Debbie Louis

DOSIMETRIC COMPARISON OF THREE DIFFERENT INVOLVED NODAL IRRADIATION TECHNIQUES FOR STAGE II HODGKIN'S LYMPHOMA PATIENTS: CONVENTIONAL RADIOTHERAPY, INTENSITY-MODULATED RADIOTHERAPY, AND THREE-DIMENSIONAL PROTON RADIOTHERAPY

PURPOSE To compare the dose distribution to targeted and nontargeted tissues in Hodgkins lymphoma patients using conventional radiotherapy (CRT), intensity-modulated RT (IMRT), and three-dimensional proton RT (3D-PRT). METHODS AND MATERIALS CRT, IMRT, and 3D-PRT treatment plans delivering 30 cobalt Gray equivalent (CGE)/Gy to an involved nodal field were created for 9 Stage II Hodgkins lymphoma patients (n = 27 plans). The dosimetric endpoints were compared. RESULTS The planning target volume was adequately treated using all three techniques. The IMRT plan produced the most conformal high-dose distribution; however, the 3D-PRT plan delivered the lowest mean dose to nontarget tissues, including the breast, lung, and total body. The relative reduction in the absolute lung volume receiving doses of 4-16 CGE/Gy for 3D-PRT compared with CRT ranged from 26% to 37% (p < .05), and the relative reduction in the absolute lung volume receiving doses of 4-10 CGE/Gy for 3D-PRT compared with IMRT was 48-65% (p < .05). The relative reduction in absolute total body volume receiving 4-30 CGE/Gy for 3D-PRT compared with CRT was 47% (p < .05). The relative reduction in absolute total body volume receiving a dose of 4 CGE/Gy for 3D-PRT compared with IMRT was 63% (p = .03). The mean dose to the breast was significantly less for 3D-PRT than for either IMRT or CRT (p = .03) The mean dose and absolute volume receiving 4-30 CGE/Gy for the heart, thyroid, and salivary glands were similar for the three modalities. CONCLUSION In this favorable subset of Hodgkins lymphoma patients without disease in or below the hila, 3D-PRT significantly reduced the dose to the breast, lung, and total body. These observed dosimetric advantages might improve the clinical outcomes of Hodgkins lymphoma patients by reducing the risk of late radiation effects related to low-to-moderate doses in nontargeted tissues.

Contouring the Middle and Inner Ear on Radiotherapy Planning Scans

The purpose of this study was to establish guidelines that help radiation oncologists contour the inner and middle ear on treatment planning scans. The radiotherapy computed tomography (CT) scans of 15 previously treated patients were reviewed for the ability to identify 3 separate auditory structures. The middle ear, the cochlea, and the vestibular apparatus were identified and contoured on each scan using anatomic landmarks. The volume and maximum axial dimension of each contour were calculated. The middle ear, cochlea, and vestibular apparatus were identified on all scans. The middle ear was defined by the tympanic membrane laterally and by the interface between air and the temporal bone in all other directions. The plane of the internal auditory canal through the temporal bone was the landmark distinguishing the vestibular apparatus from the cochlea. The mean volume of the middle ear, vestibular apparatus, and cochlea were 0.58 cm3, 0.44 cm3, and 0.14 cm3, respectively. The maximum axial dimension across the contour averaged 1.57 cm for the middle ear, 1.10 cm for the vestibular apparatus, and 0.69 cm for the cochlea. A reference atlas was constructed that shows the contour of each structure on 5 consecutive CT images. Accurate identification of the middle ear and inner ear structures on radiotherapy planning scans is possible and is necessary if critical auditory organs are to be spared during radiotherapy of targets that are located near the base of the skull. The information generated in this study will help radiation oncologists contour auditory structures accurately.

