Mean V20 Research Articles

Association of oesophageal radiation dose volume metrics, neutropenia and acute radiation oesophagitis in patients receiving chemoradiotherapy for non-small cell lung cancer.

IntroductionThe relationship between oesophageal radiation dose volume metrics and dysphagia in patients having chemoradiation (CRT) for non-small cell lung cancer (NSCLC) is well established. There is also some evidence that neutropenia is a factor contributing to the severity of oesophagitis. We retrospectively analysed acute radiation oesophagitis (ARO) rates and severity in patients with NSCLC who received concurrent chemotherapy and high dose radiation therapy (CRT). We investigated if there was an association between grade of ARO, neutropenia and radiation dose volume metrics.Material and methodsPatients with NSCLC having concurrent CRT who had RT dose and toxicity data available were eligible. Exclusion criteria included previous thoracic RT, treatment interruptions and non-standard dose regimens. RT dosimetrics included maximum and mean oesophageal dose, oesophagus dose volume and length data.ResultsFifty four patients were eligible for analysis. 42 (78 %) patients received 60 Gy. Forty four (81 %) patients received carboplatin based chemotherapy. Forty eight (89 %) patients experienced ARO ≥ grade 1 (95 % CI: 78 % to 95 %). ARO grade was associated with mean dose (rs = 0.27, p = 0.049), V20 (rs = 0.31, p = 0.024) and whole oesophageal circumference receiving 20 Gy (rs = 0.32 p = 0.019). In patients who received these doses, V20 (n = 51, rs = 0.36, p = 0.011), V35 (n = 43, rs = 0.34, p = 0.027) and V60 (n = 25, rs = 0.59, P = 0.002) were associated with RO grade. Eleven of 25 (44 %) patients with ARO ≥ grade 2 also had ≥ grade 2 acute neutropenia compared with 5 of 29 (17 %) patients with RO grade 0 or 1 (p = 0.035).ConclusionIn addition to oesophageal dose-volume metrics, neutropenia may also be a risk factor for higher grades of ARO.

Association between radiation dose to the heart and myocardial fatty acid metabolic impairment due to chemoradiation-therapy: Prospective study using I-123 BMIPP SPECT/CT

PurposeTo investigate long term changes in myocardial fatty acid metabolic impairment caused by chemoradiation-therapy (CRT). Materials and methodsWe investigated 12 esophageal cancer patients who underwent SPECT/CT using I-123-labeled fatty acid analog (BMIPP) at pre-CRT, pre-boost irradiation, 3-month post-CRT, and 1-year post-CRT. The myocardial uptake was measured using the defect score and the total percentage of uptake (%uptake), which were defined as the sum of the visual scores and that of %uptake in each of 17 segments in the left ventricle (LV), respectively. The correlations between radiation dose to the heart (mean dose, V20, V40, and V60 of the LV and the whole heart (WH)) and the change of myocardial BMIPP uptake from pre-CRT (Δmyocardial BMIPP uptake) were assessed. ResultsAt pre-boost, Δmyocardial BMIPP uptake was significantly correlated with LV-V40 and WH-V60. At 3-month post-CRT, Δmyocardial BMIPP uptake was significantly correlated with LV-V40, WH-V40, and WH-V60. However, there were no statistically significant correlations at 1-year post-CRT. Neither mean dose nor V20 of the LV/WH was significantly correlated with Δmyocardial BMIPP uptake at any time. ConclusionsIn the long term after CRT, myocardial metabolism might be affected by factors other than the radiation dose to the heart.

Dosimetric Comparison between Coplanar and Non-Coplanar Fields in Irradiation of Middle and Lower Lobes Lung Tumors

Purpose: To compare between the coplanar and non-coplanar fields regarding planning target volume (PTV) coverage, conformity index and preservation of organs at risk (heart-lungs-esophagus and spinal cord). Materials and Methods: 10 patients presented with stage IIIA or IIIB NSCLC with a tumor located in the middle or lower lobes. Because of this location, the heart is one of the main organs at risk. Two plans, coplanar and non-coplanar 3 dimensional conformal radiotherapy plans are performed for each patient. All treatment plans are created using Xio - Computerized medical system treatment planning system. The prescribed dose is 64 Gy in 32 fractions. Results: For both plans, the maximum dose to the PTV doesn’t exceed 110% of the prescribed dose; the 95% isodose (60.8 Gy) covers at least 95% of the PTV volume and the mean conformity index values are also very similar 0.59 vs 0.61 for coplanar and non-coplanar plans respectively without statistically significant difference (P = 0.1711). Regarding organs at risk, large advantage for adding a non-coplanar field in the preservation of the heart is observed. The mean V30 values for noncoplanar plan are 17.3 Gy versus 28.9 Gy for the coplanar plan with statistically significant difference (P = 0.0060). Also, the mean V40 and V50 values for the non coplanar compared to coplanar plan are 12.6 Gy and 7.9 Gy versus 23.1 Gy and 14.9 Gy respectively, and these differences are statistically significant (P = 0.0162) (P = 0.0084). No statistically significant differences are found between coplanar and non-coplanar plans for lungs, esophagus or the spinal cord. Conclusion: Using non-coplanar beams in the irradiation of middle and lower lung tumors significantly reduces the radiation dose to the heart with the same target volume coverage and conformity index.

