compared to TD plans (0.05 ± 0.01, p = 0.003), VMAT (0.08 ± 0.03, p < 0.001), ff-IMRT (0.08 ± 0.01, p < 0.001). The HI revealed that TD was superior to VMAT and ff-IMRT (p < 0.05). The CI differed significantly for the 4 techniques of TD, HT, VMAT, and ff-IMRT (0.59 ± 0.10, 0.69 ± 0.11, 0.64 ± 0.09, and 0.64 ± 0.11, respectively; p = 0.035). The best CI was yielded by HT. We found no significant difference for the V5, V10, V15, V30, and the mean lung dose (MLD) among the 4 techniques (all p > 0.05). However, the V20 differed significantly among TD, HT, VMAT, and ff-IMRT (21.50 ± 7.20%, 19.50 ± 5.55%, 17.65 ± 5.45%, and 16.35 ± 5.70%, respectively; p = 0.047). Average V20 for the lungs was significantly improved by the TD plans compared to VMAT (p = 0.047), and ff-IMRT (p = 0.008). The V5 value of the lung in TD was 49.30 ± 13.01%, lower than other plans, but there was no significant difference (p > 0.05). The D1 of the spinal cord showed no significant difference among the 4 techniques (p = 0.056). All techniques are able to provide a homogeneous and highly conformal dose distribution. The TD technique is a good option for treating upper thoracic EC involvement. It could achieve optimal low dose to the lungs and spinal cord with acceptable PTV coverage. HT is a good option as it could achieve quality dose conformality and uniformity, while TD generated superior conformality.

Dosimetric Comparisons of Volumetric Modulated Arc Therapy and Tomotherapy for Early T-Stage Nasopharyngeal Carcinoma

Purpose To compare the dosimetric differences between volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT) in treating early T-stage nasopharyngeal carcinoma (NPC). Method Ten patients with early T-stage NPC who received tomotherapy using simultaneously integrated boost (SIB) strategies were replanned with VMAT (RapidArc of Varian, dual-arc). Dosimetric comparisons between the RapidArc plan and the HT plan included the following: (1) D98, homogeneity, and conformity of PTVs; (2) sparing of organs at risk (OARs); (3) delivery time and monitor units (MUs). Results (1) Compared with RapidArc, HT achieved better dose conformity (CI of PGTVnx + nd: 0.861 versus 0.818, P = 0.004). (2) In terms of OAR protection, RapidArc exhibited significant superiority in sparing ipsilateral optic nerve (Dmax: 27.5Gy versus 49.1Gy, P < 0.001; D2: 23.5Gy versus 48.2Gy, P < 0.001), contralateral optic nerve (Dmax: 30.4Gy versus 49.2Gy, P < 0.001; D2: 26.2Gy versus 48.1Gy, P < 0.001), and optic chiasm (Dmax: 32.8Gy versus 48.3Gy, P < 0.001; D2: 30Gy versus 47.6Gy, P < 0.001). HT demonstrated a superior ability to protect the brain stem (D1cc: 43.0Gy versus 45.2Gy, P = 0.012), ipsilateral temporal lobe (Dmax 64.5Gy versus 66.4 Gy, P = 0.015), contralateral temporal lobe (Dmax: 62.8Gy versus 65.1Gy, P = 0.001), ipsilateral lens (Dmax: 4.27Gy versus 5.24Gy, P = 0.009; D2: 4.00Gy versus 5.05Gy, P = 0.002; Dmean: 2.99Gy versus 4.31Gy, P < 0.001), contralateral lens (Dmax: 4.25Gy versus 5.09Gy, P = 0.047; D2: 3.91Gy versus 4.92Gy, P = 0.005; Dmean: 2.91Gy versus 4.18Gy, P < 0.001), ipsilateral parotid (Dmean: 36.4Gy versus 41.1Gy, P = 0.002; V30Gy: 54.8% versus 70.4%, P = 0.009), and contralateral parotid (Dmean: 33.4Gy versus 39.1Gy, P < 0.001; V30Gy: 48.2% versus 67.3%, P = 0.005). There were no statistically significant differences in spinal cord or pituitary protection between the RapidArc plan and the HT plan. (3) RapidArc achieved a much shorter delivery time (3.8 min versus 7.5 min, P < 0.001) and a lower MU (618MUs versus 5646MUs, P < 0.001). Conclusion Our results show that RapidArc and HT are comparable in D98, dose homogeneity, and protection of the spinal cord and pituitary gland. RapidArc performs better in shortening delivery time, lowering MUs, and sparing the optic nerve and optic chiasm. HT is superior in dose conformity and protection of the brain stem, temporal lobe, lens, and parotid.

