Raj Selvaraj

Conventional 3D conformal versus intensity-modulated radiotherapy for the adjuvant treatment of gynecologic malignancies: a comparative dosimetric study of dose–volume histograms☆

OBJECTIVE The goals of this study were to evaluate the feasibility of pelvic intensity-modulated radiotherapy (IMRT) in the adjuvant treatment of gynecologic malignancies and to compare the dose-volume histograms (DVHs) and determine the potential impact on acute and long-term toxicity based on the dose to target and nontarget tissues for both planning techniques. METHODS Ten consecutive patients referred for adjuvant radiotherapy for gynecologic malignancies at the University of Pittsburgh School of Medicine and Magee-Womens Hospital were selected for CT-based treatment planning using the ADAC 3D version 4.2g and the NOMOS Corvus IMRT version 4.0. Normal tissues and critical structures were contoured on axial CT slices by both systems in conjunction with a gynecologic radiologist. These regions included internal, external, and common iliac nodal groups, rectum, upper 4 cm of vagina, bladder, and small bowel. Conventional treatment planning included 3D four-field box using 18-MV photons designed to treat a volume from the L(5)/S(1) border superiorly to the bottom of the ischial tuberosity on the AP/PA field and shaped blocks on the lateral fields to minimize the dose to the rectum and small bowel. A seven-field technique using 6-MV photons was used for IMRT. Restraints on small bowel for IMRT were set at 23.0 Gy +/- 5% and 35.0 Gy+/- 5% for the rectum and 37.5 Gy +/- 5% for the bladder while simultaneously delivering full dose (45.0 Gy) to the intrapelvic nodal groups in 1.8-Gy daily fractions. The dose-volume histograms where then compared for both treatment delivery systems. RESULTS The volume of each organ of interest (small bowel, bladder, and rectum) receiving doses in excess of 30 Gy was compared in the 3D and IMRT treatment plans. The mean volume of small bowel receiving doses in excess of 30 Gy was reduced by 52% with IMRT compared with 3D. A similar advantage was noted for the rectum (66% reduction) and the bladder (36% reduction). The nodal regions at risk and the upper vagina all received the prescribed dose of 45.0 Gy. CONCLUSIONS Intensity-modulated radiotherapy appears to offer several advantages over conventional 3D radiotherapy (3D CRT) planning for adjuvant radiotherapy for gynecologic malignancies. These include a significant reduction in treatment volume for bladder, rectum, and small bowel. It is anticipated that this reduction in volume of normal tissue irradiated would translate into overall reduction in acute and potentially late treatment-related toxicity. Prospective trials are necessary to better evaluate the advantages in a larger group of patients.

Comparison of 2D vs. 3D Dosimetry for Rotte ‘Y’ Applicator High Dose Rate Brachytherapy for Medically Inoperable Endometrial Cancer

