Sparing IMRT Research Articles

Contribution of submandibular gland and swallowing structure sparing to post-radiation therapy PEG dependence in oropharynx cancer patients treated with split-neck IMRT technique

BackgroundRadiation therapy-related dysphagia is worsened by xerostomia. The submandibular glands (SMG) produce saliva rich in lubricating mucins, and sparing the SMG has been shown to reduce xerostomia. The goal of this study was to determine whether SMG sparing IMRT is associated with reduced post-treatment PEG dependence in locally advanced oropharynx cancer patients.MethodsPatients treated with definitive radiation therapy for oropharynx cancer were included in this retrospective study. Those with disease recurrence were excluded. Salivary glands and swallowing-related organs at risk, including pharyngeal constrictors, were contoured. Primary endpoint was time from end of radiation treatment to freedom from gastrostomy (PEG) tube dependence. Cox proportional hazards regression and logistic regression were used to assess influence of normal tissue doses on swallowing related endpoints.ResultsSixty-nine patients were included. All had stage III/IV disease and 97% received concurrent systemic therapy. Fifty-seven percent had contralateral SMG (cSMG) mean dose <50 Gy, a level shown to predict for xerostomia. Eighty four percent of patients had a PEG tube placed electively. On univariate analysis, the strongest predictor of time to freedom from PEG tube dependence was cSMG dose (HR 0.97 per Gy (95% CI 0.95–0.98), p < 0.0001). This relationship persisted on multivariate analysis (p = 0.052). The dose to superior and middle pharyngeal constrictor muscles, and larynx were also significant on univariate analysis. Patients with cSMG dose less than median (42 Gy, n = 34) had a significantly shorter time to freedom from PEG dependence: median 1.9 vs. 3.5 months, p < 0.0001. At 6 months, 3% of patients with cSMG dose < 42 Gy were PEG dependent compared to 31% with cSMG dose > 42 Gy (p = 0.002).ConclusionsPatients treated with cSMG sparing radiotherapy had significantly shorter time to PEG tube removal after treatment, suggesting a clinically meaningful reduction in subacute dysphagia compared to non-cSMG sparing treatment.

The impact of RTOG 0614 and RTOG 0933 trials in routine clinical practice: The US Survey of Utilization of Memantine and IMRT planning for hippocampus sparing in patients receiving whole brain radiotherapy for brain metastases

IntroductionTwo recent clinical trials, phase III RTOG 0614 and phase II RTOG 0933, showed some effectiveness of Memantine and IMRT planning for hippocampus sparing, among patients receiving whole brain radiotherapy (WBRT) for brain metastases; however, their use in routine clinical practice is unknown. MethodsA survey was sent to 1933 radiation oncologists in the US. Data collected included utilization of Memantine and hippocampus sparing, reasons for adoption and non-adoption, and demographic variables. ResultsA total of 196 radiation oncologists responded to the survey, with 64% reporting using Memantine in almost none of the patients receiving WBRT for brain metastases, and only 11% considering Memantine for <10% of their patients. The most common reason for not using Memantine was a poor patient performance status, and limited life expectancy. Likewise, 56% of radiation oncologists would not change their clinical practice to include hippocampus sparing IMRT in patients receiving WBRT based on the results of RTOG 0933. Further validation of hippocampus sparing in a phase III trial was supported by 71% of radiation oncologists, whereas further exploration of Memantine for this purpose in a phase III trial was supported by 42%. ConclusionsAt this time, the majority of surveyed radiation oncologists in the US do not use Memantine, or IMRT planning for hippocampus sparing in patients receiving WBRT. Further validation of the hippocampus sparing concept in a phase III trial was supported, before adopting it in routine clinical practice.

