The role of volumetric modulated arc therapy (VMAT) in gynaecological radiation therapy: A dosimetric comparison of intensity modulated radiation therapy versus VMAT

The application of multi-arc volumetric modulated arc therapy and fixed-field intensity modulated radiotherapy in the treatment of gynecologic cancer with large planning target volume

To investigate the dosimetry and delivery efficiency differences between multi-arc volumetric modulated arc therapy (VMAT) and fixed-field intensity modulated radiotherapy (IMRT) in the treatment of gynecological cancer with large planning target volume (PTV). Thirteen patients with gynecological cancer (9 cervical and 4 vulvar) with a PTV greater than 1600 cm3 were retrospectively selected. Three-arc VMAT (3ARC) and seven-field IMRT plans were generated using identical objective functions from clinical two-arc VMAT (2ARC) plans to allow a rigorous comparison for each patient. Target coverage, OARs sparing, integral dose and delivery efficiency were compared through dose-volume histogram (DVH) analysis. Compared with 2ARC plans, IMRT exhibited a slightly superior target coverage with higher D98%, CI and lower D2%, D50%, V110% and HI (P < 0.01). For OARs, IMRT produced lower V40Gy and Dmean to the bladder and rectum (P < 0.01) and lower V40Gy to bone marrow than 2ARC (P < 0.05). No significant differences were observed for the colon, small bowel and femoral heads, while 2ARC performed worse at the low dose and integral dose to normal tissue (V5Gy, V10Gy and NTID, P < 0.01). Nevertheless, IMRT increased MUs by 1.65% and EDT by 107 s compared to 2ARC. Compared with 2ARC, 3ARC showed no improvement in target dose coverage, including D98%, D2%, D50%, V110%, CI and HI to PTV, but increased the doses to OARs (Dmean to the bladder, rectum and bone marrow, V40Gy to the bone marrow and D5% to both the left and right femoral heads, P < 0.05), low dose and integral dose to normal tissue (V10Gy,V15Gy,V20Gy and NTID, P < 0.01) and simultaneously prolonged the EDT (P < 0.001). In the treatment of gynecological cancer with a large planning target volume, the IMRT technique can be delivered superior conformal dose to the target with somewhat better OARs sparing but increasing the estimated delivery time.

Reduction of patient specific quality assurance through plan complexity metrics for VMAT plans with an open-source TPS script

PURPOSE

Volumetric modulated arc therapy (VMAT) is a widespread technique for the delivery of normo-fractionated radiation therapy (NFRT) and stereotactic body radiation therapy (SBRT). It is associated with a significant hardware burden requiring dose rate modulation, collimator movement and gantry rotation synchronisation. Patient specific quality assurance (PSQA) guarantees that the linacs can precisely and accurately deliver the planned dose. However, PSQA requires a significant time allocation and class solutions to reduce this while guaranteeing the deliverability of the plans should be investigated.

METHODS

In this study, an in-house developed Eclipse Scripting API (ESAPI) script was used to extract five independent plan complexity metrics from N = 667 VMAT treatment fields. The correlation between metrics and portal dosimetry measurements was investigated with Pearson correlation, box plot analysis and receiver operating characteristic curves, which were used to defined the best performing metric and its threshold.

RESULTS

The incidence of fields failing the clinical PSQA criteria of 3%/2mm (NFRT) and 3%/1.5mm (SBRT) was low (N = 1). The mean MLC opening was the metric with the highest correlation with the portal dosimetry data and among the best in discriminating the requirement of PSQA. The thresholds of 16.12 mm (NFRT) and 7.96 mm (SBRT) corresponded to true positive rates higher than 90%.

CONCLUSIONS

This work presents a quantitative approach to reduce the time allocation for PSQA by identifying the most complex plans demanding a dedicated measurement. The proposed method requires PSQA for approximately 10% of the plans. The ESAPI script is distributed open-source to ease the investigation and implementation at other institutions.

Three-Dimensional Conformal Radiotherapy Versus Image-Guided Intensity Modulated External Beam Radiotherapy in Locally Advanced Cervical Cancer: A Phase III Randomized Control Study

AIMS

The standard treatment of locally advanced cervical carcinoma is radical chemoradiation followed by brachytherapy which has improved survival. Hence, a major concern is our attempt to reduce the incidence of acute and late toxicities. IMRT has been shown to reduce toxicities. In this study, we have compared 3DCRT with IG-IMRT using patient-specific margins to evaluate tumor control as well as OAR-related toxicities.

