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2830 Reduction in Volume of the Parotid Glands Correlates With Acute Toxicity in Children With Nasopharyngeal Carcinoma (NPC) Treated Using Radiotherapy (RT) G. Bahl, S. Laskar, M. Muckaden, T. Gupta, D. Deshpande, S. Pai, S. K. Shrivastava, K. A. Dinshaw Tata Memorial Hospital, Mumbai, India Purpose/Objective(s): To evaluate the reduction in volume of the parotid glands during RT and correlate this with the development of acute salivary gland toxicity in children with NPC treated using Intensity Modulated Radiation Therapy (IMRT) vs. Conventional Radiotherapy (CRT). Materials/Methods: Seventeen children (11 male and 6 female), with a median age of 12yrs (range: 5 to 16yrs), diagnosed with NPC were treated with a combination of chemotherapy and RT in a prospective study at the Tata Memorial Hospital. Seven (41%) received irradiation using IMRT, while 10 (59%) received CRT. IMRT treatment plans were generating using the ‘Helios’ inverse planning software module of the ‘Cadplan Plus’ Planning System. IMRT was delivered using the sliding window technique with dynamic Multi-Leaf Collimators using 6MV photons. Standard shrinking field technique was used to deliver CRT. CT scans were done before starting and on the last day of RT to measure the volume of the parotid glands. Acute and late normal tissue effects were graded according to the Radiation Therapy Oncology Group (RTOG) radiation morbidity scoring criteria. Sialometery was done to quantitatively assess the grade of xerostomia. Results: A total of 34 parotid glands were evaluated in this study. The median volume of the glands, as assessed on the pre-RT planning CT scan, was 14.3 cc (range 6.7 to 24.6 cc). The prescribed dose to the tumour volume was 70Gy for both IMRT and CRT treatment plans. On analysis of dose volume data, the average ‘mean’ dose to the parotid glands was 31.3Gy (range: 21.3 - 49.3Gy) for the IMRT plans vs. 55.6Gy (range: 48.8 - 61.2) for CRT plans. CT scans done on the last day of RT revealed a reduction in volume of all the 34 glands. The average percentage reduction in size was 39.3% (median: 36.7%, range: 18.3 to 74.2%). Twenty five (73.5%) of the parotid glands had received a mean dose of 32Gy. Within this subgroup, 20 (80%) had a reduction in volume of 35%, while only one (11%) of the glands that received a dose of 32Gy demonstrated a reduction in size of 35% (p0.001). At the end of RT, total of seven patients had atleast one parotid gland that had lost less than or equal to 35% of its original volume. Just 3 (43%) of these children developed acute Grade 2 salivary gland toxicity during RT, as compared to 90% of those who had both parotid glands demonstrating a 35% reduction in size (p0.057). Similarly, none of the children who had a parotid gland with 35% volume loss developed Grade 3 mucositis vs. 60% with both glands having lost 35% volume (p0.017). Furthermore, the median time to development of acute grade 2 toxicity, while on RT, was considerably longer in the first subgroup of patients as compared to the second (51 vs. 27 days, p0.002). This resulted in better compliance and tolerance to treatment. Six of the 7 patients treated with IMRT had a parotid gland with 35% reduction in volume after treatment vs. only one of the 10 children who received CRT (p0.001). Conclusions: The size of the parotid glands reduces significantly during RT and a loss of 35% of volume is associated with an increase in the incidence of acute RT toxicity. The use of IMRT to treat children with NPC results in a significant reduction in the mean dose delivered to the parotid glands as compared to CRT. This leads to less loss of volume of the glands and a reduction in acute toxicity. Author Disclosure: G. Bahl, None; S. Laskar, None; M. Muckaden, None; T. Gupta, None; D. Deshpande, None; S. Pai, None; S.K. Shrivastava, None; K.A. Dinshaw, None. 2831 Accurate Heterogeneous Dose Calculation for Lung Cancer Patients Without High Resolution CT Densities A. I. Saito, J. G. Li, C. Liu, K. R. Olivier, J. F. Dempsey University of Florida, Gainesville, FL Purpose/Objective(s): The aim of this study is to investigate the