Modulated Radiation Therapy Technique Research Articles

Prospective Observational Study on Moderate Hypofractionated Radiotherapy for Localized Prostate Cancer in Rwanda: Acute Toxicity in Patients.

Moderate hypofractionation (MHF) offers logistical and financial advantages, and has become standard in Western countries but not yet in Africa. This study assessed GI and genitourinary (GU) acute toxicity in Rwandan men undergoing MHF (20 × 3 Gy) treatment. Since 2021, patients with prostate cancer at the Rwanda Cancer Centre have been informed about the study on MHF treatment and could participate by signing an informed consent. The study included patients with confirmed prostate adenocarcinoma (any T, any prostate-specific antigen any Gleason score, N0M0), excluding those with inflammatory bowel disease, previous pelvic irradiation, or previous prostatectomy. Participants received 20 fractions of 3 Gy over 4 weeks using the volumetric modulated arc radiotherapy (RT) technique with a 6 megavoltage linear accelerator. GI and GU acute toxicity was evaluated at week 2, at the end of RT, and 3 months after treatment using the Radiation Therapy Oncology Group (RTOG) acute toxicity grading system. Fifty consecutive patients with localized prostate cancer were included. The median patient age was 70 years. Most patients (86%) had high-risk disease and 94% received androgen-deprivation therapy. The cost and treatment time were reduced by 50%. The distribution of maximum acute RTOG toxicity scores were for GI 10% grade 0, 70% grade 1, 20% grade 2, 0% grade 3, and for GU scores were 0%, 40%, 54%, and 6%, respectively. By 3 months, RT symptoms had returned to baseline levels for most patients. MHF (20 × 3 Gy) was well tolerated in men treated for prostate cancer in Rwanda, showing that MHF is feasible in an African setting. However, further research on acute and late toxicity for more patients is warranted.

Brain radiotherapy and dorsal vagal complex irradiation: A new organ at risk to decrease radiation-induced nausea and vomiting?

Nausea is a common symptom in patients irradiated for benign brain tumors. The dorsal vagal complex (DVC) located in the brainstem (BS) has been identified as the center of nausea and vomiting. The objective of our study was to determine an association between mean dose to the DVC and nausea. Details of consecutive patients treated for benign brain tumors at the Bordeaux University Hospital using normofractionated intensity modulated radiotherapy technique, without chemotherapy, were accessed. DVC delineation was performed on MRI T1 sequences with gadolinium injection using a reference atlas. Among 102 patients, 68 were women, and median age was 61.5years. The tumors treated were primarily meningiomas (80%) and neurinomas (17%). The median dose was 54Gy [48.6-57.6Gy]. In the overall population, 40 (39.2%) had nausea, requiring anti-nausea treatment for 23 (57.5%). Patients with nausea were significantly younger (45.5 versus 63.2years, p=0.014).For patients without and with nausea, the mean DVC dose was 8.9Gy versus 21.6Gy (p<10-4), respectively, and the mean brainstem dose was 16.9Gy versus 27.1Gy (p<10-3). The optimal threshold for mean DVC dose was 8.82Gy (AUC=0.731, p<10-4). Patients with DVC receiving less than 8.82Gy had a 16% risk to have nausea versus 62% for patients receiving more than 8.82Gy (p<10-4). The optimal threshold for mean brainstem dose was 24Gy (AUC=0.715p<0.0001). The mean DVC dose is significantly associated with radiation-induced nausea. A dose constraint below 8.82Gy to decrease the incidence of radiation-induced nausea needs to be validated by a prospective study.

Evaluation of Inverse Planned and Forward Planned Intensity Modulated Radiotherapy Techniques in Breast Cancer

Introduction: The objective of this study is to compare the dosimetric parameters of radiation to the whole breast between the two intensity-modulated radiotherapy (IP IMRT) techniques, i.e. Inverse planned IMRT (IP IMRT) and Forward Planned IMRT (FP IMRT) with regard to target coverage (PTV) and irradiation of organs at risk (OAR). Material and Methods: Plain and Contrast enhanced computed tomography (CECT) datasets were created for 41 patients treated with whole breast radiation therapy. CT simulation and treatment is performed using deep inspiratory breath hold technique (DIBH). Radiotherapy treatment Planning is done using Eclipse Treatment Planning System (version 13.7) with a prescription dose of 40 Gy in 15#. The developed treatment plans were subjected to objective comparison of PTV and OARs using dose volume histograms (DVH). Results: IP IMRT plans provided better coverage (99.5% vs 97.6%), comparable though higher maximum dose (Dmax 45.0 VS 44.1 Gy), higher hot spot (PTV105% 49.2 vs 33), lower volumes receiving 20, 25, 30 Gy (V20, V25, V30) for heart, more homogeneous (homogeneity index 0.10 vs. 0.14) and conformal dose distribution (conformity Index 1.0 vs 0.98) compared to FP IMRT. Regarding OAR dosimetry it is observed that FP IMRT showed reduced mean dose to Coronary artery (LADCA), Contralateral Lung (CL), Contralateral breast (CB) along with reduction in low dose region (V5) to all OARs under study. It was also observed that Monitor units used and planning time were lower for FP IMRT. Conclusion: On weighing different dosimetric factors, both the techniques have displayed their own advantages and disadvantages. Choosing a planning technique needs to be customized taking into consideration various factors such as breast topography, size and volumes of breast, availability of expertise planning skills and resources.

