Arc Radiotherapy Research Articles

Dosimetric effects of oral contrast in the planning of conventional radiotherapy and IMRT, for rectal cancer treatment

Abstract Introduction: Contrast media are frequently used during radiation therapy simulation. However, there are concerns about dosimetric variations when dose calculation is done on contrast-enhanced computed tomography (CT). This study evaluates the dosimetric effect of oral contrast during three-dimensional conformal radiotherapy (3D-CRT) and volumetric modulated arc radiotherapy (VMAT) planning. Methods: Rectal cancer patients were consecutively enrolled. For each patient, one unenhanced CT and one contrast-enhanced CT were taken using oral and intravenous contrast. Then, a 3D-CRT plan and an Intensity-modulated radiation therapy (IMRT)/VMAT plan were generated in the enhanced CT, and the dose distribution was recalculated in the respective unenhanced CT. The beam intensities were kept the same as for the enhanced CT plans. Finally, the unenhanced and enhanced plans were compared by calculating the gamma index. Results: For 3D-CRT plans, there were statistically significant differences in second phase planning target volume (PTV) D2% (Mean difference (MD) between unenhanced and enhanced CT 0·01 Gy, 95% CI [0·003 to 0·02 Gy]) and in maximum doses to the bladder (MD 0·26 Gy, 95% CI [0·05 to 0·47 Gy]). For IMRT/VMAT plans, there were statistically significant differences in small intestine V45 Gy (MD 3·1 cc, 95% CI [0·81 to 5·4 cc]), bladder V45 Gy (MD 2·9%, 95% CI [1·4 to 4·3%]) and maximum dose to the bladder (MD 0·65 Gy, 95% CI [0·46 Gy to 0·85 Gy]). In addition, for PTV D98% the MD between unenhanced and enhanced CT was 0·22 Gy 95% CI [0·05 to 0·39]. Conclusions: For most of the dose metrics, the differences were not clinically meaningful. The greatest differences were found in VMAT plans, especially in V45 Gy of the small intestine. This difference could lead to an underestimation of dose–volume metrics when the plan is based on an enhanced CT. The use of small bowel oral contrast does not significantly influence dose calculations and may not affect the acceptability of plans when adhering to constraints.

Indian Data on the Response of Positive Pelvic Lymph Nodes in Carcinoma Cervix Patients Treated with Simultaneous Integrated Boost Using Volumetric Modulated Arc Radiation Therapy

Abstract Background The percentage of pelvic lymph node (LN) 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 LNs is 57%. Hence, pelvic LNs 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, 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. Materials 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 according to the dose of 5,000 cGy in 25 fractions to the whole pelvis and 5,500 cGy in 25 fractions to the involved nodes at 220 cGy per fraction 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 Radiation Therapy Oncology Group criteria. At 3 months after completion of treatment, all the patients were followed up with diffusion-weighted magnetic resonance imaging of abdomen and pelvis to assess the response after 3 months. Results Of 41 carcinoma cervix patients with significantly positive LNs treated with SIB VMAT, 9.8% of the patients (4 patients) had residual nodal disease and 87.8% of the patients (36 patients) had a complete response, and 19.5% (8 patients) had residual disease of primary and 78% (32 patients) had a 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 LNs shows a very good response with acceptable acute toxicities. But longer follow-up period is required to see if this response translates into better disease-free survival and overall survival.

Examination of the dose distribution of volumetric modulated arc radiotherapy using a high-definition multi-leaf collimator for breast cancer patients with irradiated regional lymph nodes.

BackgroundA high-definition multi-leaf collimator (HD-MLC) with 5- and 10-mm fine MLCs is useful for radiotherapy. However, it is difficult to irradiate the mammary gland and supraclavicular region using a HD-MLC because of the narrow field of volumetric modulated arc radiotherapy (VMAT). Therefore, we aimed to evaluate the dose distribution of the VMAT dose using a HD-MLC in 15 patients with left breast cancer undergoing postoperative irradiation of breast and regional lymph nodes, including the internal mammary node.Materials and methodsThe following four plans were generated: three-arc VMAT using HD-MLC (HD-VMAT), two tangential arcs and one-arc VMAT using HD-MLC (tHD-VMAT), three-dimensional conformal radiotherapy (3DCRT) using HD-MLC, and two-arc VMAT using the Millennium 120-leaf MLC (M-VMAT). We assessed the doses to the target volume and organs at risk.ResultsThe target dose distributions were higher for HD-VMAT than 3DCRT. There were no significant differences in the heart mean dose (Dmean) or lung volume receiving 20 Gy (V20 Gy) between HD-VMAT and 3DCRT. The heart Dmean and lung V20 Gy of tHD-VMAT were higher than those of HD-VMAT, and the heart Dmean of M-VMAT was higher than that of HD-VMAT. However, the target doses of tHD-VMAT, M-VMAT, and HD-VMAT were equivalent.ConclusionsIn cases of the mammary gland and regional lymph node irradiation, including the internal mammary node in patients with left breast cancer, HD-VMAT was not inferior to M-VMAT and provided a better dose distribution to the target volume and organs at risk compared with 3DCRT and tHD-VMAT.

