Tomotherapy System Research Articles

Patient positioning in head and neck cancer : Setup variations and safety margins in helical tomotherapy.

To evaluate the interfractional variations of patient positioning during intensity-modulated radiotherapy (IMRT) with helical tomotherapy in head and neck cancer and to calculate the required safety margins (sm) for bony landmarks resulting from the necessary table adjustments. In all, 15patients with head and neck cancer were irradiated using the Hi-ArtII tomotherapy system between April and September 2016. Before therapy sessions, patient position was frequently checked by megavolt computed tomography (MV-CT). Necessary table adjustments (ta) in the right-left (rl), superior-inferior (si) and anterior-posterior (ap) directions were recorded for four anatomical points: second, fourth and sixth cervical vertebral body (CVB), anterior nasal spine (ANS). Based upon these data sm were calculated for non-image-guided radiotherapy, image-guided radiotherapy (IGRT) and image guidance limited to ashortened area (CVB2). Based upon planning CT the actual treatment required ta from -0.05 ± 1.31 mm for CVB2 (ap) up to 2.63 ± 2.39 mm for ANS (rl). Considering the performed ta resulting from image control (MV-CT) we detected remaining ta from -0.10 ± 1.09 mm for CVB4 (rl) up to 1.97 ± 1.64 mm for ANS (si). After theoretical adjustment of patients position to CVB2 the resulting ta ranged from -0.11 ± 2.44 mm for CVB6 (ap) to 2.37 ± 2.17 mm for ANS (si). These data imply safety margins: uncorrected patient position: 3.63-9.95 mm, corrected positioning based upon the whole target volume (IGRT): 1.85-6.63 mm, corrected positioning based upon CVB2 (IGRT): 3.13-6.66 mm. The calculated safety margins differ between anatomic regions. Repetitive and frequent image control of patient positioning is necessary that, however, possibly may be focussed on alimited region.

RayStation: External beam treatment planning system

RaySearch Laboratories is a world leader in the field of advanced software and creator of the RayStation treatment planning system for radiation therapy. The aim with RayStation is to deliver an unmatched user experience and leading functionality. Unique features described here include multiatlas based autosegmentation for contouring, deformable registration with 2 different algorithms, multicriteria optimization, Plan Explorer, fallback planning, ultrafast computation speed, and 4-dimensional (4D) adaptive radiation therapy. RayStation can be used to plan for electrons and photons on traditional linacs, for protons on various delivery systems, and for Accuray's helical TomoTherapy system. This paper describes some of these modalities, with reference to clinical cases and including descriptions of the impact on workflow.

Comparison of Unblocked, Directionally Blocked and Full Blocked Plans in Helical Tomotherapy for Breast Cancer Radiotherapy

Introduction: The doses received by the contralateral breast, lung and heart either directionally or full blocked techniques in Hi-Art Tomotherapy systems in partial or whole breast radiotherapy has been studied. Method: In 20 breast cancer patients 3 plans with non-blocked, directionally blocked and full blocked methods were designed in Hi-Art planning system. In all planning method the dose received by the contralateral breast, the heart volume percentages V5 and V30 and the lung volume percentages V5 and V20 were compared. Results: The mean doses received by contralateral breast were 6.24 Gy (4.50-8.74 Gy) in unblocked group 3.85 Gy (2.08-5.81 Gy) in directionally blocked group and 0.99 Gy (0.69-1.39 Gy) in full blocked group. The mean Lung V5 values were 98% (79-100%) in unblocked group and it was 98% (91-100%) in directionally blocked group while it was 93% (89-97%) in full blocked group. The mean V20 values were 16% (7-23%), 20% (17-24%) and 22% (18-28%) in unblocked, directionally blocked and full blocked groups respectively. The mean Heart V5 value 100% (99-100%) in unblocked group, and it was 99% (85-100%) in directionally blocked group while it was 92% (73- 100%) in full blocked group. The mean V30 values were 11% (2-25%), 6% (0-12%) and 9% (1-22%) in unblocked, directionally blocked and full blocked groups respectively. The mean beam-on time was 261.6 s (237.6-318.2) for unblocked, 277.9 s (237.6-338.5) for directionally blocked and 314.2 s (272.6-429.1) full blocked group. The mean numbers of MUs were 3712 (3353-4536) for unblocked, 3951 (3357-4834) for directionally blocked and 4506 (3866- 6168) for full blocked group. In full blocked group both beam on time and MU values were higher. Conclusion: We propose that further efforts needed to reduce low dose volumes to normal tissues, meanwhile when using directionally and full blocked plans all parameters should be considered together.