Comparison of V10 and V20 of Bone Marrow in Patients With Carcinoma of the Cervix Receiving Radiation With Bone Marrow–Sparing (BMS) IMRT, IMRT, 3DCRT, and 4-Field Box Technique

Comparison of V10 and V20 of Bone Marrow in Patients With Carcinoma of the Cervix Receiving Radiation With Bone Marrow–Sparing (BMS) IMRT, IMRT, 3DCRT, and 4-Field Box Technique

Efficacy and Safety of Onartuzumab in Combination With First-Line Bevacizumab- or Pemetrexed-Based Chemotherapy Regimens in Advanced Nonsquamous Non-Small Cell Lung Cancer (nsNSCLC): Results From a Phase 2, Placebo-Controlled Study (GO27821): Metastatic Non-Small Cell Lung Cancer

necessary by 72% of radiation oncologists in the survey. The most common reasons for not using hippocampus sparing IMRT were (1) increased cost and problems with obtaining authorization for IMRT planning, (2) necessities for a better dosimetry support and thin slice brain MRI (1.25 -1.50 mm), and (3) time necessary for hippocampus contouring. Use of Memantine and hippocampus sparing IMRT were not associated with demographic factors, such as years of practice and geographic location, as well as WBRT volume and practice setting (academic, non-academic hospital based, or free standing). Conclusions: The majority of surveyed radiation oncologists in the United States do not use Memantine or IMRT planning for hippocampus sparing in patients receiving WBRT. Further validation of the hippocampus sparing concept in a phase 3 trial was felt to be necessary before adopting it in routine clinical practice. Author Disclosure: A. Slade: None. S. Stanic: None.

Feasibility of Cardiac-Sparing Whole Lung IMRT in Children With Lung Metastases: A Prospective Multi-institutional Clinical Trial

We conducted a prospective clinical trial for children undergoing whole lung irradiation (WLI). The 3 aims were: 1) to demonstrate the feasibility of cardiac sparing IMRT (CS-IMRT) with central quality control (QARC), 2) to prospectively determine the dosimetric advantages of CS-IMRT over WLI using AP-PA technique (AP-WLI), and 3) to determine short-term efficacy and acute tolerance of CS-IMRT.

Combining Dosimetry & Toxicity: Analysis of two UK Phase III Clinical trials

There are many advantages to performing a clinical trial when implementing a novel radiotherapy technique. The clinical trials framework enables the safety and efficacy of the "experimental arm" to be tested and ensures practical support, rigorous quality control and data monitoring for participating centres. In addition to the clinical and follow-up data collected from patients within the trial, it is also possible to collect 3-D dosimetric information from the corresponding radiotherapy treatment plans. Analysing the combination of dosimetric, clinical and follow-up data enhances the understanding of the relationship between the dose delivered to both the target and normal tissue structures and reported outcomes & toxicity. Aspects of the collection, collation and analysis of data from two UK multicentre Phase III radiotherapy trials are presented here. MRC-RT01 dose-escalation prostate radiotherapy trial ISRCTN47772397 was one of the first UK multi-centre radiotherapy trials to collect 3-D dosimetric data. A number of different analysis methodologies were implemented to investigate the relationship between the dose distribution to the rectum and specific rectal toxicities. More recently data was collected from the PARSPORT trial (Parotid Sparing IMRT vs conventional head and neck radiotherapy) ISRCTN48243537. In addition to the planned analysis, dosimetric analysis was employed to investigate an unexpected finding that acute fatigue was more prevalent in the IMRT arm of the trial. It can be challenging to collect 3-D dosimetric information from multicentre radiotherapy trials. However, analysing the relationship between dosimetric and toxicity data provides invaluable information which can influence the next generation of radiotherapy techniques.

Tumor Directed, Scalp Sparing Intensity Modulated Whole Brain Radiotherapy for Brain Metastases.

