Modulated Arc Radiotherapy Research Articles

Selection of prescription isodose line for brain metastases treated with volumetric modulated arc radiotherapy.

PurposeTo exploit the optimal prescription isodose line (IDL) for brain metastases treated with volumetric modulated arc radiotherapy (VMAT) as there is no consensus on the selection of IDL with VMAT.Methods and materialsEighteen patients with 20 brain tumors, who were treated with VMAT, were enrolled in this study. For each tumor of every patient, five plans were designed with IDL ranging from 50% to 90% in 10% increments. Different IDLs were obtained through adjusting the constraint parameters during planning optimization. Prescription dose (10 × 5 Gy) were identical for all plans, and the plans were compared in terms of gradient index (GI), conformity Index (CI), V26 Gy/VPTV, and V32 Gy/VPTV in normal brain tissue, which correlate to radiation necrosis.ResultsIDL with lowest GI has a median value of 60.0% (ranging from 50% to 80%). Except for one tumor with volume larger than 10 cc, the IDL with lowest GI varies from 50% to 70%, which depends on the shape of PTV, location, and whether the target volume is adjacent to crucial OAR. Moreover, there is no significant difference for CI with varying IDL plans. The average V26 Gy/VPTV and V32 Gy/VPTV in normal brain tissue 60% IDL plans are 27.3%, 31.7% lower than 90% IDL plans separately (P < 0.05). However, by further decreasing IDL from 60% to 50%, the average V26 Gy/VPTV and V32 Gy/VPTV may increase comparing with 60% IDL plans (P > 0.05). Furthermore, a lower IDL is found to result in higher mean dose to the target volume (P < 0.05).ConclusionsPlans using VMAT with PTV smaller than 10 cc tend to be optimal with IDL around 60–70% for lower GI, smaller V26 Gy/VPTV, V32 Gy/VPTV in normal brain tissue, and higher mean dose in tumor comparing with high IDL plans which have potential benefit in reducing risk of radiation necrosis and increasing the local control. However, IDL lower than 60% is not recommended for the disadvantage of increasing V26 Gy/VPTV and V32 Gy/VPTV in normal brain tissue.

EP1.18-14 Algorithm for Deciding Radiotherapy Technique in Stage III Non-Small Cell Lung Cancer

Concurrent chemoradiotherapy has shown superior survival outcomes in inoperable, Stage III non-small cell lung cancer (NSCLC) with good performance status. Usage of 3-dimensional conformal radiotherapy (3D-CRT) technique is commonest with intensity modulated radiotherapy (IMRT) gaining popularity owing to its ability to spare normal tissues. In our study we analysed the tumour and nodal characteristics of patients to predict which technique maybe beneficial by generating optimised plans of both 3D-CRT and volumetric modulated arc radiotherapy (VMAT), a type of IMRT. A total of 27 Stage III NSCLC patients underwent PET-CT (in the treatment position) co-registered treatment planning using either 3D-CRT or VMAT. The total prescription dose was 60 Gy in 30 fractions over 6 weeks with concurrent cisplatin based chemotherapy. Retrospectively alternate treatment plans were generated to obtain two sets of plans (3D-CRT and VMAT) of each patient for dosimetric comparison. The tumour and nodal characteristics and treatment technique were analysed to identify predictive factors limiting total dose delivery. The angle of contact of the PTV with the circumference of the vertebral body was calculated for patients where the tumour or nodal mass was in contact with the vertebral body (Figure 1). Of the 27 patients enrolled, 6 patients could not be planned to the complete dose of 60 Gy in a single phase by 3D-CRT. Dose limiting factors were high spinal cord doses due to vertebral body erosion (2 out of 6) and bilateral bulky mediastinal lymphadenopathy (4 out of 6). Alternate VMAT plans for these patients could achieve the dose constraints in all but the two patients with vertebral body erosion. Differences in the normal tissue doses of bilateral normal lungs, esophagus, heart and spinal cord were compared between both techniques to ascertain statistical significance. The spatial location of the tumour and nodal burden rather than the volume limited the maximum dose delivered. For tumours with vertebral body contact of more than 90 degrees, VMAT should be used. With gross vertebral body erosion, even VMAT falls short if the PTV includes the spinal cord. In view of high patient volume and limited resources, VMAT is not an economical option for all patients. A simple clinical algorithm is outlined (Figure 1) which will help select patients who will best benefit from VMAT.

