Small Bowel Dose Research Articles

Impact of Prone Versus Supine Positioning on Small Bowel Dose With Pelvic IMRT

Impact of Prone Versus Supine Positioning on Small Bowel Dose With Pelvic IMRT V.J. Gonzalez, C. Hullett, L. Burt, P. Rassiah-Szegedi, V. Sarkar, J.D. Tward, L.J. Hazard, J.Y. Huang, B.J. Salter, and D.K. Gaffney; Department of Radiation Oncology, University of Arizona, Tucson, AZ, College of Medicine, University of Arizona, Tucson, AZ, Department of Radiation Oncology, Huntsman Cancer Institute, University of Utah, Salt Lake City, UT, Center for Neurosciences, Tucson, AZ

Evaluating Small Bowel Dose–Volume Tolerance Limits for SBRT Using a Preoperative Rectal Radiation Therapy Model: Are We Setting the Bar Too High?

Evaluating Small Bowel Dose–Volume Tolerance Limits for SBRT Using a Preoperative Rectal Radiation Therapy Model: Are We Setting the Bar Too High?

Consolidating duodenal and small bowel toxicity data via isoeffective dose calculations based on compiled clinical data

PurposeTo consolidate duodenum and small bowel toxicity data from clinical studies with different dose fractionation schedules using the modified linear quadratic (MLQ) model. A methodology of adjusting the dose–volume (D,v) parameters to different levels of normal tissue complication probability (NTCP) was presented. Methods and MaterialsA set of NTCP model parameters for duodenum toxicity were estimated by the χ2 fitting method using literature-based tolerance dose and generalized equivalent uniform dose (gEUD) data. These model parameters were then used to convert (D,v) data into the isoeffective dose in 2 Gy per fraction, (DMLQED2,v) and convert these parameters to an isoeffective dose at another NTCP (DMLQED2’,v). ResultsThe literature search yielded 5 reports useful in making estimates of duodenum and small bowel toxicity. The NTCP model parameters were found to be TD50(1)model = 60.9 ± 7.9 Gy, m = 0.21 ± 0.05, and δ = 0.09 ± 0.03 Gy-1. Isoeffective dose calculations and toxicity rates associated with hypofractionated radiation therapy reports were found to be consistent with clinical data having different fractionation schedules. Values of (DMLQED2’,v) between different NTCP levels remain consistent over a range of 5%-20%. ConclusionsMLQ-based isoeffective calculations of dose–response data corresponding to grade ≥2 duodenum toxicity were found to be consistent with one another within the calculation uncertainty. The (DMLQED2,v) data could be used to determine duodenum and small bowel dose–volume constraints for new dose escalation strategies.

SU-E-T-708: The Role of Small Bowel in Cervical Cancer Brachytherapy

Purpose: Small bowel (SB) is the organ at risk (OAR) that has the highest rate of radiation induced late toxicity in brachytherapy of cervical cancer. Historically, however, its dose has not been systematically reported as other OARs even during image guided brachytherapy (IGBT). This study aims to evaluate the effect of including SB in BT plan optimization and to propose a possible reporting schema. Methods: Thirteen patients were included in this retrospective study. All patients were treated with external beam radiotherapy of 45Gy in 25 fractions followed by high dose rate (HDR)‐BT of 28Gy in 4 fractions/2 implants using tandem/ring applicator. MRI and CTs were obtained to define the GTV and HR‐CTV, and OARs. Treatment plans were generated for each patient without considering small bowel dose constraint, and revised for those with D2cc of SB >5Gy. Results: Six of 13 cases required plan revision due to high D2cc for SB. By sparing the SB with an average reduction of 19% in D2cc, only 2 of the 6 replanned cases resulted in less optimal target coverage, i.e. D90 of HR‐CTV less than 77Gy. However, one of them already had difficulty in achieving the coverage in the first plan due to other OAR dose restriction. On the other hand, SB mobility was noticed in the CT images, which could help in SB tolerance. Conclusion: Although SB is typically mobile compared to other OARs, it is strongly recommended that it be used as an OAR for plan optimization. Prospective reporting of D2cc index will help to better define its potential association with late complications in the future.

Beam angle selection for intensity-modulated radiotherapy (IMRT) treatment of unresectable pancreatic cancer: are noncoplanar beam angles necessary?