Assessment of the feasibility of using transrectal ultrasound for postimplant dosimetry in low-dose-rate prostate brachytherapy

A study was performed to establish whether transrectal ultrasound (TRUS)-based postimplant dosimetry (PID) is both practically feasible and comparable to computed tomography (CT)-based PID, recommended in current published guidelines. In total, 22 patients treated consecutively at a single cancer center with low-dose-rate (LDR) brachytherapy for early-stage prostate cancer had a transrectal ultrasound performed immediately after implant (d0-TRUS) and computed tomography scan 30 days after implant (d30-CT). Postimplant dosimetry planning was performed on both image sets and the results were compared. The interobserver reproducibility of the transrectal ultrasound postimplant dosimetry planning technique was also assessed. It was noticed that there was no significant difference in mean prostate D90 (136.5Gy and 144.4Gy, p = 0.2197), V100 (86.4% and 89.1%, p = 0.1480) and V150 (52.0% and 47.8%, p = 0.1657) for d30-CT and d0-TRUS, respectively. Rectal doses were significantly higher for d0-TRUS than d30-CT. Urethral doses were available with d0-TRUS only. We have shown that d0-TRUS PID is a useful tool for assessing the quality of an implant after low-dose-rate prostate brachytherapy and is comparable to d30-CT PID. There are clear advantages to its use in terms of resource and time efficiency both for the clinical team and the patient.

145 Documentation of DVLA guidance provision for patients with brain metastases

Compared with step-and-shoot intensity-modulated radiotherapy (sIMRT) and tomotherapy, volumetric-modulated arc therapy (VMAT) allows additional arc configurations in treatment planning and noncoplanar (NC) delivery. This study was first to compare VMAT planning with sIMRT planning, and the second to evaluate the toxicity of coplanar (C)/NC-VMAT treatment in patients with hepatocellular carcinoma (HCC). Fifteen patients with HCC (7 with left-lobe and 8 with right-lobe tumors) were planned with C-VMAT, C/NC-VMAT, and sIMRT. The median total dose was 49 Gy (range: 40 to 56 Gy), whereas the median fractional dose was 3.5 Gy (range: 3 to 8 Gy). Different doses/fractionations were converted to normalized doses of 2 Gy per fraction using an α/β ratio of 2.5. The mean liver dose, volume fraction receiving more than 10 Gy (V10), 20 Gy (V20), 30 Gy (V30), effective volume (Veff), and equivalent uniform dose (EUD) were compared. C/NC-VMAT in 6 patients was evaluated for delivery accuracy and treatment-related toxicity. Compared with sIMRT, both C-VMAT (p = 0.001) and C/NC-VMAT (p = 0.03) had significantly improved target conformity index. Compared with C-VMAT and sIMRT, C/NC-VMAT for treating left-lobe tumors provided significantly better liver sparing as evidenced by differences in mean liver dose (p = 0.03 and p = 0.007), V10 (p = 0.003 and p = 0.009), V20 (p = 0.006 and p = 0.01), V30 (p = 0.02 and p = 0.002), Veff (p = 0.006 and p = 0.001), and EUD (p = 0.04 and p = 0.003), respectively. For right-lobe tumors, there was no difference in liver sparing between C/NC-VMAT, C-VMAT, and sIMRT. In all patients, dose to more than 95% of target points met the 3%/3 mm criteria. All 6 patients tolerated C/NC-VMAT and none of them had treatment-related ≥ grade 2 toxicity. The C/NC-VMAT can be used clinically for HCC and provides significantly better liver sparing in patients with left-lobe tumors.