A Phase I/II Study of Stereotactic Hypofractionated Once-weekly Radiation Therapy (SHORT) for Prostate Cancer

AimsStereotactic radiation therapy has been investigated predominantly in patients with low–intermediate-risk disease. We conducted a clinical trial of stereotactic hypofractionated radiation therapy delivered in once-weekly fractions on patients with all-risk non-metastatic disease to test feasibility, acute toxicities and patient-reported outcomes. Materials and methodsIn this phase I/II study, 30 patients with prostatic adenocarcinoma, any Gleason score, T1-4N0 and prostate-specific antigen ≤60 ng/ml were treated with volumetric intensity modulated arc radiation therapy to a dose of 35 Gy in five fractions delivered once weekly. Patients with high-risk disease also received elective nodal irradiation to a dose of 25 Gy in five fractions simultaneously. Androgen deprivation was offered to intermediate- and high-risk patients. The primary outcome was acute toxicity. Secondary outcome measures included biochemical control and late toxicity. Patient-reported outcomes were measured using the International Prostate Symptom Score and European Organization for Research and Treatment of Cancer (EORTC) Quality-of-Life Questionnaire (QLQ). ResultsAll 30 patients completed treatment per-protocol. Most patients had T3 (60%) and Gleason 7 (50%) tumours. The median prostate-specific antigen was 17 ng/ml. High-risk disease was present in 20 patients (66.7%). There was a low incidence of acute toxicities (grade 2 + urinary 3.3%, grade 2 rectal 0%). Within the EORTC QLQ framework, only the urinary symptom score showed a clinically meaningful worsening from a mean of 20/100 at baseline to 34/100 at the end of treatment (P < 0.001), but reduced to 24/100 at 6 months (P = 0.08). With a median follow-up of 41.5 months, two patients each reported grade 2 late urinary and rectal toxicity. The 3- and 4-year biochemical control rates were 96.7 and 87.9%, respectively. ConclusionIn a cohort of mainly high-risk cancers, stereotactic once-weekly radiation therapy was easy to implement and well tolerated, with a low incidence of acute and late toxicity and excellent biochemical control.

Comparative Dosimetric Study of 3D Conformal Radiotherapy versus Volumetric Modulated Arc Radiotherapy in Synchronous Bilateral Breast Cancer

Prevalence of synchronous bilateral breast cancer (SBBC) is still scarce. No clear consensus to guide the specialists for best techniques to treat such complex target. Until now, 3DCRT considers an acceptable technique to treat SBBC in many cancer centers worldwide. This study will present the possible role of VMAT in treating SBBC in comparison with 3DCRT. All cases diagnosed and pathologically proven operable SBBC without any evidence of distant metastasis at our institution selected to this study. Eligible criteria are: patients are >18 years old with ECOG of 0-1 who resected all gross disease with level I to II axillary dissection with negative surgical margins and completed their adjuvant chemotherapy. We excluded Cases with metachronous bilateral breast cancer, treated with previous thoracic irradiation or have serious comorbid diseases, such as chronic obstructive pulmonary disease, connective tissue disease. We also excluded patients with postoperative wound infections, delayed wound healing, or treated with palliative intent. We delineated Planning target volumes (PTVs) and organs at risk (OARs) on the planning CTs. The dose prescribed for both plans is 50 Gy in 25 fractions+/- Boost of 10Gy over 5 fractions. We have collected a total of 9 cases with pathologically proven SBBC who were treated by adjuvant radiotherapy either post mastectomy/post conservative breast surgery in the period between January 2013 and December 2018. Indication of adjuvant treatment by radiation has been taken at our breast tumor board. The Averages of PTV coverage in VMAT vs. 3D-CRT were as following: D98%=45.9 vs. 44.2 Gy, D95%=47.3 vs. 46.1Gy, D50%=50.4 vs. 50.53 Gy, D2%=52.5 vs. 53.85 Gy, respectively. For organs at risk avoidance in VMAT vs. 3D-CRT were as following: heart V30=1.16 vs. 7.06 %, heart V25=3.66 vs. 7.75 %, Rt lung V5=98.3% vs45.64 %, Rt lung V20=12.73 vs. 25.45 %, Lt lung V5=98.30 vs. 45.64 %, Lt lung V20=10.70 vs. 23.70%, spinal cord Dmax= 16.86 vs. 7.97 Gy, Larynx Dmax=17.99vs 17.94, Larynx Dmean=6.40 vs 2.30 Gy, Esophagus Dmax=34.8 vs 5.20 Gy, Esophagus Dmean=15.60 vs 25.39 Gy, Dmean of constrictor muscles of the pharynx= 3.41 vs. 1.05 Gy, Liver Dmean=7.28 vs. 4.76 Gy, Stomach D100=3.22 vs. 0.57%, Thyroid Dmean=23.10 vs. 24.76 Gy, Thyroid Dmax=44.04 vs. 47.66 Gy, Rt humerus Dmean=14.19 vs. 17.27Gy, Lt humerus Dmean=14.14 vs. 17.15 Gy respectively. Our study revealed comparable results in regard of target volume coverage between VMAT and 3DCRT. The low dose to normal tissues is still considered as a real concern when VMAT used. In addition, VMAT was not adding much impact in terms of central structures avoidance. Hot spots outside the target volume and under coverage at fields junction is the most drawbacks when using 3DCRT. We might see some improvements in results of both techniques when using deep inspiration breath hold method along with them.