A preliminary study of the protection of bone marrow in craniospinal irradiation

Objective To analyze the relationship between the dose volume of bone marrow and acute hematologic toxicity in craniospinal irradiation (CSI), and preliminarily explore the dosimetric differences in bone marrow between helical tomotherapy (HT) and volumetric modulated arc therapy (VMAT). Methods Clinical data and HT plans of twenty patients treated with CSI in the First Affiliated Hospital of Kunming Medical University were collected, and the HT plans were transferred back to the MIM system. The skull, mandible, clavicle, sternum, scapula, ribs, vertebrae and pelvis were successively delineated on the CT images and then the V2, V5, V10, V15, V20, V25, V30, V35, Dmax, Dmean of each aforementioned bone and total bone were read on DVH images. The correlation between those indexes and the incidence of ≥grade Ⅱ hematologic toxicity was subsequently analyzed. The images of 6 patients were selected and transferred to Monaco TPS and VMAT plans were completed. The dosimetric differences of those indexes were statistically compared between HT and VMAT. Statistical analyses were performed by using Spearman correlation analysis and Wilcoxon symbol rank-sum test. Results The incidence of ≥grade Ⅱ leukopenia was positively correlated with the V25 of pelvis and the V5 of total bones (P=0.038); the risk of ≥ grade Ⅱ thrombocytopenia was positive associated with the V20 of pelvis (P=0.041); the incidence of ≥ grade Ⅱ neutropenia was positively correlated with the V10 of vertebrae (P=0.036). There was no dosimetric difference of dose volume of vertebral and pelvis between HT and VMAT plans (P>0.05). Conclusions There is a positive correlation between ≥ grade Ⅱ leukopenia and the V25 of pelvis and the V5 of total bones. The V20 of pelvis shows a positive correlation with ≥ grade Ⅱ thrombocytopenia. A positive correlation is found between ≥ grade Ⅱ neutropenia and the V10 of vertebrae. The indices of vertebral and pelvis between HT and VMAT plans show no significant differences. Key words: Helical tomotherapy; Volumetric modulated arc therapy; Craniospinal irradiation; Bone marrow-sparing

Converting Treatment Plans From Helical Tomotherapy to L-Shape Linac: Clinical Workflow and Dosimetric Evaluation.

This work evaluated a commercial fallback planning workflow designed to provide cross-platform treatment planning and delivery. A total of 27 helical tomotherapy intensity-modulated radiotherapy plans covering 4 anatomical sites were selected, including 7 brain, 5 unilateral head and neck, 5 bilateral head and neck, 5 pelvis, and 5 prostate cases. All helical tomotherapy plans were converted to 7-field/9-field intensity-modulated radiotherapy and volumetric-modulated radiotherapy plans through fallback dose-mimicking algorithm using a 6-MV beam model. The planning target volume (PTV) coverage (D 1, D 99, and homogeneity index) and organs at risk dose constraints were evaluated and compared. Overall, all 3 techniques resulted in relatively inferior target dose coverage compared to helical tomotherapy plans, with higher homogeneity index and maximum dose. The organs at risk dose ratio of fallback to helical tomotherapy plans covered a wide spectrum, from 0.87 to 1.11 on average for all sites, with fallback plans being superior for brain, pelvis, and prostate sites. The quality of fallback plans depends on the delivery technique, field numbers, and angles, as well as user selection of structures for organs at risk. In actual clinical scenario, fallback plans would typically be needed for 1 to 5 fractions of a treatment course in the event of machine breakdown. Our results suggested that <1% dose variance can be introduced in target coverage and/or organs at risk from fallback plans. The presented clinical workflow showed that the fallback plan generation typically takes 10 to 20 minutes per case. Fallback planning provides an expeditious and effective strategy for transferring patients cross platforms, and minimizing the untold risk of a patient missing treatment(s).

Comparison of Stereotactic Body Radiotherapy Delivery Techniques for Early-Stage Lung Cancer Using Lung Toxicity Modeling