Predicting dosimetric indices in IMRT planning for lung cancer patients

Purpose: For lung cancer patients treated with intensity modulated radiation therapy (IMRT) technique, several dosimetric indices of lungs such as the mean lung dose, V30, V20 and V10 have drawn high attention, given their close correlations with the occurrence of radiation pneumonitis. In this study, we developed a method to predict the indices V30, V20 and V10 before treatment planning. Methods and Materials: The work in this study utilises anatomical information to predict dosimetric indices of lungs for IMRT plans. 15 shells surrounding the PTV were created and each shell comprised voxels whose distances to PTV surface were within a certain distance. The overlap regions of the lungs and the 15 shells were determined. A linear predicting function is employed to map volumes of these regions to dosimetric indices, where parameters were fitted using previous IMRT plans from a training database consisting of 43 cases. The effectiveness of the predicting function was validated using another 14 plans. Results: Dosimetric indices of the 14 patients in validation cohort were calculated using the linear predicting function. The predicted indices were compared with the indices derived from the clinically accepted treatment plans. The absolute differences between calculated V30 and the actual clinical values of 14 plans had a mean value of 1.6% and a standard deviation of 1.0%. The mean value and standard deviation for absolute differences of V20 were 1.5% and 1.0%. And for V10, these values were 3.6% and 2.6%. Conclusions: The method proposed here can predict dosimetric indices of lungs before treatment planning using geometric information of delineated PTVs and lungs. The results show that the prediction error of V30 and V20 are less than about 2.0%.

Dosimetric predictors of hematologic toxicity in patients undergoing concurrent gemcitabine-based chemoradiation for localized pancreatic cancer

PurposeThis study was undertaken to identify parameters associated with hematologic toxicity or chemotherapy dose modification in patients undergoing concurrent chemoradiation (CRT) with gemcitabine for localized pancreatic cancer. Methods and materialsWe reviewed patients with localized pancreatic cancer undergoing CRT between 2006 and 2012. Exclusion criteria included receipt of nongemcitabine therapy, chemotherapy before CRT, or abnormal baseline hematologic indices. The T11-L3 vertebrae were contoured as bone marrow region at risk. Linear and logistic regression models were used to test associations between dosimetric parameters and gemcitabine dose modification or hematologic toxicity during or within 3 months following CRT. Receiver operator curves were generated to identify threshold doses for hematologic toxicity. ResultsForty-nine patients were included. During CRT, the maximum thoracolumbar dose was associated with grade 2+ neutropenia during CRT (P = .017) and the volume receiving 5 Gy (V5) was associated with grade 2+ leukopenia (P = .041). Post-CRT, thoracolumbar mean dose (P = .015), V5 (P = .01), and V10 (P = .012) were associated with increased grade 2+ neutropenia. On multivariable analysis, the thoracolumbar maximum dose (P = .045) and V5 (P = .045) were associated with grade 2+ neutropenia and grade 2+ leukopenia during CRT, respectively. Post-CRT, the mean dose (P = .046), V5 (P = .019), and V10 (P = .037) were associated with increased grade 2+ neutropenia. A maximum dose of 48.02 Gy and V5 of 57.6% were identified as predictors of toxicity during CRT. A V5 of 56.6%, V10 of 47.05%, and mean dose of 11.67 Gy were identified as predictors of post-CRT hematologic toxicity. Post-CRT, there was a trend toward increased dose modifications with increased V5 (P = .065). ConclusionsIn our dataset, the thoracolumbar mean dose, maximum dose, V5, and V10 correlated with hematologic toxicity during CRT and post-CRT in patients with localized pancreatic cancer. Because of the high rates of distant failure and importance of systemic therapy in these patients, this may be an important consideration during treatment planning.

Mortality, Cardiac Toxicity, and Radiation Dose to the Heart in Patients Treated With Curative Intent Fractionated Radiation Therapy for Lung Cancer

Mortality, Cardiac Toxicity, and Radiation Dose to the Heart in Patients Treated With Curative Intent Fractionated Radiation Therapy for Lung Cancer

Comparison of Risk of Ipsilateral Breast Event After Lumpectomy for Ductal Carcinoma In Situ, As Estimated by Breast Radiation Oncologists, Van Nuys Prognostic Index, Memorial Sloan Kettering Cancer Center DCIS Nomogram, and the 12-gene DCIS Score