MATERIALS AND METHODS

This was a single institution prospective phase III randomised control study including patients of squamous cell carcinoma of cervix (stage II-IIIB, FIGO 2009) without pelvic lymph node involvement. All patients were simulated using intermediate bladder filling protocol and those in the IG-IMRT arm, underwent additional scans with full and empty bladder to assess the range of internal motion and generate individualised ITV margin. EBRT dose of 46Gy/23#/4.5 weeks was delivered with weekly concurrent cisplatin followed by brachytherapy. All toxicities during EBRT and till 3 months post brachytherapy were considered acute toxicity. Post-treatment, patients were followed up every 2 months for first 2 years and then once every 6 months. Disease-related outcomes were assessed with clinical examination and symptom-directed imaging.

RESULTS

Two hundred patients were screened for inclusion and of them, 89 patients in 3DCRT and 84 patients in IG-IMRT arms were considered for final analysis. The baseline characteristics were comparable in both arms, majority of patients in both arms having stage II disease. For OARs, all dosimetric parameters were significantly better in the IG-IMRT arm. Acute radiation induced toxicities (dermatitis, genito-urinary and gastrointestinal toxicities) were significantly less in the IG-IMRT arm. The local, pelvic, and distant control were comparable in both arms.

CONCLUSION

Based on our experience, the use of IG-IMRT with patient-specific ITV margins results in reduction in acute OAR toxicities in patients without compromising on tumor control.

Dosimetric comparison of gamma knife and linear accelerator (VMAT and IMRT) plans of SBRT of Lung tumours

This study evaluates dosimetric differences in Stereotactic Body Radiation Therapy (SBRT) for lung tumors using plans of Gamma Knife, and Volumetric Modulated Arc Therapy (VMAT), Intensity-Modulated Radiation Therapy (IMRT) plans based on Linear Accelerator, aiming to inform the reader of appropriate treatment strategy selection. Ten patients with 23 lung tumor lesions treated with SBRT at Zhongshan Hospital of Dalian University were analyzed. Plans of Gamma Knife, and VMAT, IMRT plans based on Linear Accelerator were created for each lesion, totaling 18 plans per type. Lesions were treated with 30-50 Gy in 5-10 fractions. Dosimetric parameters, including gradient index (GI), heterogeneity index (HI), conformity index (CI), and doses to the plan target volumes (PTVs), the gross tumor volumes (GTVs) and organs at risk (OARs) were compared. Plans of Gamma Knife showed superior HI and GI, higher PTV and GTV doses, and reduced doses to the ipsilateral and contralateral lungs, esophagus, spinal cord, and heart compared to VMAT and IMRT plans (p < 0.05). However, Plans of Gamma Knife required longer delivery times. When comparing VMAT and IMRT plans, VMAT plans had shorter delivery times than IMRT plans, but required more monitor units (MUs). Additionally, IMRT plans delivered a lower mean dose to the ipsilateral lung compared to VMAT plans. Gamma Knife SBRT plans achieves steeper dose falloff and minimizes radiation to normal lung tissue compared to VMAT and IMRT plans, but with longer delivery times. VMAT and IMRT plans displayed similar dose distributions for lung SBRT.

Improvement of treatment plan quality with modified fixed field volumetric modulated arc therapy in cervical cancer

PURPOSE

This study aims to introduce modified fixed field volumetric modulated arc therapy (MF-VMAT) which manually opened the field size by fixing the jaws and comparing it to the typical planning technique, auto field volumetric modulated arc therapy (AF-VMAT) in cervical cancer treatment planning.

METHODS AND MATERIALS

Previously treated twenty-eight cervical cancer plans were retrospectively randomly selected and replanned in this study using two different planning techniques: AF-VMAT and MF-VMAT, resulting in a total of fifty-six treatment plans. In this study, we compared both planning techniques in three parts: (1) Organ at Risk (OARs) and whole-body dose, (2) Treatment plan efficiency, and (3) Treatment plan accuracy.