Despite significant technical advances in radiation delivery, conventional whole brain radiation therapy (WBRT) has not materially changed in the past 50 years. We hypothesized that IMRT can selectively spare uninvolved brain and scalp with the goal of reducing acute and late toxicity. MRI/CT simulation image registration was performed. We performed IMRT planning to simultaneously treat the brain tumor(s) on MRI + 5 mm margin to 37.5 Gy in 15 fractions while limiting the uninvolved brain + 2 mm margin to 30 Gy in 15 fractions and the mean scalp dose to #18 Gy. Three field IMRT plans were compared to conventional WBRT plans. Symptomatic patients were started on conventional WBRT for 2 to 3 fractions while IMRT planning was performed. Seventeen consecutive patients with brain metastases with RPA class I and II disease with no leptomeningeal spread were treated with IMRT WBRT. Compared to conventional WBRT, IMRT reduced the mean scalp dose (26.2 Gy vs. 16.4 Gy, p < 0.001) and the mean PTV30 dose (38.4 Gy vs. 32.0 Gy, p < 0.001) while achieving similar mean PTV37.5 doses (38.3 Gy vs. 38.0 Gy, p = 0.26). Using Olsen hair loss score criteria, 4 of 15 assessable patients preserved at least 50% of hair coverage at 1 to 3 months after treatment while 6 patients preserved between 25 and 50% hair coverage. At a median follow-up of 6.8 months (range: 5 to 15 months), the median overall survival was 5.4 months. Four patients relapsed within the brain, one within the PTV37.5 and three outside the PTV37.5. Tumor directed, scalp sparing IMRT is feasible, achieves rational dose distributions and preserves partial hair coverage in the majority of patients. Further studies are warranted to determine whether the increased utilization of resources needed for IMRT are appropriate in this setting.

TH‐A‐116‐05: A Robust Direct Aperture Optimization Approach for Left‐Sided Breast IMRT

Purpose: To test the feasibility of a robust direct aperture optimization (DAO) model for cardiac sparing IMRT planning of left‐sided breast cancer patients. Methods: We extended a previously developed robust optimization method to obtain a DAO approach for tangential breast IMRT that is robust against uncertainty in the patient's breathing pattern. The robust DAO model contains additional constraints on the segment shapes and weights in order to reduce the complexity of delivery and ensure that high weight segments cover the whole breast volume. A 4DCT dataset was used to test the model, and 100 simulated breathing patterns were generated. Results were compared with the previously developed robust fluence map optimization (FMO) model as well as the clinical treatment methods for breast cancer (inhale breath‐hold with active breathing control (ABC) and free breathing). Results: On average, the robust DAO approach reduced the mean heart dose by 15.1% compared to the conventional IMRT method for breast cancer (with free breathing) using an equal number of segments. The maximum dose to 10cc of the heart was reduced by 19.7%. Compared to the previous robust FMO method, the robust DAO method delivered less than 1% higher dose to the heart and 1% lower dose to the CTV on average. The dose‐volume criteria for the heart and CTV were met in all of the breathing scenarios. The robust DAO approach resulted in a 20.8% reduction in the number of cases that would have required ABC treatment in comparison with the clinical method with free breathing. Conclusions: The proposed DAO approach results in lower heart dose compared to the conventional method with free breathing and shows low sensitivity to breathing pattern uncertainty. The robust DAO method is able to derive simpler IMRT segments during free breathing and can potentially reduce the need for breath‐hold techniques. This research was supported in part by the Ontario Ministry of Economic Development and Innovation, the Canadian Breast Cancer Foundation ‐ Ontario Region, and the Ontario Consortium for Adaptive Interventions in Radiation Oncology (OCAIRO) funded by the Ontario Research Fund (ORF).

TU-G-BRB-04: A Robust-CVaR Optimization Approach to Left-Sided Breast IMRT.

To test the feasibility of a cardiac sparing IMRT planning approach for patients with left-sided breast cancer using a robust optimization model. A robust optimization model was developed for breast IMRT. The concept of conditional-value-at-risk (CVaR) was used in the robust framework to guarantee that the clinical dose volume criteria for targets and organs at risk hold under uncertainty in the patient's breathing pattern. Clinical treatment methods for breast cancer (inhale breath-hold with active breathing control (ABC) or free breathing) were simulated via optimization models. A 4DCT patient dataset with target and organs at risk on each breathing phase was used to simulate a clinical case with a total of 20% increase in lung volume from exhale to inhale over 5 phases. The results of the proposed robust model were compared with those of the current clinical models. Compared to the conventional IMRT method for breast cancer (with free breathing), the proposed robust-CVaR model resulted in a 14.6% reduction in mean heart dose without compromising the target coverage and dose homogeneity. The clinical dose-volume limits for the heart as well as the clinical target volume were met in robust results. The robust method resulted in 23.9% improvement in the maximum dose to 25cc of the heart volume. The robust results showed very low variability among the quality of planning and realized treatments. Using CVaR limits in a robust optimization framework can help improve the quality of IMRT treatments. The robust-CVaR can generate a high quality treatment plans, but is delivered during free breathing and does not require patient compliance with an external device. The quality of robust treatment remains the same under irregular breathing. Explicitly including metrics for lung and bigger motion amplitudes in the robust optimization method may further improve the results.

