Does the fluence map editing in electronic tissue compensator improve dose homogeneity in bilateral field plan of head and neck patients?

The purpose of this study was to evaluate the effect of fluence map editing in electronic tissue compensator (ETC) on the dose homogeneity for head and neck cancer patients. Treatment planning using 6-MV X-rays and bilateral field arrangement employing ETC was carried out on the computed tomography (CT) datasets of 20 patients with head and neck cancer. All the patients were planned in Varian Eclipse three-dimensional treatment planning system (3DTPS) with dynamic multileaf collimator (DMLC). The treatment plans, with and without fluence editing, was compared and the effect of pre-editing and post-editing the fluence maps in the treatment field was evaluated. The skin dose was measured with thermoluminescent dosimeters (TLDs) and was compared with the skin dose estimated by TPS. The mean percentage volume of the tissue receiving at least 107% of the prescription dose was 5.4 (range 1.5-10; SD 2.4). Post-editing fluence map showed that the mean percentage volume of the tissue receiving at least 107% of the prescription dose was 0.47 (range 0.1-0.9; SD 0.3). The mean skin dose measured with TLD was found to be 74% (range 71-80%) of the prescribed dose while the TPS showed the mean skin dose as 85% (range 80-90%). The TPS overestimated the skin dose by 11%. Fluence map editing thus proved to be a potential tool for improving dose homogeneity in head and neck cancer patients planned with ETC, thus reducing the hot spots in the treatment region as well. The treatment with ETC is feasible with DMLC and does not take any additional time for setup or delivery. The method used to edit the fluence maps is simple and time efficient. Manual control over a plan is essential to create the best treatment plan possible

Multileaf collimator transmission from the first Hi-Art II helical tomotherapy machine in India

The purpose of this study was to measure the multileaf collimator (MLC) transmission from the first Hi-Art II tomotherapy machine installed at the Advanced Center for Treatment, Research, and Education in Cancer (ACTREC). The MLC transmission was measured with an A1SL ion chamber and the radiographic extended dose range (EDR2) film in virtual water slabs at 1.5-cm depth with a source-to-surface distance of 85 cm. The MLC transmission was measured for 30 s with all leaves open and for 360 s with all leaves closed. The movable jaws were set to the calibration field size of 5 x 40 cm at isocenter. The MLC transmission was found to be 0.3% with the ion chamber and 0.32% with the film. Thus, the MLC transmission value was found well within the manufacturer tolerance of 0.5%. MLC can safely be used for the beam modulation during intensity-modulated radiotherapy (IMRT) to deliver accurate doses to the patients

Does the fluence map editing in electronic tissue compensator improve dose homogeneity in bilateral field plan of head and neck patients?

The purpose of this study was to evaluate the effect of fluence map editing in electronic tissue compensator (ETC) on the dose homogeneity for head and neck cancer patients. Treatment planning using 6-MV X-rays and bilateral field arrangement employing ETC was carried out on the computed tomography (CT) datasets of 20 patients with head and neck cancer. All the patients were planned in Varian Eclipse three-dimensional treatment planning system (3DTPS) with dynamic multileaf collimator (DMLC). The treatment plans, with and without fluence editing, was compared and the effect of pre-editing and post-editing the fluence maps in the treatment field was evaluated. The skin dose was measured with thermoluminescent dosimeters (TLDs) and was compared with the skin dose estimated by TPS. The mean percentage volume of the tissue receiving at least 107% of the prescription dose was 5.4 (range 1.5-10; SD 2.4). Post-editing fluence map showed that the mean percentage volume of the tissue receiving at least 107% of the prescription dose was 0.47 (range 0.1-0.9; SD 0.3). The mean skin dose measured with TLD was found to be 74% (range 71-80%) of the prescribed dose while the TPS showed the mean skin dose as 85% (range 80-90%). The TPS overestimated the skin dose by 11%. Fluence map editing thus proved to be a potential tool for improving dose homogeneity in head and neck cancer patients planned with ETC, thus reducing the hot spots in the treatment region as well. The treatment with ETC is feasible with DMLC and does not take any additional time for setup or delivery. The method used to edit the fluence maps is simple and time efficient. Manual control over a plan is essential to create the best treatment plan possible

Multileaf collimator transmission from the first Hi-Art II helical tomotherapy machine in India

The purpose of this study was to measure the multileaf collimator (MLC) transmission from the first Hi-Art II tomotherapy machine installed at the Advanced Center for Treatment, Research, and Education in Cancer (ACTREC). The MLC transmission was measured with an A1SL ion chamber and the radiographic extended dose range (EDR2) film in virtual water slabs at 1.5-cm depth with a source-to-surface distance of 85 cm. The MLC transmission was measured for 30 s with all leaves open and for 360 s with all leaves closed. The movable jaws were set to the calibration field size of 5 x 40 cm at isocenter. The MLC transmission was found to be 0.3% with the ion chamber and 0.32% with the film. Thus, the MLC transmission value was found well within the manufacturer tolerance of 0.5%. MLC can safely be used for the beam modulation during intensity-modulated radiotherapy (IMRT) to deliver accurate doses to the patients