External beam radiation therapy with concurrent chemotherapy (CRT) is widely used for the treatment of unresectable pancreatic cancer. Noncoplanar (NCP) 3D conformal radiotherapy (3DCRT) and coplanar (CP) IMRT have been reported to lower the radiation dose to organs at risk (OARs). The purpose of this article is to examine the utility of noncoplanar beam angles in IMRT for the management of pancreatic cancer. Sixteen patients who were treated with CRT for unresectable adenocarcinoma of the pancreatic head or neck were re-planned using CP and NCP beams in 3DCRT and IMRT with the Varian Eclipse treatment planning system. Compared to CP IMRT, NCP IMRT had similar target coverage with slightly increased maximum point dose, 5,799 versus 5,775cGy (p=0.008). NCP IMRT resulted in lower mean kidney dose, 787 versus 1,210cGy (p<0.0001) and higher mean liver dose, 1,208 versus 1,061cGy (p<0.0001). Also, NCP IMRT resulted in similar mean stomach dose, 1,257 versus 1,248cGy (p=0.86) but slightly higher mean small bowel dose, 981 versus 866cGy (p<0.0001). The NCP IMRT was able to significantly decrease bilateral kidney dose, but did not improve other dose-volume criteria. The use of NCP beam angles is preferred only in patients with risk factors for treatment-related kidney dysfunction.

Small bowel toxicity in pelvic radiotherapy for postoperative gynecological cancer: Comparison between conformal radiotherapy and intensity modulated radiotherapy

To compare the dosimetric advantages of pelvic intensity modulated radiotherapy (IMRT) with three-dimensional conformal radiotherapy (3D CRT) in small bowel dose reduction and dosimetrically correlate the clinical benefit, if any. This retrospective study included 60 patients with gynecological cancers treated postoperatively with radiotherapy to the whole pelvis. Radiation Therapy Oncology Group (RTOG) contouring guidelines were used for contouring the pelvic nodal stations. All plans were generated using Plato Sunrise treatment planning system. The RTOG acute morbidity scoring criteria were used to define acute small bowel toxicity in our patients. Treatment was delivered using the Elekta Precise system. Patients were followed up twice weekly while on treatment. Statistical analyses (Spearman's rho and Kruskal-Wallis test) were performed using SPSS software (vers. 15). In all, 65% were postoperative endometrium carcinoma and 35% were postoperative cervix carcinoma patients; 34 patients were treated with IMRT and 26 patients underwent 3D CRT. In all, 28 patients experienced ≥ grade 2 small bowel toxicity (eight in the IMRT group). IMRT was able to significantly reduce the dose to bowel for doses above 30 Gy. Small bowel toxicity showed no correlation with doses below 30 Gy. The volume of the small bowel receiving more than 35 Gy of radiation was a significant predictor of the need for medication to control diarrhea during radiotherapy. Use of IMRT resulted in lower doses to the small bowel, resulting in lesser toxicity, and translated to the better tolerability of pelvic radiotherapy.

Is Belly Board Still Needed in IMRT for Rectal Cancer? The Change of Bladder Volume Affects the Determination

Prone positioned with belly board is an efficiency method to reduce the irradiated small bowel volume (ISBV) in three-dimensional conformal radiation therapy (3DCRT) for rectal cancer patients. The downside of treating patients in prone position is that compared to supine, the setup is less reproducible between and during fractions. Intensity-modulated radiation therapy (IMRT) technique has previously been demonstrated to be effective in reducing small bowel dose in comparison to 3DCRT for rectal cancer. Whether the belly board still needed in IMRT for rectal cancer is not well answered. The aim of this study was to compare the ISBV between prone positioned with belly board and supine positioned with flat table in IMRT for rectal cancer patients. Twenty patients scheduled to receive postoperative radiation therapy for rectal cancer underwent two series of CT scans, prone positioned with a belly board and supine positioned with a flat board, both combined using a full bladder protocol. On each scan, a 7-field IMRT plan was calculated. Bladder and individual loops of small bowel were contoured on each slice of the planning CT scan. A comparison of volume for small bowel and bladder in different position were performed. Comparison of V15 (volume received dose more than 15 Gy) for small bowel was made between prone and supine position with different device. Compared with supine position, all bladder volumes were decreased in the prone position. The ISBV of eight patients were increased when use belly board. The increase of ISBV was related to the decrease of bladder volume. If the relative change of bladder volume was more than 16%, the ISBV might increase when use belly board. There were no significant differences between patients undergoing IMRT with belly board and those without in terms of V15 for small bowel and ISBV (p = 0.245 and p = 0.944, respectively). If we used 16% as cutoff value to select patients, V15 for small bowel and ISBV of different position could meet marginal statistical significant (p = 0.062 and p = 0.072, respectively). The change of bladder volume in two different positions affected the ISBV. If the change less than 16%, a belly board still attributed to a significant bowel dose reduction when using IMRT and a full bladder protocol.