SU-E-T-558: Assessing the Effect of Inter-Fractional Motion in Esophageal Sparing Plans.

To compare esophageal dose distributions in esophageal sparing IMRT plans with predicted dose distributions which include the effect of inter-fraction motion. Seven lung cancer patients were used, each with a standard and an esophageal sparing plan (74Gy, 2Gy fractions). The average max dose to esophagus was 8351cGy and 7758cGy for the standard and sparing plans, respectively. The average length of esophagus for which the total circumference was treated above 60Gy (LETT60) was 9.4cm in the standard plans and 5.8cm in the sparing plans. In order to simulate inter-fractional motion, a three-dimensional rigid shift was applied to the calculated dose field. A simulated course of treatment consisted of a single systematic shift applied throughout the treatment as well a random shift for each of the 37 fractions. Both systematic and random shifts were generated from Gaussian distributions of 3mm and 5mm standard deviation. Each treatment course was simulated 1000 times to obtain an expected distribution of the delivered dose. Simulated treatment dose received by the esophagus was less than dose seen in the treatment plan. The average reduction in maximum esophageal dose for the standard plans was 234cGy and 386cGY for the 3mm and 5mm Gaussian distributions, respectively. The average reduction in LETT60 was 0.6cm and 1.7cm, for the 3mm and 5mm distributions respectively. For the esophageal sparing plans, the average reduction in maximum esophageal dose was 94cGy and 202cGy for 3mm and 5mm Gaussian distributions, respectively. The average change in LETT60 for the esophageal sparing plans was smaller, at 0.1cm (increase) and 0.6cm (reduction), for the 3mm and 5mm distributions, respectively. Interfraction motion consistently reduced the maximum doses to the esophagus for both standard and esophageal sparing plans.

PO-0715 VARIABILITY OF NTCP PREDICTION OF SWALLOWING ORGANS AT RISK, DUE TO VARIATION IN DELINEATION GUIDELINES

Purpose/Objective: In daily practice, several different delineation guidelines can be used for the delineation of organs at risk that are involved in swallowing (SWOARs). Based on these delineation guidelines, predictive models have been developed for the different aspects of post treatment swallowing dysfunction. This study was performed to test the hypothesis that different guidelines result in different delineated SWOARs and subsequently different NTCP values for swallowing dysfunction. Materials and Methods: Thirty head and neck cancer patients with either laryngeal or pharyngeal carcinoma, treated with swallowing sparing IMRT, were included in this study. Nine SWOAR delineation guidelines derived from literature were compared. The following SWOARs were investigated: superior pharyngeal constrictor muscles (PCM), middle PCM, supraglottic larynx and esophageal inlet muscle (EIM). Especially, differences in description, geometric measures (centre of mass and coefficients of variance for volume), and resulting SWOAR dose-volume parameters were investigated. The results were used to examine the variation in the prediction of normal tissue complication probability (NTCP). For this comparison, five NTCP models for swallowing dysfunction from literature were used with the following endpoints: (1) RTOG grade 2-4; (2) problems with swallowing solid, (3) soft, and (4) liquid food; (5) choking when swallowing. Results: The description of the posterior and anterior borders of the SWOARs in the delineation atlases was similar. However, differences up to several centimeters were seen in the description of the cranial and caudal borders of some of the SWOARs. Mean differences in the position of the centre of mass in cranio-caudal direction were largest for the EIM and superior PCM: 2.2 cm ± 0.4 cm and -1.2 cm ± 0.6 cm respectively. Coefficients of variance of the volume of the SWOARs were largest for the EIM and for the middle PCM: 80% and 45% respectively. The range in differences in NTCP value per tumor location for all models was 0.1 - 18% for oropharynx (18% for endpoint 2), 0.00 - 22.4% for larynx (22.4% for endpoint 5), 0.04 - 7.7% for nasopharynx (7.7% for endpoint 5), 0.20 - 11.7% for hypopharynx (11.7% for endpoint 5), and 0.04 - 1.7% for oral cavity (1.7% for endpoint 2). Thus largest variations were found for tumors situated in the larynx and for NTCP model 'Choking when swallowing' (see figure). (Figure presented). Conclusions: Large variations in the definition of SWOARs were found among published delineation guidelines. This caused considerable variation in delineated volumes and in the position of the SWOARs which in turn resulted in different dose-volume values, and in different NTCP values. Therefore, an NTCP model from a specific group should only be used when SWOARs are delineated according to the corresponding delineation guidelines. Moreover, formulation of generally accepted guidelines for swallowing structures is strongly recommended to improve the generalisability of NTCP models.