Dosimetrically motivated beam-angle optimization for non-coplanar arc radiotherapy with and without dynamic collimator rotation.

Non-coplanar techniques have shown to improve the achievable dose distribution compared to standard coplanar techniques for multiple treatment sites but finding optimal beam directions is challenging. Dynamic collimator trajectory radiotherapy (colli-DTRT) is a new intensity modulated radiotherapy technique that uses non-coplanar partial arcs and dynamic collimator rotation. To solve the beam angle optimization (BAO) problem for colli-DTRT and non-coplanar VMAT (NC-VMAT) by determining the table-angle and the gantry-angle ranges of the partial arcs through iterative 4π fluence map optimization (FMO) and beam direction elimination. BAO considers all available beam directions sampled on a gantry-table map with the collimator angle aligned to the superior-inferior axis (colli-DTRT) or static (NC-VMAT). First, FMO is performed, and beam directions are scored based on their contributions to the objective function. The map is thresholded to remove the least contributing beam directions, and arc candidates are formed by adjacent beam directions with the same table angle. Next, FMO and arc candidate trimming, based on objective function penalty score, is performed iteratively until a desired total gantry angle range is reached. Direct aperture optimization on the final set of colli-DTRT or NC-VMAT arcs generates deliverable plans. colli-DTRT and NC-VMAT plans were created for seven clinically-motivated cases with targets in the head and neck (two cases), brain, esophagus, lung, breast, and prostate. colli-DTRT and NC-VMAT were compared to coplanar VMAT plans as well as to class-solution non-coplanar VMAT plans for the brain and head and neck cases. Dosimetric validation was performed for one colli-DTRT (head and neck) and one NC-VMAT (breast) plan using film measurements. Target coverage and conformity was similar for all techniques. colli-DTRT and NC-VMAT plans had improved dosimetric performance compared to coplanar VMAT for all treatment sites except prostate where all techniques were equivalent. For the head and neck and brain cases, mean dose reduction-in percentage of the prescription dose-to parallel organs was on average 0.7% (colli-DTRT), 0.8% (NC-VMAT) and 0.4% (class-solution) compared to VMAT. The reduction in D2% for the serial organs was on average 1.7% (colli-DTRT), 2.0% (NC-VMAT) and 0.9% (class-solution). For the esophagus, lung, and breast cases, mean dose reduction to parallel organs was on average 0.2% (colli-DTRT) and 0.3% (NC-VMAT) compared to VMAT. The reduction in D2% for the serial organs was on average 1.3% (colli-DTRT) and 0.9% (NC-VMAT). Estimated delivery times for colli-DTRT and NC-VMAT were below 4 min for a full gantry angle range of 720°, including transitions between arcs, except for the brain case where multiple arcs covered the whole table angle range. These times are in the same order as the class-solution for the head and neck and brain cases. Total optimization times were 25%-107% longer for colli-DTRT, including BAO, compared to VMAT. We successfully developed dosimetrically motivated BAO for colli-DTRT and NC-VMAT treatment planning. colli-DTRT and NC-VMAT are applicable to multiple treatment sites, including body sites, with beneficial or equivalent dosimetric performances compared to coplanar VMAT and reasonable delivery times.

Radiotherapy of prostate and head-and-neck tumour: An optimal treatment planning comparison for intensity modulated radiotherapy and volumetric modulated arctherapy techniques.

To evaluate and compare merits between intensity modulated radiotherapy and volumetric modulated arc-therapy radiotherapy techniques to determine which technique can achieve better treatment plan quality and efficient delivery. The retrospective study was conducted at the Radiation Oncology Department of SanBorotlo Hospital, Vicenza, Italy, in 2019, and comprised data from Jan 2019 to Dec 2019 related to prostate and head-and-neck patients in whom Pinnacle³ treatment planning system was used for optimisation with different prescribed doses and target geometries for intensity modulated radiotherapy and volumetric modulated arc-therapy techniques. Treatment plans were simulated using 6MV photon beam of SynergyS® Linac (Linear accelerator). The plan quality was evaluated using dose-volume indices for planning target-volume and organs-at-risk. ArcCHECK™ phantom was used for dose agreement verification between planed and delivered doses. Data of 8 patients was analysed. Intensity modulated radiotherapy and volumetric modulated arc-therapy treatment plan quality for prostate was found to be similar, but volumetric modulated arc-therapy had significant results for maximum dose (p=0.005). Intensity modulated radiotherapy and volumetric modulated arc-therapy plans for head-and-neck achieved adequate target coverage and sparing of organs at risk, and produced clinically acceptable treatment plans. The percentage of target coverage (p=0.001), dose maximum (p=0.013) and conformity index (p=0.000) were significant. A significant gain for all planning target volume dose-volume indices was noted (p<0.05). Volumetric modulated arc-therapy obtained better plan with significant values and improved sparing of organs at risk compared to intensity modulated radiotherapy for both prostate and head-and-neck treatments while maintaining doses to the organs at risk (p<0.05). Dynamic arc mode of beam delivery provided increased degrees of freedom of volumetric modulated arc-therapy beam intensity modulation, depicting superior dose distribution than intensity modulated radiotherapy.