Dose-Painted Intensity Modulated Radiation Therapy Improves Local Control for Locally Advanced Pancreas Cancer

Background. To evaluate the outcomes, adverse events, and therapeutic role of Dose-Painted Intensity-Modulated Radiation Therapy (DP-IMRT) for locally advanced pancreas cancer (LAPC). Methods. Patients with LAPC were treated with induction chemotherapy (n = 25) and those without metastasis (n = 20) received DP-IMRT consisting of 45 Gy to Planning Treatment Volume 1 (PTV1) including regional lymph nodes with a concomitant boost to the PTV2 (gross tumor volume + 0.5 cm) to either 50.4 Gy (n = 9) or 54 Gy (n = 11) in 25 fractions. DP-IMRT cases were compared to three-dimensional conformal radiation therapy (3D-CRT) plans to assess the potential relationship of radiation dose to adverse events. Kaplan-Meier and Cox regression analyses were used to calculate survival probabilities. The Fisher exact test and t-test were utilized to investigate potential prognostic factors of toxicity and survival. Results. Median overall and progression-free survivals were 11.6 and 5.9 months, respectively. Local control was 90%. Post-RT CA-19-9 levels following RT were predictive of survival (P = 0.02). Grade 2 and ≥grade 3 GI toxicity were 60% and 20%, respectively. In comparison to 3D-CRT, DP-IMRT plans demonstrated significantly lower V45 values of small bowel (P = 0.0002), stomach (P = 0.007), and mean liver doses (P = 0.001). Conclusions. Dose-escalated DP-IMRT offers improved local control in patients treated with induction chemotherapy for LAPC. Radiation-related morbidity appears reduced with DP-IMRT compared to 3D-CRT techniques, likely due to reduction in RT doses to organs at risk.

Planning Target Volume Margin Evaluation and Critical Structure Sparing for Rectal Cancer Patients Treated Prone on a Bellyboard

AimsTo calculate a planning target volume (PTV) margin that would account for inter-fractional systematic and random clinical target volume positional errors for patients treated prone on a recently available couch top bellyboard and to evaluate potential critical structure dose reduction using intensity-modulated radiotherapy (IMRT) techniques. Materials and methodsTwenty-four patients (12 men and 12 women) were included in this study, all treated on a commercial bellyboard. Cone beam computed tomography (CBCT) data were acquired once every five fractions for a total of five images per patient. A three-dimensional–three-dimensional bony anatomy auto-match was carried out off-line and the residual difference in position used as a surrogate for clinical target volume inter-fractional positional errors. Systematic (Σ) and random (σ) variations were evaluated and used in PTVmargin=1.96Σ+0.7σ. The influence of intra-fractional positional errors was evaluated in the margin analysis by introducing published values. Critical structure sparing, as a function of PTVmargin size, was investigated through the evaluation of three-dimensional conformal radiation therapy (3DCRT) and IMRT treatment plans developed using the margin derived from this work, the American Society for Radiation Oncology Contouring Atlas and the Radiation Therapy Oncology Group 0822 trial specifications. ResultsThe PTVmargin that accounts for only the inter-fractional positional errors was calculated to be (anterior–posterior (AP), superior–inferior (SI), left–right (LR))=(5.2mm, 3.1mm, 2.8mm). If we assumed a combined intra-fractional motion up to 3.0mm then the required PTVmargin increased to (AP, SI, LR)=(7.0mm, 5.0mm, 5.0mm). Treatment plan evaluation showed that the bellyboard provides excellent small bowel sparing regardless of planning technique. In most cases, IMRT reduced the average femoral head, bladder and small bowel dose by 20, 15 and 40% with respect to 3DCRT planning. ConclusionA PTVmargin expansion of (AP, SI, LR)=(7.0mm, 5.0mm, 5.0mm) is required to account for all positional uncertainties. The use of a bellyboard with IMRT provides better critical structure sparing when compared with a bellyboard with 3DCRT.