relative accuracy of megavoltage photon-beam dose calculations using bulk densities applied to 4 distinct regions identified as air, lung, soft tissue, and bone when compared to dose calculations performed with a full density CT. We are investigating the accuracy of this bulk density dose calculation technique for use in an on-board magnetic resonance imaging (MRI) image guided radiation therapy (IGRT) device that is under development at our institution. This IGRT device will utilize real-time MRI taken simultaneously to radiation delivery to compute the dose to the patient. Segmented MRI imaging studies can be used to identify bulk density regions in the patient, but the high resolution density information of CT imaging is lost with this technique. Our hypothesis is that bulk densities can provide an accurate method of heterogeneous photon-beam dose calculation, even in lung cancer patients. Materials/Methods: To test our hypothesis, full CT resolution and bulk density treatment plans were generated for 17 lung cancer cases using a commercial treatment planning system with an adaptive convolution dose calculation algorithm (Pinnacle3, Philips Medicals Systems). Bulk densities were applied to regions identified by an isodensity segmentation tool for each case. Individual and population average densities were compared to the full resolution plan for each case. Monitor units were kept constant and no normalizations were employed. Dose volume histograms (DVH) and dose difference distributions were examined for all cases. Results: The average densities as determined by CT number of the segmented air, lung, soft tissue and bone for the entire set of patients were 0.15, 0.32, 0.98 and 1.11 [g/cc], respectively. Minor density differences existed between the population averages and the individual cases. In all cases, the normal tissue DVH agreed to better than 1%. In 15 out of 17 cases, the target DVH agreed to better than 1%, while 2 cases with bullous emphysema showed inconsistent lung density and agreed to within 4%. Inclusion of pronounced lung vasculature and atelectasis as soft tissue was important for obtaining accurate results. Figure 1 shows the excellent agreement between the two methods: a) axial CT with 4 densities; b) Full CT; c) Overlay of DVHs; and d) axial dose difference. Conclusions: Dose calculation applying bulk tissue density to four regions provides an accurate method of heterogeneous dose calculation, which can be employed with MRI planning data. Dose calculation accuracy in cases with ehphysemic lung can be improved by assigning air to regions with bullous changes in the lung. S677 Proceedings of the 48th Annual ASTRO Meeting
Transcript of 2831
2830 Reduction in Volume of the Parotid Glands Correlates With Acute Toxicity in Children WithNasopharyngeal Carcinoma (NPC) Treated Using Radiotherapy (RT)
G. Bahl, S. Laskar, M. Muckaden, T. Gupta, D. Deshpande, S. Pai, S. K. Shrivastava, K. A. Dinshaw
Tata Memorial Hospital, Mumbai, India
Purpose/Objective(s): To evaluate the reduction in volume of the parotid glands during RT and correlate this with thedevelopment of acute salivary gland toxicity in children with NPC treated using Intensity Modulated Radiation Therapy (IMRT)vs. Conventional Radiotherapy (CRT).
Materials/Methods: Seventeen children (11 male and 6 female), with a median age of 12yrs (range: 5 to 16yrs), diagnosed withNPC were treated with a combination of chemotherapy and RT in a prospective study at the Tata Memorial Hospital. Seven(41%) received irradiation using IMRT, while 10 (59%) received CRT. IMRT treatment plans were generating using the‘Helios’ inverse planning software module of the ‘Cadplan Plus’ Planning System. IMRT was delivered using the slidingwindow technique with dynamic Multi-Leaf Collimators using 6MV photons. Standard shrinking field technique was used todeliver CRT. CT scans were done before starting and on the last day of RT to measure the volume of the parotid glands. Acuteand late normal tissue effects were graded according to the Radiation Therapy Oncology Group (RTOG) radiation morbidityscoring criteria. Sialometery was done to quantitatively assess the grade of xerostomia.