RESULTS

For OARs dose, bowel bag (p-value = 0.001), rectum (p-value = 0.002), and left femoral head (p-value = 0.001) and whole-body (p-value = 0.000) received a statistically significant dose reduction when using the MF-VMAT plan. Regarding plan efficiency, MF-VMAT exhibited a statistically significant increase in both number of monitor units (MUs) and control points (p-values = 0.000), while beam-on time, maximum leaf travel, average maximum leaf travel, and maximum leaf travel per gantry rotation were statistically significant decreased (p-values = 0.000). In terms of plan accuracy, the average gamma passing rate was higher in the MF-VMAT plan for both absolute dose (AD) (p-value = 0.001, 0.004) and relative dose (RD) (p-value = 0.000, 0.000) for 3%/3 and 3%/2 mm gamma criteria, respectively.

CONCLUSION

The MF-VMAT planning technique significantly reduces OAR doses and decreases the spread of low doses to normal tissues in cervical cancer patients. Additionally, this planning approach demonstrates efficient plans with lower beam-on time and reduced maximum leaf travel. Furthermore, it indicates higher plan accuracy through an increase in the average gamma passing rate compared to the AF-VMAT plan. Consequently, MF-VMAT offers an effective treatment planning technique for cervical cancer patients.

Comparative analysis of simultaneous integrated boost and sequential boost radiotherapy in node-positive cervical cancer: dosimetric and radiobiological considerations

For locally advanced cervical cancer, the standard therapeutic approach involves concomitant chemoradiation therapy, supplemented by a brachytherapy boost. Moreover, an external beam radiotherapy (RT) boost should be considered for treating gross lymph node (LN) volumes. Two boost approaches exist with Volumetric Intensity Modulated Arc Therapy (VMAT): Sequential (SEQ) and Simultaneous Integrated Boost (SIB). This study undertakes a comprehensive dosimetric and radiobiological comparison between these two boost strategies. The study encompassed ten patients who underwent RT for cervical cancer with node-positive disease. Two sets of treatment plans were generated for each patient: SIB-VMAT and SEQ-VMAT. Dosimetric as well as radiobiological parameters including tumour control probability (TCP) and normal tissue complication probability (NTCP) were compared. Both techniques were analyzed for two different levels of LN involvement - only pelvic LNs and pelvic with para-aortic LNs. Statistical analysis was performed using SPSS software version 25.0. SIB-VMAT exhibited superior target coverage, yielding improved doses to the planning target volume (PTV) and gross tumour volume (GTV). Notably, SIB-VMAT plans displayed markedly superior dose conformity. While SEQ-VMAT displayed favorable organ sparing for femoral heads, SIB-VMAT appeared as the more efficient approach for mitigating bladder and bowel doses. TCP was significantly higher with SIB-VMAT, suggesting a higher likelihood of successful tumour control. Conversely, no statistically significant difference in NTCP was observed between the two techniques. This study's findings underscore the advantages of SIB-VMAT over SEQ-VMAT in terms of improved target coverage, dose conformity, and tumour control probability. In particular, SIB-VMAT demonstrated potential benefits for cases involving para-aortic nodes. It is concluded that SIB-VMAT should be the preferred approach in all cases of locally advanced cervical cancer.

Outcome and toxicity of chemoradiation using volumetric modulated arc therapy followed by 3D image-guided brachytherapy for cervical cancer: Vietnam National Cancer Hospital experience

Background

Volumetric modulated arc therapy (VMAT) and 3D image-guided brachytherapy (3D-IGBT) have recently been introduced in Vietnam for the treatment of locally advanced cervical cancer. This study aims to assess the outcomes and toxicities of chemoradiation using VMAT followed by 3D-IGBT in Vietnamese cervical cancer patients.

Materials and methods

A prospective interventional study on 72 patients with 2018 International Federation of Gynecology and Obstetrics (FIGO) stage IB3-IIIC2 disease who underwent concurrent chemoradiation using VMAT, followed by 3D-IGBT according to EMBRACE-II protocol. Primary endpoints were locoregional control; secondary endpoints were systemic control and toxicity.