Successful management of Australian patients with extensive skin field cancerization (ESFC) with widefield volumetric arc radiation therapy (VMAT): Report with 12-month follow-up.

9582 Background: Non-melanomatous skin cancer (NMSC) diagnoses are associated with a high risk of developing new skin cancers in adjacent areas. Patients with extensive skin field cancerization (ESFC) have large areas (generally ≥50cm2) of compromised skin characterized by pre-cancerous actinic keratoses often requiring repeated interventions. Lesion-directed therapies have excellent cure rates, but therapies targeting a wider region have limited durability, including topical agents such as 5-flurouracil. The development of volumetric modulated arc radiation therapy (VMAT) to precisely target large, curved skin surfaces has generated interest in its application to ESFC. This is a report on the efficacy, safety, and cosmetic outcomes of VMAT in the management of patients with ESFC at facilities across five Australian states. Methods: Sixty-three ESFC zones on 60 patients were prescribed widefield VMAT and prospectively enrolled in the National (Australian) Dermatology Radiation Oncology Registry (NDROR). Over 80% of patients had received up to 4 prior non-radiotherapy interventions. Fields included lower and upper limb, face, scalp, or trunk regions. Total widefield VMAT RT doses ranged from 45-50 Gy delivered in 25-30 daily fractions across 5-7 weeks. 3-, 6-, and 12-month follow-up assessments rated the percentage of disease clearance, cosmesis using the Lovett’s scale, and toxicity based on CTCAE. Results: At 12-month follow-up, 97% of treated zones had achieved and maintained clinical success, defined as > 90% field clearance. Five percent of patients exhibited recurrence of original disease, whereas 10% of patients developed a new actinic keratosis or NMSC. Cosmesis was rated as excellent or good in 98% of patients. Most patients exhibited grade 1-2 radiation-induced dermatitis during therapy, which resolved by 3-month follow-up. Grade 3 dermatitis at end of treatment was exhibited in 7% of the patients, which also resolved. Eight percent of patients discontinued treatment due to acute toxicities. The most common persistent toxicity at 12-month follow-up was localized grade 1 xerosis (dryness) at 43% and/or alopecia at 33%. Conclusions: Widefield VMAT achieved very promising clinical success in patients with ESFC for whom other therapies had failed. VMAT yielded favorable cosmetic outcomes, and treatment-related toxicity was manageable and transient in most patients. While additional follow up is necessary, these results demonstrate that widefield VMAT may be an excellent option for some patients with increasingly unmanageable presentations of ESFC.

Association of volumetric-modulated arc therapy with radiation pneumonitis in thoracic esophageal cancer.

The lung volume receiving low-dose irradiation has been reported to increase in volumetric-modulated arc radiotherapy (VMAT) compared with three-dimensional conformal radiotherapy (3DCRT) for thoracic esophageal cancer, which raises concerns regarding radiation pneumonitis (RP) risk. This single institutional retrospective cohort study aimed to explore whether VMAT for thoracic esophageal cancer was associated with RP. Our study included 161 patients with thoracic esophageal cancer, of whom 142 were definitively treated with 3DCRT and 39 were treated with VMAT between 2008 and 2018. Radiotherapy details, dose–volume metrics, reported RP risk factors and RP incidence were collected. The RP risk factors were assessed via multivariate analysis. Dose–volume analysis showed that VMAT delivered more conformal dose distributions to the target volume (P < 0.001) and reduced V30 Gy of heart (57% vs 41%, P < 0.001) but increased V5 Gy (54% vs 41%, P < 0.001) and V20 Gy (20% vs 17%, P = 0.01) of lungs compared with 3DCRT. However, the 1-year incidence rates of RP did not differ between the two techniques (11.3% in 3DCRT vs 7.7% in VMAT, P = 0.53). The multivariate analysis suggested that the presence of interstitial lung disease (ILD) (P = 0.01) and V20 Gy of lungs ≥20% (P = 0.008) were associated with RP. Conclusively, VMAT increased the lung volume receiving low to middle doses irradiation, although this might not be associated with RP. Further studies are needed to investigate the effect of using VMAT for delivering conformal dose distributions on RP.

