Dosimetric risk factors for radiation esophagitis in patients with breast cancer following regional nodal radiation

BACKGROUND Radiation esophagitis(RE)is one of the most common clinical symptoms of regional lymph node radiotherapy for breast cancer.However,there are fewer studies focusing on RE caused by hypofractionated radiotherapy(HFRT).AIM To analyze the clinical and dosimetric factors that contribute to the development of RE in patients with breast cancer treated with HFRT of regional lymph nodes.METHODS Between January and December 2022,we retrospectively analysed 64 patients with breast cancer who met our inclusion criteria underwent regional nodal intensity-modulated radiotherapy at a radiotherapy dose of 43.5 Gy/15F.RESULTS Of the 64 patients in this study,24(37.5%)did not develop RE,29(45.3%)developed grade 1 RE(G1RE),11(17.2%)developed grade 2 RE(G2RE),and none developed grade 3 RE or higher.Our univariable logistic regression analysis found G2RE to be significantly correlated with the maximum dose,mean dose,relative volume 20-40,and absolute volume(AV)20-40.Our stepwise linear regression analyses found AV30 and AV35 to be significantly associated with G2RE(P<0.001).The optimal threshold for AV30 was 2.39 mL[area under the curve(AUC):0.996;sensitivity:90.9%;specificity:91.1%].The optimal threshold for AV35 was 0.71 mL(AUC:0.932;sensitivity:90.9%;specificity:83.9%).CONCLUSION AV30 and AV35 were significantly associated with G2RE.The thresholds for AV30 and AV35 should be limited to 2.39 mL and 0.71 mL,respectively.

Effects of dosimetric inadequacy on local control and toxicities in the patients with T4 nasopharyngeal carcinoma extending into the intracranial space and treated with intensity.modulated radiotherapy plus chemotherapy

Background:To protect neurological tissues,underdosing occurs in most cases of T4 nasopharyngeal carcinoma(NPC) with intracranial extension.In this study,we aimed to evaluate the effect of dosimetric inadequacy on local control and late neurological toxicities for patients treated with intensity-modulated radiotherapy(IMRT) plus chemotherapy.Methods:We prospectively enrolled patients who had non-metastaticT4 NPC with intracranial extension treated between January 2009 and November 2013.The prescribed dose was 66.0-70.4 Gy to the primary planning target volume(primary gross tumor volume [GTVp;i.e.,the nasopharyngeal tumor] +5.0 mm).Dose-volume histogram parameters were calculated,including minimum point dose(D_(min)) and dose to 95% of the target volume(D95).All patients received chemotherapy with the cisplatin,5-fluorouracil,and docetaxel regimen.Survivals were estimated using the Kaplan-Meier method and compared using the log-rank test.Results:In total,41 patients were enrolled.The local partial response rate was 87.8% after induction chemotherapy.With a median follow-up of 51 months,7 patients experienced failure in the nasopharynx;the 3-year local failure-free survival and overall survival rates of the 41 patients were 87.4% and 90.2%,respectively.The actual mean D_(min) to the GTVp was 55.2 Gy(range 48.3-67.3 Gy),and D95 was 61.6 Gy(range 52.6-69.0 Gy).All doses received by neurological organs remained well within their dose constraints.No patients developed temporal lobe necrosis or other neurological dysfunctions.Conclusions:With relative underdosed IMRT plus effective chemotherapy,the patients achieved satisfactory local control with few late toxicities of the central nervous system.Determining the acceptable extent of dosimetric inadequacy requires further exploration.

An anthropomorphic phantom study of effect of lung tumor size and location on dosimetric parameters

Objective： The aim of the study was to study the effect of the size and location of tumors on the normal lung dose-volume parameters for lung cancer. Methods： Three spheres with diameters of 2, 3 and 4 cm made of tissue-equivalent materials used for simulating tumors were inserted into the upper lobe, middle lobe, lower lobe of the right lung, upper lobe, lower lobe of the left lung of the Rando phantom, respectively. Five-field simplified IMRT （slMRT） planning were designed. The prescribed dose was 60 Gy/2 Gy/30 f, 99% of the planning target volume received this dose. Dose-volume parameters of normal lung tissues including relative volume of lung receiving 〉 5, 10, 20, 30 and 50 Gy （V5, Vl0, V2o, V30, V50）, and mean lung dose （MLD） were analyzed and compared. Results： For the dose-volume parameters, the diameter and the position of the tumor had a significant effect （P 〈 0.05）. With the diameter expanding from 2 to 3 cm, the parameters associated with tumor lying in various lobes increased by a range between 3.83%-125.38%, while the parameters linked with tumors on different lobes increased by a range between 10.46%-51.46% with the diameter expanding from 3 to 4 cm. Conclusion： Location and size of sphere-like tumor have an obvious effect on dose-volume parameters. Knowing about the degree of influence will help oncologists and physicists better evaluate treatment planning, then the probability of radiation pneumonitis can be reduced.