Characterizing and configuring motorized wedge for a new generation telecobalt machine in a treatment planning system

A new generation telecobalt unit, Theratron Equinox-80, (MDS Nordion, Canada) has been evaluated. It is equipped with a single 60-degree motorized wedge (MW), four universal wedges (UW) for 150, 300, 450 and 600. MW was configured in Eclipse (Varian, Palo Alto, USA) 3D treatment planning system (TPS). The profiles and central axis depth doses (CADD) were measured with radiation field analyzer blue water phantom for MW. These profiles and CADD for MW were compared with UW in a homogeneous phantom generated in Eclipse for various field sizes. The absolute dose was measured for a field size of 10 x 10 cm2 only in a MEDTEC water phantom at 10 cm depth with a 0.13 cc thimble ion chamber (Scanditronix Wellhofer, Uppsala, Sweden) and a NE electrometer (Nuclear Enterprises, UK). Measured dose with ion chamber was compared with the TPS predicted dose. MW angle was verified on the Equinox for four angles (15o, 30o, 45o and 60o). The variation in measured and calculated dose at 10 cm depth was within 2%. The measured and the calculated wedge angles were in well agreement within 2o. The motorized wedges were successfully configured in Eclipse for four wedge angles

Characterization of metal oxide field-effect transistors for first helical tomotherapy Hi-Art II unit in India

Purpose : To characterize metal oxide semiconductor field-effect transistors (MOSFETs) for a 6-MV photon beam with a first helical tomotherapy Hi-Art II unit in India. Materials and Methods : Standard sensitivity MOSFETs were first calibrated and then characterized for reproducibility, field size dependence, angular dependence, fade effects, and temperature dependence. The detector sensitivity was estimated for static as well as rotational modes for three jaw settings (1.0 cm 7 40 cm, 2.5 cm 7 40 cm, and 5 cm 7 40 cm) at 1.5-cm depth with a source-to-axis distance (SAD) of 85 cm in virtual water slabs. The A1SL ion chamber and thermoluminescence dosimeters (TLDs) were used to compare the results. Results : No significant difference was found in the detector sensitivity for static and rotational procedures. The average detector sensitivity for static procedures was 1.10 mV/cGy (SD 0.02) while it was 1.12 mV/cGy (SD 0.02) for rotational procedures. The average detector sensitivity found was the same within the experimental uncertainty for static and rotational dose deliveries. The MOSFET reading was consistent and its reproducibility was excellent (+0.5%) while there was no significant dependence of field size. The angular dependence of less than 1.0% was observed. There was negligible fading effect of the MOSFET. The MOSFET response was found independent of temperature in the range 18\ub0-30\ub0. The ion chamber readings were assumed to be a reference for the estimation of the MOSFET calibration factor. The ion chamber and the TLD were in good agreement (+2%) with each other. Conclusion : This study deals only with the measurements and calibration performed on the surface of the phantom. MOSFET was calibrated and validated for phantom surface measurements for a 6-MV photon beam generated by a tomotherapy machine. The sensitivity of the detector was the same for both modes of treatment delivery with tomotherapy. The performance of the MOSFET was validated for and satisfactory for the helical tomotherapy Hi-Art II unit. However, MOSFET may be used for in vivo surface dosimetry only after it is calibrated under the conditions replicating as much as possible the manner in which the dosimeter will be used clinically

Dosimetric validation of new semiconductor diode dosimetry system for intensity modulated radiotherapy

Introduction: The new diode Isorad was validated for intensity modulated radiotherapy (IMRT) and the observations during the validation are reported. Materials and Methods: The validation includes intrinsic precision, post-irradiation stability, dose linearity, dose-rate effect, angular response, source to surface (SSD) dependence, field size dependence, and dose calibration. Results: The intrinsic precision of the diode was more than 1% (1 σ). The linearity found in the whole range of dose analyzed was 1.93% (R 2 = 1). The minimum and maximum variation in the measured and calculated dose were found to be 0.78% (with 25 MU at ioscentre) and 4.8% (with 1000 MU at isocentre), respectively. The maximal variation in angular response with respect to arbitrary angle 0° found was 1.31%. The diode exhibited a 51.7% and 35% decrease in the response in the 35 cm and 20 cm SSD range, respectively. The minimum and the maximum variation in the measured dose from the diode and calculated dose were 0.82% (5 cm × 5 cm) and 3.75% (30 cm × 30 cm), respectively. At couch 270°, the response of the diode was found to vary maximum by 1.4% with ΁ 60 gantry angle. Mean variation between measured dose with diode and planned dose by TPS was found to be 1.3% (SD 0.75) for IMRT patient-specific quality assurance. Conclusion: For the evaluation of IMRT, use of cylindrical diode is strongly recommended

Electronic tissue compensation achieved with both dynamic and static multileaf collimator in eclipse treatment planning system for Clinac 6 EX and 2100 CD Varian linear accelerators: Feasibility and dosimetric study

