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LATE SIDE EFFECTS AND MODERN RADIOTHERAPY TECHNIQUES IN THE TREATMENT OF BREAST CANCER
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T REATMENT PLANNING AND DOSE CALCULATION
array, MapCHECKTM . All data are normalised relative to the dose at the central axis for the open 2020 cm2 field at 5 cm depth and a SPD of 95 cm.The new features in the beam model aim primarily at the performance for IMRT plans. The performance of the enhanced model for IMRT cases has therefore also been evaluated by comparisons with MapCHECKTM measurements. Results: The enhanced beam model underestimates the dose behind the backup diaphragm, the relative central-axis dose is 10% and 6% for measurements and TPS, respectively. For the dose behind the MLC bank, a FIL of 0.0115 reproduces the average distribution, but the peeks and dips are underestimated. A FIL of 0.0115 leds to an underestimation of the dose behind the combination of MLC and backup diaphragm. For this shielding combination a FIL of 0.015 gives a better agreement. Gamma analysis (3%/3mm) of IMRT plans calculated in water and MapCHECKTM measurements show an improved agreement relative to the classic algorithm. Conclusions: The enhanced model shows better agreement compared to the classic beam model for 2-dimensional diode array measurements for IMRT fields. Another advantage is that the enhanced algorithm is much faster than the classic algorithm. 697 poster (Radiotherapy Technologists (RTT) Track) COMPARISON OF IMRT AND IMPT IN CANCER OF THE BASE OF TONGUE L. Cederblad1 , E. Klaman2 , S. Johansson1 , U. Isacsson2 , E. Blomquist1 1 U PPSALA U NIVERSITY H OSPITAL, Department of Oncology, Radiology and Clinical Immunology, Uppsala, Sweden 2 U PPSALA U NIVERSITY H OSPITAL, Department of Hospital Physics, Uppsala, Sweden
Purpose: To investigate the feasibility and to compare the target coverage and dose to Organs at Risk (OAR), in treatment of cancer of the base of tongue by Intensity Modulated Radio Therapy (IMRT) and Intensity Modulated Proton Therapy (IMPT). To calculate Normal Tissue Complication Probability (NTCP). Materials: Eleven patients, both men and women, with advanced stage cancer of the base of tongue were chosen for the study. Age range was 44-87 years, mean age 61.2 years. Dose planning was performed for IMRT with photons and IMPT with protons, the latter derived from data from the experimental scanned beam. For each patient 9 ports of coplanar fields with 6 MV IMRT with 140 segments, step-and-shoot technique and 3 coplanar fields for 202 MeV IMPT plans were prepared. To the PTV of adjuvant volume 50 Gy in 2-Gy fractions daily was prescribed. The PTV of tumour and engaged lymph nodes was planned with 2.4 Gy to 60 Gy using a simultaneous integrated boost (SIB). Target coverage was between 95-110 % of the prescribed dose. Tolerance dose to the parotid glands was 26 Gy and to the medulla 48 Gy. The dose to the oral cavity was minimized. Dose resolution was 3x3 mm in transversal slices; resolution in axial direction was the same as in the CT study for each patient. NTCP for the parotid glands was calculated using LKB-model with parameters m=0.49, TD50=27.8, n=1. Results: Preliminary data showed that target coverage with IMPT seemed to be more conformal than with IMRT. Conformity indexes were found to be for PTVtot(IMRT)=1.97(range 1.64-2.52), PTVtot(IMPT)=1.38(range 1.24-1.71), PTVboost(IMRT)= 1.48(range 1.34-1.84), PTVboost (IMPT)=1.20(range 1.11-1.34). Using IMPT the prescribed doses could be kept within the planned interval in all patients, while using IMRT only in 10/11 patients. The volume of the oral cavity receiving more than 30 Gy was 17 % smaller in IMPT than in IMRT plans. With IMPT the median dose to medulla was 30.2 Gy, compared to 46.1 Gy using IMRT. NTCP for parotid glands was 11-14% lower for IMPT. Conclusions: Both the conformity and the uniformity of target coverage were better with IMPT. Moreover, all OAR received lower doses with IMPT, thereby NTCP could be decreased. Using IMPT for treatment of patients with advanced cancer of the base of tongue seems to be encouraging. Keyword: cancer of base of tongue, IMPT, IMRT. 698 poster (Radiotherapy Technologists (RTT) Track) LATE SIDE EFFECTS AND MODERN RADIOTHERAPY TECHNIQUES IN THE TREATMENT OF BREAST CANCER S. Johansen1 , D. R. Olsen1 1 I NSTITUTE FOR C ANCER R ESEARCH, Oslo, Norway
Purpose: Exposure of non-target organs such as contralateral breast (CB) and the thyroid gland during radiotherapy (RT) of the breast is often unavoidable. To study the radiation effects on the involved organs at risk (OARs) is thus necessary. The aim of this study was to investigate the dose distribution in the CB and the thyroid gland after treating the breast and regional lymph nodes with 4-field RT. Furthermore, the predicted risk for secondary cancer of the CB was estimated. The relationship between HTHY and radiation was discussed. Also the possibility of reducing risk of secondary cancer by introducing newer irradiation techniques has been investigated. The calculated dose in CB with both Collapsed Cone and Pencil Beam algorithms was also compared.