Definitive radical external beam radiotherapy for rectal cancer: Evaluation of local effectiveness and risk of late small bowel damage

Aim. To present a retrospective analysis of results of definitive radiotherapy for rectal cancer. Material and methods. Forty-one consecutive patients with rectal cancer (32% primary, 61% pelvic recurrence and 7% after R2 resection) who could not be treated with surgery underwent external beam radiotherapy. A median tumour dose of 64 Gy was given with 1.8–2.5 Gy per fraction using 2D or 3D technique. In 46% of patients, concurrent 5-Fu-based chemotherapy was given. The median follow-up was 54 months. Results. Clinical complete response was achieved in 39% of patients. Five-year cumulative incidence of local failure, overall survival and cancer specific survival were 76%, 26% and 30%, respectively. Of 11 patients with local control, in five cases the tumour was larger than 5 cm and in the other five the tumour was fixed. Two patients, regarded as locally controlled had non-progressive tumour without local symptoms at the last follow-up of 54 and 118 months post-radiotherapy. Late toxicity occurred in 22% of patients, all with acceptable severity. There was no bowel obstruction requiring surgery despite that in 18 patients the small bowel dose was > 60 Gy to a mean volume of 51 cm3. Conclusion. Definitive radio(chemo)therapy provides a chance for local control even in patients with large fixed or recurrent rectal cancer.

Patient-Specific PTV Margins and Their Implementation in Radiation Therapy for Bladder Cancer

Background: Precision during bladder cancer radiotherapy delivery is particularly challenging due to large daily variations in bladder position and volume. The literature suggests that the optimal approach to margin calculation is a patient-specific one, because the magnitude and direction of bladder changes varies significantly between patients. There is considerable inconsistency in the strategies used to calculate a patient-specific planning target volume (psPTV), with authors reporting the use of data from 1 to 15 with a pattern of daily to weekly fractions. Therefore, the purpose of this study is to determine the optimal number and pattern of data points to be used to generate psPTV margins and to determine if implementing those margins at the earliest opportunity would result in a reduction in organ at risk (OAR) dose. Methods and Materials: This is a secondary analysis of a prospective clinical trial. All patients provided informed consent prior to participation in the clinical trial. Of the 30 patients accrued to the clinical trial, a sample of 15 (selected reverse chronologically) will be included in this secondary analysis. These patients received 46Gy in 23f to the whole pelvis and 20Gy in 10f to the bladder or partial bladder. Daily kV conebeam CTs (CBCT) were acquired for image guidance purposes. Local current practice requires bladder contours from the first 15 daily CBCT to generate a psPTV for implementation in the phase 2 treatment. This current practice will be used as a gold standard (GS) against which various experimental strategies (ES) will be compared, such as ‘‘first five daily fractions,’’ four weekly fractions, etc. Differences between the psPTV generated using GS versus all ES will be quantified using the following study metrics: volume, superior margin, posterior margin and clinical target volume (CTV) coverage. Once the optimal margin generation strategy is identified, the psPTV will be incorporated into the treatment plan for the remaining number of fractions. Rectal and small bowel dose volume histograms will be used to quantify any differences between the strategies. Results: Although data collection is not yet complete, based on this research design and the findings from similar evaluations for other pelvic organs, we hypothesize that it will be possible to generate psPTV margins with data from less than 15 daily fractions. This would allow an earlier adoption of the psPTV margin, which could reduce doses to the small bowel and rectum. Alternatively, if our findings suggest that 15 daily data points are necessary to generate an adequate psPTV, this would support our current practice as the optimal method. Conclusions: Precision radiation therapy for bladder cancer is technically challenging. A patient-specific approach to PTV margins is clearly necessary, but there is little evidence to guide the practitioner when designing such margin generation strategies. With this study we hope to establish an optimal regimen for generating psPTV that will result in excellent CTV coverage, but the lowest possible doses to the adjacent OARs.