Prophylactic Para-Aortic Extended Field Irradiation with Concurrent Chemotherapy for FIGO Stage IIIC1 Cervical Cancer Using Intensity Modulated Radiotherapy Technique: Acute Toxicity and Dosimetric Assessment

To evaluate the efficacy of P - PART with concurrent chemotherapy in LACC with the use of intensity modulated radiotherapy technique (IMRT). Our Primary endpoint was to assess acute toxicities and secondary endpoint was to assess loco-regional control (LRC), disease free-survival (DFS), para-aortic recurrence free survival (PA-RFS). A total of 30 patients of squamous cell carcinoma of cervix with stage IIIC1 (FIGO-2018) were recruited in this prospective, single arm interventional phase II study between January 2021 to September 2022. 18FDG-PET CT was performed and those with positive PALN were excluded. IMRT was used to deliver a dose of 50 Gy in 25 fractions to whole pelvis and PALN chain below renal hilum till aortic bifurcation received 45 Gy in 25 fractions. Concurrent cisplatin was administered weekly at 40 mg/m2 during radiation. On completion of external beam radiotherapy, high dose rate intracavitary brachytherapy was given at 7 Gy per fraction in 3 fractions prescribed to HR-CTV. Acute toxicities were assessed using CTCAE version 5.0. Median age was 50 years (37-66 years). All patients had completed treatment as per protocol. All patients had positive pelvic nodes with the maximum nodal short axis dimension of 14 mm (10-18 mm). All patients had positive internal iliac group of LNs, only 2(6.6%) patients had positive common iliac group of Ln. Median number of concurrent cisplatin cycles given were 5 (3-5 cycle). Median overall treatment time was 56 days (52-63 days) and median follow up was 15 months (3-22 month). Median cumulative dose to HR-CTV was 84.3Gy (Range:79.2-86.9Gy). Cumulative median EQD2 to 2cc of bladder and rectum were 69.11Gy (Range:59.17 - 80.07 Gy) and 64.6 Gy (Range: 60.1-66.3Gy) respectively. 7(23.3%) patients having grade 3 diarrhea and 2(6.67%) patients had grade 3 anemia while no significant genitourinary or other toxicities were noted. Patient characteristics, dosimetric data are described in Table-1. All patients underwent clinical and radiological assessment at the time of last follow up with one (3.33%) patient experiencing local failure at 9 months of follow up, hence crude LRC rate is 96.6%, DFS is 13.5 months (5-22 months) and PA-RFS is 16 months (8-23 months) till last date of follow up. Prophylactic EFRT with concurrent chemotherapy using IMRT technique yielded excellent short term clinical outcomes with acceptable toxicity profiles. Longer follow up will elucidate late toxicity and long-term clinical outcomes.

Indian data on response of positive pelvic lymph nodes in carcinoma cervix patients treated with simultaneous integrated boost using volumetric modulated arc radiation therapy

Objectives The percentage of pelvic lymph node positivity in cervical cancer patients varies from 19% in early stages to 68% in advanced cases. Thirty three percent of patients will develop recurrence within 2 years following therapy and 5-year relative survival for patients with affected regional lymph nodes is 57%. Hence, pelvic lymph nodes need to be included in the definitive plan of radiation treatment for better disease control and longer survival. With conventional radiation therapy, dose escalation was not possible because of small bowel constraints. With higher conformity of intensity modulated radiotherapy technique (IMRT), doses to pelvic and abdominal organs can be minimized. The added advantage of simultaneous integrated boost (SIB) is that high dose per fraction is delivered to the gross disease and low dose to the microscopic disease, thereby reducing the total treatment time and improving the therapeutic ratio. Material and Methods Forty one patients presenting to the Department of Radiation Oncology, between January 2016 and June 2017, with newly biopsy proven carcinoma cervix Stage IB to IVA were enrolled in the study and all the investigations were performed. The radiation dose was delivered using volumetric modulated arc therapy plan to a dose of 5000 cGy in 25 fractions to the whole pelvis and 5500 cGy in 25 fractions at 220 cGy per fraction to the involved nodes using SIB along with weekly cisplatin at 40 mg/m2. After completion of external beam radiation, all the patients received three fractions of brachytherapy to a total dose of 21 Gy. Acute toxicities were assessed using RTOG criteria. At 3 months after completion of treatment, all the patients had been followed up with DW MRI of abdomen and pelvis to assess the response. Results Of the 41 carcinoma cervix patients with significantly positive lymph nodes treated with SIB VMAT, 9.8% of the patients (4 patients) had residual nodal disease, 87.8% of the patients (36 patients) had complete response, 19.5% (8 patients) had residual disease of primary disease, and 78% (32 patients) had complete response at 3 months after completion of treatment with only Grade – I and Grade – II toxicities. Conclusion Treatment with SIB VMAT in carcinoma cervix patients with significant pelvic lymph nodes shows very good response with acceptable acute toxicities. But longer follow-up period is required to see if this response translates into better DFS and OS.