Purpose: Lung toxicity is a primary side effect in stereotactic radiotherapy (SBRT) for early-stage non-small cell lung cancer (NSCLC). We aimed to use a set of radiobiological models to evaluate and compare modern IMRT delivery techniques with three-dimensional conformal techniques for SBRT treatment of NSCLC in terms of lung toxicity, and aimed to compare the results from different radiobiologcal models. Methods: Ten early-stage NSCLC patients treated with SBRT were retrospectively selected. Five treatment plans were generated to deliver 50 Gy in five fractions to the planning target volume for each case: a helical tomotherapy (HT) plan, two three-dimensional cofnromal radiotherapy (3D-CRT) plans using 6-MV and 10-MV photon beams respectively, and two volumetric modulated arc therapy (VMAT) plans using one and two arc fields respectively. The lung RDV was calculated with three parallel functional sub-unit (FSU) models and two normal tissue complication probability (NTCP) models. Results: Both the HT and VMAT plans showed significantly higher contralateral mean lung dose and lower ipsilateral mean lung dose compared to the 3D-CRT plans. There was no statistically significant difference in terms of lung toxicities between the IMRT and 3D-CRT techniques using either the FSU models or the NTCP models. Based on both the FSU and the NTCP models, there was strong correlation between lung toxicity and the mean lung dose in SBRT treatment plans. Conclusions: Based on both the NTCP and parallel FSU models, both IMRT and traditional 3D-CRT delivery techniques could achieve comparable lung sparing inn SBRT treatment of early-stage lung cancer. However, the validity of the radiobiological model results should be checked by clinical data.

Implications of leaf fluence opening factors on transfer of plans between matched helical tomotherapy machines

When helical tomotherapy plans are transferred between two matched machines, the leaf opening times are changed. A published method of checking these is based on the differences in leaf latency between the two machines. We have extended this method to account also for the differences in leaf fluence opening factors (LFOF) between the two machines. When LFOF is not taken into account, the number of false negatives (with under 95% of opening times agreeing within 5 ms or under 99% agreeing within 10 ms) is approximately 10% of patients. After correcting for LFOFs, all transfers meet the criteria.

Dosimetric Comparison of Stereotactic Body Radiation Therapy Plans With Volumetric Arc Therapy, Helical Tomotherapy, and Raystation for Liver Metastasis

To compare dosimetric data of stereotactic body radiotherapy (SBRT) plans with volumetric-arc therapy (VMAT), helical tomotherapy (HT) and RayStation (RS) for liver metastasis. The dosimetric data of 19 patients with liver metastasis treated with liver SBRT were analyzed. Three different plans were generated with same computed tomography (CT) images. The prescribed dose was 54 Gy delivered in 3 fractions and the dose was prescribed to 90% isodose line. For all patients, cumulative dose–volume histograms and dosimetric parameters were calculated and compared for the planning target volume (PTV) and organs at risk (OAR). D2 and D98 were used as a surrogate for maximum and minimum dose, respectively. D2 and D98 are the minimal doses to 2 % and 98 % of target volume, respectively. The target homogeneity and conformal index values (HI and CI, respectively) are compared. OARs doses, including kidneys, liver, bowel, and spinal cord, were also assessed. All plans meet the criteria for PTV coverage. The average maximum doses for PTV (D2) were significantly higher in VMAT plans compared to HT and RS plans (Table 1). The CI and HI indices were significantly lower in RS plans compared to HT plans and VMAT plans. Similarly CI and HI indices were significantly lower in HT plans compared to VMAT plans. Liver Dmean was significantly higher in RS plan (10.9±4.8 Gy) compared to VMAT plan (9.6±3.8 Gy; p=0.001) and HT plan (10.1±4.4 Gy; p=0.006). However there was no significant difference for Liver Dmean between VMAT and HT plans (p=0.08). The liver V5 to V45 were significantly higher in RS plan compared to VMAT and HT plans (Figure 1). There were no significant difference in liver doses between VMAT plans and HT plans except for V5 (p=0.001) and V10 (p=0.005) values. The Dmean of both kidneys were significantly higher in HT plans (2.4±1.8 Gy) compared to VMAT plans (1.9±1.6 Gy; p=0.005) and RS plans (1.4±0.8 Gy; p=0.004). However there were no significant difference in Dmeanof both kidneys between VMAT and RS plans. For the spinal cord and bowel, maximum doses did not differ significantly between each techniques. The monitor unit for RS plan was significantly less in RS plan compared to VMAT plan (2774±271 vs. 4052±1591; p=0.003). The RS plans reduced the maximum dose applied to the target area, with improved the conformality and homogeneity of radiation. However, the liver does were significantly higher in RS plan compared to HT and VMAT plans.Tabled 1Abstract 2428; Table 1ParametersVMAT(Mean±SD)HT(Mean±SD)RayStation(Mean±SD)p(VMAT vs. HT)p(VMAT vs. RS)p(HT vs. RS)D2% (Gy)57.0±1.055.4±0.354.4±0.3<0.001<0.001<0.001D100% (Gy)52.0±2.352.5±1.052.5±0.80.330.190.73D98% (Gy)54.2±0.753.9±0.253.7±0.20.140.003<0.001D95% (Gy)54.5±0.654.2±0.253.8±0.20.02<0.001<0.001D90% (Gy)54.8±0.654.3±0.253.9±0.20.001<0.001<0.001D50% (Gy)55.8±0.654.8±0.354.1±0.2<0.001<0.001<0.001CI1.53±0.101.52±0.101.51±0.100.020.0030.001HI1.05±0.021.03±0.011.01±0.01<0.001<0.001<0.001 Open table in a new tab