Quality Consortium (MROQC), a statewide assessment of breast cancer patients undergoing radiation therapy and crude rates were used for comparisons. Results: For left sided cancers, mean heart dose was 3.09 Gy. The use of a breast cup resulted in mean V20 for lung of 5.6% and V5 of 11%. Mean dose to the contralateral breast was 3.29 Gy. Twenty patients (42.5%) experienced grade 2 skin toxicity; one patient (2.1%) experienced a grade 3 skin toxicity. Moist desquamation rates: 44.7% compared to 45.5% MROQC. Moist desquamation for patients with a BMI >35 was 52.2% vs 42.8% MROQC. For a breast volume >1550cc, moist desquamation was seen in 48.6% vs 45.5% MROQC. Conclusion: Our results indicate that use of the breast cup can allow for improved dose homogeneity with similar acute toxicities as compared with patients treated without the cup while minimizing the dose to the heart and lungs. Our clinical experience shows that breast cups can be used with ease, and allow for good setup reproducibility. It appears that the slight increase in moist desquamation was associated with increased BMI. In conclusion, we recommend that use of a breast cup be considered in appropriately selected patients with large or pendulous breasts. Author Disclosure: P.R. Sevak: None. K. Aldridge: None. C. Fraser: None. C.K. Glide-Hurst: None. E.M. Walker: ACR appropriateness criteria expert panel member; ACR. RTOG Foundation advisory board member; RTOG. Breast working group; NRG. health disparities working group member; NRG. Institutional PI for NRG; NRG.

Adaptive radiotherapy for locally advanced non-small cell lung cancer, can we predict when and for whom?

ABSTRACTBackground. Adaptive radiotherapy (ART) could be a tool to reduce toxicity and to facilitate dose escalation in stage III NSCLC. Our aim was to identify the most appropriate time and potential benefit of ART.Material and methods. We analyzed volume reduction and dosimetric consequences of 41 patients who were treated with concurrent (cCRT) (n = 21) or sequential (sCRT) chemoradiotherapy to a median dose of 70 Gy, 2 Gy/F. At every treatment fraction a cone-beam CT (CBCT) was performed. The gross tumor volume (GTV-T) was adapted (exclusion of lymph nodes) to create the GTV-T-F1. Every fifth fraction (F5–F30), the GTV-T-F1 was adapted on the CBCT to create a GTV-T-Fx. Dose volume histograms were recalculated for every GTV-T-Fx, enabling to create lookup tables to predict the theoretical dosimetric advantage on common lung dose constraints.Results. The average GTV reduction was 42.1% (range 4.0–69.3%); 50.1% and 33.7% for the cCRT and sCRT patients, respectively. A linear relationship between GTV-T-F1 volume and absolute volume decrease was found for both groups. The mean V5, V20, V30 and mean lung dose increased by 0.8, 3.1, 5.2 and 3.4%, respectively. A larger increase (p < 0.05) was observed for peripheral tumors and cCRT. Lookup tables were generated.Conclusion. ART offers the most beneficial dosimetric effects when performed around fraction 15, especially for patients with a large initial GTV-T treated by cCRT.

Potential for reduced radiation-induced toxicity using intensity-modulated arc therapy for whole-brain radiotherapy with hippocampal sparing.

The purpose of this study was to retrospectively investigate the accuracy, plan quality, and efficiency of using intensity‐modulated arc therapy (IMAT) for whole brain radiotherapy (WBRT) patients with sparing not only the hippocampus (following RTOG 0933 compliance criteria) but also other organs at risk (OARs). A total of 10 patients previously treated with nonconformal opposed laterals whole‐brain radiotherapy (NC‐WBRT) were retrospectively replanned for hippocampal sparing using IMAT treatment planning. The hippocampus was volumetrically contoured on fused diagnostic T1‐weighted MRI with planning CT images and hippocampus avoidance zone (HAZ) was generated using a 5 mm uniform margin around the hippocampus. Both hippocampi were defined as one paired organ. Whole brain tissue minus HAZ was defined as the whole‐brain planning target volume (WB‐PTV). Highly conformal IMAT plans were generated in the Eclipse treatment planning system for Novalis TX linear accelerator consisting of high‐definition multileaf collimators (HD‐MLCs: 2.5 mm leaf width at isocenter) and 6 MV beam for a prescription dose of 30 Gy in 10 fractions following RTOG 0933 dosimetric criteria. Two full coplanar arcs with orbits avoidance sectors were used. In addition to RTOG criteria, doses to other organs at risk (OARs), such as parotid glands, cochlea, external/middle ear canals, skin, scalp, optic pathways, brainstem, and eyes/lens, were also evaluated. Subsequently, dose delivery efficiency and accuracy of each IMAT plan was assessed by delivering quality assurance (QA) plans with a MapCHECK device, recording actual beam‐on time and measuring planed vs. measured dose agreement using a gamma index. On IMAT plans, following RTOG 0933 dosimetric criteria, the maximum dose to WB‐PTV, mean WB‐PTV D2%, and mean WB‐PTV D98% were 34.9±0.3 Gy,33.2±0.4 Gy, and 26.0±0.4 Gy, respectively. Accordingly, WB‐PTV received the prescription dose of 30 Gy and mean V30 was 90.5%±0.5%. The D100%, and mean and maximum doses to hippocampus were 8.4±0.3 Gy,11.2±0.3 Gy, and 15.6±0.4 Gy, on average, respectively. The mean values of homogeneity index (HI) and conformity index (CI) were 0.23×0.02 and 0.96×0.02, respectively. The maximum point dose to WB‐PTV was 35.3 Gy, well below the optic pathway tolerance of 37.5 Gy. In addition, compared to NC‐WBRT, dose reduction of mean and maximum of parotid glands from IMAT were 65% and 50%, respectively. Ear canals mean and maximum doses were reduced by 26% and 12%, and mean and maximum scalp doses were reduced by 9 Gy (32%) and 2 Gy (6%), on average, respectively. The mean dose to skin was 9.7 Gy with IMAT plans compared to 16 Gy with conventional NC‐WBRT, demonstrating that absolute reduction of skin dose by a factor of 2. The mean values of the total number of monitor units (MUs) and actual beam on time were 719×44 and 2.34×0.14 min, respectively. The accuracy of IMAT QA plan delivery was (98.1±0.8) %, on average, with a 3%/3 mm gamma index passing rate criteria. All of these plans were considered clinically acceptable per RTOG 0933 criteria. IMAT planning provided highly conformal and homogenous plan with a fast and effective treatment option for WBRT patients, sparing not only hippocampi but also other OARs, which could potentially result in an additional improvement of the quality life (QoL). In the future, we plan to evaluate the clinical potential of IMAT planning and treatment option with hippocampal and other OARs avoidance in our patient's cohort and asses the QoL of the WBRT patients, as well as simultaneous integrated boost (SIB) for the brain metastases diseases.PACS number: 87