Induction Chemotherapy Followed by Concomitant Chemoradiation using Intensity Modulated Radiotherapy Technique in Locally Advanced Unresectable Pancreatic Cancer patients

Induction Chemotherapy Followed by Concomitant Chemoradiation using Intensity Modulated Radiotherapy Technique in Locally Advanced Unresectable Pancreatic Cancer patients

The effect of breath-hold technique on conformal and intensity modulated radiotherapy techniques at right breast cancer radiotherapy including internal mammarian field

Background/Aim: Significantly lower heart doses can be achieved by breath-hold technique at left-sided breast cancer radiotherapy (RT). We see high doses at organs at risk such as lung, heart, and contralateral breast during right-sided breast cancer RT planning especially in the presence of RT indication for mammaria interna (MI) lymph nodes. This study compared RT-planning methods that are conformal with intensity-modulated RT (IMRT) with breath holding and free breathing for right-sided breast cancer RT including full axillary and MI lymph node fields. Methods: Computed tomography (CT) simulations were performed using free-breath (FB) and breath-hold (BH) methods in 10 patients with right-sided breast cancer. A total of 40 RT treatment plans were calculated. Right-sided breast, level 1-2-3 axillary regions, and MI regions served for the target-planning volume. Left-sided breast, heart, as well as right-sided and left lungs were contoured as critical organs according to the atlas of the "Radiation Therapy Oncology Group." We used a Varian Eclipse v.13 for treatment planning. Conformal “FieldinField” RT (FinFRT) and dynamic IMRT (dIMRT) planning were performed separately for each patient over breath-hold and free-breath images. For PTV, 50 Gy was prescribed in 25 fractions and optimized such that the planned target volume (PTV) remained between 95% and 110% of the dose. The mean and maximum doses of the heart, V5 and V20 of the lungs, as well as V95 doses for MI were recorded. Statistical analyses were performed with SPSS version 22, and a paired t-test was used for comparison. Results: Four treatment plans (FB FinFRT, BH FinFRT, FB dIMRT, BH dIMRT) were made separately for 10 patients. For comparison, common FB FinFRT plans were accepted as the baseline plan. As expected, there were no significant differences in PTV coverage. The mean dose received by 95% of the MI volume was between 42.27 Gy and 42.4 Gy. For the maximum heart dose, the breath hold technique had no significant effect on plans. The lowest average maximum heart dose was seen in the BH FinFRT group. Mean heart doses are between 1.28 Gy – 4.85 Gy. There was no significance between BH FinFRT and FB FinFRT plan (P=0.504), and there was a significant difference for heart mean dose versus dIMRT plans (P=0.001). The mean V20 of the lungs ranged from 11.9 to 17.8. There was a significant decrease in V20 with BH or FB dIMRT plans (P=0.001). There was no difference between BH FinFRT (P=0.138). On the contrary, lung V5 values were significantly higher in dIMRT plans, and the lowest mean V5 value was seen in BH FinFRT plan. Conclusion: With the BH method, lower doses (but not significantly lower doses) were obtained in critical organ doses. There was a significant decrease with FinFRT plans in terms of heart mean and maximum dose and lung V5 percentages. The dIMRT plans were significant only in lung V20 percentages. When planning RT, we recommend evaluating all treatment techniques individually for right-sided breast cancer patients to obtain lower doses in critical organs.

