D Manigandan

Early Clinical Outcomes and Toxicity of Intensity Modulated Versus Conventional Pelvic Radiation Therapy for Locally Advanced Cervix Carcinoma: A Prospective Randomized Study

PURPOSE To evaluate the toxicity and clinical outcome in patients with locally advanced cervical cancer (LACC) treated with whole pelvic conventional radiation therapy (WP-CRT) versus intensity modulated radiation therapy (WP-IMRT). METHODS AND MATERIALS Between January 2010 and January 2012, 44 patients with International Federation of Gynecology and Obstetrics (FIGO 2009) stage IIB-IIIB squamous cell carcinoma of the cervix were randomized to receive 50.4 Gy in 28 fractions delivered via either WP-CRT or WP-IMRT with concurrent weekly cisplatin 40 mg/m(2). Acute toxicity was graded according to the Common Terminology Criteria for Adverse Events, version 3.0, and late toxicity was graded according to the Radiation Therapy Oncology Group system. The primary and secondary endpoints were acute gastrointestinal toxicity and disease-free survival, respectively. RESULTS Of 44 patients, 22 patients received WP-CRT and 22 received WP-IMRT. In the WP-CRT arm, 13 patients had stage IIB disease and 9 had stage IIIB disease; in the IMRT arm, 12 patients had stage IIB disease and 10 had stage IIIB disease. The median follow-up time in the WP-CRT arm was 21.7 months (range, 10.7-37.4 months), and in the WP-IMRT arm it was 21.6 months (range, 7.7-34.4 months). At 27 months, disease-free survival was 79.4% in the WP-CRT group versus 60% in the WP-IMRT group (P=.651), and overall survival was 76% in the WP-CRT group versus 85.7% in the WP-IMRT group (P=.645). Patients in the WP-IMRT arm experienced significantly fewer grade ≥2 acute gastrointestinal toxicities (31.8% vs 63.6%, P=.034) and grade ≥3 gastrointestinal toxicities (4.5% vs 27.3%, P=.047) than did patients receiving WP-CRT and had less chronic gastrointestinal toxicity (13.6% vs 50%, P=.011). CONCLUSION WP-IMRT is associated with significantly less toxicity compared with WP-CRT and has a comparable clinical outcome. Further studies with larger sample sizes and longer follow-up times are warranted to justify its use in routine clinical practice.

SU‐E‐T‐636: Impact of Different Intensity Levels On Step and Shoot IMRT Plan Quality and Deliverability

PURPOSE To evaluate the impact of different intensity-levels on step and shoot IMRT plan quality and deliverability. METHODS Five previously treated patients of carcinoma rectum (pre-operative) were studied. Planning target volume (PTV) and organ at risk (OAR) i.e. bladder and bowel were contoured. Step and shoot IMRT plans (6MV, 45Gy/25fraction prescribed at 95% isodose) were created in Eclipse TPS for Varian CL2300C/D linear accelerator at 300MU/min. During optimization, dose volume constraints and priorities were kept constant and only intensity-levels were varied as follows: 5, 10 and 15. Plan quality was analyzed in terms of maximum and mean doses of PTV, coverage index (CI=PTV covered by prescription dose/PTV), heterogeneity index (HI)=D5 /D9 5 (D5 =dose received by 5% of PTV and D9 5 =dose received by 95% of PTV), OAR mean-doses and normal tissue integral-dose (NTID) (liter-Gray). Total monitor units (MUs) required to deliver a plan was noted. Deliverability of treatment plans were verified with I-matriXX array and compared with TPS dose-plane using gamma index of 3% dose difference and 3mm distance to agreement (DTA) criteria. RESULTS Maximum dose to PTV was 5219.06±54.55cGy, 5071.30±49.01cGy and 5053.26±71.85cGy for 5, 10 and 15 intensity-levels, respectively. Mean dose to the PTV was 4655.02±27.29cGy, 4664.00±23.29cGy and 4659.98±22.01cGy. The CI of PTV was 0.8573±0.07, 0.9661±0.02 and 0.9686±0.01 and HI of PTV was 1.0800±0.02, 1.0701±0.01, and 1.0677±0.01 for 5, 10 and 15 intensity-levels. Mean dose to bladder was 3491.88±365.15cGy, 3513.98±387.04cGy and 3501.93±380.91cGy. Bowel mean dose was 1352.05±365.20cGy, 1369.65±378.76cGy and 1369.53±375.30cGy. NTID (liter-Gray) was 144.64±11.88, 145.77±12.85 and 145.60±12.73. Total MU required to deliver a plan was 1060±307, 1081±309 and 1061±303. Gamma pass rate was 99.65±0.35%, 99.81±0.16% and 99.87±0.12%. CONCLUSION PTV coverage and homogeneity increases with increase in intensity-level. Plan quality was better at intensity-level 5 in terms of OAR mean-doses, NTID and total MU. Gamma pass rates were improved with increase of intensity-level.