The purpose of our research is to compare CT-based volumetric calculations and International Commission on Radiation Units and Measurements (ICRU) reference-point estimates of radiation doses to the target volume, bladder, rectum, and sigmoid colon in patients with carcinoma of the endometrium treated with high dose rate intracavitary Rotte ‘Y’ applicator brachytherapy (HDRB). Eleven patients with cancer of the endometrium were treated with CT-compatible HDR intracavitary Rotte ‘Y’ applicators (Nucletron) and underwent post-implant pelvic CT scans with applicators in place. All patients were treated using orthogonal radiography-based planning. The dose was prescribed to uterine point (a point located 2 cm below the center of a line drawn between the tips of the two ends of the Rotte applicator extending laterally from the tandem by half the maximum uterine width), Point A, and 0.5 cm depth along the upper 3 cm vagina. CT-images were transferred to the PLATO treatment planning system version 14.2.6 and retrospectively planned for volumetric calculations. The clinical target volume (CTV) included the entire uterus, cervix, and upper 3 cm of vagina. The volumes of organs at risk (OAR) were digitized. Dwell positions were identified and registered in both the uterine tandem for each patient. For those receiving HDRB alone, the prescribed dose was 7 Gy x 5 fractions. Patients who were treated following external beam radiation therapy (EBRT) received 4Gy x 5 fractions. The interfraction interval was 6–8 hours. The DVHs were computed for the CTV, bladder, rectum, and sigmoid colon. To compare doses of OARs, 1.0 cc, 2.0 cc, and 5.0 cc volumes receiving the highest dose were calculated from DVHs. 3D optimization was done to improve target coverage and decrease dose to critical organs and compared with the 2D orthogonal radiograph-based plan. The mean of percentage of prescribed dose ± S.D to 1 cc, 2 cc, and 5 cc of the OARs of interest were as follows: Rectum 44 ± 21%, 39 ± 18%, and 33 ± 15%; bladder 104 ± 36%, 91 ± 31%, and 73.9 ± 24%; and sigmoid 124 ± 35%, 109 ± 30%, and 89 ± 25%, respectively. The corresponding dose to ICRU 38 bladder and rectal points were 98 ± 55% and 50.5 ± 32%, respectively. The mean dose to uterine point and point A were 99 ± 1.7% and 98 ± 3%, respectively. The mean CTV volume was 160 ± 89 cc with the percentage of volume getting 100% and 90% of the dose being 62 ± 12% and 68 ± 12% with 2D plan versus 57 ± 8% and 67 ± 8.9% with 3D plan. The dose to critical organs were reduced with 3D optimization for rectum, bladder, and sigmoid by 5.6% (p = 0.04), 20.6% (p = 0.02), and 26.8% (p = 0.005), respectively. Compared to the 3-D volume dose, the prescription points overestimated the dose to the target volume. The under-dosing was because of inability of two channel applicator to cover volumes in the region of the cervix and vagina. The dose to sigmoid colon was high and attention should be given to the sigmoid dose at the time of treatment planning. 3D planning helped in reducing the dose to the critical organs without compromising target coverage. Correlations with outcome are needed to better define the role of 3D dosimetry in treatment planning.

The potential nephrotoxic effects of intensity modulated radiotherapy delivered to the para-aortic area of women with gynecologic malignancies: preliminary results.

Objective:To assess kidney function via creatinine clearance before and after radiotherapy in gynecologic cancer patients treated to the para-aortic (PA) area via Intensity Modulated Radiotherapy (IMRT). Methods:Twenty-three patients underwent IMRT to the para-aortic area, were followed for at least 5 months, and had the necessary laboratory data to calculate creatinine clearance. Various patient-related factors and radiotherapy-treatment related factors were analyzed to determine their association with changes in CrCl. Results:Median follow-up was 10.9 months (range, 5–19 months). Median patient age was 51.7 years (range, 22–78). The average initial CrCl was noted to be 109.23 mL/min (range, 38.64–188.38) before radiotherapy and decreased to 90.00 mL/min (29.31–175.61) after radiotherapy (P = 0.004). Although 17 patients had a decrease in their CrCl, 6 were found to have a slight elevation. Five factors were associated with a decrement in CrCl greater than the average decrease (17.6%): presence of hydronephrosis, age <50, no history of cisplatin treatment, a BED to gross adenopathy exceeding mean BED, and salvage treatment of PA node recurrence. Subgroup analysis revealed that the only statistically significant change within the group of patient and/or treatment-related factors was between patients who were <50-year-old and patients who were ≥50 years of age (P = 0.03). No patient exhibited clinical signs of radiation-induced nephropathy. Conclusion:With a median follow-up of 10.9 months, the estimated CrCl decreased by 17.6% after IMRT to the para-aortic area ± cisplatin chemotherapy. The greatest decrease in CrCl occurred in patients who had a history of hydronephrosis. Subgroup analysis revealed that the decline in CrCl was significantly greater for patients younger than 50 years of age. Interestingly, a greater decline in CrCl was noted for those patients who did not have a history of cisplatin treatment. Our preliminary results indicate that IMRT ± cisplatin chemotherapy to the para-aortic area of women is safe and is not associated with any clinical sequelae of renal toxicity despite a small decrement in CrCl in most, but not all patients.