Results: A total of 34 parotid glands were evaluated in this study. The median volume of the glands, as assessed on the pre-RTplanning CT scan, was 14.3 cc (range 6.7 to 24.6 cc). The prescribed dose to the tumour volume was 70Gy for both IMRT andCRT treatment plans. On analysis of dose volume data, the average ‘mean’ dose to the parotid glands was 31.3Gy (range: 21.3- 49.3Gy) for the IMRT plans vs. 55.6Gy (range: 48.8 - 61.2) for CRT plans. CT scans done on the last day of RT revealeda reduction in volume of all the 34 glands. The average percentage reduction in size was 39.3% (median: 36.7%, range: 18.3to 74.2%). Twenty five (73.5%) of the parotid glands had received a mean dose of � 32Gy. Within this subgroup, 20 (80%)had a reduction in volume of � 35%, while only one (11%) of the glands that received a dose of � 32Gy demonstrated areduction in size of �35% (p�0.001). At the end of RT, total of seven patients had atleast one parotid gland that had lost lessthan or equal to 35% of its original volume. Just 3 (43%) of these children developed acute Grade 2 salivary gland toxicityduring RT, as compared to 90% of those who had both parotid glands demonstrating a �35% reduction in size (p�0.057).Similarly, none of the children who had a parotid gland with � 35% volume loss developed Grade 3 mucositis vs. 60% withboth glands having lost �35% volume (p�0.017). Furthermore, the median time to development of acute grade 2 toxicity, whileon RT, was considerably longer in the first subgroup of patients as compared to the second (51 vs. 27 days, p�0.002). Thisresulted in better compliance and tolerance to treatment. Six of the 7 patients treated with IMRT had a parotid gland with �35% reduction in volume after treatment vs. only one of the 10 children who received CRT (p�0.001).
Conclusions: The size of the parotid glands reduces significantly during RT and a loss of �35% of volume is associated withan increase in the incidence of acute RT toxicity. The use of IMRT to treat children with NPC results in a significant reductionin the mean dose delivered to the parotid glands as compared to CRT. This leads to less loss of volume of the glands and areduction in acute toxicity.
Author Disclosure: G. Bahl, None; S. Laskar, None; M. Muckaden, None; T. Gupta, None; D. Deshpande, None; S. Pai, None;S.K. Shrivastava, None; K.A. Dinshaw, None.
2831 Accurate Heterogeneous Dose Calculation for Lung Cancer Patients Without High Resolution CTDensities
A. I. Saito, J. G. Li, C. Liu, K. R. Olivier, J. F. Dempsey
University of Florida, Gainesville, FL
Purpose/Objective(s): The aim of this study is to investigate the relative accuracy of megavoltage photon-beam dosecalculations using bulk densities applied to 4 distinct regions identified as air, lung, soft tissue, and bone when compared to dosecalculations performed with a full density CT. We are investigating the accuracy of this bulk density dose calculation techniquefor use in an on-board magnetic resonance imaging (MRI) image guided radiation therapy (IGRT) device that is underdevelopment at our institution. This IGRT device will utilize real-time MRI taken simultaneously to radiation delivery tocompute the dose to the patient. Segmented MRI imaging studies can be used to identify bulk density regions in the patient,but the high resolution density information of CT imaging is lost with this technique. Our hypothesis is that bulk densities canprovide an accurate method of heterogeneous photon-beam dose calculation, even in lung cancer patients.
Materials/Methods: To test our hypothesis, full CT resolution and bulk density treatment plans were generated for 17 lungcancer cases using a commercial treatment planning system with an adaptive convolution dose calculation algorithm (Pinnacle3,Philips Medicals Systems). Bulk densities were applied to regions identified by an isodensity segmentation tool for each case.Individual and population average densities were compared to the full resolution plan for each case. Monitor units were keptconstant and no normalizations were employed. Dose volume histograms (DVH) and dose difference distributions wereexamined for all cases.