Dosimetric comparison of jaw tracking in intensity modulated and volumetric modulated arc radiotherapy for carcinoma of cervix

Abstract Aim: To study the dosimetric advantages of the jaw tracking technique in intensity-modulated radiotherapy (IMRT) and volumetric modulated arc radiotherapy (VMAT) for carcinoma of cervix patients. Materials and Methods: We retrospectively selected ten previously treated cervix patients in this study. All the ten patients underwent CT simulation along with immobilization and positional devices. Targets and organ at risks (OARs) were delineated slice by slice for all the patients. All the patients were planned for IMRT and VMAT with intend to deliver 50 Gy in 25 fractions. All the plans were planned with 6 MV photon beam using millennium-120 multi leaf collimator (MLC) using the TrueBeam linear accelerator. IMRT and VMAT plans were performed with jaw tracking (JT) and with static jaw (SJ) techniques by keeping the same constraints and priorities for the target volumes and critical structures for a particular patient. For standardization, all the plans were normalized to the target mean of the planning target volume. All the plans were accepted with the criteria of bladder mean dose &lt; 40 Gy and rectum mean dose &lt; 40 Gy without compromising the target volumes. Target conformity, dose to the critical structures and low dose volumes were recorded and analyzed for IMRT and VMAT plans with and without jaw tracking for all the patients. Results: The conformity index average of all patients followed by standard deviation (̄x± σ̄x) for JT-IMRT, SJ-IMRT, JT-VMAT and SJ-VMAT were 1.176 ± 0.139, 1.175 ± 0.139, 1.193 ± 0.220 and 1.228 ± 0.192 and homogeneity index were 0.089 ± 0.022, 0.085 ± 0.024, 0.102 ± 0.016 and 0.101 ± 0.016. In low dose volume J,T-IMRT shows a 5.4% (p-value &lt; 0.001) overall reduction in volume receiving at least 5 Gy (V5) compared to SJ-IMRT, whereas 1.2% reduction was observed in V5 volume in JT-VMAT compared to SJ-VMAT. JT-IMRT showed mean reduction in rectum and bladder of 1.34% (p-value &lt; 0.001) and 1.46% (p-value &lt; 0.001) compared to SJ-IMRT, while only 0.30% and 0.03% reduction were observed between JT-VMAT and SJ-VMAT. JT-IMRT plans also showed considerable dose reduction to inthe testine, right femoral head, left femoral head and cauda compared to the SJ-IMRT plans. Conclusion: Jaw tracking resulted in decreased dose to critical structures in IMRT and VMAT plans. But significant dose reductions were observed for critical structures in the JT-IMRT compared to SJ-IMRT technique. In JT-VMAT plans dose reduction to the critical structures were not significant compared to the JT-IMRT due to relatively lesser monitor units in the VMAT plans.

Dosimetric and Radiobiological Comparison of External Beam Radiotherapy Using Simultaneous Integrated Boost Technique for Esophageal Cancer in Different Location.

Objectives: To compare treatment plans of intensity modulated radiotherapy (IMRT), volumetric modulated arc radiotherapy (VMAT), and helical tomotherapy (HT) with simultaneous integrated boost (SIB) technique for esophageal cancer (EC) of different locations using dosimetry and radiobiology.Methods: Forty EC patients were planned for IMRT, VMAT, and HT plans, including 10 cases located in the cervix, upper, middle, and lower thorax, respectively. Dose-volume metrics, conformity index (CI), homogeneity index (HI), tumor control probability (TCP), and normal tissue complication probability (NTCP) were analyzed to evaluate treatment plans.Results: HT showed significant improvement over IMRT and VMAT in terms of CI (p = 0.007), HI (p < 0.001), and TCP (p < 0.001) in cervical EC. IMRT yielded more superior CI, HI and TCP compared with VMAT and HT in upper and middle thoracic EC (all p < 0.05). Additionally, V30 (27.72 ± 8.67%), mean dose (1801.47 ± 989.58cGy), and NTCP (Niemierko model: 0.44 ± 0.55%; Lyman-Kutcher-Burman model: 0.61 ± 0.59%) of heart in IMRT were sharply reduced than VMAT and HT in middle thoracic EC. For lower thoracic EC, the three techniques offered similar CI and HI (all p > 0.05). But VMAT dramatically lowered liver V30 (9.97 ± 2.84%), and reduced NTCP of lungs (Niemierko model: 0.47 ± 0.48%; Lyman-Kutcher-Burman model: 1.41 ± 1.07%) and liver (Niemierko model: 0.10 ± 0.08%; Lyman-Kutcher-Burman model: 0.17 ± 0.17%).Conclusions: HT was a good option for cervical EC with complex target coverage but little lungs and heart involvement as it achieved superior dose conformity and uniformity. Due to potentially improving tumor control and reducing heart dose with acceptable lungs sparing, IMRT was a preferred choice for upper and middle thoracic EC with large lungs involvement. VMAT could ameliorate therapeutic ratio and lower lungs and liver toxicity, which was beneficial for lower thoracic EC with little thoracic involvement but being closer to heart and liver. Individually choosing optimal technique for EC in different location will be warranted.

Preserving Endocrine Function in Premenopausal Women Undergoing Whole Pelvis Radiation for Cervical Cancer.