Comparison of Three-Dimensional (3D) Conformal Proton Radiotherapy (RT), 3D Conformal Photon RT, and Intensity-Modulated RT for Retroperitoneal and Intra-Abdominal Sarcomas

PURPOSE To compare three-dimensional conformal proton radiotherapy (3DCPT), intensity-modulated photon radiotherapy (IMRT), and 3D conformal photon radiotherapy (3DCRT) to predict the optimal RT technique for retroperitoneal sarcomas. METHODS AND MATERIALS 3DCRT, IMRT, and 3DCPT plans were created for treating eight patients with retroperitoneal or intra-abdominal sarcomas. The clinical target volume (CTV) included the gross tumor plus a 2-cm margin, limited by bone and intact fascial planes. For photon plans, the planning target volume (PTV) included a uniform expansion of 5 mm. For the proton plans, the PTV was nonuniform and beam-specific. The prescription dose was 50.4 Gy/Cobalt gray equivalent CGE. Plans were normalized so that >95% of the CTV received 100% of the dose. RESULTS The CTV was covered adequately by all techniques. The median conformity index was 0.69 for 3DCPT, 0.75 for IMRT, and 0.51 for 3DCRT. The median inhomogeneity coefficient was 0.062 for 3DCPT, 0.066 for IMRT, and 0.073 for 3DCRT. The bowel median volume receiving 15 Gy (V15) was 16.4% for 3DCPT, 52.2% for IMRT, and 66.1% for 3DCRT. The bowel median V45 was 6.3% for 3DCPT, 4.7% for IMRT, and 15.6% for 3DCRT. The median ipsilateral mean kidney dose was 22.5 CGE for 3DCPT, 34.1 Gy for IMRT, and 37.8 Gy for 3DCRT. The median contralateral mean kidney dose was 0 CGE for 3DCPT, 6.4 Gy for IMRT, and 11 Gy for 3DCRT. The median contralateral kidney V5 was 0% for 3DCPT, 49.9% for IMRT, and 99.7% for 3DCRT. Regardless of technique, the median mean liver dose was <30 Gy, and the median cord V50 was 0%. The median integral dose was 126 J for 3DCPT, 400 J for IMRT, and 432 J for 3DCRT. CONCLUSIONS IMRT and 3DCPT result in plans that are more conformal and homogenous than 3DCRT. Based on Quantitative Analysis of Normal Tissue Effects in Clinic benchmarks, the dosimetric advantage of proton therapy may be less gastrointestinal and genitourinary toxicity.

Proton therapy for maxillary sinus carcinoma.

Objectives:To compare the dose-volume data of three-dimensional conformal proton therapy (3DCPT) versus intensity-modulated radiotherapy (IMRT) for a paranasal sinus malignancy. Methods:3DCPT and IMRT plans were created for a T4N0 maxillary sinus carcinoma. Results:The target volume dose distributions were comparable for 3DCPT and IMRT. The mean and integral doses for all normal tissues were lower for 3DCPT. The maximum doses for both plans to the ipsilateral optic nerve/retina/lens, temporal lobe, pituitary, and brain exceeded tolerance doses. The contralateral parotid, lacrimal gland, and lens were avoided with 3DCPT. Neither 3DCPT nor IMRT exceeded the maximal tolerated dose for the brainstem, optic chiasm, contralateral temporal lobe, parotid, or lacrimal gland. Conclusions:Both 3DCPT and IMRT sufficiently covered the target volume(s). Although 3DCPT reduced the mean and integral dose to all of the normal tissues, both 3DCPT and IMRT irradiated the ipsilateral optic structures beyond acceptable tolerance doses.

The role of intensity modulated radiation therapy for favorable stage tumor of the nasal cavity or ethmoid sinus.

Objectives:To compare intensity-modulated radiation therapy (IMRT), 4-field conformal, and the standard 3-field conventional technique of radiotherapy for favorable stage tumors of the nasal cavity or ethmoid sinus. Methods and Materials:We compared the 3 techniques in 3 patients with tumors of the nasal cavity or ethmoid sinus that did not involve the eye or optic pathways. We required that each plan deliver the prescription dose (70.2 Gy at 1.8 Gy per fraction) to 95% of the planning target volume. We compared the maximum point dose to critical normal structures (brainstem, optic chiasm, optic nerves, retina, lens). Results:IMRT and the 4-field conformal technique were clearly better than the 3-field conventional technique. The 4-field conformal plan was as good as IMRT. Conclusions:The conventional 3-field technique is not the best way to treat most patients with tumors between the eyes. A 4-field conformal plan is an excellent alternative to IMRT for some patients with tumors of the nasal cavity or ethmoid sinus. Conformal radiotherapy with a noncoplaner field that exits into the low neck may make it difficult to electively irradiate the neck lymphatics. IMRT may be a better option in this situation.