Revisiting the Radical Radiotherapy-Radiochemotherapy Results in Anal Canal Cancers: (TROD Gastrointestinal Group Study 02-005)

Background and AimThis study aimed to determine treatment outcomes and factors affecting prognosis in patients diagnosed with anal canal cancer who received radical radiotherapy (RT) or radiotherapy combined with chemotherapy (CT-RT) in radiation oncology centers in Turkey and compare the results with literature. Material and MethodThe study included 193 patients with anal canal cancer reported between 1995 and 2019, of which 162 had complete data. The study was conducted in 11 radiation oncology centers, and a joint database was shared among them. Patients received radiotherapy doses of 45 Gy to 60 Gy. Data analysis was done using SPSS for Windows version 20. ResultsMedian follow-up was 48.51 months (2-214). All patients received radiotherapy, and 140 (86.4%) received concurrent chemotherapy. Radiotherapy doses of 50.4 Gy to 60 Gy were administered to 74 patients (45.7%) using 2-dimensional-3-dimensional (2D-3D) conformal therapy and 70 patients (43.2%) using intensity modulated radiotherapy technique (IMRT). Acute phase hematologic toxicity was observed in 62 patients (38.3%), and nonhematologic toxicity in 123 patients (75.9%). The 5-year overall survival (OS) rate was 75.1% and disease-specific survival (DSS) rate was 76.4%. OS without colostomy was achieved in 79,8 % at 5 years, and complete response in 112 patients (69.1%). OS rate was significantly higher in 142 patients with positive response (P < .000) and 112 with complete response (P < .000). Anemia (P < .002), local progression, and systemic progression (P < .000) resulted in lower OS (P < .002). In univariate analysis, factors affecting OS rate were: gender, age, stage, lymph node status, T stage, RT treatment duration, and treatment planning with PET fusion, which were found to be statistically significant. Completing radiotherapy in less than 45 days, concurrent chemotherapy, and continued administration of mitomycin and 5 FU as chemotherapy had a significant positive effect on overall survival. OS rate was higher in patients receiving RT dose of 58 Gy or less and undergoing IMRT planning in radiotherapy. IMRT was associated with lower acute and late side effects. ConclusionRadiochemotherapy is the primary treatment for anal canal cancer and advanced radiotherapy techniques may increase survival by reducing side effects and improving treatment continuation. Higher treatment doses require further investigation. The efficacy of treatment can be improved by including patients treated with modern radiotherapy techniques in multicenter prospective studies using new and more effective chemotherapy and immunotherapy agents.

Abstract P1-10-15: Concious sparing of contralateral thyroid lobe in Ca Breast patients receiving post mastectomy radiotherapy by IMRT technique – A single institution dosimetric study

Abstract Purpose/Objective(s): The purpose of this paper is to report the dosimetric effects of conscious sparing of contralateral lobe of thyroid gland in carcinoma breast patient receiving locoregional radiation by tangential beam Intensity Modulated radiotherapy technique. Materials/Methods: Treatment plans of 20 Ca Breast patients, who received post mastectomy adjuvant locoregional radiotherapy, were evaluated. Since October 2021 we adopted a department protocol of conscious sparing of contralateral thyroid in breast radiotherapy. 10 of these had conscious sparing of contralateral thyroid (group A) whereas 10 of old plans were evaluated when C/L thyroid were not given constraints &amp; are being passively spared due to location on contralateral/non treatment side of neck (group B). Treatment planning was done using tangential beam (6 MV) IMRT in Eclipse 13.7 TPS in all of these patients. All of these patients received treatment to chest wall &amp; SCF. RTOG contouring guidelines were followed in all the patients. Prescription Dose was 40Gy in 15# for both groups. The best treatment plans were selected ensuring 95% PTV dose coverage and acceptable dose to OARs. Uniform contouring, plan optimization &amp; evaluation protocols were followed for all of these patients. Results: The mean thyroid volume in group A is 4.30cc &amp; in group B is 3.99cc which is not statistically different (P value -0.639) The mean dose of thyroid in group A is 7.98Gy whereas in group B it is 17.00Gy which is spastically significant (P value – 0.000003). Comparison of mean dose to contralateral lobe (in Gy) between the two groups Groups No. Mean ± SD ‘t’ value P value Thyroid dose with constraint 10 7.98±1.46 -6.702, df=18 0.000003* Thyroid dose without constraint 10 17.00±3.99 Unpaired ‘t’ test applied. P value = 0.000003, Significant Conclusion: OARs present on contralateral side are passively spared due to the location. This often results in a tendency of not actively prescribing constraints to these. This study emphasizes that conscious sparing of contralateral Thyroid lobe can further reduce the dose to significant levels. This reduction can preserve thyroid function further. Further clinical trials are required to corroborate this dosimetric gain with clinical thyroid function preservation. Citation Format: Manish Chomal, Minaal Iyer, Ananth Kalimurthy, Joshua Sahay, Sushanta Banik. Concious sparing of contralateral thyroid lobe in Ca Breast patients receiving post mastectomy radiotherapy by IMRT technique – A single institution dosimetric study [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-10-15.