Dynamic multileaf collimator (DMLC) and static multileaf collimator (SMLC), along with three-dimensional treatment planning system (3-D TPS), open the possibility of tissue compensation. A method using electronic tissue compensator (ETC) has been implemented in Eclipse 3-D TPS (V 7.3, Varian Medical Systems, Palo Alto, USA) at our center. The ETC was tested for head and neck conformal radiotherapy planning. The purpose of this study was to verify the feasibility of DMLC and SMLC in head and neck field irradiation for delivering homogeneous dose in the midplane at a pre-defined depth. In addition, emphasis was given to the dosimetric aspects in commissioning ETC in Eclipse. A Head and Neck Phantom (The Phantom Laboratory, USA) was used for the dosimetric verification. Planning was carried out for both DMLC and SMLC ETC plans. The dose calculated at central axis by eclipse with DMLC and SMLC was noted. This was compared with the doses measured on machine with ion chamber and thermoluminescence dosimetry (TLD). The calculated isodose curves and profiles were compared with the measured ones. The dose profiles along the two major axes from Eclipse were also compared with the profiles obtained from Amorphous Silicon (AS500) Electronic portal imaging device (EPID) on Clinac 6 EX machine. In uniform dose regions, measured dose values agreed with the calculated doses within 3%. Agreement between calculated and measured isodoses in the dose gradient zone was within 3 mm. The isodose curves and the profiles were found to be in good agreement with the measured curves and profiles. The measured and the calculated dose profiles along the two major axes were flat for both DMLC and SMLC. The dosimetric verification of ETC for both the linacs demonstrated the feasibility and the accuracy of the ETC treatment modality for achieving uniform dose distributions. Therefore, ETC can be used as a tool in head and neck treatment planning optimization for improved dose uniformity

On the transit dose from motorized wedge treatment in Equinox-80 telecobalt unit

Purpose: To estimate the transit dose from motorized wedge (MW) treatment in Equinox-80 telecobalt machine. Materials and Methods: Two plans were generated in Eclipse treatment planning system with universal wedge (UW) and MW each for 10x10 cm 2 . The transit dose was measured with 0.6 cc cylindrical ion chamber and thermoluminescent dosimeters (TLD) chips at a depth of 5 cm with source to axis distance (SAD) 80 cm. Results: The measured dose with ion chamber was in well agreement with the calculated dose from Eclipse within ± 2%. The planned dose was 100 cGy while the measured absorbed dose with ion chamber for 15°, 30°, 45° and 60° MW treatment was found to be 100.94, 101.04, 100.72 and 99.33 cGy respectively. For 15°, 30°, 45° and 60° UW treatment, the measured absorbed dose was 99.33, 97.67, 97.77 and 99.57 cGy respectively. Similarly the measured absorbed dose with TLD was within ± 3% with the planned dose for universal wedge (UW) and MW. From the experimental measurements, it was found that there was no significant contribution of transit dose during MW treatment. Conclusion: The actual measurements carried out with ion chamber in Equinox-80 machine for UW and MW revealed no variation between the doses delivered. The doses were comparable for both UW and MW treatments. The results from TLD measurements additionally confirmed no variation between the doses delivered with UW and MW. It was also demonstrated that the observed excess or less transit dose with MW does not have any significant clinical impact. This assured the safe dose delivery with MW

On the transit dose from motorized wedge treatment in Equinox-80 telecobalt unit

Purpose: To estimate the transit dose from motorized wedge (MW) treatment in Equinox-80 telecobalt machine. Materials and Methods: Two plans were generated in Eclipse treatment planning system with universal wedge (UW) and MW each for 10x10 cm 2 . The transit dose was measured with 0.6 cc cylindrical ion chamber and thermoluminescent dosimeters (TLD) chips at a depth of 5 cm with source to axis distance (SAD) 80 cm. Results: The measured dose with ion chamber was in well agreement with the calculated dose from Eclipse within \ub1 2%. The planned dose was 100 cGy while the measured absorbed dose with ion chamber for 15\ub0, 30\ub0, 45\ub0 and 60\ub0 MW treatment was found to be 100.94, 101.04, 100.72 and 99.33 cGy respectively. For 15\ub0, 30\ub0, 45\ub0 and 60\ub0 UW treatment, the measured absorbed dose was 99.33, 97.67, 97.77 and 99.57 cGy respectively. Similarly the measured absorbed dose with TLD was within \ub1 3% with the planned dose for universal wedge (UW) and MW. From the experimental measurements, it was found that there was no significant contribution of transit dose during MW treatment. Conclusion: The actual measurements carried out with ion chamber in Equinox-80 machine for UW and MW revealed no variation between the doses delivered. The doses were comparable for both UW and MW treatments. The results from TLD measurements additionally confirmed no variation between the doses delivered with UW and MW. It was also demonstrated that the observed excess or less transit dose with MW does not have any significant clinical impact. This assured the safe dose delivery with MW