Determination of water equivalent ratio for some dosimetric materials in proton therapy using MNCPX simulation tool

The water equivalent ratio(WER) was calculated for polypropylene(PP), paraffin, polyethylene(PE), polystyrene(PS), polymethyl methacrylate(PMMA), and polycarbonate materials with potential applications in dosimetry and medical physics. This was performed using the Monte Carlo simulation code, MCNPX, at different proton energies. The calculated WER values were compared with National Institute of Standards and Technology(NIST) data, available experimental and analytical results,as well as the FLUKA, SRIM, and SEICS codes. PP and PMMA were associated with the minimum and maximum WER values, respectively. Good agreement was observed between the MCNPX and NIST data. The biggest difference was 0.71% for PS at 150 MeV proton energy. In addition, a relatively large positive correlation between the WER values and the electron density of the dosimetric materials was observed. Finally, it was noted that PE presented the most analogous Depth Dose Characteristics to liquid water.

Dosimetric Comparison between Three Dimensional Conformal Radiation Therapy (3DCRT) &Intensity Modulated Radiation Therapy (IMRT) in Mid-Lower Oesophageal Carcinoma

Purpose: To investigate if intensity modulated radiation therapy (IMRT) offers a better planning target volume (PTV) coverage and/or lower dose to normal thoracic structures in comparison to three dimensional conformal radiation therapy (3DCRT) in the treatment of mid and lower oesophageal carcinoma patients. Materials and Methods: A prospective study in the period from 2014 till 2015 was held in the radiation therapy department of the National Cancer Institute, Cairo University, in which 20 locally advanced or inoperable mid and lower oesophageal cancer patients were treated by chemo-radiation using 3DCRT technique. IMRT plans were generated for those 20 patients. The 3DCRT and IMRT plans were compared as regards PTV coverage and doses to critical organs at risk. Results: All plans had produced satisfactory PTV coverage with no significant differences noted. The lung V20 for both lungs in 3DCRT was 16.94% ± 4.2% which was increased to 21.42% ± 3.6% in IMRT (p = 0.017). The mean dose to the heart and V30 were higher in IMRT plans while the mean dose to the spinal cord was higher with 3DCRT plans, yet that didn’t reach a statistically significant level (p = 0.156). The dose delivered to the liver didn’t pose any difference between both techniques. Conclusion: 3DCRT remains to be a feasible cost effective treatment delivery option for mid and lower oesophageal cancer cases with a lower optimization and delivery time than that for IMRT. Moreover, that calls for further dosimetric studies and clinical trials to assess IMRT technique. In our study, IMRT using nine fields didn’t prove to be superior to 3DCRT.

Evaluation of Dosimetric Performance and Global Uncertainty of the Harshaw 6600 Plus System Used to Staff Monitoring in Côte d’Ivoire

The objective of this work is to check the dosimetric performances of the TLD-100 as stated by the manufacturer as well as the technical standards of radiation protection. The purpose of the performance audit is to assess the inhomogeneity of TLD sensitivity, repeatability and reproducibility, linearity, energy dependence, angular dependence, and fading. All tests were performed under the conditions of ambient temperature and relative humidity recommended by the manufacturer. We began the study by calibrating the Harshaw 6600 Plus, and checking its performance. The TLD-100 performance verification results were all acceptable and in accordance with the manufacturer’s advertised values and the radiation protection technical standards. However the performance of the TLD-100 that we have evaluated may have some limitations;these limits, which are sources of uncertainty, have been taken into account in this work by evaluating the overall uncertainty of the Hp (10) dose in the uncertainty range 9.45% to 15.80% by simple formulas. The TLD-100 personal dosimeters and the 6600 Plus reader system indicate that the calculated values of the overall uncertainty Hp (10) are well below the allowable values of 21% to 42% suggested for personal dosimetry services. The obtained data encourage the use of the system for the routine evaluation of the external exposure of workers under ionizing radiation in our laboratory.