Impact of split X-jaw technique on target volume coverage and organ at risk sparing in prostate cancer: a comparative dosimetric study

Abstract Introduction: The Varian Trilogy linear accelerator’s multi-leaf collimator moves on a carriage with a maximum leaf span of 15 cm. The traditional open and limited X-jaw technique of volumetric-modulated arc radiotherapy (VMAT) yields a relatively compromised dose distribution within the planning target volume (PTV) region. This study aimed to determine whether the split X-jaw planning technique for VMAT improves plan quality regarding target dose coverage and organs at risk (OAR) sparing for PTVs that require a field size of more than 15 cm in the X-jaw direction in prostate cancer patients. Method: Computed tomography data sets from 15 patients with prostate cancer were enrolled in the study. Only the PTVs requiring a field size larger than 18 cm in the X-jaw position were considered, and a dose of 4500 cGy in 25 fractions was prescribed. For each case, three separate treatment plans were generated: open, limited and split X-jaw planning techniques with similar planning objectives Results: The split X-jaw technique resulted in statistically significant superior coverage of PTV when compared with the open (P &lt; 0·0001) and limited methods (P &lt; 0·001). The split technique delivered a lower dose to the OARs, although statistical significance could not be achieved. D2% (cGy) was lowest for the PTV in the split technique (4684·8 ± 18·16) and highest for the open technique (4710 ± 18·75), P &lt; 0·001. Conclusion: The x-split jaw technique can replace the traditional open X-jaw practice of VMAT for PTVs requiring an X-jaw width of more than 15 cm in the Varian linear accelerator.

Artificial Intelligence-Based Automated Treatment Planning of Postmastectomy Volumetric Modulated Arc Radiotherapy.

As a useful tool, artificial intelligence has surpassed human beings in many fields. Artificial intelligence-based automated radiotherapy planning strategies have been proposed in lots of cancer sites and are the future of treatment planning. Postmastectomy radiotherapy (PMRT) decreases local recurrence probability and improves overall survival, and volumetric modulated arc therapy (VMAT) has gradually become the mainstream technique of radiotherapy. However, there are few customized effective automated treatment planning schemes for postmastectomy VMAT so far. This study investigated an artificial intelligence based automated planning using the MD Anderson Cancer Center AutoPlan (MDAP) system and Pinnacle treatment planning system (TPS), to effectively generate high-quality postmastectomy VMAT plans. In this study, 20 patients treated with PMRT were retrospectively investigated, including 10 left- and 10 right-sided postmastectomy patients. Chest wall and the supraclavicular, subclavicular, and internal mammary regions were delineated as target volume by radiation oncologists, and 50 Gy in 25 fractions was prescribed. Organs at risk including heart, spinal cord, left lung, right lung, and lungs were also contoured. All patients were planned with VMAT using 2 arcs. An optimization objective template was summarized based on the dose of clinical plans and requirements from oncologists. Several treatment planning parameters were investigated using an artificial intelligence algorithm, including collimation angle, jaw collimator mode, gantry spacing resolution (GSR), and number of start optimization times. The treatment planning parameters with the best performance or that were most preferred were applied to the automated treatment planning method. Dosimetric indexes of automated treatment plans (autoplans) and manual clinical plans were compared by the paired t-test. The jaw tracking mode, 2-degree GSR, and 3 rounds of optimization were selected in all the PMRT autoplans. Additionally, the 350- and 10-degree collimation angles were selected in the left- and right-sided PMRT autoplans, respectively. The uniformity index and conformity index of the planning target volume, mean heart dose, spinal cord D0.03cc, mean lung dose, and V5Gy and V20Gy of the lung of autoplans were significantly better compared with the manual clinical plans. An artificial intelligence-based automated treatment planning method for postmastectomy VMAT has been developed to ensure plan quality and improve clinical efficiency.

Evaluation of an automated template-based treatment planning system for radiotherapy of anal, rectal and prostate cancer.