Dosimetric Definitions of Total Lung Volumes in Calculating Parameters Predictive for Radiation-induced Pneumonitis

The volume of normal lung receiving 20 Gy (V20) and the mean lung dose (MLD) represent dosimetric parameters used for identifying risk of radiation pneumonitis. However, the total lung volume for dosimetric analysis has been defined differently. Herein we investigate to quantify the dosimetric differences when analysis is based on either definition (ie, excluding planning target volume [PTV] vs. gross tumor volume [GTV] from the total bilateral lung volume). Sixty-one patients with lung cancer who had undergone definitive radiation therapy were retrospectively reviewed. Dosimetric parameters were calculated when excluding GTV or PTV from the total bilateral lung volume. Median GTV to PTV margin was 1.3 cm (range, 0.4 to 3.8 cm). Median heterogeneity-corrected RT dose was 74 Gy with the median GTV of 110 mL (range, 13.79 to 665.8 mL) and the median PTV of 346 mL (range, 39.8 to 1258 mL).The MLD, V5, V10, V20, and V30 were all slightly higher and significant when excluding GTV from the total bilateral lung volume compared with similar dosimetric parameters when excluding PTV (P<0.001). Average MLD was 14.8 and 16.7 Gy when excluding PTV and GTV, respectively. Mean V5, V10, V20, and V30 were 49.8%, 38%, 25%, and 18.8% when excluding PTV versus 51.3%, 40%, 28%, and 21.5% when excluding GTV. There were 4 patients with clinical pneumonitis and all had the V20>23% when excluding the PTV versus the V20>27% when excluding the GTV from total bilateral lung volume. A small but significant difference exists between the 2 approaches used to calculate dosimetric variables for lung dose. This difference should be taken into account when comparing dosimetric information between different institutions and when optimizing treatment plans.

Dosimetric effect due to the motion during deep inspiration breath hold for left-sided breast cancer radiotherapy.