Bladder Filling Reduces Dose to Small Intestines During Intracavitary Tandem and Ovoid Brachytherapy for Cervical Cancer

Radiation treatment of cervical cancer requires full integration of pelvic external beam irradiation and brachytherapy. Current RTOG protocols recommend simulating patients for external beam with a full bladder in order to limit the dose to the small intestine. By similar reasoning, the small bowel dose from tandem and ovoid (T and O) brachytherapy may be reduced by filling the bladder during HDR treatment. This study proposes to identify the optimal bladder fill volume to confer this dose reduction to the small intestine during HDR T and O treatments.

The Relationship between Chronic Bowel Dysfunction and the Small Bowel Dose Volume Histogram of Rectal Cancer Survivors

Materials/Methods: Billing records and tumor registry were used to identify all living patients treated with RT for rectal cancer between January 1996 and January 2009. After exclusions for stomas, active metastatic disease, no 3D treatment planning, inadequate small bowel contrast, unrecoverable treatment data, repeat pelvic RT, wide local excision/no surgery, lost to follow-up, incapacitation from other disease, or declining participation, the remaining patients answered a validated 18 item questionnaire (Temple, et al. Diseases Colon Rectum 2005;48:1353-65). This resulted in a frequency score, a dietary score, an urgency/soilage score, and four scores from independent questions. These seven scores were tested using linear regression to evaluate the correlation the absolute small bowel volume for each dose at 5 Gy increments. The Student’s unpaired t test and Pearson chi-square/Fisher’s Exact test were used to compare continuous and categorical variables between preoperative and postoperative groups, respectively. A p value of 0.05 was considered statistically significant. Statistical analyses were performed with SPSS Version 17.0 (SPSS Inc., Chicago, IL), and all statistical tests were two-sided.

SU‐E‐T‐801: VMAT for the Treatment for Cervical Carcinoma and Para‐Aortic Nodes

Purpose: The PTV of cervical carcinoma and para‐aortic nodes is unique for its large width and length which pose a challenge to VMAT because of the MLC leaf length, speed and gantry rotation speed restrictions. This study establishes a field arrangement for VMAT and assesses the differences between VMAT and IMRT plans. Methods: Six patients were randomly selected for the study. The CTV included the areas of subclinical risk around the GTV and associated lymph node drainage sites. The PTV margin includes a 0.7cm expansion around the lymph nodes and 0.5cm margin elsewhere. Organs at risk included rectum, bladder, small bowel and kidneys. Six plans, each consisting of three arcs (collimator angle 90 degrees on one and 0 on others) and 9 field IMRT plans were generated with Eclipse treatment planning system and delivered with a 6MV beam and 120 leaf MLC. Planning goals for both VMAT and IMRT plans were: V100 of the PTV covered by 98% prescription dose with a maximum dose &lt;112%, V15 &lt; 33% for both kidneys, V40&lt;60% for bladder and rectum and mean small bowel dose &lt; 30Gy. Treatment time was measured from when the beam data was loaded into the treatment console to the end of beam delivery. Results: The average PTV was 1850cm3. The PTV coverage met the constraints on all plans. The average rectal V40 (VMAT: 56%; IMRT: 62%), bladder V40 (VMAT: 55%; IMRT: 59%) and mean small bowel dose (VMAT: 23Gy; IMRT: 24Gy) were comparable. The mean left and right kidneys V15 were substantially reduced with VMAT (VMAT: 15%; IMRT: 28.1%) and (VMAT: 14.1%; IMRT: 29.5%). VMAT reduced the average MU from 2581 to 662 resulting mean delivery time of 791s to 292s. Conclusions: VMAT results substantial kidney sparing for the same coverage while reducing treatment time and monitor units.

Dosimetric Analysis of Small Bowel Doses Received During MRI-Based 3D Brachytherapy for Cervical Cancer

Dosimetric Analysis of Small Bowel Doses Received During MRI-Based 3D Brachytherapy for Cervical Cancer

Comparison of 4D CT Planning and 3D Conformal Planning in Locally Advanced Pancreatic Cancer