Dosimetric comparison study of intensity modulated radiotherapy technique (IMRT/VMAT) with three dimensional field-in-field tangents for left breast cancer irradiation

Purpose: To retrospectively compare dosimetrically three dimensional field-in-field tangents (3D F-in-F), Intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) left breast irradiation plans. Materials and Methods: A total of 30 patients were included in this study. All patients diagnosed with early–stage malignant neoplasm of the breast prior to treatment. Patients were contoured with three main PTV-Chest wall (PTVCW), PTV-Axilla (PTVAX), and PTV-IMC (PTVIMC). Monaco treatment planning system was used to create the plans. For each patient, three treatment plans were created; three dimensional conformal radiotherapy (3D-CRT), intensity modulated radiotherapy (IMRT), and volumetric modulated arc therapy (VMAT). The dose coverage of PTVs and the dose constraints of Organ-at-Risks (OARs) were compared and analyzed. Results: The dose objective to cover the PTVs; PTVCW, PTVAX, and PTVIMC were V40.43Gy (95%) ≥ 95%, V38.3Gy (90%) ≥ 95%, and V34.05Gy (80%) ≥ 95% respectively. Comparing the dose coverage of PTVCW between 3D-CRT and VMAT, resulted in a significant difference (P= 0.003) and the VMAT was superior for the coverage of target than 3D-CRT. For PTVAX, the coverage was 45.80±0.55, 45.96±0.73, and 45.58±0.63 for 3D-CRT, IMRT, and VMAT respectively. For PTVIMC, the coverage was 45.80±0.55, 45.96±0.73, and 45.58±0.63 for 3D-CRT, IMRT, and VMAT respectively.

Dosimetric effect of modelling non-homogeneous LINAC couch using cone-beam computed tomography on quality assurance (QA) results

Abstract Aim: To evaluate the dosimetric effect of modelling a non-homogeneous couch on patients’ quality assurance (QA) gamma pass rates for intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) techniques. Materials and Methods: A non-homogeneous treatment couch (TxT 550 TTM, CIVCO, USA) was imaged using the LINAC mounted cone-beam computer tomography (CBCT) system. Modelling this couch in different situations, including incomplete (homogeneous model), correct model and not defined situations in the treatment planning system (TPS), was performed based on the geometrical and material densities data extracted from the CBCT images. Calculated gamma pass rates between TPS dose calculations and the measurements in a phantom for different couch models were obtained and compared at two gamma criteria (2%-2 mm and 3%-3 mm). Results: Comparing TPS calculations for the correct modelled couch and the measurements showed high gamma pass rates for both the IMRT and VMAT techniques (96·5 ± 0·9%, 99·2 ± 0·5% for IMRT in 2%-2 mm and 3%-3 mm criteria; 97·5 ± 0·8%, 99·4 ± 0·5% for VMAT). The overall gamma pass rate of the IMRT plan QAs was reduced by about 2% and 3% on average for incomplete and no couch modelling, respectively. These reductions for VMAT techniques were 2·5% and 4·3%, respectively. Conclusions: Non-homogeneous couches have different parts with different attenuations, which can be correctly defined using LINAC CBCT. Modelling of treatment couch has a significant effect on patient QA results for VMAT and IMRT plans, especially in radiation fields/subfield transmitting from the couch. We suggest using LINAC CBCTs as an appropriate device for couch modelling in modulated radiotherapy techniques.

Comparison and Evaluation of Different Radiotherapy Techniques Using Biodosimetry Based on Cytogenetics.

Simple SummaryCell killing and tumor response in cancer patients depends not only on the absorbed radiation dose but also on the dose rate and delivery time. In this study, a biodosimetry assay based on the frequency of dicentrics chromosomes scored in peripheral blood lymphocytes from prostate cancer patients and PC3 human prostate cancer cell line was used to investigate the radiobiological impact of the relative prolonged dose delivery time and/or decreased dose rate met in advanced modulated radiotherapy techniques (VMAT and IMRT) compared to conventional non-modulated (3D-CRT) in prostate patient plan irradiations. The results showed a small but statistically significant decrease in the number of dicentrics following radiation with the modulated techniques, suggesting a corresponding decrease on the radiation dose efficiency. The biodosimetry assay could be used as an alternative to the laborious conventional clonogenic assay, while both lymphocytes and cancer cell line could effectively be used for estimation of the biological absorbed dose.While rapid technological advances in radiotherapy techniques have led to a more precise delivery of radiation dose and to a decreased risk of side effects, there is still a need to evaluate the efficacy of the new techniques estimating the biological dose and to investigate the radiobiological impact of the protracted radiotherapy treatment duration. The aim of this study is to compare, at a cytogenetic level, advanced radiotherapy techniques VMAT and IMRT with the conventional 3D-CRT, using biological dosimetry. A dicentric biodosimetry assay based on the frequency of dicentrics chromosomes scored in peripheral blood lymphocytes from prostate cancer patients and PC3 human prostate cancer cell line was used. For each patient blood sample and each subpopulation of the cultured cell line, three different irradiations were performed using the 3D-CRT, IMRT, and VMAT technique. The absorbed dose was estimated with the biodosimetry method based on the induced dicentric chromosomes. The results showed a statistically significant underestimation of the biological absorbed dose of ~6% for the IMRT and VMAT compared to 3D-CRT irradiations for peripheral blood lymphocytes, whereas IMRT and VMAT results were comparable without a statistically significant difference, although slightly lower values were observed for VMAT compared to IMRT irradiation. Similar results were obtained using the PC3 cell line. The observed biological dose underestimation could be associated with the relative decreased dose rate and increase irradiation time met in modulated techniques compared to the conventional 3D-CRT irradiations.