The potential benefit of swallowing sparing intensity modulated radiotherapy to reduce swallowing dysfunction: An in silico planning comparative study

PurposeTo apply recently developed predictive models for swallowing dysfunction to compare the predicted probabilities of swallowing dysfunction for standard intensity modulated radiotherapy (ST-IMRT) and swallowing sparing IMRT (SW-IMRT). Materials and methodsThirty head and neck cancer patients who previously underwent radiotherapy for the bilateral neck were selected for this study. For each patient, ST-IMRT and SW-IMRT simultaneous integrated boost treatment plans were created. ST-IMRT treatment plan optimisation aimed at obtaining adequate target volume coverage and sparing of the parotid and submandibular glands as much as possible. Objectives for SW-IMRT were similar, with additional objectives to spare the organs at risk related to swallowing dysfunction (SWOARs). Dose-volume data with ST-IMRT and SW-IMRT and normal tissue complication probabilities for physician-rated and patient-rated swallowing dysfunction were calculated with recently developed predictive models. ResultsAll plans had adequate target volume coverage and dose to critical organs was within accepted limits. Sparing of parotid glands was similar for ST-IMRT and SW-IMRT. With SW-IMRT, the mean dose to the various SWOARs was reduced. Absolute dose values and dose reductions with SW-IMRT differed per patient and per SWOAR and depended on N stage and tumour location. The mean reduction in predicted physician-rated Radiation Therapy Oncology Group (RTOG) grade 2–4 swallowing dysfunction was 9% (range, 3–20%). Mean reductions of the probability of patient-rated moderate to severe complaints with regard to the swallowing of solid food, soft food, liquid food and choking when swallowing were 8%, 2%, 1% and 1%, respectively. ConclusionsNew predictive models for swallowing dysfunction were applied to show potential reductions in physician and patient-rated swallowing dysfunction with IMRT that was specifically optimised to spare SWOARs.

MRI to quantify early radiation-induced changes in the salivary glands

PurposeWe investigated radiation-induced changes in the salivary glands, 6weeks after RT, using MRI. Materials and methodsEighteen oropharyngeal cancer patients were treated with salivary gland sparing IMRT. All patients received a 3T MRI exam before and 6weeks after the end of RT, including a T1-weighted (T1w), a T2-weighted (T2w), and a dynamic contrast-enhanced (DCE) MRI.For both time points separately, the parotid and submandibular glands were delineated on the MR images. Differences in median signal intensity and signal variation within the glands were tested for significance. Correlations were studied between the MR changes and the planned RT dose. ResultsThe volume of the glands reduced significantly by 25%. The T1w signal decreased by 10% and the T2w signal increased by 23%. The kep value decreased, while the ve increased. A correlation of the changes in T2w signal with the mean dose was found in both glands. ConclusionsOverall radiation-induced changes and volume loss were observed in the parotid and submandibular gland using MR. The observed differences indicated an increased water content such as found in oedema. The overall changes could be related to the mean dose, with a slightly greater impact in the high dose area.