Dosimetric and Efficiency Comparisons between Volumetric Modulated Arc Therapy and IMRT for Cervical-Thoracic Esophageal Cancers

Purpose: This study aims to evaluate the treatment plans of Volumetric-modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT) techniques for cervical-thoracic esophageal cancers. Methods and Materials: Sixty patients were retrospectively identified. Several parameters were evaluated based on target conformity and dose-volume histograms of organs at risk (lung, spinal cord, and heart). A phantom for time comparison was also assessed for each plan. Results: The IMRT plans (5f-IMRT: V95% = 99.4 ± 0.3, 7f-IMRT: V95% = 99.8 ± 0.1) results in better PTV coverage than RA plans (Single-arc: V95% = 95.8 ± 3.2, Double-arc: V95% = 95.4 ± 2.3). The target dose conformity of the 5f-IMRT plan was inferior to all plans (CI = 70.4 ± 7.1). The Single-arc plan achieved the best conformity (CI = 72.5 ± 4.6), whereas the Double-arc plan (CI = 72.1 ± 5.1) was slightly inferior to the Single-arc plan but superior to the 7f-IMRT plan (CI = 71.7 ± 8.6). The total MU was reduced by 42.1% in VMAT plan. The average MU needed to deliver the dose of 60 Gy for Single-arc (423.5 ± 52.1 MU) was found to be the least. Similarly, the average MU for the 5f-IMRT, 7f-IMRT and Double-arc were 868.2 ± 182.0 MU, 870.0 ± 225.3 MU and 548.8 ± 47.2 MU, respectively. The delivery time in VMAT plans was reduced from 193.8 seconds to 99.2 seconds by around 48.8% compared to IMRT plans. Conclusion: For similar PTV parameters, VMAT delivers a lower dose to organs at risk than IMRT in a shorter time, and this has warranted clinical implementation.

A dosimetric comparison between 3D-Conformal radiation therapy and intensity modulated radiation therapy plans in the treatment of posterior fossa boost in children with high risk medulloblastom

Objective： The work is a comparative study between two modalities of radiation therapy, the aim of which is to compare 3D conformal radiation therapy （3D-CRT） and intensity modulated radiation therapy （IMRT） in treating posterior fossa boost in children with high risk medulloblastorna; dosimetrically evaluating and comparing both techniques as regard target coverage and doses to organs at risk （OAR）. Methods： Twenty patients with high risk medulloblastoma were treated by 3D-CRT technique. A dosimetric comparison was done by performing two plans for the posterior fossa boost, 3D-CRT and IMRT plans, for the same patient using Eclipse planning system （version 8.6）. Results： IMRT had a better conformity index compared to 3D-CRT plans （P value of 0.000）. As for the dose homogeneity it was also better in the IMRT plans, yet it hasn＇t reached the statistical significant value. Also, doses received by the cochleae, brainstem and spinal cord were significantly less in the IMRT plans than those of 3D-CRT （P value 〈 0.05）. Conclusion： IMRT technique was clearly able to improve conformity and homogeneity index, spare the cochleae, reduce dose to the brainstem and spinal cord in comparison to 3D- CRT technique.

Clinical performance evaluation of O-Ring Halcyon Linac:A realworld study

BACKGROUND Radiation therapy,especially the development of linear accelerators,plays a key role in cancer management.The fast-rotating coplanar O-ring Halcyon Linac has demonstrated many advantages.The previous literature has mainly focused on the machine parameters and plan quality of Halcyon,with a lack of relevant research on its clinical application.AIM To evaluate the clinical performance of the O-ring Halcyon treatment system in a real-world application setting.METHODS Data from sixty-one patients who were treated with the Halcyon system throughout the entire radiotherapy process in Peking Union Medical College Hospital between August 2019 and September 2020 were retrospectively reviewed.We evaluated the target tumour response to radiotherapy and irradiation toxicity from 1 to 3 mo after treatment.Dosimetric verification of Halcyon plans was performed using a quality assurance procedure,including portal dosimetry,ArcCHECK and point dose measurements for verification of the system delivery accuracy.RESULTS Of the 61 patients in the five groups,16,12,7 and 26 patients had complete response,partial response,progressive disease and stable disease,respectively.No increase in the irradiated target tumour volume was observed when separately evaluating the local response.Regarding irradiation toxicity,no radiation-induced deaths were observed.Thirty-eight percent(23/61 patients)had no radiation toxicity after radiotherapy,56%(34/61 patients)experienced radiation toxicity that resolved after treatment,and 6%(4/61 patients)had irreversible adverse reactions.The average gamma passing rates with a 2%dose difference and 2-mm distance to agreement for IMRT/VMAT/SRT plans were ArcCHECK at 96.4%and portal dosimetry at 96.7%,respectively.All of the validated clinical plans were within 3%for point dose measurements,and Halcyon’s ArcCHECK demonstrated a high pass rate of 99.1%±1.1%for clinical gamma passing criteria of 3%/3 mm.CONCLUSION The O-ring Halcyon Linac could achieve a better therapeutic effect on the target volume by providing accurate treatment delivery plans with tolerable irradiation toxicity.