Results

Median body volume received 43 Gy was 1589.1 cm3 (range 1214.8-2574.8). Median high-risk clinical target volume (CTV-HR) was 18.8 cm3 (range 8.6-61.2) with a median dose to 90% (D90) of CTV-HR of 90.6 Gy (range 86.8-99.6). Mean doses to 2cc (D2cc) of bladder, rectum, and sigmoid were 75.8, 55.2, and 62.1 Gy, respectively. At median 19-month follow-up (range 12-25), locoregional control and systemic control were 95.8% and 81.9%, respectively. Systemic control was the lowest in N2 disease (54.5%). Grade ≥ 3 acute toxicities were less than 10%, except neutropenia (31.9%). Extended-field radiation increased significantly nausea, fatigue, and thrombocytopenia. No grade ≥ 3 proctitis or cystitis; 8.3% had grade 3 vaginal stenosis.

Conclusions

VMAT-based chemoradiation therapy followed by 3D-IGBT achieved high locoregional control with manageable toxicities in locally advanced cervical cancer. Systemic control correlated with disease stage.

Safety Review of Radiotherapy for Tumor Patients with Implantable Cardiac Pacemaker

Permanent pacemaker implantation is one of the most effective treatments for chronic arrhythmia. However, there is a certain risk associated with radiation therapy in cancer patients with implantable cardiac pacemakers. To prevent radiotherapy-induced pacemaker failure, there are established medical guidelines for the use of pacemakers in patients undergoing radiotherapy. With advancements in science and technology, the variety of available pacemakers has considerably increased, and radiotherapy equipment has also been updated. Given the variations in irradiation methods and the types of radiation used in clinical practice, there is a pressing need for international consensus on the regulations governing the use of cardiac pacemakers in cancer patients. Currently, many countries lack clinical guidelines for radiotherapy in cancer patients with cardiac pacemakers. This review summarizes recent reports and studies from PubMed (National Center for Biotechnology Information) regarding the safety of radiotherapy in cancer patients with implanted cardiac pacemakers, and provides valuable insights for clinical practice.

A dosimetric comparison of intensity-modulated radiotherapy versus rapid arc in gynecological malignancies: Dose beyond planning target volume, precisely 5Gy volume

Introduction

Aim of radiotherapy is precise dose delivery with objective of achieving maximum local control and minimal toxicity by decreasing dose to organ at risk (OAR).This aim can be achieved by technologies like intensity-modulated radiotherapy (IMRT) and volumetric arc therapy. However, later offers comparable or even better plan quality with shorter treatment time. It is important to note that low dose regions are also a concern due long-term risk of developing a second cancer after radiotherapy. The objective of our study is to do dosimetric comparison of IMRT vs. Rapid arc (RA) plan in gynecology cancer and specifically to assess dose beyond planning target volume (PTV), precisely 5 Gy volume.

Methods

Each 20 eligible patients underwent radiotherapy planning on eclipse by both IMRT and RA plans as per institution protocols. Comparative dosimetric analysis of both plans was done by paired sample t-test. PTV metrics compared were D95%, homogenecity index (HI), and conformity index (CI). OAR dose compared were bowel V40 Gy <30%, Rectum V30 Gy <60%, Bladder V45 Gy <35%, and bilateral femur head and neck V30 Gy < 50%. Futhermore, calculated monitor units (MUs) were also compared. Finally, volume of normal tissue beyond the PTV, specifically 5 Gy volume, was compared between plans.

Results

Dosimetric plan comparison showed statistically significant difference in RA and IMRT plans with improved PTV coverage and better OAR tolerance with RA plan. In addition, MU used were significantly less in RA plan, coupled with reduced V5 Gy volume.

Conclusion

In sum, RA plans are dosimetrically significantly better compared to IMRT plans in gynecological malignancies in terms of PTV coverage and OAR sparing. Importantly, not only less MU used but also significantly less normal tissue V5 Gy volume is less in RA compared to IMRT plans.

Ninety-degree angled collimator: a dosimetric study related to dynamic intensity-modulated radiotherapy in patients with endometrial carcinoma

BACKGROUND

Our purpose was to ensure that the dose constraints of the organs at risk (OARs) were not exceeded while increasing the prescription dose to the planning target volume (PTV) from 45 to 50.4 Gray (Gy) with the dynamic intensity-modulated radiotherapy (IMRT) technique. While trying for this purpose, a new dynamic IMRT technique named 90° angled collimated dynamic IMRT (A-IMRT) planning was developed by us.