Deep inspiration breath‐hold (DIBH) radiotherapy for left‐sided breast cancer can reduce cardiac exposure and internal motion. We modified our in‐house treatment planning system (TPS) to retrospectively analyze breath‐hold motion log files to calculate the dosimetric effect of the motion during breath hold. Thirty left‐sided supine DIBH breast patients treated using AlignRT were studied. Breath‐hold motion was recorded — three translational and three rotational displacements of the treatment surface — the Real Time Deltas (RTD). The corresponding delivered dose was estimated using the beam‐on portions of the RTDs. Each motion was used to calculate dose, and the final estimated dose was the equally weighted average of the multiple resultant doses. Ten of thirty patients had internal mammary nodes (IMN) purposefully included in the tangential fields, and we evaluated the percentage of IMN covered by 40 Gy. The planned and delivered heart mean dose, lungs V20 (volume of the lungs receiving >20 Gy), percentage of IMN covered by 40 Gy, and IMN mean dose were compared. The averaged mean and standard deviation of the beam‐on portions of the absolute RTDs were 0.81±1.29 mm, 0.68±0.85 mm, 0.76±0.85 mm, 0.96°±0.49°,0.93°±0.43°, and 1.03°±0.50°, for vertical, longitudinal, lateral, yaw, roll, and pitch, respectively. The averaged planned and delivered mean heart dose were 99 and 101 cGy. Lungs V20 were 6.59% and 6.74%. IMN 40 Gy coverage was 83% and 77%, and mean IMN dose was 4642 and 4518 cGy. The averaged mean motion during DIBH was smaller than 1 mm and 1°, which reflects the relative reproducibility of the patient breath hold. On average, the mean heart dose and lungs V20 were reasonably close to what have been planned. IMN 40 Gy coverage might be modestly reduced for certain cases.PACS number: 87.55.km, 87.55.N

Pulmonary function and quality of life after VMAT-based stereotactic ablative radiotherapy for early stage inoperable NSCLC: a prospective study.

To analyze changes in pulmonary function and quality of life (QoL) at different time points after Stereotactic Ablative Radiotherapy (SABR) for early stage inoperable lung cancer, and potential correlations between radiation dose-volume parameters and pulmonary toxicity or changes in pulmonary function tests (PFT) and QoL. From July 2012 to October 2013, 30 patients were enrolled in this prospective observational study. Complete PFT were performed and Lung Cancer Symptoms Scale (LCSS) questionnaire administered prior to SABR; all patients then underwent Computed Tomography (CT) scan and PFT at 45, 135, 225 and 315 days after SABR, together with LCSS questionnaire. Clinical lung toxicity and radiological toxicity (acute and late) were prospectively recorded by using the Radiation Therapy Oncology Group (RTOG) scoring system. A decline in Slow Vital Capacity (SVC), Forced Expiratory Volume in 1s (FEV1), Single-breath lung diffusing capacity (DLCO) and blood partial pressure of oxygen (PaO2) was seen at 135 days post-SABR. PaO2 values rescued to normal levels at 315 days. None of the baseline PFT parameters resulted to be associated with the occurrence of pulmonary toxicity or with late radiological changes. Mean V5, V10, and V20 and MLD2Gy were higher in patients who developed radiation pneumonitis, even if not significantly associated at Cox regression analysis. LCSS QoL showed a significant worsening of the single item fatigue at 135 days after SABR. A small (mean 10%) but significant decline in lung volumes and DLCO was recorded after SABR, with clinical impact of such change difficult to estimate in individual patients. Global QoL was not significantly impaired. Dose-volume parameters did not emerge as significantly predictive of any clinical, radiological or functional toxicity.

Comparison of manual and inverse optimisation techniques in high dose rate intracavitary brachytherapy of cervical cancer: A dosimetric study

Aims and objectivesTo compare dosimetrically the manual optimisation with IPSA using dose volume histograms (DVH) among patients treated for carcinoma of cervix with intracavitary brachytherapy. BackgroundWith the advent of advanced imaging modalities, there has been a shift from conventional X-ray based planning to three-dimensional planning. Manual optimisation is widely used across various institutions but it is time consuming and operator dependant. Inverse planning simulated annealing (IPSA) is now available in various brachytherapy planning systems. But there is a paucity of studies comparing manual optimisation and IPSA in treatment of carcinoma cervix with intracavitary brachytherapy and hence this study. Materials and methodsFifteen consecutive patients treated between December 2013 and March 2014 with intracavitary brachytherapy for carcinoma of cervix were selected for this study. All patients were initially treated with external beam radiotherapy followed by intracavitary brachytherapy. The DVH was evaluated and compared between manually optimised plans and IPSA in the same set of patients. ResultsThere was a significant improvement in the HRCTV coverage, mean V100 of 87.75% and 82.37% (p=0.001) and conformity index 0.67 and 0.6 (p=0.007) for plans generated using IPSA and manual optimisation, respectively. Homogeneity index and dose to the OARs remained similar between the two groups. ConclusionThe use of inverse planning in intracavitary brachytherapy of cervix has shown a significant improvement in the target volume coverage when compared with manual planning.