Whole pelvis radiation therapy (WPRT) in premenopausal women with cervical cancer can cause permanent ovarian damage, resulting in premature menopause. Oophoropexy, often considered as an initial step, demonstrates safety of sparing 1 ovary at the cost of delay in initiating WPRT. Therefore, we dosimetrically compared volumetric modulated arc radiotherapy (VMAT) and intensity modulated proton therapy (IMPT) techniques to allow for ovarian-sparing WPRT. Ten patients previously treated for cervical cancer at our institution were included in this institutional review board-approved analysis. A modified clinical treatment volume (CTV) was designed, sparing 1 ovary (left or right), as determined by the physician (ovarian-sparing CTV) and disease extent, including physical exam, positron emission tomography/computed tomography and magnetic resonance imaging. An ovarian-sparing planning target volume was determined as the ovarian-sparing CTV+5 mm for patients who were supine and 7 mm for those who were prone. All plans were calculated to a dose of 45 Gy with specific optimization goals for target volumes, while attempting to maintain a mean ovary dose (Dmean) < 15 Gy. Dosimetric goals were compared across the 2 modalities using the Mann-Whitney U test. Both treatment modalities were able to achieve primary clinical goal coverage to the uterus/cervix (P = .529, comparing VMAT versus IMPT), ovarian-sparing CTV (P = .796) and ovarian-sparing planning target volume (P = .004). All 10 IMPT plans were able to accomplish the ovary objective (14.0 ± 1.66 Gy). However, only 4 of the 10 VMAT plans were able to achieve a Dmean < 15 Gy to the prioritized ovary, with an average dose of 15.3 ± 4.10 Gy. Sparing an ovary in women undergoing WPRT for cervical cancer is dosimetrically feasible with IMPT without sacrificing coverage to important clinical targets. Future work will incorporate the brachytherapy dose to the ovarian-sparing CTV and assess the clinical response of this technique as a means to preserve ovarian endocrine function.

Dosimetric and radiobiological comparison of external beam radiotherapy using simultaneous integrated boost technique for esophageal cancer in different location.

e15505 Background: Based on dosimetry and radiobiology to compare treatment plans for esophageal cancer (EC) in different location using intensity modulated radiotherapy (IMRT), volumetric modulated arc radiotherapy (VMAT) and helical tomotherapy(HT) with simultaneous integrated boost (SIB) technique. Methods: A total of 20 patients including 5 cases respectively located in the cervix, upper, middle and lower thorax were generated for IMRT, VMAT and HT plans. The dose volume histogram statistics, conformity index (CI), homogeneity index (HI), tumor control probability (TCP) and normal tissues control probability (NTCP) were analyzed to evaluate treatment plans. Results: HT showed significantly improvement over IMRT and VMAT in terms of CI(0.93±0.03), HI(0.07±0.03) and TCP(88.08±0.82%) in cervical EC(p&lt;0.05). IMRT greatly developed TCP(88.29±1.79%;85.11±0.79%), and offered superior CIs (0.87±0.04;0.90±0.01) and HIs(0.10±0.01; 0.06±0.01) compared with VMAT and HT in upper and middle thoracic EC(p&lt;0.05). Meanwhile, the V30(33.30±6.49%), mean dose (2559.00±219.64cGy) and NTCP(0.50±0.61%) of heart for IMRT were significantly reduced than other two techniques in middle thoracic EC. Patients with lower thoracic EC yielded the similar CIs and HIs(all p&gt;0.05) for the 3 techniques, but VMAT showed the lowest NTCP of lungs (0.01±0.01%) with improved TCP (84.84±1.13%). Conclusions: HT was a good option with little lung and heart involvement as it achieved superior dose conformality and uniformity. IMRT was a perfect strategy with large thoracic involvement. It significantly improved tumor local control and reduced heart dose and complications with acceptable dose to lungs. VMAT was preferred with a smaller target volume but surrounded by more heart and less lungs. Individually choosing optimal technique for EC in different location will be warranted.

P54 - Second Malignancy Risk Assessment for Female Pelvis Patients Treated with Intensity Modulated Arc Radiation Therapy

P54 - Second Malignancy Risk Assessment for Female Pelvis Patients Treated with Intensity Modulated Arc Radiation Therapy

Geometric and dosimetric impact of anatomical changes for MR-only radiation therapy for the prostate.

PurposeWith the move towards magnetic resonance imaging (MRI) as a primary treatment planning modality option for men with prostate cancer, it becomes critical to quantify the potential uncertainties introduced for MR‐only planning. This work characterized geometric and dosimetric intra‐fractional changes between the prostate, seminal vesicles (SVs), and organs at risk (OARs) in response to bladder filling conditions.Materials and methodsT2‐weighted and mDixon sequences (3–4 time points/subject, at 1, 1.5 and 3.0 T with totally 34 evaluable time points) were acquired in nine subjects using a fixed bladder filling protocol (bladder void, 20 oz water consumed pre‐imaging, 10 oz mid‐session). Using mDixon images, Magnetic Resonance for Calculating Attenuation (MR‐CAT) synthetic computed tomography (CT) images were generated by classifying voxels as muscle, adipose, spongy, and compact bone and by assignment of bulk Hounsfield Unit values. Organs including the prostate, SVs, bladder, and rectum were delineated on the T2 images at each time point by one physician. The displacement of the prostate and SVs was assessed based on the shift of the center of mass of the delineated organs from the reference state (fullest bladder). Changes in dose plans at different bladder states were assessed based on volumetric modulated arc radiotherapy (VMAT) plans generated for the reference state.ResultsBladder volume reduction of 70 ± 14% from the final to initial time point (relative to the final volume) was observed in the subject population. In the empty bladder condition, the dose delivered to 95% of the planning target volume (PTV) (D95%) reduced significantly for all cases (11.53 ± 6.00%) likely due to anterior shifts of prostate/SVs relative to full bladder conditions. D15% to the bladder increased consistently in all subjects (42.27 ± 40.52%). Changes in D15% to the rectum were patient‐specific, ranging from −23.93% to 22.28% (−0.76 ± 15.30%).ConclusionsVariations in the bladder and rectal volume can significantly dislocate the prostate and OARs, which can negatively impact the dose delivered to these organs. This warrants proper preparation of patients during treatment and imaging sessions, especially when imaging required longer scan times such as MR protocols.