METHODS

This study was based on the computed tomography data sets of 20 patients with postoperatively diagnosed International Federation of Gynecology and Obstetrics stage 2 endometrial carcinoma. For each patient, conventional dynamic IMRT (C-IMRT, collimator angle of 0° at all gantry angles), A-IMRT (collimator angle of 90° at gantry angles of 110°, 180°, 215°, and 285°), and volumetric modulated arc therapy (VMAT) were planned. Planning techniques were compared with parameters used to evaluate PTV and OARs via dose-volume-histogram analysis using the paired two-tailed Wilcoxon's signed-rank test; p < 0.05 was considered indicative of statistical significance.

RESULTS

All plans achieved adequate dose coverage for PTV. Although the technique with the lowest mean conformality index was A-IMRT (0.76 ± 0.05) compared to both C-IMRT (0.79 ± 0.04, p = 0.000) and VMAT (0.83 ± 0.03, p = 0.000), it protected the OARs especially the bladder (V45 = 32.84 ± 2.03 vs. 44.21 ± 6.67, p = 0.000), rectum (V30 = 56.18 ± 2.05 vs. 73.80 ± 4.75, p = 0.000) and both femoral heads (V30 for right = 12.19 ± 1.34 vs. 21.42 ± 4.03, p = 0.000 and V30 for left = 12.58 ± 1.48 vs. 21.35 ± 4.16, p = 0.000) better than C-IMRT. While the dose constraints of the bladder, rectum and bilateral femoral heads were not exceeded in any patient with A-IMRT or VMAT, they were exceeded in 19 (95%), 20 (100%) and 20 (100%) patients with C-IMRT, respectively.

CONCLUSIONS

OARs are better protected when external beam radiotherapy is applied to the pelvis at a dose of 50.4 Gy by turning the collimator angle to 90° at some gantry angles with the dynamic IMRT technique in the absence of VMAT.

Improving normal tissue sparing using scripting in endometrial cancer radiation therapy planning

The aim of this study was to improve the protection of organs at risk (OARs), decrease the total planning time and maintain sufficient target doses using scripting endometrial cancer external beam radiation therapy (EBRT) planning. Computed tomography (CT) data of 14 endometrial cancer patients were included in this study. Manual and automatic planning with scripting were performed for each CT. Scripts were created in the RayStation™ (RaySearch Laboratories AB, Stockholm, Sweden) planning system using a Python code. In scripting, seven additional contours were automatically created to reduce the OAR doses. The scripted and manual plans were compared to each other in terms of planning time, dose-volume histogram (DVH) parameters, and total monitor unit (MU) values. While the mean total planning time for manual planning was 368 ± 8 s, it was only 55 ± 2 s for the automatic planning with scripting (p < 0.001). The mean doses of OARs decreased with automatic planning (p < 0.001). In addition, the maximum doses (D2% and D1%) for bilateral femoral heads and the rectum were significantly reduced. It was observed that the total MU value increased from 1146 ± 126 (manual planning) to 1369 ± 95 (scripted planning). It is concluded that scripted planning has significant time and dosimetric advantages over manual planning for endometrial cancer EBRT planning.

Decision regret in breast cancer patients after adjuvant radiotherapy

PURPOSE

Breast cancer patients often engage in shared decision-making to select an individualized treatment regimen from multiple options. However, dissatisfaction with treatment outcomes can lead to decision regret. We evaluated decision regret and physical and psychological well-being among breast cancer patients who underwent adjuvant radiotherapy and explored their associations with patient, tumor, treatment, and symptom characteristics.

METHODS

This cross-sectional study involved retrospectively obtaining clinical data and data collected through interviews carried out as part of regular long-term medical aftercare. Decision regret regarding the radiotherapy was assessed using the Ottawa Decision Regret Scale, physical and psychological well-being were assessed using the PROMIS Global Health-10 questionnaire, and patients were asked about their treatment outcomes and symptoms. The questionnaire was administered 14 months to 4 years after completion of radiotherapy.

RESULTS

Of the 172 included breast cancer patients, only 13.9% expressed high decision regret, with most patients expressing little or no decision regret. More decision regret was associated with volumetric modulated arc therapy, chest wall irradiation, use of docetaxel as a chemotherapy agent, lymphangiosis carcinomatosa, new heart disease after radiotherapy, and lower psychological well-being.