ESTIMATION OF MEDICAL EQUIPMENT PRICES – A CASE STUDY OF TOMOTHERAPY EQUIPMENT IN THE CZECH REPUBLIC

Medical equipment (ME) is often considered to be an important factor in the growth of healthcare expenditures. In the Czech Republic (CR) validated approach does not yet exist for hospitals to use to assess commercial offers, nor is there a generally accepted methodology for regulatory bodies to allow for the evaluation of the effectiveness of prior purchases. This study intends to present a methodological approach that will allow for assessing the effectiveness of the procurement of capital ME based on international prices. The case of the purchase of tomotherapy system in the CR was used to demonstrate the developed approach. We performed a multiway search for international estimated and exact prices for tomotherapy unit using public-procurement databases, scientific papers, health technology assessment studies, professional reports, and Internet searches. All of the data that was gathered on prices was subjected to critical assessment vis-à-vis the reliability of the information. This research lays new methodology that may provide general background of international comparison studies focused on ME. The results provide support for decision making about the acquisitions of ME.

Megavoltage 2D topographic imaging: An attractive alternative to megavoltage CT for the localization of breast cancer patients treated with TomoDirect

PurposeTo show the usefulness of topographic 2D megavoltage images (MV2D) for the localization of breast cancer patients treated with TomoDirect (TD), a radiotherapy treatment technique with fixed-angle beams performed on a TomoTherapy system. MethodsA method was developed to quickly localize breast cancer patients treated with TD by registering the MV2D images produced before a TD treatment with reference images reconstructed from a kilovoltage CT simulation scanner and by using the projection of the beam-eye-view TD treatment field. Dose and image quality measurements were performed to determine the optimal parameters for acquiring MV2D images. A TD treatment was simulated on a chest phantom equipped with a breast attachment. MVCT and MV2D images were performed for 7 different shifted positions of the phantom and registered by 10 different operators with the simulation kilovoltage CT images. ResultsCompared to MVCT, MV2D imaging reduces the dose by a factor of up to 45 and the acquisition time by a factor of up to 49. Comparing the registration shift values obtained for the phantom images obtained with MVCT in the coarse mode to those obtained with MV2D, the mean difference is 1.0±1.1mm, −1.1mm±1.1, and −0.1±2.2mm, respectively, in the lateral, longitudinal, and vertical directions. ConclusionsWith dual advantages (very fast imaging and a potentially reduced dose to the heart and contralateral organs), MV2D topographic images may be an attractive alternative to MVCT for the localization of breast cancer patients treated with TomoDirect.

Dosimetric aspects of breast radiotherapy with three-dimensional and intensity-modulated radiotherapy helical tomotherapy planning modules

In this work, we investigated the dosimetric differences between the intensity-modulated radiotherapy (IMRT) plans and the three-dimensional (3D) helical plans based on the TomoTherapy system. A total of 15 patients with supine setup were randomly selected from the data base. For patients with lumpectomy planning target volume (PTV), regional lymph nodes were also included as part of the target. For dose sparing, the significant differences between the helical IMRT and helical 3D were only found in the heart and contralateral breast. For the dose to the heart, helical IMRT reduced the maximum point dose by 6.98Gy compared to the helical 3D plan (p = 0.01). For contralateral breast, the helical IMRT plans significantly reduced the maximum point dose by 5.6Gy compared to the helical 3D plan. However, compared to the helical 3D plan, the helical IMRT plan increased the volume for lower dose (13.08% increase in V5Gy, p = 0.01). In general, there are no significant differences in dose sparing between helical IMRT and helical 3D plans.

A Feasibility Study on the Use of TomoTherapy Megavoltage Computed Tomography Images for Palliative Patient Treatment Planning.

