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289 Dose determination in rectum and urethra with TLD dosimeters in prostate brachytherapy with High Dose Rate (HDR)
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POSTERS Brachytherapy 288 Correlation between Computed Dose And Clinical Doses using TL Measurement and Evaluation of Doses to Local A n a t o m y in Gynecological Radiotherapy
S. P. Mishra 1, B. PauP, R.R. Ghosh 2, V. Gupta I, A.Kr. Srivastava 1 IRegional Cancer Centre, Karnala Nehru Memorial Hospital, Medical Physics Allahabad, India 2Regional Cancer Hospital, Kamala Nehru Memorial Hospital, Radiation Oncology Allahabad, India Introduction: The advent of 3-D imaging and computation technology has felicitated the co-relation of tumour with local anatomy and the doses received by them. In this study a comprehensive evaluation has been carried out for establishing the correlation between the planned dose, delivered and doses to local anatomy in gynaecological radiotherapy. 3- D Plato and Rad Plan treatment planning systems have been utilized for RT planning TPS projected doses and in-vivo dosimetry have been compared and corrective measures suggested. Radiation reaction data in the light of ICRU 50 and 62 recommendations have been studied. Methods: The CT scanner has been used for auto contouring, segregation of mid plane and off axis plane, tumour shrinkage and 3-D view of tumour topology in corelation to the local anatomy. The two TPS have been utilised for obtaining the 3-D isodose and dose volume histogram in cases planned. A well calibrated TLD dosimeter and PTW dosimeter have been utilised to measure the in-vivo doses. Rectal, Bladder, Cervical and entrance and exit doses has been measured and compared with the doses projected by TPS. Results and Discussion: PTW dosimetry for "On line' dosimetry to verify the clinical dose delivery was utilised. TLD has been used to measure the bladder and rectum dose during gynaecological radiotherapy. By comparing the measured dose and calculated dose out put of the two types of TPS were accredited. It was found that the variation in the planned dose and delivered dose are wide. Bladder and Rectum receives 30%-45% dose in respect to reference dose. The results will be presented. The valuation of dosimetry status for teletherapy and brachytherapy is very important and in brachytherapy it was found that there is a variation of ± 8% in the source strength than quoted. The difference between calculated dose and measured dose was ± 7%. Two TPS were found to vary + 9.5% in dose profile projected. Conclusion: In the last two decades the development in imaging, 3-D dosimeter and conformal Radiotherapy has yielded a better optimized view of matched peripheral dose to the tumour and local anatomy. It is thus important that calculated dosimetry data should be commensurate (± 3%) with the in-vivo delivery dose. This will improve the results and help in establishing treatment auditing of TPS. References 1. Munzenrider, John F., Use of body scanner in radiotherapy treatment planning in cancer, 40, 170-179, (1997) 2. Stewart J. R., Hicks J. A., Mot. Boone and Simpson L. D.: Computed tomography in radiation therapy. Int. J. Radiation oncology. Biol Physc. 4, 313-324, (1978) 3. ICRU-62, (2001)
Fernandez1, P. SanchezI, J. Vivanco 1, D. SanzI, A. De la Rua2, P. Prada 2 1Hospital Central de Asturias Unidad de Radiofisica, Oviedo, Spain 2Hospital Central de Asturias Oncologia Radioterapica, Oviedo, Spain Introduction: In our hospital the patients of prostate cancer are treated with external radiotherapy and two sessions (1150 cGy/session) of HDR along the course of the treatment. I t is known that the two structures that limit the total dose with this last technique are the rectum and the urethra. Thus, it is very important to verify that the dose calculated by the treatment planning system (Plato BPS v14.2) is correct, above all bearing in mind that during the irradiation the transrectal probe is moved away, as that the irradiation conditions do not correspond with those of the planning in real time and the distribution of the dose calculated in the rectum is theoretically inferior. Hyaluronic acid (Restylane sub-Q) has recently begun to be used in the second application of HDR, with the purpose of separating the prostate gland from the rectum and reducing the dose to the latter. To verify its usefulness, estimate the real dose that the rectum receives and to check the accuracy of the treatment planning system (TPS), TLD dosimeters have been used bearing in mind its great special resolution