SU‐E‐T‐587: Whole IMRT, Hybrid IMRT and 3D Conformal Plan a Dosimetric Comparison for Large Target

PURPOSE To dosimetrically compare the whole-IMRT, hybrid-IMRT (combination of IMRT and 3D-CRT) and 3D-conformal radiotherapy (3D- CRT) plans for larger targets. METHODS Five previously treated patients of carcinoma cervix with para-aortic lymph-nodes (target length 33-34cm) were selected. PTV-P (PTV-Primary), PTV-PA (PTV-para-aortic) and organ at risks (OARs) were defined. Three plans were generated using Eclipse TPS for Varian CL2300C/D linear accelerator using 6MV photon beam. Three plans were: (i) Whole-IMRT: IMRT for both PTV-P and PTV-PA (ii) Hybrid-IMRT: IMRT for PTV-P and 3D-CRT for PTV-PA (iii) 3D-CRT: 3D-CRT for both PTV-P and PTV-PA. Prescription dose for PTV-P is 50.4Gy and PTV-PA is 45Gy in 28 fractions. Coverage index (CI=Target volume covered by prescription dose/Target volume), mean doses to bladder, rectum and bowel were used for plan comparison by using DVH. Integral dose (liter-Gray) to normal tissue (i.e., patient volume minus PTV-P and PTV-PA) and total monitor units (MUs) required to deliver a plan was also noted. RESULTS The CI for PTV-P is 0.98±0.20, 0.96±0.09, and 0.95±0.01 for Whole-IMRT, Hybrid-IMRT and 3D-CRT plan and for PTV- PA is 0.98±0.01, 0.98±0.01, and 0.97±0.20. Maximum doses to PTV-P are 5660.85±90.85cGy, 5640.35±70.35cGy and 5813.80±97.40cGy. Maximum doses to PTV-PA are 5000.60±109.10cGy, 5079.85±20.25cGy and 5092.25±19.75cGy. Mean doses to the bladder are 3810±225.80cGy, 3842.10±182.70cGy and 5204±98.25cGy for Whole-IMRT, Hybrid-IMRT and 3D-CRT plan, respectively. Mean doses to rectum are 3955.35±324.95cGy, 3971.15±354.15cGy and 4741.20±371.60cGy. Mean doses to bowel are 2623.35±320.85cGy, 2855.30±371.05cGy and 3011.7±433.80cGy. Average MUs required to deliver one fraction is 1285±87, 1585±186, 485±46 for Whole-IMRT, Hybrid-IMRT and 3D-CRT plans, respectively. Higher integral doses to normal tissue were observed for whole-IMRT (267.60±76 liter-Gy) followed by hybrid-IMRT (259.20±53 liter-Gy) and 3D-CRT (186.30±33 liter-Gy). CONCLUSIONS Whole-IMRT is useful for larger targets compared to hybrid-IMRT in terms of dose conformity, lesser MUs and reduced critical organ doses with little compromise on integral dose, where 3D-CRT sacrificed the OAR sparing.