Predicting changes in dose distribution to tumor and normal tissue when correcting for heterogeneity in radiotherapy for lung cancer.

Purposes:The purposes of this study were to examine dose alterations to gross tumor volume (GTV) and lung using heterogeneity corrections and to predict the magnitude of these changes. Methods:Three separate conformal plans were generated for 37 patients with lung cancer: plan 1 corrected for heterogeneity, plan 2 did not correct for heterogeneity, and plan 3 used identical beams and monitor units from plan 2 but with heterogeneous calculations. Plans 1 and 2 were normalized to the 95% isodose line. Mean dose (MeanDGTV), maximum dose (MaxDGTV), and minimum dose (MinDGTV) to GTV and V20 were compared between plans 1 and 3. For each patient, the amount of lung in all beam paths of plan 3 was quantified by a density correction factor and correlated with the percent change. Results:The median percent change in MeanDGTV, MaxDGTV, and MinDGTV between plan 3 and plan 1 was −4.7% (−0.1% to −19.1%, P < 0.0001), −5.59% (0.16% to −31.86%, P < 0.0001), and −4.88% (2.90% to −24.88%, P < 0.0001), respectively. The median V20 difference was −1% (1% to −8%). The density correction factor correlated with larger differences in MeanDGTV on univariate analysis. Conclusions:Heterogeneity correction lowers the dose to GTV by 5%. This difference can be correlated with the density correction factor.

Comparing Breath Hold and Free Breathing during Intensity-Modulated Radiation Therapy and Proton Therapy in Patients with Mediastinal Hodgkin Lymphoma

In the treatment of mediastinal lymphoma, there has been increased interest over the last 5 years in utilizing proton therapy techniques as well as breath-hold techniques with 3-dimensional conformal radiation therapy (RT) or intensity-modulated RT in an effort to reduce the radiation dose to the organs at risk [1–6]. Combining both breath-hold techniques and proton therapy has been less common owing to concerns about the reproducibility of breath hold, the impact of poor reproducibility when using proton therapy, and the lack of volumetric image-guided RT and real-time diaphragm monitoring of the breath hold. Additionally, the length of treatment may be of concern, especially when matching fields are required due to large treatment volumes. Yet newer RT treatment centers with faster delivery systems and more advanced image-guided RT equipment make the combination of proton therapy and breath hold a more realistic possibility. In the present report, we investigate the impact of using the breath-hold technique with 3 female patients treated for bulky mediastinal stage II Hodgkin lymphoma with proton therapy, and compare our findings with the free-breathing technique.

Dose–Volume Differences for Computed Tomography and Magnetic Resonance Imaging Segmentation and Planning for Proton Prostate Cancer Therapy

PURPOSE To determine the influence of magnetic-resonance-imaging (MRI)-vs. computed-tomography (CT)-based prostate and normal structure delineation on the dose to the target and organs at risk during proton therapy. METHODS AND MATERIALS Fourteen patients were simulated in the supine position using both CT and T2 MRI. The prostate, rectum, and bladder were delineated on both imaging modalities. The planning target volume (PTV) was generated from the delineated prostates with a 5-mm axial and 8-mm superior and inferior margin. Two plans were generated and analyzed for each patient: an MRI plan based on the MRI-delineated PTV, and a CT plan based on the CT-delineated PTV. Doses of 78 Gy equivalents (GE) were prescribed to the PTV. RESULTS Doses to normal structures were lower when MRI was used to delineate the rectum and bladder compared with CT: bladder V50 was 15.3% lower (p = 0.04), and rectum V50 was 23.9% lower (p = 0.003). Poor agreement on the definition of the prostate apex was seen between CT and MRI (p = 0.007). The CT-defined prostate apex was within 2 mm of the apex on MRI only 35.7% of the time. Coverage of the MRI-delineated PTV was significantly decreased with the CT-based plan: the minimum dose to the PTV was reduced by 43% (p < 0.001), and the PTV V99% was reduced by 11% (p < 0.001). CONCLUSIONS Using MRI to delineate the prostate results in more accurate target definition and a smaller target volume compared with CT, allowing for improved target coverage and decreased doses to critical normal structures.