Total Body Irradiation Using Fixed-beam Tomotherapy in Patients With Width Larger Than 40cm

To investigate the feasibility of TBI using TomoDirect (TD) for patients with width larger than 40cm and to perform a dosimetric comparison study of treatment plans using Helical Tomotherapy (HT) and TD techniques. 10 TBI patients were selected with median field width in lateral direction of 51.91cm (44.77 cm - 62.89 cm). TBI planning target volume (PTV) was defined as the external body contour minus the bilateral lung expanded by 5 mm. For optimization the lungs were divided into inner (lungs minus 1.5cm), mid lung ring (lungs minus 0.5cm) and outer lung ring (lungs minus mid lung). A virtual bolus was created by expanding the patient’s external contour by 1cm and assigning a density of 0.2 g/cm3. The TBI prescription was at least 80% of the PTV to receive 12 Gy in 6 fractions. For each patient, two treatment plans were generated using both TD, with 8 beam angles, and HT techniques. A dynamic jaw size of 5 cm, a pitch of 0.43, and a modulation factor of 2.0 were used in this study. All other optimization objectives were kept the same for both treatment techniques. The dosimetric evaluation parameters included: PTV mean dose (Dmean), 98% and 95% of PTV dose coverage (D98, D95), homogeneity index (HI), TBI beam-on time and bilateral lungs dose. Student t-test was performed to evaluate the dosimetric differences between TD and HT plans. A p-value of ≤ 0.05was considered significant. Median and ranges for PTV Dmean, D98, D95, HI and beam-on time from TD and HT plans for all ten patients are shown in Table 1.Abstract 3690; Table 1Dmean (Gy)D98 (Gy)D95 (Gy)HITime (minutes)TD12.08(12.01-12.15)10.9(10.6-11.7)11.48(11.25-11.66)0.146(0.03-0.19)22.41(18.27-30.54)HT12.10(12.08-12.23)10.8(9.7-11.5)11.46(10.89-11.65)0.17(0.11-0.28)17.79(14.96-21.49)Significant?NoYesNoYesYes Open table in a new tab Table 1 showed that there was no statistical significant difference between TD and HT techniques for all the patients (n=10) for Dmean and D95. TD plans had better dose coverage of D98 and better HI and longer beam-on times compared to HT plans. For the lung doses, there was a significant difference between HT and TD plans. HT plans spared the lungs better as compared to TD plans, with median dose and ranges of 8.37Gy (7.97Gy to 8.81Gy) for TD plans and 7.93Gy (7.45Gy to 8.26Gy) for HT plans. TD and HT plans were compared for 10 TBI patients. All plans had comparable Dmean and D95 PTV dose coverage and were acceptable for clinical use. However, TD plans had both better D98 dose coverage and dose homogeneity especially for the patients who had more than 50cm width in the lateral direction (7 out of 10 patients). HT treatment plans generally had less beam-on time and spared more lungs as compared to TD plans.

Validation of a method for “dose of the day” calculation in head-neck tomotherapy by using planning ct-to-MVCT deformable image registration

PurposeThe aim of this study was to test the feasibility and dosimetric accuracy of a method that employs planning CT-to-MVCT deformable image registration (DIR) for calculation of the daily dose for head and neck (HN) patients treated with Helical Tomotherapy (HT). MethodsFor each patient, the planning kVCT (CTplan) was deformably registered to the MVCT acquired at the 15th therapy session (MV15) with a B-Spline Free Form algorithm using Mattes mutual information (open-source software 3D Slicer), resulting in a deformed CT (CTdef). On the same day as MVCT15, a kVCT was acquired with the patient in the same treatment position (CT15). The original HT plans were recalculated both on CTdef and CT15, and the corresponding dose distributions were compared; local dose differences <2% of the prescribed dose (DD2%) and 2D/3D gamma-index values (2%-2mm) were assessed respectively with Mapcheck SNC Patient software (Sun Nuclear) and with 3D-Slicer. ResultsOn average, 87.9%±1.2% of voxels were found for DD2% (on average 27 slices available for each patient) and 94.6%±0.8% of points passed the 2D gamma analysis test while the 3D gamma test was satisfied in 94.8%±0.8% of body’s voxels. ConclusionsThis study represents the first demonstration of the dosimetric accuracy of kVCT-to-MVCT DIR for dose of the day computations. The suggested method is sufficiently fast and reliable to be used for daily delivered dose evaluations in clinical strategies for adaptive Tomotherapy of HN cancer.