Evaluation of Two Intensity Modulated Radiotherapy Techniques for Total Body Irradiation: Initial Clinical Experience From an Ongoing Pilot Study

A multi-institutional pilot study is initiated to compare two IMRT delivery techniques (volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT)) for total body irradiation as conditioning regimen in patients undergoing hematopoietic stem cell transplant with an updated lung dose limit based on recently published clinical data on lung toxicities. We report comparison and initial clinical experience in dosimetric plan quality, patient setup correction techniques, and dose delivery efficiency.We reviewed treatment planning and delivery record for the initial seven patients that were prospectively enrolled in this study. TBI was given to each patient in 8 fractions at 165 cGy per fraction. Patient height ranged from 154.9 to 193.5 cm. The planning target volume (PTV) is the whole body excluding the lung volume. The total lung and 15 additional normal organs were included in plan optimization and dosimetric evaluation. In planning, mean lung dose (MLD) limit was 8 Gy and maximum dose (Dmax) to normal organs was required to be < 130% of the prescribed dose with a recommended goal of < 115%. Four patients received TBI with HT and the other three on a conventional Linac. Patients treated with HT had an upper body HT plan with a rotating gantry using a 5-cm jaw and a lower extremity HT plan using static AP/PA HT fields. Patients treated on a conventional Linac had an upper body VMAT plan using 9 to 10 VMAT fields and a lower body plan with either VMAT fields or static AP/PA fields. The virtual bolus technique was used in VMAT plans to reduce dose variation due to setup uncertainty. The VMAT fields used a 6 MV photon beam with a 90° collimator angle and had an overlap of at least 2 cm between adjacent fields along the longitudinal direction. All the plans were normalized so that 85% of the PTV received at least 13.2 Gy in total dose.In the upper body HT plans the average PTV dose was 13.6 Gy (range: 13.5 - 13.7 Gy), the MLD averaged at 7.71 Gy (range: 7.21 - 7.95 Gy), and Dmax was < 115% of prescribed dose for at least 14 normal organs. In the upper-body VMAT plans the average PTV dose was 13.95 Gy (range: 13.86 - 14.02 Gy), the MLD averaged at 7.12 Gy (range: 6.85 - 7.63 Gy), and Dmax was < 115% of prescribed dose with 1 to 9 normal organs. The Dmax limit of 130% of prescribed dose was achieved in all the plans. In HT treatments, an MVCT scan was used for daily patient setup corrections in both the upper and lower body treatments and the overall treatment time per fraction was 1.23 ± 0.21 hours (range: 0.90 - 1.88 hours). In VMAT treatments, both cone beam CT scans and orthogonal kilovoltage images were used for daily patient setup on a conventional Linac and the overall treatment time per fraction was 1.39 ± 0.20 hours.Both the HT and VMAT plans achieved adequate lung sparing under our new institutional lung dose limit in TBI. VMAT TBI is clinically feasible and could provide access to more patients for TBI treatments. The two IMRT techniques also allow selective sparing of additional organs in TBI treatments.

Quality assurance of dysphagia-optimised intensity modulated radiotherapy treatment planning for head and neck cancer.

This study aimed to assess the impact of the margin applied to the clinical target volume, to create the planning target volume, on plan quality of a novel dysphagia-optimised intensity modulated radiotherapy technique developed within a head and neck cancer multicentre randomised controlled trial. Protocol compliant plans were used for a single benchmark planning case. Larger margins were associated with higher doses to adjacent organs at risk, particularly the inferior pharyngeal constrictor muscle, but coincided with some improved low dose target coverage. A 3mm margin is recommended for this technique if local practices allow.

OC-0620 A multicenter study on Intensity Modulated Radiotherapy techniques for anal carcinoma (RAINSTORM).

OC-0620 A multicenter study on Intensity Modulated Radiotherapy techniques for anal carcinoma (RAINSTORM).