and small size Materials and Methods: In this work a total of 40 rods of LiF (TLD-100) of Harshaw with dimensions of 1 minx6 mm have been used, together with the reader model 3500 of the same brand. For the annealing a PTW-TLDO oven has been used with a cycle of lh at 400oc and 2h at 80oc. In the reading of TLD's a pre-readout annealing of 20 s at 160oc has been used. The calibration of the dosimeters has been carried out in a 60-Co unit with a dose of 1000 cGy at a depth of 5 mm with a field size of 18x18 cm in slabs of solid water. The sensitivity factor for each of the dosimeters has been calculated by subtracting the reading of the background. The non-linearity factor has been measured in the dose range between 50-1600 cGy that exceeds the one received in the rectum and urethra with our application technique and optimization. Finally, the response of the TLD's due to spectral change has been measured in a range of distance of 1-8 cm from the source. We have found that this response varies from 1.00±0.02 to 1.15±0.09, respectively. Results: In the 27 measures carried out a mean of 10 dosimeters has been used for the dose determination in the rectum and urethra. The difference between the urethra mean dose calculated by the TPS and the measured with the TLD's has been of 0.2%±6.5%. The rectum mean dose measured is inferior to the one calculated by the TPS in a value of -51.3%±14.7% without correcting the TLD's doses due the highest distance of the 192-Ir source positions. The percentage of mean dose in rectum regarding the mean dose in urethra measured with TLD is of 39.0%±9.5% without the use of the Restylane Sub-Q and 27.4%±6.4% with the use of the Restylane with p=0.007. Discussion: The calculated doses in the rectum by the TPS when the transrectal probe is moved away represent an overestimation of around 50%. The use of the Restyilane sub-Q seems promising because the doses in the rectum are even inferior. The coincidence in the mean dose in urethra between the TPS and the measures by TLD it excellent
290 Quality system
control
of a
brachytherapy
dose
planning
289 Dose determination in rectum and urethra with TLD dosimeters in prostate brachytherapy with High Dose Rate ( H D R )
P. Sioil~, R. Parkkinen Radiation and Nuclear Safety Authority, Helsinki, Finland
J. Gonzalez1, A. Rodriguez1, D. Crelgo 1, A. Villac~I, J.
Quality control in brachytherapy usually covers the source
POSTERS Brachytherapy 288 Correlation between Computed Dose And Clinical Doses using TL Measurement and Evaluation of Doses to Local A n a t o m y in Gynecological Radiotherapy
S. P. Mishra 1, B. PauP, R.R. Ghosh 2, V. Gupta I, A.Kr. Srivastava 1 IRegional Cancer Centre, Karnala Nehru Memorial Hospital, Medical Physics Allahabad, India 2Regional Cancer Hospital, Kamala Nehru Memorial Hospital, Radiation Oncology Allahabad, India Introduction: The advent of 3-D imaging and computation technology has felicitated the co-relation of tumour with local anatomy and the doses received by them. In this study a comprehensive evaluation has been carried out for establishing the correlation between the planned dose, delivered and doses to local anatomy in gynaecological radiotherapy. 3- D Plato and Rad Plan treatment planning systems have been utilized for RT planning TPS projected doses and in-vivo dosimetry have been compared and corrective measures suggested. Radiation reaction data in the light of ICRU 50 and 62 recommendations have been studied. Methods: The CT scanner has been used for auto contouring, segregation of mid plane and off axis plane, tumour shrinkage and 3-D view of tumour topology in corelation to the local anatomy. The two TPS have been utilised for obtaining the 3-D isodose and dose volume histogram in cases planned. A well calibrated TLD dosimeter and PTW dosimeter have been utilised to measure the in-vivo doses. Rectal, Bladder, Cervical and entrance and exit doses has been measured and compared with the doses projected by TPS. Results and Discussion: PTW dosimetry for "On line' dosimetry to verify the clinical dose delivery was utilised. TLD has been used to measure the bladder and rectum dose during gynaecological radiotherapy. By comparing the measured dose and calculated dose out put of the two types of TPS were accredited. It was found that the variation in the planned dose and delivered dose are wide. Bladder and Rectum receives 30%-45% dose in respect to reference dose. The results will be presented. The valuation of dosimetry status for teletherapy and brachytherapy is very important and in brachytherapy it was found that there is a variation