SU‐E‐T‐198: Evaluation of Dosimetric Characteristics of MOSFET Dosimeter for the Quality Assurance of Photon and Electron Beams

Purpose: To study the basic dosimetric characteristics of MOSFET dosimeter for its suitability on constructing the quality assurance phantom. Methods: For all the measurements, the high sensitivity MOSFET with standard bias settings (3mV/cGy) was used. Solid water phantoms were used for both photon and electron beams. Tests were performed for 60Co beams, 6 and 15MV photonbeams and 9MeV electrons. The dose‐linearity of MOSFET was studied up to 500 cGy with small increment at lowerdoses. Results were compared with the farmer chamber for photons and PP chamber for electrons. Reproducibility of the MOSFET was studied for the absorbed dose of 100cGy. Beam symmetry was measured at 5‐cm off‐axis position for 15×15cm2 field and comparisons were made with the farmer chamber and EDR‐2 film for photons and PP chamber and Kodak Xomat‐V for electrons. Also, the beam quality index was derived by measuring the dose at 10 and 20cm depth for photonbeams. Measurements were done for five different days and compared with ion chamber measurements. Results: The correlation co‐efficient (R2) for MOSFET and ion chamber linearity curve is 0.9999, 0.9999, 0.9998 and 0.9999 for 6MV, 15MV and 60Co beams and 9MeV electrons. High sensitivity MOSFET showed good linearity at lower doses even with standard bias settings. Reproducibility of the MOSFET is 1.680%, 1.815%, 1.7194% and 1.754% for 6MV, 15MV and 60Co beams and 9MeV electrons. Beam Symmetry measured with MOSFET showed maximum variation up to 4.2% where as ion chamber and EDR‐2 was within 2.7% and 3.1%. MOSFET over‐responded consistently at the off‐axis position. Quality index measured with MOSFET was within 0.701% and 1.355% for 6 and 15MV photons, whereas the ion chamber was within 0.450%. Conclusions: The high sensitivity MOSFET may be used as a dosimeter with proper cross‐calibration for the quality assurance phantom, which is under construction.

SU‐E‐T‐610: Investigation on Four‐Dimensional Computed Tomography Imaging for Stereotactic Body Radiotherapy: The Patient and Programmable Respiratory Motion Phantom Study

Purpose: To compare and evaluate volumatric and dosimetric accuracy of 4DCT for stereotactic body radiotherapy between free breathing and maximum‐intensity projection (MIP) imaging. Methods: Three lungcancer patients who had undergone the treatment of stereotactic body radiotherapy and QUASAR respiratory motion phantom were used in this study. The Philips 85cm Big‐bore brilliance 16‐slice CT scanner with bellow‐belt system was used to generate the 4DCT data sets. The planning CT was done in free breathing (FB) conditions for treatment verification purpose. The patient 4DCT was obtained and its amplitude of motion parameters was used to acquire 4DCT data of moving phantom. Each patient had 13 different 4DCT sets. All these images were imported into the 3D‐RTP system. Treatment planning was made using ADAC Pinnacle 8.0 system for Synergy‐S linear accelerator for both phantom and patients for conformal stereotactic body radiotherapy. The treatment planning was made such as 0%‐plan, 10%‐plan, 20%‐plan 30%‐plan 40%‐plan 50%‐plan 60%‐plan 70%‐plan 80%‐plan, and 90%‐plan, AvgiP‐plan, MIP‐plan and FB‐plan for both phantom and patients for comparison. Results: In the phantom study, the percent of volume differences were found to be 55%, 35%, 74% between FB vs MIP for GTV, OAR‐1 and OAR‐2 respectively. In the patient study, the percent of volume differences were found to be 38% for GTV and 74%, for the spinal cord between FB vs MIP, respectively. All dosimetric variations between FB vs Avg‐iP CT based plans were found to be 10– 19.2% for target and OAR for both phantom and patients studies. Conclusions: The volumetric and dosimetric variations between free‐ breathing and MIP images for both phantom and patient targets and organs‐ at‐risk were significant. The free‐breathing CT was underestimated the volumes compared to MIP images. The effect of motion becomes important for accurate dose planning in stereotactic body radiotherapy.

