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Scalp and Ear Sparing Whole Brain Radiation Therapy Using Helical Tomotherapy
Proceedings of the 49th Annual ASTRO Meeting
2941
Evaluation of a 2D Array Planar Dose Verification System for IMRT Dose Delivery
H. K. Malhotra, J. Liu, T. Tran, M. B. Podgorsak Roswell Park Cancer Institute, Buffalo, NY Purpose/Objective(s): 2D array based multi detector planar dose verification systems play an important role in the pre-treatment quality assurance of an IMRT plan. There are a number of devices available in the market which differ from each other in the type of detectors employed, detector size, spatial distribution of the detectors, maximum field-size available etc. In the present study, we have evaluated the usefulness of PTW729 2D array system in a clinical environment for the pretreatment QA of IMRT dose delivery technique. The results were also compared with those from SunNuclear Mapcheck system. Materials/Methods: 5 patients having IMRT plans generated with Eclipse Treatment Planning system for different targets were used in this study. The plans were designed for sliding-window IMRT dose delivery technique on a Varian 6 MV linear accelerator fitted with millennium MLC. An individual verification plan per field was generated from the clinically approved plans on a standard solid water phantom after resetting the gantry, collimator and couch angles to 0. The SSD of the fields was set to 95 cm and the dose computation was carried out using a grid-size of 2.5 mm. The computed planar dose matrix in the coronal section was then exported to the PTW729 system as well as Sun Nuclear Mapcheck system. PTW729 incorporates 729 5 mm * 5 mm * 5 mm sized cube vented ion-chambers uniformly spaced with center to center distance of 10 mm and useful field size of 27 * 27 cm2. The effective point of measurement of the chambers is assumed to be the back of the front surface of the ion-chambers. Mapcheck systems uses 445 diode detectors [0.8 mm * 0.8 mm] designed for use up to 20 20 cm2 field-size. More over the system has differential spacing of detectors with more detectors located near its central region. Prior to use, both the systems were self-calibrated for absolute dosimetry using a 10 * 10 cm2 field at 95 cm SSD and 5 cm depth in the phantom and 10 cm back-scatter medium. Results: The two systems were compared using the following criterion: the percentage of detectors passing 3%/3 mm criterion as well as the CAX dose measured by the system and the computed plan in absolute dose values. Analysis of our results showed that the mean, median & standard deviation at CAX for the 30 fields were 0.46, 0, 2.32 for PTW729 while the corresponding values for Mapcheck were 2.29, 1.8, 2.59, respectively. Analysis of detectors satisfying 3%/3 mm criterion for PTW729 showed the mean, median & standard deviation of 90.2, 92.16, 6.3 while the respective values for Mapcheck were 90.44, 91.65, 6.68. It is important to know that Mapcheck by default uses a dose threshold of 10% which excludes the detectors having\10% of the maximum dose value from 3%/3 mm computation. These detectors usually lie at the field edges. In PTW729, this threshold is set to 5% and can’t be changed by user. It has been observed that the pass-rate of PTW729 is slightly poorer than Mapcheck as these failures occurs at the detectors which are outside the useful fluence pattern. Once these outliers are removed, PTW729 gives results which are consistent with the treatment planning system computations. Conclusions: Our preliminary measurements demonstrate the usefulness of PTW729 as a pretreatment IMRT QA device for planar dose verification. Author Disclosure: H.K. Malhotra, The 2D array system was provided by PTW-New York Corporation for evaluation, C. Other Research Support; J. Liu, None; T. Tran, None; M.B. Podgorsak, None.