Rationale and early outcomes for the management of thymoma with proton therapy

Background Radiotherapy for thymic malignancies is technically challenging due to their close proximity to the heart, lungs, esophagus, and breasts, raising concerns about significant acute and late toxicities from conventional photon radiotherapy. Proton therapy (PT) may reduce the radiation dose to these vital organs, leading to less toxicity. We reviewed the dosimetry and outcomes among patients treated with PT for thymic malignancies at our institution. Methods From January 2008 to March 2017, six patients with de novo Masaoka stages II-III thymic malignancies were treated with PT on an IRB-approved outcomes tracking protocol. Patients were evaluated weekly during treatment, then every 3 months for 2 years, then every 6 months for 3 more years, and then annually for CTCAE vs. four toxicities and disease recurrence. Comparison intensity-modulated radiotherapy (IMRT) plans were developed for each patient. Mean doses to the heart, esophagus, bilateral breasts, lungs, and V20 of bilateral lungs were evaluated for the two treatment plans. Results At last follow-up (median follow-up, 2.6 years), there were two patients with recurrences, including metastatic disease in the patient treated definitively with chemotherapy and PT without surgery and a local-regional recurrence in the lung outside the proton field in one of the post-operative cases. No patients with de novo disease experienced grade ≥3 toxicities after PT. The mean dose to the heart, lung, and esophagus was reduced on average by 36.5%, 33.5%, and 60%, respectively, using PT compared with IMRT (P<0.05 for each dose parameter). Conclusions PT achieved superior dose sparing to the heart, lung, and esophagus compared to IMRT for thymic malignancies. Patients treated with PT had few radiation-induced toxicities and similar survival compared to historic proton data.

SU‐GG‐T‐562: Dosimetric Comparison of 3D Conformal Proton Therapy and IMRT for Retroperitoneal‐Sarcoma Treatments

Purpose: To determine the difference in dose to target and critical structures when treating retroperitoneal sarcoma with 3D conformal proton therapy or IMRT, and to evaluate the sensitivity to setup errors for both techniques. Method and Materials: 3D conformal proton,IMRT, and 3D conformal photon plans were made for 8 patients. GTV volumes varied between 277 and 3482cc. A uniform 2cm GTV to CTV margin was applied, followed by a 0.5cm CTV to PTV margin. Laterally the proton plans were conformed to the PTV, while a distal margin equal to 1.5% of the range plus 1mm was applied to the CTV. Range‐compensator smearing of 0.5cm was used. For proton plans 2 to 4 beams were used; 5 to 8 for photon plans. Prescribed dose is 50.4CGE. To evaluate the effect of setup uncertainty on target coverage and dose to critical structures, proton and IMRT plans were re‐calculated for 5mm shifts along the cardinal axes. Pinnacle (Philips) treatment planning system was used to generate photon plans; Eclipse (Varian) to generate proton plans. Results: The bowel V15Gy is lower in the proton plan (19.9% versus 51.7% averaged over all patients), while V45Gy is near identical (6.9% versus 6.3%). Mean dose to liver is 5.8 and 13.2Gy for proton and IMRT respectively. When not involved in the CTV, the V20Gy of the ipsilateral kidney is significantly lower in proton plans (by up to 45%). Both techniques avoid the contralateral kidney giving comparable V20Gy (0.2% and 2.3%). Conclusion: Conformity of the dose to the target is comparable for both techniques. Critical‐structure volumes receiving high doses are comparable, while the volume receiving low dose is reduced significantly in proton plans. IMRT plans are less sensitive to variations in setup.