CONCLUSION

Although most patients reported little or no decision regret, we identified several patient, treatment, and symptom characteristics associated with more decision regret. Our findings suggest that psychological well-being influences patients' satisfaction with therapy decisions, implying that practitioners should pay special attention to maintaining psychological well-being during shared decision-making and ensuring that psychological assessment and treatment is provided after cancer therapy to deal with long-term effects of radiotherapy.

Complete Remission of Vulvar Squamous Cell Carcinoma After Volumetric Modulated Arc Therapy in Copper Smelting and Purification Workers: A Case Report

Vulvar squamous cell carcinoma (VSCC) is the most frequent vulvar neoplasia, with invasiveness and metastasis. Typically, surgery is the preferred treatment. Radiotherapy is commonly used for unresectable locally advanced tumors and for early-stage patients who are at risk of serious complications from surgery or have a severe concomitant disease that prevents them from undergoing surgery. Compared to external irradiation, three-dimensional conformal radiotherapy (3D-CRT), and intensity-modulated radiotherapy (IMRT), various studies using volumetric modulated arc therapy (VMAT) alone in early-stage VSCC have been reported rarely. In this case, the patient had a large skin lesion and no lymph node metastasis. Surgical excision would seriously affect the urinary function and vulvar shape, so radical radiotherapy was given. To ensure the radiation dose for the radical treatment effect and to avoid high-dose radiation to normal organs, the volumetric intensity-modulated radiotherapy technique was chosen. After treatment, the patient's vulvar appearance returned to normal, and the tumor achieved complete remission without further surgery or chemotherapy, with no local recurrence or associated toxic side effects. This suggests that the efficacy of VMAT alone in early-stage VSCC is accurate and worthy of clinical promotion. The patient had been engaged in copper smelting and purification for many years, and it is unusual for her to have skin lesions with such a large surface area. In conjunction with her previous history of nasal basal cell carcinoma, the mechanism of oxidative stress during metal exposure should be further clinically examined, as it may be crucial in the formation and progression of malignancies.

Endometrial carcinosarcoma: a poor prognosis debut with favourable therapeutic outcome

Endometrial carcinosarcoma (ECS) is a rare, highly aggressive disease characterised by a biphasic growth of malignant epithelial (carcinomatous) and mesenchymal (sarcomatous) components. Clinically, it cannot be distinguished from endometrial carcinoma or uterine sarcoma. The definitive diagnosis can only be made based on histological examination and immunohistochemistry. To date, there aren't standardised treatment protocols for its management. We report a case of a 73-year-old patient who presented postmenopausal abnormal uterine bleeding and was diagnosed with ECS. A non-conventional treatment approach was conducted with favourable oncological outcomes.

Evaluating the influence of 6MV and 10MV photon beams on cervical volumetric-modulated arc therapy plans

BACKGROUND

Cervical cancer is a common gynecological cancer among women worldwide.

OBJECTIVE

To determine the effects of 6 MV and 10 MV volumetric-modulated arc therapy (VMAT) photon beams on the target volume (TV) planning and critical organs in cases of cervical cancer.

METHODS

Fifty patients with carcinoma of the cervix who underwent radiotherapy were selected. The transverse diameter (T) of the cross section of the upper edge of the sacroiliac joint on computerized tomography images of the patients was measured, and the mean value was calculated as 34 cm. All patients were divided into two groups: Group A (T < 34 cm) and Group B (T > 34 cm). The VMAT plans were generated using 6 MV and 10 MV plans separately. The prescription dose was 47.5 Gy, and the daily dose was 1.9 Gy.

RESULTS

In Group A, the planned TV (PTV) dose assessment parameters of 6 MV and 10 MV plans and their homogeneity and conformity indices were not statistically significantly different. A significant difference was observed between the 6 MV and 10 MV plans for the PTV dose assessment parameters and the homogeneity index of the plans for Group B. The monitor units of the 10 MV plans were lower than in the 6 MV plans in both Groups A and B, and the difference was statistically significant. The assessment parameter V40 Gy of both the rectum and bladder in the 6 MV plans was smaller than the corresponding parameter in the 10 MV plans in Group A; in Group B, the assessment parameter V50 Gy of the rectum in the 10 MV plans was smaller than in the 6 MV plans.