SU-E-T-749: Effect of Different Optimization Techniques on Interstitial Breast Brachytherapy

Purpose: Purpose of this study is to compare the three doseoptimization techniques based on basal point, target dose point and inverse planning simulated annealing (IPSA) for flexible interstitial breast implant. Methods: Five carcinoma breast patients implanted with the flexible catheters (double plane, triangular geometry) were studied. After CT scan acquisition, clinical target volume (CTV), Organ at risks (OAR) such as lung and heart (in case of left breast) were delineated. Three plans were made for all the patients based on basal dose point, target dose point and IPSA using Nucletron Plato BPS (V3.5.1) planning system. All the plans were evaluated using following indices: Coverage Index (CI), External Volume Index (EI), Homogeneity Index (HI), Overdose Index (OI) and Conformity Index (COIN). For OAR lung and heart maximum dose(dose received by 1cc volume) was noted. Maximum dose to the skin was analyzed visually. Results: The CI (0.9049±0.024, 0.8920±0.015, and 0.96037±0.009), EI (0.1146±0.088, 0.1869±0.077, and 0.1985±0.064), HI (0.4128±0.079, 0.3482±0.080, and 0.3780±0.096), OI (0.2777±0.085, 0.3564±0.059, 0.2529±0.052) and COIN (0.8077±0.081, 0.7385±0.031, and 0.7969±0.041) were shown for basal dose point, target dose point and IPSA based plan respectively. The average of the maximum dose received by the ipsilateral lung is 892.8±378.8, 961.6±545.4 and 812.6±341.6 cGy for basal dose point, target dose point and IPSA based plan respectively. The average of the maximum dose received by heart 625.8±524.2, 687.2±712.8 and 580.0±391 cGy for basal dose point, target dose point and IPSA based plan respectively. Conclusions: IPSA plan showed better target coverage followed by basal dose point and target dose point based plans. Lesser doses of heart and lung volumes were observed for IPSA. For skindoses, no significant difference was found. Even though the classical basal dose point plan was slightly inferior to IPSA, it is easy to plan with the lesser resources.

SU-GG-T-310: Dose Perturbation Caused by MOSFET Dosimeter during in Vivo Dosimetry of Photon and Electron Beam Radiotherapy - a Film Dosimetry Study

Purpose: In in vivodosimetry, build‐up caps were used to (i) promote electronic equilibrium (ii) reduce correction factors (iii) avoid steep dose gradient of depth dose curve (iv) radiation damage per unit accumulated dose. However, it attenuates the beam both qualitatively and quantitatively. Hence, the dose attenuation MOSFETdetector with and without build‐up was studied at different depths for 60Co beams, 6 and 15 MV X‐rays and electrons using film dosimetry.Method and Materials:Dose attenuation was studied using solid water phantom. For electron beams, Kodak Xomat‐V film was used and EDR‐2 films used for photon beams. In 6, 9 12 and 15 MeV, attenuation of bare MOSFET was studied. In 15 MeV, Wide Energy Hemi‐spherical build‐up cap (WEHSBC) was used as recommended by the manufacturer. For 60Co beams, 5 mm bolus was used. WEHSBC was used for 6 and 15 MV X‐rays. Dose profiles were analyzed at surface and Dmax. Doses were normalized at the central axis of the field measured without MOSFET.Results: Presence of bolus with the MOSFET increased the surface dose up to 85% and decreased the dmax dose to 5%. Field area of 1.5 × 1.5 cm2 was perturbated. Attenuation of WEHSBC at dmax is 21.1% and 4.8% for 6 and 15 MV. Total area of 1.4 × 1.4 cm2 and 1.6 × 1.6 cm2 attenuated. Bare MOSFET showed 10%, 3.9%, 2.9% and 2.8% reduction in 6, 9, 12 and 15 MeV, respectively. No attenuation was found at dmax. In 15 MeV, MOSFET+WEHSBC, showed 35.6% and 54% reduction at surface and dmax. Conclusion: WEHSBC can be used as a build‐up cap for 6 and 15 MV X‐rays with limited number of fractions. Attenuation of bare MOSFET in electron beams is negligible. WEHSBC should not be used for electron beamin vivodose measurements.