Comparative Dosimetric Study for Treating Left Sided Breast Cancer Using Three Different Radiotherapy Techniques:Tangential Wedged Fields, Forward Planned Segmented Filed, and IP-IMRT

Background: Radiation therapy should not only be directed to improve the local control, which has a survival benefit, but also should be directed to minimize the risk of complications, which may develop in critical organs. Several studies have reported that field-in-field (FiF) radiotherapy technique improves the dose homogeneity, decreases doses to lungs, heart and contralateral breast compared with conventional wedged technique. Purpose: compare the dosimetry for the left breast cancer radiotherapy using three different radiotherapy techniques, tangential wedged fields (TW), segmented field (FiF) and inverse planning IMRT (IP-IMRT). Material and Methods: Twenty patients have undergone left breast-conservative surgery and received a prescribed dose of 50 Gy/25 fractions. Results: The mean PTV receiving >105% (V105) dose was1.75% for IP-IMRT, 2.03% for FiF, and 4.82% for TW. The mean V95% was 92.1% for TW, 96% for FiF, and 95.1% for IP-IMRT;these differences regarding V105% and V95% are statistically significant through paired comparison between FiF vs TW and IP-IMRT vs TW, with no statistically significant difference between FiF and IP-IMRT. Better conformity and homogeneity indices for FiF and IMRT compared to TW with statistical significant difference. Regarding organs at risk, left lung and heart have higher values of V5, V10, and V20 for IP-IMRT compared to TW and FiF;the differences are statistically significant, lower coronary artery regionV30 vules for IPIMRT compared to TW and FiF but no difference in the Dmean between IPIMRT and FIF. FiF and TW decrease the contralateral breast dose significantly compared to IP IMRT. Conclusion: FiF technique is an efficient and reliable method for achieving a uniform dose throughout the whole breast resulting in improved coverage, sparing of organs at risk and reduction of acute and late toxicities.

Imaging and Dosimetric Consideration for Titanium Prosthesis Implanted within the Irradiated Region by Cobalt-60 Teletherapy Unit

The aim of this research is to observe dose distributions in the vicinity of titanium prosthetic implants during radiotherapy procedures on 60Co teletherapy machine, Prowess Panther treatment planning system (TPS). Data were obtained using a locally fabricated tissue equivalent phantom CT images with titanium prosthesis which was irradiated with 60Co gamma radiation. Prowess TPS (1.25 MeV) estimated less variations. Proximal ends of the metal recorded slight increase in doses as a result of backscatter with dose increment below acceptable tolerance of ±3%. Doses measured decreases on the distal side of the prosthesis at a distance less than dmax from the plate on each beam energy. The depth dose increases marginally after a certain depth level which generally originated from the unperturbed dose due to increase in the electron fluence. The percentage of depth doses decrease with the increase in plate thickness. A reduction in the above trend was also noticed with an increase in beam energy primarily because scattered photons are more forwardly directed. Prowess TPS (convolution superposition algorithm) was found to be better at reducing dose variation when correction for artifact. Manual calculations on blue phantom data agree with results from Prowess. This treatment system is capable of simulating dose around titanium prosthesis as its range of densities, 0.00121 to 2.83, excludes titanium density (rED for titanium is 3.74).

The Effect of Treatment Position on Rectal and Bladder Dose-Volume Histograms for Prostate Radiotherapy Planned with 3-Dimensional Conformal Radiotherapy, Intensity-Modulated Radiotherapy and Volumetric Modulated Arc Therapy

Purpose: To compare target coverage and organ at risk (OAR) sparing in the supine and prone positions with 3-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) in low- and high-risk prostate radiotherapy cases. Materials and Methods: Using magnetic resonance images of five healthy volunteers, six treatment plans (supine 3DCRT, prone 3DCRT, supine IMRT, prone IMRT, supine VMAT and prone VMAT) were generated. Planning target volume 1 (PTV1) was defined as the prostate gland plus the seminal vesicles with adequate margins in a high-risk setting, while PTV2 was defined as prostate only with margins in a low-risk setting. The mean dose for both PTV1 and PTV2 was set at 78 Gy. Plans generated by each of the 3 techniques were compared between the supine and prone positions using dose-volume histograms (DVHs). Results: For PTV1, prone 3DCRT provided a significantly higher D98% than did supine 3DCRT, and its homogeneity index (HI) was significantly better. IMRT and VMAT values did not differ significantly between the prone and supine positions. For PTV2, no values differed significantly between the supine and prone positions under any treatment plan. With respect to OAR, the rectal D mean, D2%, V50, and V60 values of PTV1 were statistically higher in supine 3DCRT than in prone 3DCRT, while there were no significant differences in rectal values between the supine and prone positions with IMRT or VMAT. The rectal Dmean, V50, V60, V70, and V75 values of prone 3DCRT were significantly higher than those of supine IMRT or supine VMAT. There were no significant differences in any values for the rectum and bladder for PTV2. Conclusion: Although prone 3DCRT was found to be superior to supine 3DCRT in terms of rectal sparing in high-risk prostate cancer, IMRT and VMAT techniques could possibly cover this disadvantage.