Dosimetric Effects of Rotational Setup Error in Volumetric Modulated Arc Radiotherapy on Brain Tumor Patients

Introduction: This study examined the dosimetric effects based on the rotational setup error to correct patient setup errors occur during volumetric modulated arc radiotherapy (VMAT) for brain tumor patients. Material and Methods: This study included 1129 cases of cone beam computed tomography (CBCT) images obtained from 46 brain tumor patients, who experienced VMAT and used the 6DoF (degree of freedom) treatment couch. The dosimetric effects regarding the application of the rotational setup error were examined by comparing the treatment plans. Results: The mean patient setup errors at the lateral (X-axis), longitudinal (Y-axis), and vertical (Z-axis) directions were 0.1±1.4, 0.0±1.1, and -0.4±1.2 mm, respectively. The pitch, roll, and yaw were -0.29±0.61°,-0.42±0.98°, and -0.53±0.69°, respectively. When an absolute value was taken for the setup error, the mean error was 1.06±0.14 mm at the three translation directions, and the error of rotation was 0.82±0.14°, showing a larger error than that of translation. In terms of the mean dose difference by each region of interest (ROI) before and after correcting for the rotational setup error on the treatment plan, Brain_max was 2.17 Gy, and Brain_mean was 0.28 Gy, whereas the maximum and mean of Brain_stem were -3.58 and -4.43 Gy, respectively. These findings suggested a dose difference according to the correction of the rotational setup error. Conclusion: This study indicated that the dose effect is influenced by the rotational setup error in VMAT of brain tumor patients. Moreover, the 6DoF positional correction could reduce the positional uncertainties and deliver a more accurate dose.

On the Instantaneous Dose Rate and Angular Dependence of Monolithic Silicon Array Detectors

The use of small radiation fields characterized by very steep dose gradients is common in modulated arc X-ray radiotherapy. Dosimeters for quality assurance (QA) applications would ideally have sensitive volumes (SVs) relatively small with respect to the field, along with negligible instantaneous dose rate and angular dependence. Silicon-based dosimeters can be fabricated with SVs $ across, provide a stable and near energy-independent response in megavoltage photon beams, along with a good linearity with accumulated dose and real-time readout. However, their sensitivity is instantaneous dose rate and angular dependent. Monolithic silicon array detectors with sufficiently small SVs and pitch are suitable for high-resolution 2-D dose mapping in radiation fields with steep dose gradients. The Octa is a 2-D monolithic silicon array detector. It has 512 diode- SVs arranged with a sub-millimeter pitch. The physical characteristics of the substrate on which it is based, in terms of resistivity and defects concentration, strongly affect its performance. We report on the experimental characterization of two versions of the Octa, manufactured on a bulk and on an epitaxial substrate, respectively. Their performance is compared and discussed in terms of their instantaneous dose rate and angular dependence in the context of QA applications in small radiation fields delivered with modulated arc radiotherapy.

Comparison of Error Range of Delivery Quality Assurance by Type of Intensity Modulated Radiation Therapy

Delivery Quality Assurance (DQA) is performed to evaluate the intensity modulated radiotherapy (IMRT). However, differences in the DQA results may be caused by factors such as the IMRT technique, treatment volume, etc. In this study, we compared five types of gamma index and four types of dose differences as IMRT technique, Treatment site, Volume of Planning Target Volume (PTV), Regularity Shape Index (RSI), indices of treatment planning evaluation. From January 1, 2016 to December 31, 2017, 32 patients who underwent IMRT plan were used to perform Step and Shoot (SNS) technique, Sliding Window (SW) technique, and Volumetric Modulated Arc radio-Therapy (VMAT) technique. After obtaining the Treatment Site, Volume of PTV, RSI, CI, HI, QOC according to each planning technique, nine factors of DQA were compared. As a result of the comparison, it was not possible to confirm the tendency of the items except the IMRT technique. The results of the IMRT technique showed the highest values for area gamma ( 1.0) and area dose difference ( 0.8) for SNS technique, and the lowest values for the other seven factors. For VMAT technique, the lowest value was obtained for area gamma ( 1.0) and area dose difference ( 0.8), and the highest value was obtained for the other seven factors. This study is limited to Electronic Portal Image Device(EPID). Therefore, it is necessary to study various equipment and program version in order to evaluate various DQA tools. In addition, there are limitations on the Treatment Site, Volume of PTV, and etc. necessary for evaluation. Therefore, it is considered that evaluation using various cases will be needed in the future. Nine factors, results of DQA, were a tendency by the IMRT techniques. The tolerance range of gamma index should be tightly in 80 % and 60 %, and the tolerance range of dose difference index should be tightly in 75 % and 25 %. Therefore, it can be concluded that accurate electromagnetic radiation therapy can be performed by applying the appropriate tolerance according to the IMRT technique in the future.