Sensitivity evaluation of two commercial dosimeters in detecting Helical TomoTherapy treatment delivery errors

PurposeTo assess the sensitivity of two commercial dosimetry systems in detecting Helical TomoTherapy (HT) delivery errors. MethodTwo commercial dosimeters i) MatriXXEvolution and ii) ArcCHECK® were considered. Ten retrospective nasopharynx HT patients were analysed. For each patient, error plans were created by independently introducing systematic offsets in: a) Jaw width error ±1, ±1.5 and ±2mm, b) Couch speed error ±2%, ±2.5, ±3% and ±4%, and c) MLC Leaf Open Time (MLCLOT) errors (3 separate MLC errors: either leaf 32 open or leaf 42 remains open during delivery, and 4% random reductions in MLCLOT). All error plans, along with the no error plan for each patient, were measured using both dosimeters in the same session. Gamma evaluation (3%/3mm) was applied to quantitatively compare the measured dose from each dosimeter to the treatment planning system. The error sensitivity was quantified as the rate of decrease in gamma pass rate. ResultsThe gamma pass rate decreases with increase in error magnitude for both dosimeters. ArcCHECK was insensitive for couch speed error up to 2.5% and jaw width error up to −1.5mm while MatriXXEvolution was found to be insensitive to couch speed error up to 2% and couch speed up to −1mm. Both of the detectors show similar sensitivity to all the MLCLOT errors that were clinically relevant. ConclusionNo statistically significant (p>0.05) differences exist in detecting the simulated delivery errors between MatriXXEvolution and ArcCHECK dosimeter systems for HT plans. Both dosimeters were able to pick up clinically relevant delivery errors.

Dosimetric comparison of helical tomotherapy using different techniques, simultaneous integrated boost and sequential boost for craniospinal irradiation: a single institution experience

AbstractPurposeCraniospinal irradiation (CSI) has become an important and challenging radiation technique for radiation oncologists. Helical tomotherapy (HT) seems to have dosimetric advantage for CSI compared with other radiation modalities. The purpose of this study was to compare dosimetric data between two different HT plans; simultaneous integrated boost (SIB) and sequential boost (Sq).MethodTwelve previously treated CSI contoured datasets by SIB technique were replanned. Dosimetric comparative parameters of targets were conformity index (CI) and homogeneity index (HI). For organ at risk (OARs), the mean dose of parallel organs, D2% of serial organs and whole body integral dose (ID) were also investigated.ResultSIB plan significantly provided more conformed dose to CSI and tumour boost while resulting in a similar CI in spinal boost region compared with Sq plan. The HI showed no differences between two plans. Radiation exposure to serial organs and ID were also significantly lower in SIB plan.ConclusionCSI treatment using HT, SIB technique was feasible and had more target coverage while minimising the radiation dose to healthy tissues.

Comparison of spinal Stereotactic Body Radiotherapy (SBRT) planning techniques: intensity-modulated radiation therapy, modulated arc therapy, and helical tomotherapy

Stereotactic body radiotherapy (SBRT) delivers a highly conformal, hypofractionated radiation dose to a small target with minimal radiation applied to the surrounding areas. Therefore, using the proper treatment planning techniques for SBRT is important. Intensity modulation techniques, such as static intensity-modulated radiation therapy (IMRT), modulated arc therapy (mARC), and helical tomotherapy (HT), are useful for spinal SBRT because of a rapid dose fall-off and spinal cord avoidance. This study compared the planning characteristics for hypofractionated spinal SBRT administered using 3 treatment techniques. The factors evaluated for spinal SBRT planning were dose coverage, cord avoidance, target conformity, homogeneity, and dose spillage. Target coverage was 82.74% ± 3.35%, 80.92% ± 0.81%, and 85.01% ± 7.27% for IMRT, mARC, and HT, respectively. HT was therefore a powerful technique with respect to target coverage. The spinal cord dose for HT (mean, 1763.96 cGy; standard deviation [SD], 164.48) was significantly different from those for mARC (mean, 1991.75 cGy; SD, 248.00) and IMRT (mean, 2053.24 cGy; SD, 164.48). In addition, the partial spinal cord volume at 2000 cGy for HT (mean, 0.12 cc, SD, 0.01) was significantly different from those for IMRT and mARC (0.50 ± 0.10 cc and 0.56 ± 0.25 cc, respectively). The conformity index was 1.30 ± 0.12, 1.08 ± 0.05, and 1.36 ± 0.23 for IMRT, mARC, and HT planning, respectively. mARC showed the highest conformity (p = 0.000). HT used a narrow field fan beam and exhibited remarkable improvement of target coverage and cord dose, offering an important benefit to spinal SBRT. mARC had the highest target conformity and better high- and intermediate-dose spillage than HT and IMRT did, respectively. These planning techniques have different advantages. In the case of spine SBRT, HT should be used for cord avoidance. In some cases, such as for a short treatment duration when the patient is considered to be in a poor general condition, mARC can be used.