The Ethos system has enabled online adaptive radiotherapy (oART) by implementing an automated treatment planning system (aTPS) for both intensity-modulated radiotherapy (IMRT) and volumetric modulated arc radiotherapy (VMAT) plan creation. The purpose of this study is to evaluate the quality of aTPS plans in the pelvic region. Sixty patients with anal (n=20), rectal (n=20) or prostate (n=20) cancer were retrospectively re-planned with the aTPS. Three IMRT (7-, 9- and 12-field) and two VMAT (2 and 3 arc) automatically generated plans (APs) were created per patient. The duration of the automated plan generation was registered. The best IMRT-AP and VMAT-AP for each patient were selected based on target coverage and dose to organs at risk (OARs). The AP quality was analyzed and compared to corresponding clinically accepted and manually generated VMAT plans (MPs) using several clinically relevant dose metrics. Calculation-based pre-treatment plan quality assurance (QA) was performed for all plans. The median total duration to generate the five APs with the aTPS was 55min, 39min and 35min for anal, prostate and rectal plans, respectively. The target coverage and the OAR sparing were equivalent for IMRT-APs and VMAT-MPs, while VMAT-Aps.demonstrated lower target dose homogeneity and higher dose to some OARs. Both conformity and homogeneity index were equivalent (rectal) or better (anal and prostate) for IMRT-APs compared to VMAT-MPs. All plans passed the patient-specific QA tolerance limit. The aTPS generates plans comparable to MPs within a short time-frame which is highly relevant for oART treatments.

Does CyberKnife improve dose distribution versus IMRT and VMAT on a linear accelerator in low-risk prostate cancer?

BackgroundHypofractionated stereotactic body radiation therapy (SBRT) for prostate cancer (PCa) can be delivered with the robot-assisted CyberKnife (CK) system or on a linear accelerator using dynamic intensity-modulated radiotherapy (IMRT) or volumetric arc radiotherapy (VMAT). This retrospective study was performed to determine whether CK offers better dose distribution than IMRT and/or VMAT.Materials and methodsTreatment plans for three techniques were prepared using the same treatment parameters (36.35 Gy, 7.25 Gy/fr). We evaluated target coverage, conformity index (CI), homogeneity index (HI), gamma index (GI), and organs at risk (OAR) constraints.ResultsThe mean planning target volume (PTV) dose for CK (39.58 Gy) was significantly greater than VMAT or IMRT (both 36.25 Gy). However, CK resulted in a wider dose range (31.48 to 45.89 Gy) vs. VMAT and IMRT (34.6–38.76 Gy). The mean dose to the rectum (V36Gy, mm3) was significantly lower (p < 0.001) in the CK plans (219.78 vs. 519.59 and 422.62, respectively). The mean bladder dose (V37Gy, mm3) was significantly greater for CK (3256 vs. 1090.75 for VMAT and 4.5 for IMRT (p < 0.001). CK yielded significantly better CI (1.07 vs. 1.17 and 1.25 for VMAT and IMRT, respectively; p < 0.01) and HI values (1.27 vs. 1.07 and 1.04; p < 0.01). GI values for the δd = 3mm, δ% = 3% criteria were 99.86 (VMAT), 99.07 (IMRT) and 99.99 (CK). For δd = 2mm, δ% = 2%, the corresponding values were 98.3, 93.35, and 97.12, respectively.ConclusionsFor most variables, CK was superior to both VMAT and IMRT. However, dynamic IMRT techniques, especially VMAT, do not differ significantly from CK plans and are therefore acceptable alternatives to CyberKnife.

Treatment Results and Dosimetric Comparison of Synchronous Bilateral Breast Cancer with Helical Tomotherapy and Volumetric-Modulated Arc Radiotherapy

Treatment Results and Dosimetric Comparison of Synchronous Bilateral Breast Cancer with Helical Tomotherapy and Volumetric-Modulated Arc Radiotherapy

Normal Lung Tissue CT Density Changes after Volumetric-Arc Radiotherapy (VMAT) for Lung Cancer.

Radiation-induced lung injury remains a significant toxicity in thoracic radiotherapy. Because a precise diagnosis is difficult and commonly used assessment scales are unclear and subjective, there is a need to establish quantitative and sensitive grading methods. The lung tissue density change expressed in Hounsfield units (HUs) derived from CT scans seems a useful numeric surrogate. The study aimed to confirm a dose-response effect on HU value changes (ΔHU), their evolution in time, and the impact of selected clinical and demographic factors. We used dedicated, self-developed software to register and analyze 120 pairs of initial and follow-up CT scans of 47 lung cancer patients treated with dynamic arc radiotherapy. The differences in HU values between CT scans were calculated within discretized dose-bins limited by isodose lines. We have proved the dose-effect relationship, which is well described with a sigmoid model. We found the time evolution of HU changes to suit a typical clinical presentation of radiation-induced toxicity. Some clinical factors were found to correlate with ΔHU degree: planning target volume (PTV), V35 in the lung, patient’s age and a history of arterial hypertension, and initial lung ventilation intensity. Lung density change assessment turned out to be a sensitive and valuable method of grading post-RT lung toxicity.