Effect of arc length on skin dose from hypofractionated volumetric modulated arc radiotherapy treatments of the lung and spine

Due to large doses per fraction, stereotactic ablative radiotherapy of lung or spine can lead to skin tissue toxicity, the amount of which depends on a variety of factors such as target location, beam geometry, and immobilization. The effect of arc length on spreading out entrance and exit doses and the corresponding predictions of skin reactions has not yet been studied for stereotactic body radiotherapy volumetric modulated arc therapy (VMAT) treatments. 58 clinically relevant VMAT stereotactic body radiotherapy spine and lung plans were created for an anthropomorphic phantom utilizing a range of target locations, beam geometries and arc lengths. Skin dose was assessed by considering the National Cancer Institute skin reaction grades adjusted for 3 fraction treatments. While the skin volumes predicted to exhibit low grade reactions decreased with arc length, high grade reactions were found to increase at smaller arcs as well as at full arcs where a superposition of entrance and exit doses would occur. It is possible for skin dose to be effectively optimized by choice of arc length (within clinically relevant boundaries) and thus minimize the skin reaction. High skin doses are often attributed to effects arising from the distance between the planning target volume and patient surface but this study has demonstrated that VMAT arc length is of equal importance. Understanding this relationship will assist in minimizing skin reactions through modification of plan parameters and will provide clinicians more information for patient selection.

Which nasopharyngeal cancer patients need adaptive radiotherapy?

BackgroundAdaptive radiotherapy (ART) has potential benefits in patients with nasopharyngeal cancer (NPC). This retrospective study aimed to identify the factors favoring ART.Materials and methodsForty NPC patients were retrospectively included in this study. All patients received two-phase, volumetric modulated arc radiotherapy (VMAT) and underwent a second computed tomography (CT) for the phase II ART. We generated phantom, non-ART plans by a hybrid method for comparison with ART plans. A paired t-test was used to evaluate the dose differences between these two plans. A subgroup analysis through a paired t-test was used to evaluate the factors favoring ART.ResultsThe second CT images were captured at the median 22 fractions. The median total dose of the planning target volume-one (PTV-1) was 72 Gy, and the phase II dose was 16 Gy. The volumes of the ipsilateral parotid gland (23.2 vs. 19.2 ml, p < 0.000), contralateral parotid gland (23.0 vs. 18.4 ml, p < 0.000), clinical target volume-1 (CTV-1, 32.2 vs. 20.9 ml, p < 0.000), and PTV-1 (125.8 vs. 107.3 ml, p < 0.000) all shrunk significantly between these two CT simulation procedures. Among the nearby critical organs, only the ipsilateral parotid gland displayed significant dose reduction by the ART plan (5.3 vs. 6.0 Gy, p = 0.004). Compared to the phantom plan, the ART could significantly improve the PTV-1 target volume coverage of D98 (15.4 vs. 12.3 Gy, p < 0.000). Based on the D98 of PTV-1, the factors of a large initial weight (> 60 kg, p < 0.000), large body mass index (BMI) (> 21.5, p < 0.000), obvious weight loss (> 2.8 kg, p < 0.000), concurrent chemoradiotherapy (p < 0.000), and stages III–IV (p < 0.000) favored the use of ART.ConclusionsART could significantly reduce the mean dose to the ipsilateral parotid gland. ART has dosimetrical benefit for patients with a heavy initial weight, large BMI, obvious weight loss, concurrent chemoradiotherapy, and cancer in stages III–IV.

Comparison of Flattening Filter and Flattening Filter-Free Volumetric Modulated Arc Radiotherapy in Patients with Locally Advanced Nasopharyngeal Carcinoma.

BackgroundThis study aimed to investigate the therapeutic role of flattening filter-free (FFF) mode in volumetric modulated arc therapy (VMAT) compared with flattening filter (FF) mode in patients with locally advanced nasopharyngeal carcinoma (NPC).Material/MethodsTen previously treated patients with NPC underwent treatment re-planning with FFF and FF VMAT. Radiotherapy dose distribution on planning target volume (PTV), organs at risk (OAR), target conformity index (CI), total monitor units (MUs), and therapeutic time were compared.ResultsMaximum and mean radiotherapy dose in PTV and PGTV (primary lesions of NPC and cervical lymph node metastases) in FFF VMAT planning were significantly increased compared with FF VMAT planning, but PTV and OAR showed no significant differences. The CI value of PTV in FFF VMAT planning was significantly reduced compared with FF planning (P<0.05). No differences were found for the maximum radiotherapy dose in the spinal cord and left and right optic nerve, and the mean radiotherapy dose in the brainstem, left and right parotid gland (P>0.05). The maximum dose in the brainstem in the FFF planning was significantly higher compared with FF planning (P>0.05). The maximum radiotherapy dose in left and right crystalline lens (P<0.05) in FFF planning was significantly reduced compared with FF planning. The total hop count in FFF planning was significantly increased compared with FF planning (P<0.05).ConclusionsBoth 6 MV X-ray FFF mode and FF mode in the treatment of patients with NPC showed that FFF VMAT planning provided improved protection for OAR.