Dedicated rapid access palliative radiation therapy improves patients’ access to care, allowing more timely treatment which would positively impact on quality of life. The TomoTherapy (Accuray, Sunnyvale, CA) system provides megavoltage (MV) fan-beam computed tomography (FBCT) as the image guidance technique, and a module called “statRT” that allows the use of these MV FBCT images for direct planning. The possibility of using this imaging modality for palliative radiotherapy treatment planning is assessed against accepted planning CT standards by performing tests following AAPM TG 66 and an end-to-end measurement. Results have shown that MV FBCT images acquired by TomoTherapy are of sufficient quality for the purpose of target delineation and dose calculation for palliative treatments. Large image noise and extended scan acquisition time are the two main drawbacks, so this imaging modality should only be used for palliative treatments at areas with well-known, easily distinguishable, and relatively immobile targets such as spine and whole brain.

Efficacy of stereotactic radiotherapy for brain metastases using dynamic jaws technology in the helical tomotherapy system.

Objective:Dynamic jaws (DJ) are expected to be useful in stereotactic radiotherapy (SRT) for brain metastases (BM). The efficacy and optimal dose fractionation were investigated.Methods:In a planning study, 63 treatment plans were generated for the following 3 conditions: 1.0-cm fixed jaws (FJ), 2.5-cm FJ and 2.5-cm DJ. In a clinical study, 30 Gy/3 fr, 35 Gy/5 fr or 37.5 Gy/5 fr were prescribed depending on tumour size. Clinical results of groups treated with 2.5-cm DJ plans and 1.0-cm FJ were compared.Results:In the planning study, the treatment times in 2.5-cm DJ and FJ plans were less than that in 1.0-cm FJ plans (p < 0.001). The brain doses in 1.0-cm FJ plans and 2.5-cm DJ plans were smaller than those in 2.5-cm FJ plans (p < 0.05). In the clinical study, 34 patients with 68 BM were treated with SRT. Of those, 15 patients with 34 BM were treated with 2.5-cm DJ plans and 19 patients with 34 BM were treated with 1.0-cm FJ plans. The overall survival and local tumour control (LC) rates were 52 and 93% at 12 months, respectively. The DJ system achieved favourable LC and 29% shorter treatment time compared with the FJ system (p < 0.001). Grade 2 or 3 necrosis occurred more frequently in patients with 15 cc or larger tumour volumes (p = 0.05).Conclusion:DJ technology enables treatment time to be reduced without worsening the dose distribution and clinical efficacy. The prescribed doses in this study may be acceptable for patients with small tumour volumes.Advances in knowledge:DJ technology enables treatment time to be reduced without worsening the dose.

SU‐G‐BRA‐14: Dose in a Rigidly Moving Phantom with Jaw and MLC Compensation

Purpose:To validate dose calculation for a rigidly moving object with jaw motion and MLC shifts to compensate for the motion in a TomoTherapy™ treatment delivery.Methods:An off‐line version of the TomoTherapy dose calculator was extended to perform dose calculations for rigidly moving objects. A variety of motion traces were added to treatment delivery plans, along with corresponding jaw compensation and MLC shift compensation profiles. Jaw compensation profiles were calculated by shifting the jaws such that the center of the treatment beam moved by an amount equal to the motion in the longitudinal direction. Similarly, MLC compensation profiles were calculated by shifting the MLC leaves by an amount that most closely matched the motion in the transverse direction. The same jaw and MLC compensation profiles were used during simulated treatment deliveries on a TomoTherapy system, and film measurements were obtained in a rigidly moving phantom.Results:The off‐line TomoTherapy dose calculator accurately predicted dose profiles for a rigidly moving phantom along with jaw motion and MLC shifts to compensate for the motion. Calculations matched film measurements to within 2%/1 mm. Jaw and MLC compensation substantially reduced the discrepancy between the delivered dose distribution and the calculated dose with no motion. For axial motion, the compensated dose matched the no‐motion dose within 2%/1mm. For transverse motion, the dose matched within 2%/3mm (approximately half the width of an MLC leaf).Conclusion:The off‐line TomoTherapy dose calculator accurately computes dose delivered to a rigidly moving object, and accurately models the impact of moving the jaws and shifting the MLC leaf patterns to compensate for the motion. Jaw tracking and MLC leaf shifting can effectively compensate for the dosimetric impact of motion during a TomoTherapy treatment delivery.