Results: The average densities as determined by CT number of the segmented air, lung, soft tissue and bone for the entire setof patients were 0.15, 0.32, 0.98 and 1.11 [g/cc], respectively. Minor density differences existed between the populationaverages and the individual cases. In all cases, the normal tissue DVH agreed to better than 1%. In 15 out of 17 cases, the targetDVH agreed to better than 1%, while 2 cases with bullous emphysema showed inconsistent lung density and agreed to within4%. Inclusion of pronounced lung vasculature and atelectasis as soft tissue was important for obtaining accurate results. Figure1 shows the excellent agreement between the two methods: a) axial CT with 4 densities; b) Full CT; c) Overlay of DVHs; andd) axial dose difference.
Conclusions: Dose calculation applying bulk tissue density to four regions provides an accurate method of heterogeneous dosecalculation, which can be employed with MRI planning data. Dose calculation accuracy in cases with ehphysemic lung can beimproved by assigning air to regions with bullous changes in the lung.
S677Proceedings of the 48th Annual ASTRO Meeting
Author Disclosure: A.I. Saito, ViewRay, Inc., A. Employment; J.G. Li, None; C. Liu, None; K.R. Olivier, None; J.F. Dempsey,ViewRay, Inc., A. Employment; ViewRay, Inc., E. Ownership Interest.
2832 The Trade-Off Between Neutron Dose and Skin Dose for 6MV Versus 18MV for Prostate IMRT: Doesthe 20cm Rule Still Apply?
R. M. Howell, W. Koontz-Raisig, P. A. S. Johnstone
Emory University Hospital, Atlanta, GA
Background: A general rule in radiotherapy is to prescribe high beam energies when treating patients with AP/PA separationsgreater than 20cm. Beams with energies greater than 10MV can generate unwanted secondary neutrons. This author previouslyreported results of organ equivalent doses (x-ray and neutron doses). Peripheral organ dose was much greater for high energyIMRT compared to high energy conventional radiotherapy; using low beam energies for IMRT significantly decreasedunwanted dose to peripheral organs. Yet, many clinicians remain reluctant to prescribe low energies when using IMRT for deepseated targets due to concerns about possible skin reactions.
Purpose/Objective(s): This research compared measured skin dose for 6MV and 18MV IMRT and conventional prostateradiation therapy.
Materials/Methods: In an earlier investigation, 6MV and 18MV IMRT and conventional treatment plans were created usinga CT scan of the ART male dosimetry phantom. Since the average male patient is larger than the ART phantom, the phantomwas rescanned with 3cm of bolus added to the anterior surface and 2 cm added to each side (ART�B), increasing the AP/PAsep from 20cm to 23cm and the Rt/Lt sep from 32cm to 36 cm.
Both the static MLC shaping for the conventional and the dynamic MLC field for the IMRT treatment plans were identicalfor the ART and ART�B treatment plans, comparable DVHs achieved. MU given in table below. TLD measurements wereperformed at 9 locations on the phantom surface; at central axis, and at 2 and 4 cm superior, inferior, right and left of beamcax. Standard deviation was 0.085 and batch error was �4%.
Results: Skin dose results are given as a ratio of measured dose at each TLD location to the prescribed dose. While 6MV IMRTresults in higher skin doses compared to 18MV IMRT, it still results in substantially lower skin doses than 18MV conventionalradiotherapy. It reasonable to enter a new era where 6MV IMRT is used to treat even large patients with deep seated tumors.
Author Disclosure: R.M. Howell, None; W. Koontz-Raisig, None; P.A.S. Johnstone, None.
cax 2cm Avg 4cm Avg Total MU (1.8Gy/Fx)
6Conv ART 27.15% 27.01% 8.98% 2916IMRT ART 10.24% 9.92% 1.68% 57118Conv ART 18.91% 17.97% 9.50% 22518IMRT ART 5.24% 4.87% 1.61% 4606Conv ART�B 28.05% 28.87% 8.51% 3156IMRT ART�B 11.60% 11.94% 1.66% 61418Conv ART�B 19.29% 18.66% 9.46% 23418IMRT ART�B 5.81% 5.29% 1.68% 488
S678 I. J. Radiation Oncology ● Biology ● Physics Volume 66, Number 3, Supplement, 2006