Research on Low-Voltage AC Series Arc-Fault Detection Method Based on Electromagnetic Radiation Characteristics

Arc fault is an important cause of electrical fire. At present, the arc-fault detection method based on current and voltage is vulnerable to the influence of a nonlinear load and switching operation in the line, resulting in misjudgment and omission. Therefore, an arc-fault detection method based on the characteristics of electromagnetic radiation is proposed. A low-voltage AC series arc-fault simulation platform is built, and a simple annular antenna is designed to receive an electromagnetic radiation signal. It is proved by experiments that electromagnetic radiation signals have similar characteristic frequencies (13.6–14.2 MHz) under different currents, loads, arc positions and arc occurrence times. At the same time, the electromagnetic radiation signal of a low-voltage AC series arc and normal switching operations are compared. The pulse oscillation time of the radiation signals of the operating arc (2 μs) is far shorter than that of the faulty arc (4 μs), and the characteristic frequency of the radiation signal generated by the switching operation (9.35 MHz) is significantly lower than that of the series arc radiation signal (14 MHz). Compared with the existing methods, this method does not need to consider the influence of current, nonlinear load and other factors in the line, and can accurately distinguish the operating arc and faulty arc.

Planning evaluation of a novel volume-based algorithm for personalized optimization of lung dose in VMAT for esophageal cancer

Radiotherapy treatment planning (RTP) is time-consuming and labor-intensive since medical physicists must devise treatment plans carefully to reduce damage to tissues and organs for patients. Previously, we proposed the volume-based algorithm (VBA) method, providing optimal partial arcs (OPA) angle to achieve the low-dose volume of lungs in dynamic arc radiotherapy. This study aimed to implement the VBA for esophageal cancer (EC) patients and compare the lung dose and delivery time between full arcs (FA) without using VBA and OPA angle using VBA in volumetric modulated arc therapy (VMAT) plans. We retrospectively included 30 patients diagnosed with EC. RTP of each patient was replanned to 4 VMAT plans, including FA plans without (FA-C) and with (FA + C) dose constraints of OARs and OPA plans without (OPA-C) and with (OPA + C) dose constraints of OARs. The prescribed dose was 45 Gy. The OARs included the lungs, heart, and spinal cord. The dose distribution, dose-volume histogram, monitor units (MUs), delivery time, and gamma passing rates were analyzed. The results showed that the lung V5 and V10 in OPA + C plans were significantly lower than in FA + C plans (p < 0.05). No significant differences were noted in planning target volume (PTV) coverage, lung V15, lung V20, mean lung dose, heart V30, heart V40, mean heart dose, and maximal spinal cord dose between FA + C and OPA + C plans. The delivery time was significantly longer in FA + C plans than in OPA + C plans (237 vs. 192 s, p < 0.05). There were no significant differences between FA + C and OPA + C plans in gamma passing rates. We successfully applied the OPA angle based on the VBA to clinical EC patients and simplified the arc angle selection in RTP. The VBA could provide a personalized OPA angle for each patient and effectively reduce lung V5, V10, and delivery time in VMAT.

Evaluation of Conformity and Homogeneity Indices Consistency Throughout the Course of Head and Neck Cancer Treatment With and Without Using Adaptive Volumetric Modulated Arc Radiation Therapy