SU‐F‐P‐11: Long Term Dosimetric Stability of 6 TomoTherapy Systems

Purpose:The dosimetric stability of six TomoTherapy units was analyzed to investigate changes in performance over time and with system upgrades.Methods:Energy and output were tracked using monitor chamber signal, onboard MVCT detector signal and external ion chamber measurements. The systems (and monitoring periods) include 3 Hi‐Art (67, 61 and 65 mos.), 2 HDA (29 and 25 mos.) and one research unit (7 mo.). Dose Control Stability system (DCS) was installed on 4 systems. Output stability is reported as deviation from reference monitor chamber signal for all systems, and from an external chamber for 4 systems. Energy stability was monitored using the relative (center versus off‐axis) MVCT detector signal and/or the ratio of chamber measurements at 2 depths. The results from the clinical systems were used to benchmark the stability of the research unit, which has the same linear accelerator but runs at a higher dose rate.Results:The output based on monitor chamber data of all six systems is very stable. Non‐ DCS had a standard deviation of 1.7% and 1.8%. As expected, DCS systems had improved standard deviation: 0.003–0.05%. The energy was also very stable for all units. The standard deviation in exit detector flatness was 0.02–0.3%. Ion chamber output and 20/10 cm ratios supported these results. The stability for the research system, as monitored with a variety of metrics, is on par with the existing systems.Conclusion:The output and energy of six TomoTherapy units over a total of almost 10 years is quite stable. For each system, the results are consistent between the different measurement tools and techniques, proving not only the dosimetric stability, but that these quality parameters can be confirmed with various metrics. A research unit operating at a higher dose rate performed as well as the clinical treatment units.University of Wisconsin and Accuray Inc. (vendor of TomoTherapy systems) have a research agreement which supplies funds for research to the University. This project was partially supporting with these funds.

SU‐F‐T‐289: MLC Fluence Sonogram Based Delivery Quality Assurance for Bilateral Breast Irradiation

Purpose:Performing DQA for Bilateral (B‐L) breast tomotherapy is a challenging task due to the limitation of any commercially available detector array or film. Aim of this study is to perform DQA for B‐L breast tomotherapy plan using MLC fluence sinogram.Methods:Treatment plan was generated on Tomotherapy system for B‐L breast tumour. B‐L breast targets were given 50.4 Gy prescribed over 28 fractions. Plan is generated with 6 MV photon beam &amp; pitch was set to 0.3. As the width of the total target is 39 cm (left &amp; right) length is 20 cm. DQA plan delivered without any phantom on the mega voltage computed tomography (MCVT) detector system. The pulses recorded by MVCT system were exported to the delivery analysis software (Tomotherapy Inc.) for reconstruction. The detector signals are reconstructed to a sonogram and converted to MLC fluence sonogram. The MLC fluence sinogram compared with the planned fluence sinogram. Also point dose measured with cheese phantom and ionization chamber to verify the absolute dose componentResults:Planned fluence sinogram and reconstructed MLC fluence sinogram were compared using Gamma metric. MLC positional difference and intensity of the beamlet were used as parameters to evaluate gamma. 3 mm positional difference and 3% beamlet intensity difference were used set for gamma calculation. A total of 26784 non‐zero beamlets were included in the analysis out of which 161 beamlets had gamma more than 1. The gamma passing rate found to be 99.4%. Point dose measurements were within 1.3% of the calculated dose.Conclusion:MLC fluence sinogram based delivery quality assurance performed for bilateral breast irradiation. This would be a suitable alternate for large volume targets like bilateral breast, Total body irradiation etc. However conventional method of DQA should be used to validate this method periodically.