of ± 8% in the source strength than quoted. The difference between calculated dose and measured dose was ± 7%. Two TPS were found to vary + 9.5% in dose profile projected. Conclusion: In the last two decades the development in imaging, 3-D dosimeter and conformal Radiotherapy has yielded a better optimized view of matched peripheral dose to the tumour and local anatomy. It is thus important that calculated dosimetry data should be commensurate (± 3%) with the in-vivo delivery dose. This will improve the results and help in establishing treatment auditing of TPS. References 1. Munzenrider, John F., Use of body scanner in radiotherapy treatment planning in cancer, 40, 170-179, (1997) 2. Stewart J. R., Hicks J. A., Mot. Boone and Simpson L. D.: Computed tomography in radiation therapy. Int. J. Radiation oncology. Biol Physc. 4, 313-324, (1978) 3. ICRU-62, (2001)
Fernandez1, P. SanchezI, J. Vivanco 1, D. SanzI, A. De la Rua2, P. Prada 2 1Hospital Central de Asturias Unidad de Radiofisica, Oviedo, Spain 2Hospital Central de Asturias Oncologia Radioterapica, Oviedo, Spain Introduction: In our hospital the patients of prostate cancer are treated with external radiotherapy and two sessions (1150 cGy/session) of HDR along the course of the treatment. I t is known that the two structures that limit the total dose with this last technique are the rectum and the urethra. Thus, it is very important to verify that the dose calculated by the treatment planning system (Plato BPS v14.2) is correct, above all bearing in mind that during the irradiation the transrectal probe is moved away, as that the irradiation conditions do not correspond with those of the planning in real time and the distribution of the dose calculated in the rectum is theoretically inferior. Hyaluronic acid (Restylane sub-Q) has recently begun to be used in the second application of HDR, with the purpose of separating the prostate gland from the rectum and reducing the dose to the latter. To verify its usefulness, estimate the real dose that the rectum receives and to check the accuracy of the treatment planning system (TPS), TLD dosimeters have been used bearing in mind its great special resolution and small size Materials and Methods: In this work a total of 40 rods of LiF (TLD-100) of Harshaw with dimensions of 1 minx6 mm have been used, together with the reader model 3500 of the same brand. For the annealing a PTW-TLDO oven has been used with a cycle of lh at 400oc and 2h at 80oc. In the reading of TLD's a pre-readout annealing of 20 s at 160oc has been used. The calibration of the dosimeters has been carried out in a 60-Co unit with a dose of 1000 cGy at a depth of 5 mm with a field size of 18x18 cm in slabs of solid water. The sensitivity factor for each of the dosimeters has been calculated by subtracting the reading of the background. The non-linearity factor has been measured in the dose range between 50-1600 cGy that exceeds the one received in the rectum and urethra with our application technique and optimization. Finally, the response of the TLD's due to spectral change has been measured in a range of distance of 1-8 cm from the source. We have found that this response varies from 1.00±0.02 to 1.15±0.09, respectively. Results: In the 27 measures carried out a mean of 10 dosimeters has been used for the dose determination in the rectum and urethra. The difference between the urethra mean dose calculated by the TPS and the measured with the TLD's has been of 0.2%±6.5%. The rectum mean dose measured is inferior to the one calculated by the TPS in a value of -51.3%±14.7% without correcting the TLD's doses due the highest distance of the 192-Ir source positions. The percentage of mean dose in rectum regarding the mean dose in urethra measured with TLD is of 39.0%±9.5% without the use of the Restylane Sub-Q and 27.4%±6.4% with the use of the Restylane with p=0.007. Discussion: The calculated doses in the rectum by the TPS when the transrectal probe is moved away represent an overestimation of around 50%. The use of the Restyilane sub-Q seems promising because the doses in the rectum are even inferior. The coincidence in the mean dose in urethra between the TPS and the measures by TLD it excellent
290 Quality system
control
of a
brachytherapy
dose
planning
289 Dose determination in rectum and urethra with TLD dosimeters in prostate brachytherapy with High Dose Rate ( H D R )
P. Sioil~, R. Parkkinen Radiation and Nuclear Safety Authority, Helsinki, Finland
J. Gonzalez1, A. Rodriguez1, D. Crelgo 1, A. Villac~I, J.
Quality control in brachytherapy usually covers the source