Materials: For the investigation of dose distribution in the CB and impact of newer radiation techniques on the possibility of reducing dose to the OARs, eight patients with stage IIIII breast cancer undergoing post-operative radiotherapy of the breast and regional lymph nodes were studied. These patients received 46 Gy to the lymph nodes and 50 Gy to the breast/breast wall, given in 2 Gy fractions, using 4 half-beams of 6 MV. For the dose distribution in the thyroid gland, thirty-two breast cancer patients treated with 4-fields RT technique were included. Results: A CB surface and internal dose of 1-15% and 1-3% was shown, respectively. A better agreement between the measured and calculated CB dose with Collapsed Cone algorithm was observed. The data indicated a negligible difference for low doses and a significant difference for higher dose level when using linear and non linear risk models. Our data indicted a median average dose to the thyroid gland of 31 Gy, but a difference in dose characteristics between BC patients who developed hypothyroidism as compared to matched controls could not be revealed. The impact of using three different RT techniques on OARs doses and planning target volume (PTV) coverage of breast cancer patients was investigated. Our data could not demonstrate a preference RT technique, as all three solutions offered a high quality treatment of patients with small differences. Conclusions: The 4-field RT technique exposed the contralateral breast to significant doses. Small differences in CB dose when employing IMRT and RapidArc RT techniques. Robust and valid risk assessment is required, when predicting the risk for radiation induced secondary malignancies in the CB. Our results revealed no difference in dose characteristics between BC patients with and without hypothyroidism."
T REATMENT PLANNING AND DOSE CALCULATION
array, MapCHECKTM . All data are normalised relative to the dose at the central axis for the open 2020 cm2 field at 5 cm depth and a SPD of 95 cm.The new features in the beam model aim primarily at the performance for IMRT plans. The performance of the enhanced model for IMRT cases has therefore also been evaluated by comparisons with MapCHECKTM measurements. Results: The enhanced beam model underestimates the dose behind the backup diaphragm, the relative central-axis dose is 10% and 6% for measurements and TPS, respectively. For the dose behind the MLC bank, a FIL of 0.0115 reproduces the average distribution, but the peeks and dips are underestimated. A FIL of 0.0115 leds to an underestimation of the dose behind the combination of MLC and backup diaphragm. For this shielding combination a FIL of 0.015 gives a better agreement. Gamma analysis (3%/3mm) of IMRT plans calculated in water and MapCHECKTM measurements show an improved agreement relative to the classic algorithm. Conclusions: The enhanced model shows better agreement compared to the classic beam model for 2-dimensional diode array measurements for IMRT fields. Another advantage is that the enhanced algorithm is much faster than the classic algorithm. 697 poster (Radiotherapy Technologists (RTT) Track) COMPARISON OF IMRT AND IMPT IN CANCER OF THE BASE OF TONGUE L. Cederblad1 , E. Klaman2 , S. Johansson1 , U. Isacsson2 , E. Blomquist1 1 U PPSALA U NIVERSITY H OSPITAL, Department of Oncology, Radiology and Clinical Immunology, Uppsala, Sweden 2 U PPSALA U NIVERSITY H OSPITAL, Department of Hospital Physics, Uppsala, Sweden
Purpose: To investigate the feasibility and to compare the target coverage and dose to Organs at Risk (OAR), in treatment of cancer of the base of tongue by Intensity Modulated Radio Therapy (IMRT) and Intensity Modulated Proton Therapy (IMPT). To calculate Normal Tissue Complication Probability (NTCP). Materials: Eleven patients, both men and women, with advanced stage cancer of the base of tongue were chosen for the study. Age range was 44-87 years, mean age 61.2 years. Dose planning was performed for IMRT with photons and IMPT with protons, the latter derived from data from the experimental scanned beam. For each patient 9 ports of coplanar fields with 6 MV IMRT with 140 segments, step-and-shoot technique and 3 coplanar fields for 202 MeV IMPT plans were prepared. To the PTV of adjuvant volume 50 Gy in 2-Gy fractions daily was prescribed. The