Clinical significance of treatment delivery errors for helical TomoTherapy nasopharyngeal plans – A dosimetric simulation study

PurposeDevelop a framework to characterize helical TomoTherapy (HT) machine delivery errors and their clinical significance. Method and materialsTen nasopharynx HT plans were edited to introduce errors in Jaw width (JW), couch speed (CS), gantry period (GP), gantry start position (GSP), multi leaf collimator leaf open times (MLC LOT). In case of MLC LOT only, both systematic and random delivery errors were investigated. Each error type was simulated independently for a range of magnitudes. Dose distributions for the clinical reference plans and the error simulated plans were compared to establish the magnitude for each error type which resulted in a change in clinical tolerance, defined as 5% variation in D95 of PTV70, D0.1cc of spinal cord, D0.1cc of brainstem and the smallest value of either a 10% or 3.6Gy dose variation in mean parotid dose. ResultsDose variation from systematic delivery errors in JW ±0.5mm, CS ranges between −1% to 1.5%, GP ±1s, GSP ranges between −20 to 2.50 and MLC LOT random error up to 2% from the planned value relative to the clinical reference plan was within the set tolerance values for all the patient cohorts. GSP errors and the random MLC LOT errors with up to 10% standard deviation were found to be relatively insensitive compared to other delivery errors. ConclusionThis work has established a framework to characterize HT machine delivery errors. This framework could be applied to any patient dataset to determine clinically relevant HT QA tolerances.

Helical tomotherapy to LINAC plan conversion utilizing RayStation Fallback planning.

RaySearch RayStation Fallback (FB) planning module can generate an equivalent backup radiotherapy treatment plan facilitating treatment on other linear accelerators. FB plans were generated from the RayStation FB module by simulating the original plan target and organ at risk (OAR) dose distribution and delivered in various backup linear accelerators. In this study, helical tomotherapy (HT) backup plans used in Varian TrueBeam linear accelerator were generated with the RayStation FB module. About 30 patients, 10 with lung cancer, 10 with head and neck (HN) cancer, and 10 with prostate cancer, who were treated with HT, were included in this study. Intensity‐modulated radiotherapy Fallback plans (FB‐IMRT) were generated for all patients, and three‐dimensional conformal radiotherapy Fallback plans (FB‐3D) were only generated for lung cancer patients. Dosimetric comparison study evaluated FB plans based on dose coverage to 95% of the PTV volume (R95), PTV mean dose (Dmean), Paddick's conformity index (CI), and dose homogeneity index (HI). The evaluation results showed that all IMRT plans were statistically comparable between HT and FB‐IMRT plans except that PTV HI was worse in prostate, and PTV R95 and HI were worse in HN multitarget plans for FB‐IMRT plans. For 3D lung cancer plans, only the PTV R95 was statistically comparable between HT and FB‐3D plans, PTV Dmean was higher, and CI and HI were worse compared to HT plans. The FB plans using a TrueBeam linear accelerator generally offer better OAR sparing compared to HT plans for all the patients. In this study, all cases of FB‐IMRT plans and 9/10 cases of FB‐3D plans were clinically acceptable without further modification and optimization once the FB plans were generated. However, the statistical differences between HT and FB‐IMRT/3D plans might not be of any clinically significant. One FB‐3D plan failed to simulate the original plan without further optimization.

PUB045 The Capability and Characteristic of Helical Tomotherapy at Sparing Hippocampus in Prophylactic Cranial Irradiation