Breast skin doses from brachytherapy using MammoSite® HDR, intensity modulated radiation therapy, and tangential fields techniques

Skin doses from brachytherapy using MammoSite® HDR, Intensity Modulated Radiation Therapy (IMRT), and conventional tangential fields techniques were compared. For each treatment technique, skin doses were measured using paired thermoluminescent dosimeters placed on the patients skin: (i) directly above the balloon catheter during MammoSite® HDR brachytherapy treatments and (ii) 4 cm inside the treatment borders during the IMRT and conventional breast treatments. The mean dose measured was about 58% of the prescription dose for the patients treated using the MammoSite® technique. On the other hand, for patients treated with IMRT and tangential fields, the mean dose was found to be about 69% and 71% of the corresponding prescription dose. This study suggests that in breast cancer radiation treatments the MammoSite® HDR technique reduces skin doses compared to IMRT and tangential field techniques. PACS numbers: 87.53.Jw, 87.53.Xd, 87.66.Sq

TU‐C‐T‐6E‐05: Dosimetry Acccracy Of Delivery Of Gold Beam Data IMRT Plans On Similar Linear Accelerators With Same Vendor

Purpose: Under certain circumstances, IMRT patients need to be transferred from one Linac to another. Since a same set of commercial Gold Beam Data (GBD) have been used to model the treatment planning systems for multiple similar types of Linacs at our centers, the dosimetric accuracy needs to be investigated to determine the necessity of replanning when the treatment of an IMRT patient is moved from one machine to another. In this study, we investigated the dosimetric accuracies of IMRT plans delivered on different similar Varian accelerators. Method and Materials: In our institution, GBD has been used to model the Eclipse™ treatment planning systems for certain types of Varian machines (23 EX). IMRT treatments were planned using the Eclipse™ systems with 6 and 10 MV photon beams for different anatomical sites. Corresponding QA plans were also generated. The QA plans were used in the validation measurements, and the same measurements (same plans, same MU & dMLC files and phantom) were repeated on five of those Linacs. The measurements were performed using both ion chambers and films. Results: For plans using 6 MV photon beams, the mean ratios of planned to measured dose on the five machines for breast, prostate, tonsil, pelvis and brain plans were 0.984(SD0.0078), 0.998(SD0.0029), 0.979(SD0.0121), 1.006(SD0.0132) and 1.012(SD0.0054), respectively. For plans using 10 MV photon beams, the mean ratios of planned to measured dose on two of the machines for breast and pelvis were 0.979(SD0.00) and 0.949(SD0.0042), respectively. In the film analysis, a good agreement was found between films and plan isodoses on a coronal plane (for high dose gradients ± 2 mm and low dose gradients ± 4 mm). Conclusion: This study demonstrated that the IMRT patients could be transferred from one machine to another similar Varian machine with same energy without replanning.

TU‐EE‐A1‐03: Comparison of High Dose Rate (HDR) Vs Intensity Modulated Radiation Therapy (IMRT) for Prostate Boost Treatment

Purpose: The objective of this study is to compare dosimetric characteristics of prostate treatments using HDR brachytherapy and IMRT technique. Method and Materials: Five HDR patients were selected for IMRT planning. Patients underwent ultrasound guided catheter placement for HDR. CTimages were obtained and imported into the Nucletron PLATO Brachytherapy system. The prostate, urethra, bladder and rectum were contoured on axial slices. The dose was calculated and optimized by graphical optimization. The CTimages of these structures were exported from the PLATO to Eclipse workstation for IMRT planning and comparison. For each patient, the DVH of HDR and IMRT plans were generated, drawn on the same scale and compared. Results: In IMRT plans the DVH curves for PTV dropped sharply and reached to zero volume of the prostate at about 6.4 Gy. In HDR plans the DVH curves for PTV showed a long tail up to a very high dose. About 10% of the PTV for prostate received greater than 12 Gy (200%) of the prescribed dose (6 Gy) in HDR plans. In contrast, the same volume in IMRT plans received less than 6 Gy (100%). Average prostate V90 and V100 dose was about 6.3 Gy and 4.12 Gy respectively for HDR, and 6.09 Gy and 5.74 Gy for IMRT plans, respectively. UrethraV90 dose for IMRT plans showed similar levels (93%), whereas in HDR the dose varied widely (60 to 100%). In all plans, the dose to the bladder and rectum was significantly lower in HDR than in IMRT plans. Conclusions: HDR brachytherapy may reduce normal tissue toxicities in prostate boost treatments, even though the dose homogeneity inside the PTV is far worse than in IMRTtreatments. Another advantage of HDR over IMRT is that the organ motion is not a significant concern as in IMRT.