PurposeConformity indices (CI) and homogeneity indices (HI) are important tools for evaluating treatment plan quality. In this study, we evaluate the consistency of these indices with respect to anatomic changes undergone by patients. Methods and MaterialsFifty-five patients with advanced head and neck cancer were treated with simultaneous integrated boost volumetric modulated arc therapy. The initial plan (iplan) then was projected on the new computed tomographs (CT) and 2 adaptive plans (Aplans) for each patient were performed on the new CTs. A comparison of CI and HI between the iplan, hybrid plan (Hplan), and Aplan was performed. ResultsThere was a significant weight loss (P < .001) between CT1, CT2, and CT3, where the median weight at CT1 was 75.78 (68.95-83.42) kg, and 74.88 (68.35-82.2) kg at CT2 and 73.1 (67.6-80.7) kg at CT3. Also, gross tumor volume (GTV) showed significant decrease at CT1, CT2, and CT3. The initial GTV was 32.3 (21-58.6) cc and 28.24 (15.85-48.63) cc at CT2 and 25.12 (14.1-42.2) at CT3. In addition, there was a significant decrease in left parotid volume after 10 and 20 fractions; the median left parotid gland volume at CT1 was 31.04 (26.34-36.27) cc, then was 25.84 (19.19-28.59) cc after 10 fractions and 19.5 (13.53-22.25) cc after 20 fractions; the median right parotid volume at CT1 was 29.81 (24.6-38.75) cc and 22.38 (18.19-30.12) cc at CT2, then the volume fell to 17.74 (13.41-22.66) cc at CT3. Also, a significant increase in dose to organs at risk were noticed at Hplans, the median dose for brain stem at iplan was 5156 (4561-5324) cGy then increased to 5321 (4688-5545) cGy at Hplan1 then increased again to reach 5401 (4821-5812) cGy at Hplan2. The CI showed regression at Hplan1 and Hplan2 and then improvement at Aplan1 and Aplan2. The HI also showed regression in its value at the Hplans and then improved at the Aplans. ConclusionsBased on the results, we conclude that anatomic changes such as weight loss greatly affect the quality of plan, and with Aplans, we maintained the quality of plan by sustaining the values of CI and HI as in the iplan

Dosimetric evaluation of photons versus protons in postmastectomy planning for ultrahypofractionated breast radiotherapy

BackgroundUltrahypofractionation can shorten the irradiation period. This study is the first dosimetric investigation comparing ultrahypofractionation using volumetric arc radiation therapy (VMAT) and intensity-modulated proton radiation therapy (IMPT) techniques in postmastectomy treatment planning.Materials and methodsTwenty postmastectomy patients (10-left and 10-right sided) were replanned with both VMAT and IMPT techniques. There were four scenarios: left chest wall, left chest wall including regional nodes, right chest wall, and right chest wall including regional nodes. The prescribed dose was 26 Gy(RBE) in 5 fractions. For VMAT, a 1-cm bolus was added for 2 in 5 fractions. For IMPT, robust optimization was performed on the CTV structure with a 3-mm setup uncertainty and a 3.5% range uncertainty. This study aimed to compare the dosimetric parameters of the PTV, ipsilateral lung, contralateral lung, heart, skin, esophageal, and thyroid doses.ResultsThe PTV-D95 was kept above 24.7 Gy(RBE) in both VMAT and IMPT plans. The ipsilateral lung mean dose of the IMPT plans was comparable to that of the VMAT plans. In three of four scenarios, the V5 of the ipsilateral lung in IMPT plans was lower than in VMAT plans. The Dmean and V5 of heart dose were reduced by a factor of 4 in the IMPT plans of the left side. For the right side, the Dmean of the heart was less than 1 Gy(RBE) for IMPT, while the VMAT delivered approximately 3 Gy(RBE). The IMPT plans showed a significantly higher skin dose owing to the lack of a skin-sparing effect in the proton beam. The IMPT plans provided lower esophageal and thyroid mean dose.ConclusionDespite the higher skin dose with the proton plan, IMPT significantly reduced the dose to adjacent organs at risk, which might translate into the reduction of late toxicities when compared with the photon plan.

Clinical Implementation of Robust Multi-isocentric Volumetric Modulated Arc Radiotherapy for Craniospinal Irradiation

AimsTo determine if multi-isocentric volumetric modulated arc radiotherapy for craniospinal irradiation (CSI-VMAT) can be implemented safely and accurately using robust optimisation in a commercially available treatment planning system. Our initial clinical experience is reported for the first 20 patients treated with the technique. Materials and methodsPatients received between 23.4 and 39.6 Gy (mode 23.4 Gy) in 13–22 fractions with CSI-VMAT. The heart mean dose was 4.2–10.3 Gy (median 5.3 Gy) for patients prescribed up to 24 Gy and 6.5–16.3 Gy (median 10.1 Gy) for patients receiving 35 Gy or more. The lung mean dose was 5.5–7.6 Gy (median 6.8 Gy) for patients prescribed up to 24 Gy and 6.9–11.1 Gy (median 10.0 Gy) for patients receiving 35 Gy or more. The robustness of the planning target volume D0.1cm3 and D99% to systematic errors in the isocentre superoinferior position of up to 5 mm was evaluated. These remained acceptable but were correlated to the length of the available beam overlap through the neck. ResultsAs of January 2021, one patient was deceased after 508 days and one patient was lost to follow-up after completing treatment. The median follow-up was 399 days (range 175–756 days) and progression-free survival was 131 days (34–490 days). Acute toxicities at Common Terminology Criteria for Adverse Events v5.0 grade 3+ included lowered white blood cell count (16/20), decreased platelet count (8/20), nausea (5/20), vomiting (2/20), pharyngeal mucositis (1/20) and oral mucositis (1/20). Three patients developed grade 4 neutropenia or decreased white blood cell count. ConclusionsCSI-VMAT can be implemented safely and accurately using robust optimisation functions in a commercially available treatment planning system.