2942
Scalp and Ear Sparing Whole Brain Radiation Therapy Using Helical Tomotherapy
J. P. Limmer1, J. Buskerud1, D. Henrich1, R. Adkins2, V. Mullins2, J. S. Welsh2,3 1 UW Cancer Center-Aspirus, Wausau, WI, 2UW Cancer Center-Riverview, Wisconsin Rapids, WI, 3University of Wisconsin School of Medicine, Madison, WI
Purpose/Objective(s): Whole brain radiation therapy is routinely used for palliation of brain metastases and prophylactic cranial irradiation to prevent brain metastases in small cell lung cancer patients. Common acute adverse effects include scalp irritation, otitis externa, otitis media, and alopecia. We explored the ability of helical tomotherapy to minimize such adverse effects through a scalp and ear sparing approach to whole brain radiotherapy. Materials/Methods: Three patients received whole brain radiation therapy that was planned and administered using the HI-ART TomoTherapy treatment planning software and treatment unit. Dose-volume histograms were generated to evaluate the potential of the scalp-sparing technique in minimizing dose to the scalp and ears. Patient treatment consisted of 30 Gy in 10 fractions for 2 patients. One patient received 30 Gy in 10 fraction and a simultaneous in-field boost to 35 Gy for 4 large symptomatic lesions. Thermoluminescent diodes were used to verify actual dose to the scalp. Results: The DVH’s illustrated effective sparing of the scalp and ears in every patient. The average maximum dose to the scalp was 25 Gy with no more than 50% of the scalp receiving more than 15 Gy. TLD’s confirmed that the expected doses to the scalp based on the isodose curves and DVH’s were what was received. Treatments were efficient with an average beam on time of 5 minutes and pretreatment limited field-of-view MVCT imaging taking about 90 seconds. Overall treatment time including set up, MVCT imaging, readjustment and treatment was typically under 20 minutes even with simultaneous in-field boost. Treatment planning took on average 2 hours. Before, during and after pictures were obtained in all 3 patients and showed no early alopecia but one patient died before the next set of follow-up photographs, another patient shaved his head in anticipation of planned stereotactic radiosurgery and the third patient went on to receive chemotherapy and developed alopecia. No patient complained of any otic/ auditory symptoms during or after the course of treatment. Conclusions: Scalp and ear sparing whole brain radiation therapy is feasible and relatively easily implemented using helical tomotherapy. TLD’s confirmed the low doses predicted from the planning software. Treatment planning and daily treatment requires more input from physicians, radiation therapists, physicists and dosimetrists but can be accomplished efficiently without affecting throughput in a busy clinic. The full value of this approach in terms of reducing alopecia and otitis awaits further clinical experience. Author Disclosure: J.P. Limmer, None; J. Buskerud, None; D. Henrich, None; R. Adkins, None; V. Mullins, None; J.S. Welsh, None.
S729
2941
Evaluation of a 2D Array Planar Dose Verification System for IMRT Dose Delivery
H. K. Malhotra, J. Liu, T. Tran, M. B. Podgorsak Roswell Park Cancer Institute, Buffalo, NY Purpose/Objective(s): 2D array based multi detector planar dose verification systems play an important role in the pre-treatment quality assurance of an IMRT plan. There are a number of devices available in the market which differ from each other in the type of detectors employed, detector size, spatial distribution of the detectors, maximum field-size available etc. In the present study, we have evaluated the usefulness of PTW729 2D array system in a clinical environment for the pretreatment QA of IMRT dose delivery technique. The results were also compared with those from SunNuclear Mapcheck system. Materials/Methods: 5 patients having IMRT plans generated with Eclipse Treatment Planning system for different targets were used in this study. The plans were designed for sliding-window IMRT dose delivery technique on a Varian 6 MV linear accelerator fitted with millennium MLC. An individual verification plan per field was generated from the clinically approved plans on a standard solid water phantom after resetting the gantry, collimator and couch angles to 0. The SSD of the fields was set to 95 cm and the dose computation was carried out using a grid-size of 2.5 mm. The computed planar dose matrix in the coronal section was then exported to the PTW729 system as well as Sun Nuclear Mapcheck system. PTW729 incorporates 729 5 mm * 5 mm * 5 mm sized cube vented ion-chambers uniformly spaced with center to center distance of 10 mm and useful field size of 27 * 27 cm2. The effective point of measurement of the chambers is assumed to be the back of the front surface of the ion-chambers. Mapcheck systems uses 445 diode detectors [0.8 mm * 0.8 mm] designed