Bilateral Superficial Parotid Gland Sparing IMRT Produces Similar Long-term Xerostomia Scores when Compared to Unilateral Parotid Sparing IMRT in Midline Head and Neck Squamous Cell Cancers (HNSCC)

Bilateral Superficial Parotid Gland Sparing IMRT Produces Similar Long-term Xerostomia Scores when Compared to Unilateral Parotid Sparing IMRT in Midline Head and Neck Squamous Cell Cancers (HNSCC)

Improved Fixation and Position Verification for Salivary Gland Sparing Head and Neck IMRT

Improved Fixation and Position Verification for Salivary Gland Sparing Head and Neck IMRT

SU-GG-T-79: Structure Sparing IMRT by Fluence Avoidance Method: Application To a Pelvic Case With Bilateral Hip Replacements

Purpose: To develop a technique for planning large targets in pelvic cases with double hip replacements where the recommended physical avoidance approach is not an option. Method and Materials: Throughout this report, the Eclipse treatment planning system (Varian Medical System, Palo Alto, CA) was used. All calculations are performed using the Eclipse PBC Algorithm with Modified Batho heterogeneity corrections turned on. A method referred to here as fluence avoidance technique was developed. It uses an iterative approach to prevent photons from reaching the target through a prosthesis. This is because it is not possible, in the Eclipse optimizer, to apply a dose constraint only through beams that enter through a region (entrance region beam) and not to beams that exit through one (exit region beam). To circumvent this weakness of the optimizer, an iterative process was developed. First, low target dose constraints that do not compromise target coverage are set to both prostheses. The optimizer then treats both of them as any other critical structure. Once this step is complete, the fluence through each prosthesis is minimized but not zeroed. To proceed with zeroing of the fluence through each prosthesis path, a manual iterative process is used. Results: A drastic improvement of the dose distribution compared to physical avoidance is obtained. A comparison between the first and the final iteration needed to achieve complete fluence avoidance of the right and left prosthesis shows significantly better target dose homogeneity without increasing the dose to critical structures. Conclusion: The fluence avoidance method described above and applied to a bilateral hip replacement IMRT case allows for homogeneous target coverage while minimizing dose to critical structures. The principle behind the fluence avoidance method can be generalized to improve the sparing of other critical structures such as the parotids in head & neck cancer.

Analysis of the Quality of Saliva After Parotid-Sparing IMRT for Head and Neck Cancer (HN)

Following parotid sparing IMRT for HN, salivary flow has been shown to increase over time. However, the quality of the recovered saliva has not been previously assessed and is the subject of the current study.

MRI PWI and CSI Imaging Studies of Brain for IMRT Treatment Planning Because of Differentiated Gliomas

To characterize correlation between metabolic CSI imaging of brain, PWI (Perfusion Weighted Images) MRI and early progression. 43 patients with newly diagnosed differentiated gliomas (WHO grade II tumors) had MRI scans before radical radiotherapy treatment planning. 31 patients were irradiated postoperatively, 12 had biopsy. MR studies consisted of T1, T2 imaging without and with contrast enhancement, FLAIR, perfusion studies and CSI MRS using Siemens MAGNETOM AVANTO 1.5 T. Images were fused to treatment CT scans using Helios treatment planning system. All patients were treated with IMRT (both IMRT and 3D conformal plans were prepared for each patient but due to better normal tissue sparing IMRT treatment was selected for all patients) using 6 or 20 MV photons to total doses 54–60 Gy, 2 Gy/fx for PTV. Second MR study was done 0–3 days after the end of RT including all imaging and CSI MRS using the same localization and sequences as had been done for each patient before RT. MR scans were repeated every 6 months after radiotherapy. Volume of brain selected for CSI MRS was the biggest possible free from non-brain lipids artifacts. Relative intensities of the signals (choline, creatine [Cr] N-acetyl aspartate [NAA], lactate, and lipids) were obtained by automatic numeric integration of fitted signals in 3D array of 1 × 1 × 1 cm voxels. Total dimensions of registered arrays were 10 × 12 × 7 cm. PWI were registered according to standard procedures. In majority of patients (30) decrease of NAA/Cr and increase of Cho/Cr ratio was registered in PTV, metabolic alterations decreased progressively with the distance from PTV borders. Alterations were registered up to 3 cm outside PTV borders. Strong lipids and lactate signals were registered for 8 patients. We did not observe correlation between PTV volume, mean radiation dose to brain and results of MRS. Results of MRS were not changed significantly after RT when compared to spectra registered before RT. Regions of increased perfusion were registered for 12 patients. After a median follow up of 13 months we observed radiologic progression for 9 patients, defined as increased regions of perfusion and increased regions of contrast enhancement. All patients with strong lactate signals had early progression up to 18 months after the end of radiotherapy. Lactate/lipids signals registered by 3D CSI MRS are indicators of aggressive disease, and may suggest malignant disease despite of the results of pathological examination of postoperative/biopsy material.