SU-E-T-307: Dosimetric Comparison of Prone Versus Supine Positioning for Adjuvant Breast Radiation Therapy

Purpose: The prone treatment position has been used to reduce ipsilateral lung and heart dose in left breast radiation. We conducted a retrospective study to evaluate the difference in the dosimetry between prone and supine treatment positions. Methods: Eight left breast cancer patients were simulated in both the supine and prone positions as a pretreatment evaluation for the optimal treatment position. Treatment plans were created for all patients in both the supine and prone positions using a field in field three dimensional planning technique. Prescribed dose was 45 Gy delivered by two tangential photon fields. Irradiated volume (IV) was evaluated by V50, V100, and dose to lung and heart by V5, V10, V20, and the mean dose were evaluated. Results: All dosimetry metrics for both the supine and prone plans met our internal normal structure guidelines which are based on Quantec data. The average IVs (50% and 100%) were 2223cc and 1361cc prone, 2315cc and 1315cc supine. The average ipsilateral lung Mean dose (0.83Gy prone vs 5.8Gy supine), V5 (1.6% prone vs 20.9% supine), V10 (0.78% prone vs 15% supine) and V20 (0.36% prone vs 11% supine) were significantly lower in prone position. Heart Mean dose (1.4Gy prone vs 2.9Gy supine), V10 (1.4% prone vs 5.0% supine) and V20 (0.4% prone vs 3.5% supine) were found improved for all patients except one where the mean dose was the same and all other values were improved. Conclusion: The prone position offer preferable dosimetry for all patients planned in our study. These patients were chosen based on the physician’s belief that they would benefit from prone treatment either because they had large pendulous breasts or due to the amount of heart seen in the field on CT simulation.

TH‐AB‐304‐08: Computational Modeling of Risk of Radiation Pneumonitis

Purpose:Current normal tissue complication probability models estimate incidence of radiation pneumonitis (RP) in the treatment of lung cancer based on single parameters, e.g. mean lung dose or V20, and therefore do not capture specific variations contained in dose volume histograms (DVHs). We therefore developed an RP‐risk model which utilizes the entire DVH reasoning that such a model would be more robust for predicating radiation‐induced lung disease (RILD).Methods:A logistic regression model was developed to predict RP‐risk on each point of the cumulative DVH utilizing &gt;1200 patient outcomes summarized in the Quantitative Analysis of Normal Tissue Effects in the Clinic (QUANTEC) lung study. Stepwise regression including linear, quadratic, and mixed terms in dose and volume was applied to the single dose‐volume parameter‐versus‐outcome data. The model computes a relative importance at each dose‐volume point and these values were linearly combined to estimate an overall RP‐risk. A set of 80 DVHs were used to validate the algorithm prediction by comparison with an independent predictor of RP‐risk using mean lung dose.Results:The logistic regression coefficients were all statistically significant (p&lt;0.005). The proposed model predicted RP‐risk consistently in agreement with the QUANTEC‐RP estimates computed utilizing only mean dose (average difference 0.5%±1.8%) for the 80 DVH set. Most (&gt;70%) of the model variability occurs at doses &lt;30 Gy for DVH levels ranging from 30%‐100%. The model is most sensitive to DVH variations in the V5‐V30 range.Conclusion:The model's predictive power is comparable to estimates from QUANTEC which use mean dose as input. Since the model conveys the relative importance of each dose‐volume level it has the potential to better predict RILD than currently available models. In order to determine if our hypothesis is correct we will compare the model to established methods including complete DVH data and clinical outcomes.This abstract was supported by the George Amorino Pilot Grants in Radiation Oncology from the Department of Radiation Oncology, Univeristy of Virginia.

SU-E-T-277: Dose Calculation Comparisons Between Monaco, Pinnacle and Eclipse Treatment Planning Systems

Purpose: Monaco treatment planning system (TPS) version 5.0 uses a Monte-Carlo based dose calculation engine. The aim of this study is to verify and compare the Monaco based dose calculations with both Pinnacle3 collapsed cone convolution superposition (CCC) and Eclipse analytical anisotropic algorithm (AAA) calculations. Methods: For this study, previously treated SBRT lung, head and neck and abdomen patients were chosen to compare dose calculations between Pinnacle, Monaco and Eclipse. Plans were chosen from those that had been treated using the Elekta VersaHD or a NovalisTX linac. The plans included 3D conventional and IMRT beams using 6MV and 6MV Flattening filter free (FFF) photon beams. The original plans calculated with CCCS or AAA along with the recalculated ones using MC from the three TPS were exported into Velocity software for inter-comparison. Results: To compare the dose calculations, Mean Lung Dose (MLD), lung V5 and V20 values, and PTV Heterogeneity indexes (HI) and Conformity indexes (CI) were all calculated and recorded from the dose volume histograms (DVH). For each patient, the CI values were identical but there were differences in all other parameters. The HI was computed higher by 5 and 4% for calculated plans AAA and CCCS respectively, compared to the MC ones. The DVH graphs showed large differences between the CCCS and AAA and Monaco for 3D FFF, VMAT and IMRT plans. Better DVH agreement between was observed for 3D conventional plans. Conclusion: Better agreement was observed between CCCS and MC calculations than AAA and MC calculations. Those differences were more profound as the field size was decreasing and in the presence of inhomogeneities.