for use up to 20 20 cm2 field-size. More over the system has differential spacing of detectors with more detectors located near its central region. Prior to use, both the systems were self-calibrated for absolute dosimetry using a 10 * 10 cm2 field at 95 cm SSD and 5 cm depth in the phantom and 10 cm back-scatter medium. Results: The two systems were compared using the following criterion: the percentage of detectors passing 3%/3 mm criterion as well as the CAX dose measured by the system and the computed plan in absolute dose values. Analysis of our results showed that the mean, median & standard deviation at CAX for the 30 fields were 0.46, 0, 2.32 for PTW729 while the corresponding values for Mapcheck were 2.29, 1.8, 2.59, respectively. Analysis of detectors satisfying 3%/3 mm criterion for PTW729 showed the mean, median & standard deviation of 90.2, 92.16, 6.3 while the respective values for Mapcheck were 90.44, 91.65, 6.68. It is important to know that Mapcheck by default uses a dose threshold of 10% which excludes the detectors having\10% of the maximum dose value from 3%/3 mm computation. These detectors usually lie at the field edges. In PTW729, this threshold is set to 5% and can’t be changed by user. It has been observed that the pass-rate of PTW729 is slightly poorer than Mapcheck as these failures occurs at the detectors which are outside the useful fluence pattern. Once these outliers are removed, PTW729 gives results which are consistent with the treatment planning system computations. Conclusions: Our preliminary measurements demonstrate the usefulness of PTW729 as a pretreatment IMRT QA device for planar dose verification. Author Disclosure: H.K. Malhotra, The 2D array system was provided by PTW-New York Corporation for evaluation, C. Other Research Support; J. Liu, None; T. Tran, None; M.B. Podgorsak, None.
2942
Scalp and Ear Sparing Whole Brain Radiation Therapy Using Helical Tomotherapy
J. P. Limmer1, J. Buskerud1, D. Henrich1, R. Adkins2, V. Mullins2, J. S. Welsh2,3 1 UW Cancer Center-Aspirus, Wausau, WI, 2UW Cancer Center-Riverview, Wisconsin Rapids, WI, 3University of Wisconsin School of Medicine, Madison, WI
Purpose/Objective(s): Whole brain radiation therapy is routinely used for palliation of brain metastases and prophylactic cranial irradiation to prevent brain metastases in small cell lung cancer patients. Common acute adverse effects include scalp irritation, otitis externa, otitis media, and alopecia. We explored the ability of helical tomotherapy to minimize such adverse effects through a scalp and ear sparing approach to whole brain radiotherapy. Materials/Methods: Three patients received whole brain radiation therapy that was planned and administered using the HI-ART TomoTherapy treatment planning software and treatment unit. Dose-volume histograms were generated to evaluate the potential of the scalp-sparing technique in minimizing dose to the scalp and ears. Patient treatment consisted of 30 Gy in 10 fractions for 2 patients. One patient received 30 Gy in 10 fraction and a simultaneous in-field boost to 35 Gy for 4 large symptomatic lesions. Thermoluminescent diodes were used to verify actual dose to the scalp. Results: The DVH’s illustrated effective sparing of the scalp and ears in every patient. The average maximum dose to the scalp was 25 Gy with no more than 50% of the scalp receiving more than 15 Gy. TLD’s confirmed that the expected doses to the scalp based on the isodose curves and DVH’s were what was received. Treatments were efficient with an average beam on time of 5 minutes and pretreatment limited field-of-view MVCT imaging taking about 90 seconds. Overall treatment time including set up, MVCT imaging, readjustment and treatment was typically under 20 minutes even with simultaneous in-field boost. Treatment planning took on average 2 hours. Before, during and after pictures were obtained in all 3 patients and showed no early alopecia but one patient died before the next set of follow-up photographs, another patient shaved his head in anticipation of planned stereotactic radiosurgery and the third patient went on to receive chemotherapy and developed alopecia. No patient complained of any otic/ auditory symptoms during or after the course of treatment. Conclusions: Scalp and ear sparing whole brain radiation therapy is feasible and relatively easily implemented using helical tomotherapy. TLD’s confirmed the low doses predicted from the planning software. Treatment planning and daily treatment requires more input from physicians, radiation therapists, physicists and dosimetrists but can be accomplished efficiently without affecting throughput in a busy clinic. The full value of this approach in terms of reducing alopecia and otitis awaits further clinical experience. Author Disclosure: J.P. Limmer, None; J. Buskerud, None; D. Henrich, None; R. Adkins, None; V. Mullins, None; J.S. Welsh, None.
S729