Multi-institutional comparison of secondary check of treatment planning using computer-based independent dose calculation for non-C-arm linear accelerators

PurposeThis report covers the first multi-institutional study of independent monitor unit (MU)/dose calculation verification for the CyberKnife, Vero4DRT, and TomoTherapy radiotherapy delivery systems. MethodsA total of 973 clinical treatment plans were collected from 12 institutions. Commercial software employing the Clarkson algorithm was used for verification after a measurement validation study, and the doses from the treatment planning systems (TPSs) and verification programs were compared on the basis of the mean value ± two standard deviations. The impact of heterogeneous conditions was assessed in two types of sites: non-lung and lung. ResultsThe dose difference for all locations was 0.5 ± 7.2%. There was a statistically significant difference (P < 0.01) in dose difference between non-lung (−0.3 ± 4.4%) and lung sites (3.5 ± 6.7%). Inter-institutional comparisons showed that various systematic differences were associated with the proportion of different treatment sites and heterogeneity correction. ConclusionsThis multi-institutional comparison should help to determine the departmental action levels for CyberKnife, Vero4DRT, and TomoTherapy, as patient populations and treatment sites may vary between the modalities. An action level of ±5% could be considered for intensity-modulated radiation therapy (IMRT), non-IMRT, and volumetric modulated arc radiotherapy using these modalities in homogenous and heterogeneous conditions with a large treatment field applied to a large region of homogeneous media. There were larger systematic differences in heterogeneous conditions with a small treatment field because of differences in heterogeneity correction with the different dose calculation algorithms of the primary TPS and verification program.

Optimal selection of optimization bolus thickness in planning of VMAT breast radiotherapy treatments

The aim of this study was to find an optimal optimization skin flash thickness in volumetric modulated arc radiotherapy of the breast in consideration of soft tissue deformations during the treatment course. Ten breast radiotherapy patients with axillary lymph node inclusion were retrospectively planned with volumetric modulated arc radiotherapy technique. The plans were optimized with the planning target volume (PTV) extending outside the skin contour by 0, 5, 7, and 10 mm; and with optimization boluses of 3 or 5 mm on the extended PTV. The final dose was calculated without the bolus. The plans were compared in terms of PTV homogeneity and conformity, and dose minima and maxima. The doses to organs at risk were also evaluated. The doses were recalculated in real patient geometries based on cone beam computed tomography (CBCT) images captured 3 to 6 times during each patient's treatment course. The optimization to the PTV without the PTV extension resulted in the best CTV coverage in the original plans (V95% = 98.0% ± 1.2%). However, when these plans were studied in real CBCT-based patient geometries, the CTV V95% was compromised (94.6% ± 8.3%). In addition, for the surface (4 mm slap inside the PTV 4 mm below the body contour) dose V95% was reduced from the planned 74.7% ± 7.5% to the recalculated 65.5% ± 11.5%. Optimization with an 8-mm bolus to a PTV with 5-mm extension was the most robust choice to ensure the CTV and surface dose coverage (recalculated V95% was 95.2% ± 6.4% and 74.6% ± 8.4%, respectively). In cases with the largest observed deformations, even a 10-mm PTV extension did not suffice to cover the target. Optimization with a 5-mm PTV extension and an 8-mm optimization bolus improved the surface dose and slightly improved the CTV dose when compared to no extension plans. For deformations over 1 cm, no benefit was seen in PTV extensions and replanning is recommended. Frequent tangential and CBCT imaging should be used during treatment course to detect potential large anatomical changes.

Dosimetric Analysis of Multiple Breath-Hold Segmented Volumetric Modulated Arc Radiation Therapy Plans with and without Fiducial Markers for Pancreatic Cancer