PTV of tumour and engaged lymph nodes was planned with 2.4 Gy to 60 Gy using a simultaneous integrated boost (SIB). Target coverage was between 95-110 % of the prescribed dose. Tolerance dose to the parotid glands was 26 Gy and to the medulla 48 Gy. The dose to the oral cavity was minimized. Dose resolution was 3x3 mm in transversal slices; resolution in axial direction was the same as in the CT study for each patient. NTCP for the parotid glands was calculated using LKB-model with parameters m=0.49, TD50=27.8, n=1. Results: Preliminary data showed that target coverage with IMPT seemed to be more conformal than with IMRT. Conformity indexes were found to be for PTVtot(IMRT)=1.97(range 1.64-2.52), PTVtot(IMPT)=1.38(range 1.24-1.71), PTVboost(IMRT)= 1.48(range 1.34-1.84), PTVboost (IMPT)=1.20(range 1.11-1.34). Using IMPT the prescribed doses could be kept within the planned interval in all patients, while using IMRT only in 10/11 patients. The volume of the oral cavity receiving more than 30 Gy was 17 % smaller in IMPT than in IMRT plans. With IMPT the median dose to medulla was 30.2 Gy, compared to 46.1 Gy using IMRT. NTCP for parotid glands was 11-14% lower for IMPT. Conclusions: Both the conformity and the uniformity of target coverage were better with IMPT. Moreover, all OAR received lower doses with IMPT, thereby NTCP could be decreased. Using IMPT for treatment of patients with advanced cancer of the base of tongue seems to be encouraging. Keyword: cancer of base of tongue, IMPT, IMRT. 698 poster (Radiotherapy Technologists (RTT) Track) LATE SIDE EFFECTS AND MODERN RADIOTHERAPY TECHNIQUES IN THE TREATMENT OF BREAST CANCER S. Johansen1 , D. R. Olsen1 1 I NSTITUTE FOR C ANCER R ESEARCH, Oslo, Norway
Purpose: Exposure of non-target organs such as contralateral breast (CB) and the thyroid gland during radiotherapy (RT) of the breast is often unavoidable. To study the radiation effects on the involved organs at risk (OARs) is thus necessary. The aim of this study was to investigate the dose distribution in the CB and the thyroid gland after treating the breast and regional lymph nodes with 4-field RT. Furthermore, the predicted risk for secondary cancer of the CB was estimated. The relationship between HTHY and radiation was discussed. Also the possibility of reducing risk of secondary cancer by introducing newer irradiation techniques has been investigated. The calculated dose in CB with both Collapsed Cone and Pencil Beam algorithms was also compared.
Materials: For the investigation of dose distribution in the CB and impact of newer radiation techniques on the possibility of reducing dose to the OARs, eight patients with stage IIIII breast cancer undergoing post-operative radiotherapy of the breast and regional lymph nodes were studied. These patients received 46 Gy to the lymph nodes and 50 Gy to the breast/breast wall, given in 2 Gy fractions, using 4 half-beams of 6 MV. For the dose distribution in the thyroid gland, thirty-two breast cancer patients treated with 4-fields RT technique were included. Results: A CB surface and internal dose of 1-15% and 1-3% was shown, respectively. A better agreement between the measured and calculated CB dose with Collapsed Cone algorithm was observed. The data indicated a negligible difference for low doses and a significant difference for higher dose level when using linear and non linear risk models. Our data indicted a median average dose to the thyroid gland of 31 Gy, but a difference in dose characteristics between BC patients who developed hypothyroidism as compared to matched controls could not be revealed. The impact of using three different RT techniques on OARs doses and planning target volume (PTV) coverage of breast cancer patients was investigated. Our data could not demonstrate a preference RT technique, as all three solutions offered a high quality treatment of patients with small differences. Conclusions: The 4-field RT technique exposed the contralateral breast to significant doses. Small differences in CB dose when employing IMRT and RapidArc RT techniques. Robust and valid risk assessment is required, when predicting the risk for radiation induced secondary malignancies in the CB. Our results revealed no difference in dose characteristics between BC patients with and without hypothyroidism."