CONCLUSION

When T < 34 cm, 6 MV energy is more suitable for the external irradiation of cervical cancer. When T > 34 cm, 10 MV energy is more suitable for cervical cancer radiotherapy. Therefore, 10 MV should be considered for patients with a large abdominal size.

Use of specific duodenal dose constraints during treatment planning reduces toxicity after definitive para-aortic radiotherapy for cervical cancer

PURPOSE

To validate the safety of paraaortic nodal (PAN) radiation therapy (RT) for patients with cervical cancer when the duodenal dose is limited to V₅₅<15 cm³ and V₆₀<2 cm³.

METHODS AND MATERIALS

Ninety-seven patients who were treated with RT for cervical cancer between 2010 and 2018, received at least 56 Gy to grossly involved PANs. Patients were treated with concurrent chemoradiation (n=88, 91%), with 93% (n=90) receiving intensity-modulated RT (IMRT) to the initial PAN field, and 98% (n=95) receiving IMRT to a sequential PAN boost. V₅₅<15 cm³ and V₆₀ <2 cm³ criteria were implemented in 2014. Normal tissues were contoured on CT simulation datasets; the duodenum was contoured from the gastric outlet to the duodenojejunal flexure. Sixty-six patients (68%) had a resimulation scan after approximately 20 fractions. Composite duodenal doses were calculated using the initial CT for 50 patients (52%) and the resimulation CT for 47 patients (48%) depending on anatomic changes throughout treatment.

RESULTS

The median duodenal V₅₅ was 3.5 cm³ (interquartile range [IQR] 0.2-8.1 cm³) and the median V₆₀ was 0.3 cm³ (IQR 0.0-1.8). Constraints were exceeded in 18 patients, 16 (89%) of whom had been treated before 2014. Treatment for the 2 patients treated after 2014 had been complicated by significant weight loss and reduced anterior-posterior diameter, which likely overestimated the true dose on the composite plan. Only 1 patient experienced grade 3 duodenal toxicity (stricture requiring endoscopic balloon dilation 3 months after treatment); however, the stricture was outside the high-dose boost volume and the patient had a history of gastritis. Six patients (6%) had a first recurrence within the PAN region.

CONCLUSIONS

Limiting duodenal dose to V₅₅<15 cm³ and V₆₀<2 cm³ for patients with cervical cancer and PAN involvement is feasible and minimizes duodenal toxicity while maintaining acceptable local control rates.

A robust VMAT delivery solution for single-fraction lung SABR utilizing FFF beams minimizing dosimetric compromise

Peripheral lung lesions treated with a single fraction of stereotactic ablative body radiotherapy (SABR) utilizing volumetric modulated arc therapy (VMAT) delivery and flattening filter‐free (FFF) beams represent a potentially high‐risk scenario for clinically significant dose blurring effects due to interplay between the respiratory motion of the lesion and dynamic multi‐leaf collimators (MLCs). The aim of this study was to determine an efficient means of developing low‐modulation VMAT plans in the Eclipse treatment planning system (v15.5, Varian Medical Systems, Palo Alto, USA) in order to minimize this risk, while maintaining dosimetric quality. The study involved 19 patients where an internal target volume (ITV) was contoured to encompass the entire range of tumor motion, and a planning target volume (PTV) created using a 5‐mm isotropic expansion of this contour. Each patient had seven plan variations created, with each rescaled to achieve the clinical planning goal for PTV coverage. All plan variations used the same field arrangement, and consisted of one dynamic conformal arc therapy (DCAT) plan, and six VMAT plans with varying degrees of modulation restriction, achieved through utilizing different combinations of the aperture shape controller (ASC) in the calculation parameters, and monitor unit (MU) objective during optimization. The dosimetric quality was assessed based on RTOG conformity indices (CI100/CI50), as well as adherence to dose–volume metrics used clinically at our institution. Plan complexity was assessed based on the modulation factor (MU/cGy) and the field edge metric. While VMAT plans with the least modulation restriction achieved the best dosimetry, it was found that there was no clinically significant trade‐off in terms of dose to organs at risk and conformity by reducing complexity. Furthermore, it was found that utilizing the ASC and MU objective could reduce plan complexity to near‐DCAT levels with improved dosimetry, which may be sufficiently robust to overcome the interplay effect.