Given the proximity of the target volume to critical structures, radiation therapy for pancreatic cancer is challenging. The present study aimed to estimate planning target volume (PTV) margins of pancreatic tumors using daily image guided radiation therapy (IGRT) and to compare the dosimetric outcomes with and without fiducial markers (with-FM and without-FM) during multiple breath-hold segmented volumetric modulated arc therapy (MBHS-VMAT). Based on re-planned VMAT technique, two types of PTV margins, with-FM or without-FM, were retrospectively estimated in 10 patients with unresected pancreatic cancer. Daily IGRT shifts based on MBHS-cone-beam volume CT obtained prior to daily fractionated MBHS-VMAT and cone-beam motion CT under fractionated MBHS-VMAT were recorded and evaluated to estimate the two PTV margin types. Accordingly, 10 patients, 270 3D images, and 1080 2D images were considered. Appropriate margins were estimated using the equation M = 2.5Σ + 0.7σ. Regarding the treatment plans, the organs at risk (OAR) included the kidneys, liver, stomach, duodenum, jejunum, and spinal cord. The prescribed dose was 55 Gy in 25 fractions and was set to encompass 95% of the PTV. For both the plans, the planning objectives used in the optimizer were constant and were based on NCCN guidelines. Homogeneity and conformity indices, doses to OARs with attention to the digestive tract (stomach, duodenum, and jejunum), and PTV doses were evaluated between the two margin types. The respective PTV margins in the lateral, vertical, and longitudinal directions were 4, 4, and 5 mm with-FM and 7, 6, and 10 mm without-FM. For each patient, treatment planning implied two PTV margin types. For the digestive tract, a consistent trend indicated a significantly (p <0.05) lower V45, V50, and V55 using the with-FM MBHS-VMAT technique; these respective values decreased by 4.9%, 3.8% and 2.0% using with-FM MBHS-VMAT plans. There were no differences (p >0.05) in digestive tract (mean), PTV, liver dose (mean), and total kidney (V18) between the two margin types. Conformity and homogeneity indexes were also similar. The pancreas carries the potential for significant motion. In the absence of fiducial markers, our data suggest that the PTV margin will increase from 5 to 10 mm. These margins would surely overlap the surrounding bowel, duodenum, and/or stomach, suggesting that the dose coverage of margin-based PTVs is not be feasible. Our comparison shows that with-FM plans provide superior OAR-sparing abilities (particularly for the digestive tract) without decreasing target coverage.Abstract TU_41_3298; Table 1Comparison of various parameters for the two margin typesWith-FMWithout-FMp-valueDigestive tractV458.4 %13.3 %< 0.05V504.2 %8.0 %< 0.05V551.1 %3.1 %< 0.05Dmean, digestive tract (Gy)22.125.60.118PTVD2 (Gy)59.959.80.543D98 (Gy)53.853.40.342D50 (Gy)58.558.30.384LiverDmean, liver (Gy)8.410.30.190KidneysV1814.6 %16.6 %0.668 Open table in a new tab

A Prospective Analysis of Ototoxicity in Modern Radiation Therapy Treatments for Head and Neck Squamous Cell Carcinoma (HNSCC) Patients Receiving Concomitant Chemo-Radiation (CRT) with Weekly or Tri-weekly Cisplatin (Cis)

Radiation therapy can be ototoxic and dose constraints to the cochlea – mean <45Gy will give ∼<30% sensory-neural hearing loss. Cis is one of the most ototoxic chemotherapy drugs, resulting in a permanent and irreversible hearing loss in up to 50% of patients. Little is known about the incidence of hearing loss when using different cisplatin regimens in patients receiving concomitant CRT with modern day radiation therapy techniques. Therefore, we assessed prospectively the incidence of ototoxicity in patients receiving weekly or tri-weekly Cis concomitantly with volumetric modulated arc radiotherapy (VMAT). HNSCC patients receiving definitive or adjuvant cis-based CRT were included. Cis was administered weekly (40 mg/m2 weekly, total 7 cycles) or tri-weekly (100 mg/m2 every three weeks, total 3 cycles). Radiation was administered to a total dose of 70 Gy for definitive treatment or 66 Gy for adjuvant treatment (2 Gy/fraction). Intensity-modulated radiation therapy was used in all cases. Pure-tone air-conduction audiometry was performed in all patients before and after completion of CRT. The primary endpoint of the analysis was Common Terminology Criteria for Adverse Event (CTCAE v4.0) hearing change ≥3 at the completion of CRT. The cochlea was contoured by one dosimetrist and assessed by two physicians for accuracy. A total of 96 patients (M:77/F:19) were included (56 oropharynx patients and 40 non-oropharynx HNSCC)). The median age was 55 years (range 26-78) 68 patients received weekly cis and 28 received the tri-weekly regimen. 58 patients received definitive treatment and 38 adjuvant treatment. Nine patients (13%) receiving weekly cis experienced G3 ototoxicity vs 14 patients (50%) who received tri-weekly cis (p<0.001, OR=6.4, 95% CI= 2.1-20.7). Risk of ototoxicity was not associated with age, cis cumulative dose, sex, tumor primary site, or CRT modality (definitive vs. adjuvant). After adjusting for these factors in a multivariable model cis schedule remained significant (OR=8.7, 95% CI 2.31-32.75, p=0.001). With a minimum follow-up of three months, the complete response rate after treatment was 84% for weekly CRT and 86% for tri-weekly CRT (p=NS). Cochlear mean dose of 13.76 Gy +/- 8.5 Gy to bilateral cochlea was achieved. With mean cochlear doses of ≤ 22Gy bilaterally, tri-weekly Cis-based CRT increased the risk of grade 3 irreversible severe ototoxicity compared to weekly Cis. This risk of ototoxicity should be discussed with patients that are candidates for cis-based CRT.