Evaluation of plan robustness on the dosimetry of volumetric arc radiotherapy (VMAT) with set-up uncertainty in Nasopharyngeal carcinoma (NPC) radiotherapy

PurposeTo evaluate the sensitivity to set up the uncertainty of VMAT plans in Nasopharyngeal carcinoma (NPC) treatment by proposing a plan robustness evaluation method.Methods10 patients were selected for this study. A 2-arc volumetric-modulated arc therapy (VMAT) plan was generated for each patient using Varian Eclipse (13.6 Version) treatment planning system (TPS). 5 uncertainty plans (U-plans) were recalculated based on the first 5 times set-up errors acquired from cone-beam computer tomography (CBCT). The dose differences of the original plan and perturbed plan corresponded to the plan robustness for the structure. Tumor control probability (TCP) and normal tissues complication probability (NTCP) were calculated for biological evaluation.ResultsThe mean dose differences of D98% and D95% (ΔD98% and ΔD95%) of PTVp were respectively 3.30 Gy and 2.02 Gy. The ΔD98% and ΔD95% of CTVp were 1.12 Gy and 0.58 Gy. The ΔD98% and ΔD95% of CTVn were 1.39 Gy and 1.03 Gy, distinctively lower than those in PTVn (2.8 Gy and 2.0 Gy). The CTV-to-PTV margin increased the robustness of CTVs. The ΔD98% and ΔD95% of GTVp were 0.56 Gy and 0.33 Gy. GTVn exhibited strong robustness with little variation of D98% (0.64 Gy) and D95% (0.39 Gy). No marked mean dose variations of Dmean were seen. The mean reduction of TCP (ΔTCP) in GTVp and CTVp were respectively 0.4% and 0.3%. The mean ΔTCPs of GTVn and CTVn were 0.92% and 1.3% respectively. The CTV exhibited the largest ΔTCP (2.2%). In OARs, the brain stem exhibited weak robustness due to their locations in the vicinity of PTV. Bilateral parotid glands were sensitive to set-up uncertainty with a mean reduction of NTCP (ΔNTCP) of 6.17% (left) and 7.70% (right). The Dmax of optical nerves and lens varied slightly.ConclusionVMAT plans had a strong sensitivity to set-up uncertainty in NPC radiotherapy, with increasing risk of underdose of tumor and overdose of vicinal OARs. We proposed an effective method to evaluate the plan robustness of VMAT plans. Plan robustness and complexity should be taken into account in photon radiotherapy.

Statistical analysis of correlation of gamma passing results for two quality assurance phantoms used for patient-specific quality assurance in volumetric modulated arc radiotherapy.

Patient-specific quality assurance (QA) data must be migrated from outdated QA systems to new ones to produce objective results that can be understood by oncologists. We aimed to evaluate a method for obtaining a high correlation of dose distributions according to various gamma passing rates among two types of 2D detectors for the migration of patient-specific QA data of volumetric modulated arc therapy (VMAT). The patient-specific QA of 20 patients undergoing VMAT was measured in two different modes: standard single measurement (SM) mode and multiple merged measurements (MM) techniques using ArcCHECK (AC) and OCTAVIUS (OT). The correlation of the measured and calculated dose distributions was evaluated according to varying gamma passing rates (3%/3 mm, 2%/3 mm, 2%/2 mm, and 1%/1 mm). The gamma passing rates were analyzed using the Anderson-Darling normality test. Treatment plan dose distributions were calculated by intentionally shifting the calculation isocenter position (x,y,z ± 0.5, ± 1.0, ± 1.5, and ± 2.0 mm). The highest correlation between the SM and MM was observed with a gamma passing rate of 1%/1 mm with AC (r = 0.866) and 3%/2 mm with OT (r = 0.916). However, SM and MM did not follow a normal distribution with a rate of 3%/2 mm in OT. The second-highest correlation was obtained with a rate of 2%/2 mm (r = 0.900). Among the two 2D detectors, the highest correlation between the calculated and measured dose distributions was obtained for a gamma passing rate of 1%/1 mm using SM in AC and 2%/2 mm using MM in OT (r = 0.716). Adjusting the gamma passing rate and measurement mode of AC and OT resulted in higher correlations between measured and calculated dose distributions. The high correlation between different 2D detectors objectively indicated a potential migration method. This enabled the sharing of more accurate patient-specific QA data from 2D detectors with different phantoms. A high correlation was observed between the two types of detectors in this study (r = 0.716); therefore, the proposed method should be useful for oncologists to share information regarding patient-specific QA for VMAT.