Prophylactic cranial irradiation (PCI) is efficient at avoiding lung cancer intra-cranial metastasis. However, PCI may cause neurocognitive impairment because of the hippocampal toxicities. It is reported that hippocampus V7.3Gy > 40% is associated with long-term impairment. Considering helical tomotherapy (HT) has higher modulation capabilities, we investigated the capability and characteristic of HT at sparing hippocampus in PCI. Six anonymous patients previously treated with whole-brain radiotherapy with hippocampal sparing were reviewed. Under T1-weighted MRI, the hippocampus was contoured, and hippocampal avoidance regions (HAR) were created using a 5-mm volumetric expansion around the hippocampus. The prescription dose 3.0Gy * 10 fractions was assigned on planning target volume (PTV) which was defined as whole-brain minus HAR and bilateral hippocampus. During the HT plan optimization process, evaluation factors of PTV and other dosimetry factors were recorded whenever the mean dose of hippocampus decreased by every 2Gy. The average of six HT plans without hippocampus sparing constraints are as follow: hippo_Dmean 27.33±2.22Gy, HAR_Dmean 28.62±1.84Gy, PTV_Dmean 30.77±0.74Gy, PTV_D2% 30.93±0.61Gy, PTV_D98% 29.86±0.34Gy, PTV_V30Gy 0.97±0.02% and conformal index (CI) 0.85±0.03, homogeneity index (HI) 0.04±0.01, plan delivery duration 13.70±1.92min. When V7.3Gy of bilateral hippocampus achieved 40%, the average dosimetry factors are as follow: hippo_Dmean 8.26±0.24Gy, HAR_Dmean 12.88±1.27Gy, PTV_Dmean 31.00±0.47Gy, PTV_D2% 31.97±0.63Gy, PTV_D98% 21.74±5.44Gy, PTV_V30Gy 0.93±0.02%, CI 0.77±0.08, HI 0.35±0.20, plan delivery duration 21.30±4.97min. During the process of hippocampus sparing, HAR_Dmean decreased linearly as well. However, dosimetry variation of PTV presented three steps: plateau region (> 20Gy), gradient region (∼20 to ∼10Gy) and falling region (<10Gy). There’s almost no significant impact on the PTV dosimetry factors when hippo_Dmean was not lower than 15Gy. With the hippocampus dose decreasing, CI decreased linearly and slightly, however, HI was impaired severely in the falling region. Plan delivery duration time was significantly prolonged process (from 13min to 23 min).View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Meta-analysis of dosemetric comparision between helical tomotherapy and intensity-modulated radiotherapy for early-stage postoperative breast cancer

Objective To compare the dosemetry between helical tomotherapy (HT) and intensity-modulated radiotherapy (IMRT) for early-stage postoperative breast cancer and provide more valuable evidences to the clinical researches. Methods Clinical trails of dosimetric comparing between HT and IMRT for early-stage breast cancer were obtained from PubMed, Embase, Sciencedirect, CNKI, VIP and Wanfang databases, evaluated and analyzed with the Cochrane Collaboration's RevMan 5.2 software. Results 10 studies were included with a total of 135 patients. Compared to IMRT plans, HT plans provided a significantly better conformity index (P 0.05). Conclusion Compared to IMRT plans, HT plans have the dosimetry superiority for early-stage breast cancer with significantly better coverage and dose conformity while maintaining lower doses to high risk organs. Key words: Breast neoplasms; Radiotherapy; Helical tomotherapy; Intensity-modulated radiotherapy; Meta-analysis

95P Radiotherapy (RT) for breast cancer patients- clinical implementation of the first ever Tomotherapy-H in a tertiary cancer centre in India

Background The first ever Tomotherapy-H system in India became operational in Feb 2016 in our hospital, Health care global enterprises, a tertiary level cancer care centre. In order to implement Tomotherapy as a routine technique to treat breast cancers we under took dosimetric comparison of helical Tomotherapy plans and five field forward planning intensity modulated radiotherapy (IMRT) plans. Methods We compared the Helical Tomotherapy plans with IMRT plans of the first 10 patients with early breast cancer who underwent adjuvant RT using helical Tomotherapy technique in our centre between February 2016 and June 2016. The treatment planning objectives were to cover 95% of the planning target volume (PTV) using a 95% isodose (V95 >/= 95%), with a minimum of 90% isodose covering 100% of PTV (V100 >/= 90%) and no more than 10% ofPTV to receive 110% (V110 <10%). The heart and lungs were contoured as organs at risk (OAR) and doses received were recorded in both the planning techniques. Results All patients were females with four right and six left sided cancers. Seven patients had undergone breast conserving surgery and three had mastectomy. When we compared the forward planning IMRT plans with Helical Tomotherapy plans, we found thattheadvantageofusingHelicalTomotherapyincludedsignificantlybettercoverage forV95(p<0.000),V100(p<0.000)andmedianV110was0.06%and0.14%in Helical Tomotherapy and IMRT plans respectively. Helical Tomotherapy plans had lower dose to ipsilateral lung (V35 P < 0.01) and lower median dose to the heart (Tomotherapy=8.2andIMRT=9Gy).Therewasimprovedcoverageoftheplanning target volume, including the regional nodes, without any field junction problems. None ofthepatientshadanymorethangrade1 skintoxicityandgrade1 oesophagitis. Conclusions Helical Tomotherapy, compared to forward planning IMRT for breast cancer treatment, demonstrated better target coverage and sparing ofOARs. The treatment was well tolerated with minimal toxicity. Long term toxicity is yet to be established by continued follow up ofthese patients in late side effects clinics. Legal entity responsible for the study Health Care Global Enterprises Funding Health Care Global Enterprises Disclosure All authors have declared no conflicts ofinterest.