SU-FF-J-96: The Application of Varian's Markermatch Software in a Retrospective Study of Inter-Fractional Prostate Motion

Purpose: MarkerMatch is an automated marker match software feature developed by Varian in on-board imaging. It may calculate inter-fractional prostate motion with internal fiducial markers identified on CT scans. Before each treatment, a pair of portal images was taken and fiducial markers are identified. Based on the portal image pair, MarkerMatch calculates the optimized couch displacement in 3D to maximally restore the marker positions to their reference positions. To evaluate MarkerMatchs clinical performance, we did a phantom test and a retrospective study on patients implanted with radio-opaque fiducial markers. Method and Materials: We used a phantom implanted with 4 cylindrical-shaped markers of 1mm in diameter and 3mm in length. MarkerMatch localizes the markers based on CT images. In order to test MarkerMatchs ability to handle CT images of different quality, we scanned the phantom with four CT spacing. The portal image pair taken before treatment is normally at AP/Lateral gantry angles, but sometimes it is difficult to identify markers from the lateral image. To test MarkerMatchs ability to handle non-orthogonal portal image pair, we took portal images at 7 different gantry angles. As a preliminary test for the use of Markermatch in clinic, we retrospectively analyzed five patients implanted with 2–3 gold markers based on 43 pairs of weekly setup portal images. Results: In our phantom test, MarkerMatch is able to measure overall marker displacements within 1mm in each direction, regardless of the spacing used in the CT scans. Using different gantry separation angles, the measured overall marker displacements agree with each other within 1mm. Retrospective analysis of five patients is also presented. Conclusion: Initial studies indicate that MarkerMatch is robust in detecting and analyzing patient motion in 3D and can provide valuable information of inter-fractional prostate motion in clinic. Conflict of Interest: Funded in part by Varian Research Grant.

SU-FF-T-32: Imaged-Based Simulation Technique To Determine Stepping Source Dwell Position For MammoSite(r) Brachytherapy Procedures

Purpose: Incorrect dwell position for the stepping source in MammoSite® radiation therapy system would result in severe dose error to the treated volume. In many centers, CT‐simulators have replaced the fluoroscopic simulators. An alternative method must be developed for this purpose. This project evaluates the feasibility of CT‐based simulation to determine the dwell position for the stepping source of the Nucletron® High‐Dose Rate (HDR) unit. Method and Materials: A MammoSite® balloon applicator is placed in the surgical cavity intraoperatively at the time of segmented mastectomy for breast cancer. The balloon is inflated to near spherical shape with saline solution mixed with a small amount of radiographic contrast to aid in visualization. After recovery, the patient is brought to the radiation oncology facility to determine the quality of the implant and also to determine the stepping source dwell position. A dummy source train is initially inserted in the applicator and pushed to the distal end. The distance is measured using the Nucletron® measuring tool. CT scans of the breast was taken with 1 mm slice thickness. After the images have been acquired, a virtual 3‐dimensional breast is generated. Based on the virtual breast, the path of the dummy source train inside the applicator is assessed. Results: A digitally reconstructed radiography(DRR) that maximizes the projection of the pathway is created. A method is formulated to determine the center of the sphere and marks on the source pathway. The dwell position is determined by subtracting the difference of distance between the distal seed and center of the sphere from the maximum source distance as set on the HDR unit. Conclusion: For institutions where the fluoroscopic simulator has been replaced by a CT‐simulator, imaged‐based simulation allows an effective method of determining the stepping source dwell position for MammoSite® brachytherapy procedures.