An Evaluation of Inter-Fractional Set-Up Errors in Patients Treated with Distinct Immobilization Equipment for Varying Anatomical Regions

This study aims to evaluate inter-fractional set-up errors in patients treated with distinct immobilization equipment (thermoplastic mask, knee-fix and feet-fix, wing board and vac-lok) for four anatomical regions including brain, head and neck (HN), thorax and pelvis. Data of randomly selected 140 patients who were treated for four anatomical regions were obtained using Hi-Art Helical Tomotherapy (HT) system. Pre-treatment planning was based on automatic registration readings of computed tomography (CT) and mega-voltage computed tomography (MVCT) on a daily basis. Distinct immobilization equipment was used for varying anatomical regions. Individual mean set-up error (M), systematic error (Σ), and random error (σ) values were calculated through daily translational and rotational deviation values. The size of translational, systematic and random error was 1.31 - 4.93 mm for brain, 2.28 - 4.88 mm for HN, 4.04 - 9.90 mm for thorax, and 6.34 - 14.68 mm for pelvis. Rotational values were as follows: 0.06˚ - 0.73˚ for brain, 0.42˚ - 0.6˚ for HN, 0.48˚ - 1.14˚ for thorax and 0.65˚ - 1.05˚ for pelvis. The highest translational, systematic and random error value was obtained from the pelvic regional. The highest standard and random error value in pitch and roll was produced in the rotational direction of the pelvis (0.05˚ and 0.71˚), while the highest error value in yaw was (1.14˚) produced from thorax. Inter-fractional set-up errors were most commonly produced in the pelvis, followed by thorax. Our study results suggest that the highest systematic and random errors are found for thorax and pelvis. Distinct immobilization equipment was important in these results. Safety margins around the clinical target volume (CTV) are changeable for different anatomical regions. A future work could be developed to new equipment for immobilization because of the reduced margins CTV.

Establishment of the Commissioning Procedure for Modifying the Beam Model of Helical Tomotherapy.

Although much evidence about the helical tomotherapy system are available, there is not a document about the procedure of quality assurance (QA) for changing the beam model. This study establishes the commissioning procedure for modifying the beam model of helical tomotherapy. Firstly, some intensity-modulated radiotherapy (IMRT) plans were created, and compared them with the calculated dose and the measured dose. Secondly, the absorbed doses to water in the machine-specific reference field and the plan-class specific reference field with a protocol in Japan; Standard Dosimetry of Absorbed Dose to Water in External Beam Radiotherapy (Standard Dosimetry 12) were measured. Thirdly, we reconfirmed patient-specific quality assurance. The recommended commissioning procedure after the change of the beam model was shown through three verification processes. This report would be helpful for not only changing the beam model of helical tomotherapy but also introducing Standard Dosimetry 12 to a clinic.

Geometric validation of MV topograms for patient localization on TomoTherapy

Our goal was to geometrically validate the use of mega-voltage orthogonal scout images (MV topograms) as a fast and low-dose alternative to mega-voltage computed tomography (MVCT) for daily patient localization on the TomoTherapy system. To achieve this, anthropomorphic head and pelvis phantoms were imaged on a 16-slice kilo-voltage computed tomography (kVCT) scanner to synthesize kilo-voltage digitally reconstructed topograms (kV-DRT) in the Tomotherapy detector geometry. MV topograms were generated for couch speeds of 1–4 cm s−1 in 1 cm s−1 increments with static gantry angles in the anterior-posterior and left-lateral directions. Phantoms were rigidly translated in the anterior-posterior (AP), superior-inferior (SI), and lateral (LAT) directions to simulate potential setup errors. Image quality improvement was demonstrated by estimating the noise level in the unenhanced and enhanced MV topograms using a principle component analysis-based noise level estimation algorithm. Average noise levels for the head phantom were reduced by 2.53 HU (AP) and 0.18 HU (LAT). The pelvis phantom exhibited average noise level reduction of 1.98 HU (AP) and 0.48 HU (LAT). Mattes Mutual Information rigid registration was used to register enhanced MV topograms with corresponding kV-DRT. Registration results were compared to the known rigid displacements, which assessed the MV topogram localization’s sensitivity to daily positioning errors. Reduced noise levels in the MV topograms enhanced the registration results so that registration errors were <1 mm. The unenhanced head MV topograms had discrepancies <2.1 mm and the pelvis topograms had discrepancies <2.7 mm. Result were found to be consistent regardless of couch speed. In total, 64.7% of the head phantom MV topograms and 60.0% of the pelvis phantom MV topograms exactly measured the phantom offsets. These consistencies demonstrated the potential for daily patient positioning using MV topogram pairs in the context bony-anatomy based procedures such as total marrow irradiation, total body irradiation, and cranial spinal irradiation.