SU‐E‐T‐541: Measurement of CT Density Model Variations and the Impact On the Accuracy of Monte Carlo (MC) Dose Calculation in Stereotactic Body Radiation Therapy for Lung Cancer

Purpose:To measure the CT density model variations between different CT scanners used for treatment planning and impact on the accuracy of MC dose calculation in lung SBRT.Methods:A Gammex electron density phantom (RMI 465) was scanned on two 64‐slice CT scanners (GE LightSpeed VCT64) and a 16‐slice CT (Philips Brilliance Big Bore CT). All three scanners had been used to acquire CT for CyberKnife lung SBRT treatment planning. To minimize the influences of beam hardening and scatter for improving reproducibility, three scans were acquired with the phantom rotated 120° between scans. The mean CT HU of each density insert, averaged over the three scans, was used to build the CT density models. For 14 patient plans, repeat MC dose calculations were performed by using the scanner‐specific CT density models and compared to a baseline CT density model in the base plans. All dose re‐calculations were done using the same plan beam configurations and MUs. Comparisons of dosimetric parameters included PTV volume covered by prescription dose, mean PTV dose, V5 and V20 for lungs, and the maximum dose to the closest critical organ.Results:Up to 50.7 HU variations in CT density models were observed over the baseline CT density model. For 14 patient plans examined, maximum differences in MC dose re‐calculations were less than 2% in 71.4% of the cases, less than 5% in 85.7% of the cases, and 5–10% for 14.3% of the cases. As all the base plans well exceeded the clinical objectives of target coverage and OAR sparing, none of the observed differences led to clinically significant concerns.Conclusion:Marked variations of CT density models were observed for three different CT scanners. Though the differences can cause up to 5–10% differences in MC dose calculations, it was found that they caused no clinically significant concerns.

SU‐F‐BRB‐13: Correlation of Improved Target and Organ‐At‐Risk Dosimetric Quantities and Clinical Outcomes for Helical Tomotherapy Treated Mesothelioma

Purpose:We have observed improved local control probability (LCP) for adjuvant mesothelioma radiotherapy following pleurectomy/decortication using Tomotherapy compared to the conventional 3D technique (p&lt;0.05). This work assesses the correlation between the improved clinical outcomes against dosimetry quantities.Methods:Thirty‐eight mesothelioma cases consecutively treated at our clinic were retrospectively analyzed. Sixteen patients were treated using 3D technique planned on the Eclipse for c‐arm accelerators prior to 7/2012; the other 22 cases were treated on Tomotherapy using helical IMRT after 7/2012. Typical 3D plans consisting of 15 MV AP/PA photon fields prescribed to 10 cm depth followed by matching electron fields with energy ranging from 8–16 MeV. Tomotherapy plans were designed using 2.5cm jaw, 0.287 pitch with directional blocking of the contralateral lung. The same prescription of 45 Gy (1.8GyX25) was used for both techniques. The dosimetry metrics for the critical structures: ipsilateral‐/contralateral‐lung, heart, cord, esophagus, etc were compared between two techniques.Results:Superior LCP is closely associated with improved target coverage. Tomotherapy plans yielded dramatically better target coverage and less dose heterogeneity despite of more advanced/larger disease. The averaged PTV volumes were 2287.3±569.9 (Tomotherapy) vs. 1904.8±312.3cc (3D); V100s were: 91.1±4.0 (%) vs. 47.8±12.7 (%) with heterogeneity indices of 1.20±0.1 vs.1.37±0.38 and for the Tomotherapy and 3D plans, respectively. Compared to the 3D technique, we observed significant lower maximum cord doses (p&lt;0.001), lower mean esophagus doses (p&lt;0.002), and lower heart mean doses when tumor was left‐sided (p=0.002). For ipsilateral‐/contralateral‐lungs, however, the mean doses and V20, V5 of Tomotherapy plans were significantly higher than the 3D plans (p&lt;0.01) regardless which sides of lung were treated. However, rates of radiation pneumonitis were no different.Conclusion:Tomotherapy achieved great improvement of plan quality including target coverage, resulting in significantly better local control over the traditional 3D technique for adjuvant radiotherapy for mesothelioma.