The impact of volumetric modulated arc radiotherapy on clinical outcomes of patients with gynecological malignancies

Introduction. In locally advanced cancers of the cervix, endometrium and vulva, radiotherapy is the primary treatment modality. In recent years, new modern techniques of external radiation have been developed in radiation oncology, with the goal of dose escalation to the target volume, while sparing healthy tissues. The aim of this study is to determine the impact of volumetric modulated arc therapy on clinical outcomes of patients with gynecological malignancies. Material and Methods. Data were retrospectively collected from 60 patients treated for International Federation of Gynecology and Obstetrics stage I - III cervical, endometrial and vulvar cancers, using definitive (n = 35) or adjuvant (n = 25) radiotherapy/ chemoradiotherapy. Thirty patients underwent three-dimensional conformal radiation therapy (definitive in 22 and adjuvant in 8) and the other 30 patients were treated with volumetric modulated arc therapy (definitive in 13 and adjuvant in 17). The following clinical outcome parameters were compared between the two groups: complete clinical response, disease free survival, progression free survival, and 4-year overall survival. Results. Progression free survival of patients treated with definitive radiotherapy/ chemoradiotherapy using volumetric modulated arc therapy was 17.2 months, while in the group treated with three-dimensional conformal radiation therapy it was 7.9 months (p = 0.300). Four-year overall survival in patients who were treated with definitive radiotherapy/ chemoradiotherapy using three-dimensional conformal radiation therapy was 50%, and 61.5% in the group treated with definitive volumetric modulated arc therapy (p = 0.200), while in patients treated using adjuvant radiotherapy/chemoradiotherapy it was 75% vs. 88.2%, respectively (p = 0.400). Conclusion. Although without statistical significance, volumetric modulated arc therapy showed better results with respect to progression free survival and 4-year overall survival in previously unoperated patients who underwent definitive radiotherapy/chemoradiotherapy.

Flattening Filter-Free Volumetric-Modulated Arc Radiotherapy for Left-Sided Whole-Breast, Partial-Breast, and Postmastectomy Irradiations.

Purpose:Unflattened photon beams exhibit many benefits over traditional flattened beams for radiotherapy (RT), but comprehensive evaluations of dosimetric results and beam-on time using flattening filter-free (FFF) beams for all types of breast irradiations are still lacking. The purpose of this study was to investigate if FFF RT can maintain equal or better dose coverage than standard flattened-beam RT while reducing doses to organs at risk (OARs) and beam-on time for various types of breast cancer irradiations.Methods and Materials:FFF volumetric-modulated arc therapy (FFF-VMAT) and standard VMAT (STD-VMAT) treatment plans were created for 15 whole-breast irradiation (WBI) patients with 50 Gy/25 fractions, 13 partial-breast irradiation (PBI) patients with 38.5 Gy/10 fractions, and 9 postmastectomy irradiation (PMI) patients with 50 Gy/25 fractions. Planning target volume (PTV) coverage and dose to OARs were evaluated.Results:Both techniques produced clinically acceptable plans for all three types of irradiations. For WBI, FFF-VMAT plans exhibited similar PTV and OARs evaluation metrics as STD-VMAT. For PBI, FFF-VMAT plans showed significantly lower mean and maximum doses for ipsilateral and contralateral lungs, contralateral breast, and heart. For PMI, FFF-VMAT plans showed significantly lower mean dose and V5 for contralateral breast but significantly higher Dmean, Dmax, and V20 for ipsilateral lung and significantly higher Dmean, V22.5, and V30 for heart. FFF-VMAT techniques significantly reduced beam-on time than STD-VMAT for all cases.Conclusion:This work has shown that FFF beams are most beneficial for small-field irradiation such as PBI, and breast cancer patients could potentially benefit from the shortened beam-on time.