Evaluation of Three-Dimensional Conformal Radiotherapy and Intensity Modulated Radiotherapy Techniques for Left Breast Post-Mastectomy Patients: Our Experience in Nigerian Sovereign Investment Authority-Lagos University Teaching Hospital Cancer Center, South-West Nigeria

This study aimed to evaluate the dosimetric properties of treatment plans obtained from three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy techniques (IMRT) plans for left chest wall breast cancer patients. A total of 20 patients with left-sided chest wall radiotherapy were randomly selected with the dose prescriptions: 42 Gy and 45 Gy in 15 and 18 fractions, respectively. Treatment plans were obtained using 3D-CRT and IMRT for each patient. Five to seven beams were used for IMRT, while tangential beams were used for 3D-CRT. Planning target volume, Dnear-max (D2 ), Dnear-min (D98 ), Dmean, Homogeneity and Conformity Indices (HI and CI) were obtained. Similarly, mean doses to organs at risk (OAR), V5, V10, V20, V25 were generated from the dose-volume histogram and compared. IMRT showed a significant improvement in HI compared to 3D-CRT (p<0.0001). Although there was no significant difference in sparing of the left lung between both plans for high-dose volumes (V20: 18.2 vs 30.55, p<0.0001), (V25: 11.17 vs 28.12, p<0.0001). IMRT however showed supremacy to 3D-CRT with high-dose volumes for the heart, including V20 (4.44 vs 10.29, p = 0.02), V25 (2.08 vs 8.94, p = 0.002). 3D-CRT was better than IMRT in low-dose volumes for left lung (V5: 92.23 vs 56.60, p<0.001; V10: 60.98 vs 47.20, p = 0.04) and heart (V5: 57.45 vs 30.39, p = 0.004). IMRT showed better homogeneity and sparing of high-dose volumes to OAR than 3D-CRT. On the other hand, 3D-CRT showed a reduction of low-dose volumes to OARs than IMRT.

Visualising the urethra for prostate radiotherapy planning.

IntroductionThe prostatic urethra is an organ at risk for prostate radiotherapy with genitourinary toxicities a common side effect. Many external beam radiation therapy protocols call for urethral sparing, and with modulated radiotherapy techniques, the radiation dose distribution can be controlled so that maximum doses do not fall within the prostatic urethral volume. Whilst traditional diagnostic MRI sequences provide excellent delineation of the prostate, uncertainty often remains as to the true path of the urethra within the gland. This study aims to assess if a high‐resolution isotropic 3D T2 MRI series can reduce inter‐observer variability in urethral delineation for radiotherapy planning.MethodsFive independent observers contoured the prostatic urethra for ten patients on three data sets; a 2 mm axial CT, a diagnostic 3 mm axial T2 TSE MRI and a 0.9 mm isotropic 3D T2 SPACE MRI. The observers were blinded from each other’s contours. A Dice Similarity Coefficient (DSC) score was calculated using the intersection and union of the five observer contours vs an expert reference contour for each data set.ResultsThe mean DSC of the observer vs reference contours was 0.47 for CT, 0.62 for T2 TSE and 0.78 for T2 SPACE (P < 0.001).ConclusionsThe introduction of a 0.9 mm isotropic 3D T2 SPACE MRI for treatment planning provides improved urethral visualisation and can lead to a significant reduction in inter‐observer variation in prostatic urethral contouring.

Determining the incidence of interstitial pneumonitis and chronic kidney disease following full intensity haemopoetic stem cell transplant conditioned using a forward-planned intensity modulated total body irradiation technique

Purpose/ObjectiveTotal body irradiation (TBI) remains a key component of conditioning for allogeneic haemopoietic stem cell transplant (HSCT), with interstitial pneumonitis (IP) and chronic kidney disease (CKD) important late sequelae. We undertook a retrospective service evaluation of TBI patients treated with a forward-planned intensity modulated radiotherapy technique (FP IMRT). Material/Methods74 adult patients were identified; all received step and shoot FP IMRT TBI, 14.4 Gy in 8 fractions over 4 days. Mean doses to the lungs and kidneys were 12–12.5 Gy. Toxicities were defined as per CTCAE v4.0: IP as multilobar infiltrates on CT with symptoms of dyspnoea, and renal dysfunction as an Estimated Glomerular Filtration rate (eGFR) < 60 ml/min/1.73 m2 for > 3 months. Secondary endpoints were overall survival (OS), progression free survival (PFS), cumulative incidence of non-relapse mortality (NRM), relapse risk and of acute and chronic GvHD. ResultsPatients received treatment for the following diagnosis: ALL/LBL (n = 37); AML (n = 33), CML-BC (n = 2) and High grade NHL (n = 2). The rate of IP due to any cause was 30%; positive microbiological evidence in 73% (16 /22). Idiopathic IP was seen in 8%, with only 4% (n = 3) having IP Grade ≥ 3.Two (4%) of 52 long term survivors developed CKD, one with thrombotic microangiopathy.4 year NRM was 16% (CI 11–32%); no treatment related deaths in matched sibling or umbilical cord blood HSCT. ConclusionFP IMRT TBI, reducing dose to the lungs and kidneys, has lower rates of idiopathic IP and CKD compared to the literature. This technique is safe and effective conditioning for full intensity HSCT.