Estimation of radiation-induced secondary cancer risks for early-stage non–small cell lung cancer patients after stereotactic body radiation therapy

PurposeIn this study, we evaluated radiation-induced secondary lung cancer risks for the lung and the breast from stereotactic body radiation therapy treatment of early-stage non–small cell lung cancer with different radiation therapy treatment modalities. Methods and materialsTen patients (5 men and 5 women) with early-stage non–small cell lung cancer who received definitive stereotactic body radiation therapy treatments were retrospectively selected. For each patient, two 3-dimensional conformal radiation therapy (3D-CRT) plans using 6- and 10-MV photons, respectively; a helical tomotherapy (HT) plan; and 2 volumetric modulated arc therapy (VMAT) plans using 1 and 2 arcs, respectively, were generated. The excess absolute risk (EAR) for secondary cancer occurrence was calculated using 3 organ equivalent dose models: the linear-exponential model, the plateau model, and the linear model for prescription dose range of 30 to 70 Gy. ResultsThe 3D-CRT plans showed significantly lower monitor units compared with the rotational intensity modulate radiation therapy plans. Based on each of the 3 organ equivalent dose models, HT and VMAT plans showed comparable average EARs to both the lung and the breast compared with the 3D-CRT plans in the prescription dose range of 30 to 70 Gy. At a prescription dose of 50 Gy and using the linear-exponential model, the average lung EAR estimation ranged from 15.7 ± 5.3 to 16.0 ± 6.5 per 10,000 patients per year with the 5 delivery techniques, and the average EAR estimation for the breast ranged from 18.0 ± 14.0 to 21.0 ± 15.0 per 10,000 patients per year. The secondary cancer risk increased approximately linearly with mean organ dose. The 3D-CRT plans showed significantly higher secondary cancer risk for the ipsilateral lung and lower risk for the contralateral lung compared with the HT and VMAT plans. ConclusionsRotational intensity modulate radiation therapy techniques including helical tomotherapy and VMAT do not increase secondary cancer risks for the lung or the breast compared with 3D-CRT techniques, despite higher monitor units used.

Comprehensive dosimetric planning comparison for early-stage, non-small cell lung cancer with SABR: fixed-beam IMRT versus VMAT versus TomoTherapy.

Volumetric‐modulated arc therapy (VMAT) is emerging as a leading technology in treating early‐stage, non‐small cell lung cancer (NSCLC) with stereotactic ablative radiotherapy (SABR). However, two other modalities capable of delivering intensity‐modulated radiation therapy (IMRT) include fixed‐beam and helical TomoTherapy (HT). This study aims to provide an extensive dosimetric comparison among these various IMRT techniques for treating early‐stage NSCLC with SABR. Ten early‐stage NSCLC patients were retrospectively optimized using three fixed‐beam techniques via nine to eleven beams (high and low modulation step‐and‐shoot (SS), and sliding window (SW)), two VMAT techniques via two partial arcs (SmartArc (SA) and RapidArc (RA)), and three HT techniques via three different fan beam widths (1 cm, 2.5 cm, and 5 cm) for 80 plans total. Fixed‐beam and VMAT plans were generated using flattening filter‐free beams. SS and SA, HT treatment plans, and SW and RA were optimized using Pinnacle v9.1, Tomoplan v.3.1.1, and Eclipse (Acuros XB v11.3 algorithm), respectively. Dose‐volume histogram statistics, dose conformality, and treatment delivery efficiency were analyzed. VMAT treatment plans achieved significantly lower values for contralateral lung V5Gy(p≤0.05) compared to the HT plans, and significantly lower mean lung dose (p<0.006) compared to HT 5 cm treatment plans. In the comparison between the VMAT techniques, a significant reduction in the total monitor units (p=0.05) was found in the SA plans, while a significant decrease was observed in the dose falloff parameter, D2cm, (p=0.05), for the RA treatments. The maximum cord dose was significantly reduced (p=0.017) in grouped RA&SA plans compared to SS. Estimated treatment time was significantly higher for HT and fixed‐beam plans compared to RA&SA (p<0.001). Although, a significant difference was not observed in the RA vs. SA (p=0.393). RA&SA outperformed HT in all parameters measured. Despite an increase in dose to the heart and bronchus, this study demonstrates that VMAT is dosimetrically advantageous in treating early‐stage NSCLC with SABR compared to fixed‐beam, while providing significantly shorter treatment times.PACS number(s): 87.55.D, 87.55.dk, 87.55.kd