Introduction: Approximately 30% of patients diagnosed with pancreatic cancer will present with locally advanced unresectable disease (LAPC). Improved planning techniques provide the opportunity for dose escalation. Methods: From February 2010 to September 2010, patients with LAPC suitable for CRT were planned using contrast enhanced 4D CT scanning. We compared 4D CT treatment planned according to local protocol using 50.4 Gy (4D50.4) and 55.8 Gy (4D55.8) compared with the NCRN/SCALOP protocol (50.4 Gy SCALOP50.4). Our local protocol defines gross tumour volume (GTV) outlined on all respiratory phases of image sets generated by 4D CT with a radiologist (using the SCALOP study protocol). An internal target volume (ITV) was generated as a composite of all GTVs. This ITV was grown with 1 cm circumferential margin and 1.2 cm superior–inferiorly to define a PTV. Dose constraints and PTV coverage were defined by the SCALOP protocol. Results: We identified nine patients who had 4D CT scans from April to October 2010. We found that the mean reduction in small bowel doses for V15small bowel was 17% and the mean V45small bowel was reduced by 28% when 4D50.4 was compared with SCALOP50.4. With dose escalation to 55.8 Gy, 4D55.8 remained compliant with the organs at risk constraints and these values, including the mean small bowel doses (V15small bowel and V45small bowel) remained comparable to the SCALOP50.4. Patients set-up errors were reviewed during treatment and found to be acceptable for our PTV margins. No acute grade 3 or 4 toxicity was observed of the eight patients treated with 4D50.4 plans. Conclusion: In this study, 4D CT planning using our protocol would allow dose escalation without a significant increase in the small bowel dose.

Preoperative chemoradiotherapy for locally advanced rectal adenocarcinoma: A dosimetric comparison of intensity-modulated radiation therapy (IMRT) with three-dimensional conformal radiotherapy (3D-CRT).

615 Background: Small bowel and bladder toxicities (bleeding, obstruction, perforation, and stricture) are rare but serious late complications of pelvic radiotherapy (RT) related to dose received by these organs. IMRT has been used effectively in other pelvic malignancies (prostate and gynecologic) to decrease the dose to normal tissues when compared to 3D-CRT. Few studies have examined the use of IMRT in rectal cancer to assess whether a similar dose reduction is feasible. Methods: Eight consecutively treated patients with T2/T3 and N0/N1 rectal adenocarcinoma underwent 5-FU based neoadjuvant chemo-RT using 7-field sliding-window IMRT between 2008 and 2010. Retrospectively, conventional 4-field 3D-CRT plans were generated for dosimetric comparison with IMRT treatment plans. Planning target volumes included the gross tumor, rectum, peri-rectal tissues, pre-sacral space, and common and internal iliac lymphatics. Organs at risk included small bowel (contoured as all small bowel identified on the planning CT plus a 1 cm symmetrical expansion), bladder, and femoral heads. Small bowel, bladder, and femoral head mean doses and volumes receiving 45 Gy (V45) were compared between conventional and IMRT plans, respectively. Paired Student's t-test was used for statistical analysis. Results: Mean prescription dose was 52.9 ± 3.3 Gy. Compared to 3D-CRT, IMRT plans had an 11% lower mean dose delivered to the bladder (38.2 ± 4.5 Gy vs 43.1 ± 1.9 Gy, p = 0.028) and 24% lower mean dose to the small bowel (24.0 ± 2.9 Gy vs 31.7 ± 7.7 Gy, p = 0.014). IMRT plans also had a 55% lower bladder V45 (27 ± 19% vs 61 ± 22%, p = 0.0077) and a 96% lower small bowel V45 (1 ± 0% vs 21± 20%, p = 0.021). The femoral heads received a nonsignificant higher mean dose (19.2 ± 3.9 Gy vs 16.6 ± 3.0 Gy, p = 0.069). Conclusions: Small bowel and bladder volume receiving 45 Gy and mean dose were significantly lower using IMRT compared with 3D-CRT planning. More stringent volumetric planning constraints may be necessary to further reduce the dose to the femoral heads. Further study is warranted to examine the clinical benefit of these dosimetric findings. No significant financial relationships to disclose.

High-dose, Spot Scanning Based Proton Therapy For Paraspinal / Retroperitoneal Neoplasms and Small Bowel Tolerance: Dose Distribution Analysis in a Patient Cohort

Mesenchymal tumors require high-dose RT. Small bowel dose constraints have historically restricted dose delivery to paraspinal targets and moderate doses to large abdominal volumes carry the risk of long term morbidity. Pre-clinical comparisons of proton radiation therapy (PT) vs. photon RT have suggested a reduction in integral dose to normal tissues by PT. This study correlated target coverage with small bowel dose-volume histograms and clinical tolerance.