SU‐FF‐T‐240: Hair Sparing IMRT for Whole Brain with Simultaneous Integrated Boosts

Purpose: To investigate inclusion of the hair‐sparing limitation of scalp dose as a secondary objective in a protocol for whole brain IMRT treatment along with high dose simultaneous integrated boosts (SIB) added to help control gross brain metastases. Methods and Materials: Three patients were selected to simulate a variety of brain tumors using artificial GTVs. The target doses were 54 Gy or 45 Gy for the boosts, and 27 Gy for the remainder of the whole brain, in 15 fx. To implement hair sparing, a 5 mm thick hair shell within the patient contour was created. Typical planning objectives for the hair shell were a max DVH constraint of 1250 cGy to 50% volume, and a max dose objective of 2300 cGy. Planning was done using Phillips Pinnacle3 (V7.4f) software configured for step‐and‐shoot treatment on a Siemens Primus unit with 6‐MV photons. Results: The high‐dose boost regions were found to require at least 5 beams but did not substantially degrade the whole brain DVH or hair DVH. However, for a PTV near the surface it was not possible to keep the hair dose low. The DVH may appear acceptable in such cases, but dose on the inner side of the 5 mm region will not cause hair loss, while a patch of high dose on the surface will. Conclusions: IMRT can provide a clinically viable avenue for hair‐sparing whole brain treatment with SIB to higher primary tumor doses. A specific region of interest that would represent the “hair sparing” region might need to be defined and be assigned a specific dose limiting objective during the optimization process. We found that hair‐sparing cannot successfully be satisfied for primary targets situated closer to the surface.

SU‐DD‐A1‐06: Prostate IMRT Dose Escalation with Urethra Sparing: Dose Painting with IGRT

Purpose: With IGRT, the geometric uncertainty in treatment can be reduced, which makes it feasible to implement IMRT dose painting with a reasonable resolution. In this cancer center, an on‐line realignment protocol is utilized for prostate cancer patients. This IGRT protocol is based on use of implanted gold fiducial markers and EPI. In this study, dose escalations with urethra sparing have been tested by using IMRT dose painting. Method and Materials: CT scans of three patients were chosen from the IGRT group. The original 3D‐CRT plan (74Gy/37fr, 10mm PTV margin) was used as a reference. In test IMRT plans two PTVs were generated. PTV1 was defined as 5mm extension of prostate. PTV2 was generated from PTV1 with 5mm margin subtracted for bladder, rectum, and urethra. Two raw plans were generated. Plan 1 was 74Gy/37fr to PTV1, and Plan 2 was 74Gy/37fr to PTV2. Then, the urethra sparing IMRT boost plan was generated as a weighted sum of the two raw plans, e.g. . Different combinations of weighting factors were tested: w1∈[0.6, 1], w2∈. [0.1, 0.5]. The dose to each organ was calculated with organ motion simulated based on actually recorded EPI image mismatches. The tumor control probability (TCP) and effective dose were used to evaluate the plans. Results: To achieve the same urethra D50 (minimum dose to 50% volume) as the reference plan, the highest weighting combination was w1=0.7, w2=0.5 . This yields significant dose reduction in bladder and rectum. For the considered patient the TCP increases from ∼74% to ∼95%. Conclusion: With IGRT, the urethra sparing IMRT dose painting is superior to the 3D‐CRT plan. The total prescription dose can be as high as 88Gy, with TCP of ∼95% and lower GI complication. Since urethra has been spared, the GU complication will be less.