Virtual bolus for total body irradiation treated with helical tomotherapy.

Intensity‐modulated radiation therapy (IMRT) for total body irradiation (TBI) is practiced in several centers using the TomoTherapy System. In this context the planning target volume (PTV) is the entire body including the skin. A safety margin in the air surrounding the body should be added to take into account setup errors. But using inverse planning, over‐fluence peak could be generated in the skin region to insure dose homogeneity. This work proposes to study the performance of the use of a virtual bolus (VB). A VB is a material placed on the skin surface during planning, but absent for the real treatment. The optimal VB that compensates large setup errors without introducing a high‐dose increase or hot spots for small setup errors was determined. For two cylindrical phantoms, 20 VBs with different densities, thicknesses or designs were tested. Dose coverage of the PTV (V95%) in the presence of simulated setup errors was computed to assess the VB performance. A measure of the dose increase in the phantom center due to the absence of the VB during treatment was also achieved. Finally, the fluence peak at the phantom edge was measured in complete buildup conditions using a large phantom and a detector matrix. Using these VBs, simulated setup errors were compensated to a minimum value of 2.6 and 2.1 cm for small and large phantom, respectively (and only 1.2 and 1.7 cm with no VB). An optimal double‐layer VB was found with a density of 0.4 kg.m−3 and a total thickness of 8 mm; an inner layer of 5 mm was declared as the target for the treatment planning system and an additional layer of 3 mm was added to avoid the over‐fluence peak. Using this VB, setup errors were compensated up to 2.9 cm. The dose increase was measured to be only +1.5% at the phantom center and over‐fluence peak was strongly decreased.PACS numbers: 87.53 Bn, 87.55 D‐, 87.55 de, 87.55 dk

Evaluation of Time Efficiency of a Tomo HDA System for Helical Tomotherapy Treatment Planning Calculations

Tomo HDA is the latest improved helical tomotherapy system available in the market today. Major improvements of the system comprise of the dynamic jaws, new Linac with a fixed target, dose control system, low arcing magnetron, improved workflow at the operator station and voxel less optimization (VoLO) calculation performed on a graphic processor unit (GPU) platform. After using two Tomo HiArt II systems for nearly a decade we have acquired a Tomo HDA. In this study we have tried to evaluate the relative time efficiency of the VoLO calculation over previous non-VoLO (Central Processor Unit based) calculation in ten different treatment sites and the resulting cost savings. A new Tomo HDA system was installed in our center replacing the older Tomo Hi Art II in December 2013. We used ten different treatment sites on different patients to compare the plan calculation time between the VoLO and the previous non-VoLO system. This did not include the time for CT transfer, contouring, dose constraint set up and patient-specific DQA planning and measurement. The dose per fraction ranged from 1.8 Gy to 3.5 Gy. The number of fractions ranged from 5 to 30. The total dose ranged from 10 Gy to 54 Gy. Eight sites were planned with 5 cm field width and two with 2.5 cm field width. Calculation grid was chosen to be in fine mode except for two cases where it was set at normal. The VoLO calculations were done with dynamic jaws and the non-VoLO with fixed jaws. The actual time spent on VoLO and non-VoLO calculations were recorded for comparison. The non-VoLO calculation time also included the beamlet calculation time. From the total time contribution by different people involved in the planning process, the labor cost was determined. The length of the treatment regions varied from 9.5 cm to 42.5 cm for the ten sites planned. The VoLO calculation time ranged from 15 min to an hour with an average of 34 min. For the non-VoLO calculations, the time ranged from 51 min to 4 hours and 47 min with an average of 1 hour 26 min. Additionally, an average of 4 hours was needed for CT transfer, contouring, dose constraint set up and DQA measurements. From the contribution of time spent by a dosimetrist, radiation oncologist and physicist, the labor cost was determined for two typical cases. The cost saving in treatment planning with VoLO was 32%. The VoLO calculation time was faster resulting in an average of 60% time saving for dose calculation only. When the total treatment planning time is considered, the VoLO planning saved 16% of time on average. The actual beam on time and the MUs for these ten plans were nearly the same by the two methods. From the analysis of the labor cost of the individuals involved in the entire planning process, there was a cost saving of 32% using VoLO.