WE‐A‐BRC‐01: IMRT in Gynecological Malignancies

Intensity modulated radiation therapy (IMRT) is increasingly used for the treatment of gynecological tumors. Successful implementation requires careful attention to every detail from patient selection to simulation, to planning, to setup, to localization, and to delivery. At the University of Chicago, all patients are simulated and treated in supine position using customized alpha cradles indexed to the treatment table. Oral, IV and rectal contrast are used to help in the delineation of the CTV and surrounding normal tissues. The CTV consists of the upper half of the vagina, uterus (if present), parametrial tissues, parasacral region, and the contrast enhanced vessels plus a 2cm margin to identify the common, external and internal nodal regions. PTV is constructed by adding a margin based on the setup uncertainty and organ motion data. Normal tissues contoured include bladder, rectum, small bowel and pelvic bone marrow. For treatment planning, 9 equally spaced co‐planar beams are used. Input parameters derived for the PTV and surrounding normal tissues were developed over the time, and their evolution will be discussed. Treatment plans are evaluated primarily based on the PTV coverage and normal tissue DVHs. 3‐D dose distribution plays an important role in the IMRT delivery and is rigorously evaluated by both physicists and physicians at our institutions. Acceptable plans are the ones that have a minimum coverage of 98% of the PTV volume with the prescription dose while no more than 2% of the PTV receives more than 110% of the prescription dose. Evaluation of small bowel dose is based on a NTCP analysis for the incidence of acute gastrointestinal toxicity of IMRT patients treated in our center. From this analysis, small bowel volume receiving prescription dose (45Gy) should be less than 200cc. Plan acceptance criteria for rectum and bladder will also be discussed during this course. Recent studies conducted in our center studies have associated the volume of pelvic and lumbosacral bone marrow (PBM and LSBM) receiving 10 and 20 Gy with acute hematologic toxicity (AHT) in patients receiving concurrent chemotherapy and IMRT. We will discuss and present plan consideration for bone marrow sparing IMRT to reduce AHT in these patients. QA is one of the most important and integral part of any radiation therapy procedure. IMRT QA, in our institution, is performed using independent monitor unit verification (MUV) and patient specific measurements and will be discussed in details. In addition, recent studies reporting adaptive treatment and image guided approaches in the treatment of gynecological tumors will be briefly reviewed.Learning Objectives:1. To understand the practical and fundamental aspects of IMRT planning for gynecological malignancies2. To discuss the GYN‐IMRT plan evaluation and acceptance criteria3. To review and discuss the IMRT quality assurance issues for this disease site.4. To briefly review and critique adaptive and image guided GYN‐IMRT approaches.

Evaluation of Four-Dimensional Computed Tomography-Based Intensity-Modulated and Respiratory-Gated Radiotherapy Techniques for Pancreatic Carcinoma

To compare conformal radiotherapy (CRT), intensity-modulated radiotherapy (IMRT), and respiration-gated radiotherapy (RGRT) planning techniques for pancreatic cancer. All target volumes were determined using four-dimensional computed tomography scans (4D CT). The pancreatic tumor and enlarged regional lymph nodes were contoured on all 10 phases of a planning 4D CT scan for 10 patients, and the planning target volumes (PTV(all phases)) were generated. Three consecutive respiratory phases for RGRT delivery in both inspiration and expiration were identified, and the corresponding PTVs (PTV(inspiration) and PTV(expiration)) and organ at risk volumes created. Treatment plans using CRT and IMRT, with and without RGRT, were created for each PTV. Compared with the CRT plans, IMRT significantly reduced the mean volume of right kidney exposed to 20 Gy from 27.7% +/- 17.7% to 16.0% +/- 18.2% (standard deviation) (p < 0.01), but this was not achieved for the left kidney (11.1% +/- 14.2% to 5.7% +/- 6.5%; p = 0.1). The IMRT plans also reduced the mean gastric, hepatic, and small bowel doses (p < 0.01). No additional reductions in the dose to the kidneys or other organs at risk were seen when RGRT plans were combined with either CRT or IMRT, and the findings for RGRT in end-expiration and end-inspiration were similar. 4D CT-based IMRT plans for pancreatic tumors significantly reduced the radiation doses to the right kidney, liver, stomach, and small bowel compared with CRT plans. The additional dosimetric benefits from RGRT appear limited in this setting.