Efficacy of Stereotactic Radiation Therapy for Brain Metastases Using Dynamic Jaws Technology in the Helical Tomotherapy System: Planning and Clinical Studies

Efficacy of Stereotactic Radiation Therapy for Brain Metastases Using Dynamic Jaws Technology in the Helical Tomotherapy System: Planning and Clinical Studies

Treatment plan comparison of linac step and shoot, tomotherapy, rapidarc, and proton therapy for prostate cancer by using the dosimetrical and the biological indices

The purpose of this study was to use various dosimetrical indices to determine the best intensitymodulated radiation therapy (IMRT) modality - for treating patients with prostate cancer. Ten patients with prostate cancer were included in this study. IMRT plans were designed to include different modalities, including the linac step and shoot, tomotherapy, RapidArc, and proton systems. Various dosimetrical indices, like the prescription isodose to target volume (PITV) ratio, conformity index (CI), homogeneity index (HI), target coverage index (TCI), modified dose homogeneity index (MHI), conformation number (CN), critical organ scoring index (COSI), and quality factor (QF), were determined to compare the different treatment plans. Biological indices, such as the generalized equivalent uniform dose (gEUD) based the tumor control probability (TCP), and the normal tissue complication probability (NTCP), were also calculated and used to compare the treatment plans. The RapidArc plan attained better PTV coverage, as evidenced by its superior PITV, CI, TCI, MHI, and CN values. Regarding organ at risks (OARs), proton therapy exhibited superior dose sparing for the rectum and the bowel in low dose volumes, whereas the tomotherapy and RapidArc plans achieved better dose sparing in high dose volumes. The QF scores showed no significant difference among these plans (p = 0.701). The average TCPs for prostate tumors in the RapidArc, linac and proton plans were higher than the average TCP for Tomotherapy (98.79%, 98.76%, and 98.75% vs. 98.70%, respectively). Regarding the rectum NTCP, RapidArc showed the most favorable result (0.09%) whereas linac resulted in the best bladder NTCP (0.08%).

Tolerance of Superficial Dose to Setup Error With Tomotherapy: Is a Skin Flash Tool Required?

In cancers of the head and neck, gross tumor or areas at risk of microscopic disease often lie close to the skin, while the skin itself may not be at risk. With intensity-modulated radiotherapy, setup errors can lead to underdosage of superficial structures because the collimator will not by default open beyond the skin surface to apply coverage in the air overlying the skin. Thus, small setup errors can move superficial structures out of field for some beams. Some planning systems allow for manually extrapolating fluence for beams tangential to superficial targets. It is unclear whether this problem is significant with tomotherapy. A head and neck phantom was utilized. A 3-mm bolus was used to represent the skin and allow placement of dosimeters at 3 mm depth. Thermoluminescent dosimeters were placed at reproducible points on the skin surface and at 3 mm depth. The phantom was irradiated, with the target volume deep to the thermoluminescent dosimeters receiving a dose of 5 Gy. This process was repeated with the phantom displaced 2.5 mm and again with a displacement of 5 mm. These displacements simulated setup errors that in clinical practice would correspond to bending or twisting of the neck that could not be corrected with rotations or translations. When the phantom was displaced 2.5 mm, the dose measured at 3 mm depth was 99.2% (95.9%-102.5%) of the control. With a 5-mm displacement, the dose at 3 mm only dropped to 91.1% (88.8%-93.4%) of the control. Dose measured at skin surface decreased to a greater degree with such setup error. Dose at superficial depths degraded only slightly with 2.5-mm and even 5-mm displacements. With the tomotherapy system, superficial dose appears to be robust to clinically relevant setup errors. However, if the skin is at risk, bolus should be used to ensure adequate coverage.

Evaluation of Transit Dosimetry Software for Helical Tomotherapy

3D in vivo dosimetry is the only method capable of verifying the entire radiation therapy chain, including a potential machine malfunctioning, data corruption, or changes in patient anatomy. The purpose of this work was to evaluate limits and capabilities of a new transit dosimetry software for use with tomotherapy system by testing on heterogeneous phantom.