A comparative dosimetric study of 3-dimensional conformal radical radiotherapy for bladder cancer patients versus conventional 2-dimensional radical radiotherapy in NCI-Cairo, Egypt

Objective: This study was to compare this multiple-field conformal technique to the 2-dimensional (2D) conventional technique with respect to target volume coverage and dose to normal tissues. Methods: We conducted a single institutional prospective comparative dosimetric analysis of 15 patients who received radical radiation therapy for bladder cancer presented to Radiotherapy Department in National Cancer Institute, Cairo (Egypt), in period between November 2011 to July 2012 using 3-dimensional (3D) conformal radiotherapy technique for each patient, a second 2D conventional radiotherapy treatment plan was done, the two techniques were then compared using dose volume histogram (DVH) analysis. Results: Comparing different DVHs, it was found that the planning target volume (PTV) was adequately covered in both (3D & 2D) plans while it was demonstrated that this multiple field conformal technique produced superior distribution compared to 2D technique, with considerable sparing of rectum and to lesser extent for the head of both femora. Conclusion: From the present study, it is recommended to use 3D planning for cases of bladder cancer especially in elderly patients as it produces good coverage of the target volume as well as good sparing of the surrounding critical organs.

Dosimetric evaluation of a beam matching procedure

Objective: The dosimetric characteristics for linear accelerators with the same model, and nominal energy are known to be very similar, as long as the machines are unaltered from the manufacturer's original specifications. In this preliminary study, a quantitative investigation of the similarity in the basic photon and electron dosimetry data from the Siemens Oncor linear accelerators at our hospital(Children's Cancer Hospital, Cairo, Egypt) was reported. Methods: The output factor(OF), wedge factors(WF), percentage depth dose(PDD), and beam profile for the 6 and 10 MV photon beams were measured. Results: The measured output factors varied by less than about 1% for each field size. The difference between the maximum and minimum PDD values at each depth was less than about 1%. The difference between the beam flattnes and symetry was no more than 1% at all off-axis distances. For electron the results showed that the PDD, OF, and the beam profiles were matched within 1% differences. Conclusion: These results strongly suggest that it is feasible to establish one reference photon and electron dosimetry data set for the two machines and nominal energies.

Dosimetric Impact of Inter-Fraction Variation in Interstitial HDR Brachytherapy

Background: Patient setup errors in External Beam Radiotherapy (EBRT) are minimized to a great extent, due to recent technological developments but in contrary brachytherapy received least attention in inter-fraction catheter movement and its impact in dose delivery. This article deals with inter-fraction interstitial catheter movement and its impact in dose delivery to the target. An attempt is made to study the dosimetric impact of this variation. Objectives: The objective of the study is to evaluate the inter-fraction variation in the position of implanted interstitial applicators and to assess the dosimetric impact in interstitial High Dose Rate (HDR) brachytherapy. Materials and Methods: 55 patients treated for carcinoma tongue, breast, buccal mucosa, cervix, floor of mouth and soft tissue sarcoma over a period of 2 years (December 2011-May 2013) were considered. All the patients underwent CT scan on the next day of the implant and 3D planning was done either by Eclipse or Oncentra Master plan Treatment Planning System (TPS). Patients were treated by HDR brachytherapy remote after-loading units, either by Gamma Med iX plus or Microselectron. At the end of the last fraction, CT scan was repeated and re-planning done. The variation in position of the implanted applicators/catheters and its impact on dosimetric parameters were evaluated and analyzed. Results: The range of positional displacement of the interstitial catheters ranges from 4.5 mm to 6.8 mm. The maximum variation in prescribed dose to D90 of Clinical Target Volume was 10.88%. Conclusions: If the total duration of interstitial implant of HDR brachytherapy extends for more than a week from the day of imaging, it is recommended to do CT imaging and re-plan again. It is mandatory to suture the buttons of the implant to the skin. Edema and movement of organs (e.g., tongue) are the main cause for the positional variation of the catheters.

Dosimetric Analysis of Three Different Radiotherapy Techniques in Patients with Breast Cancer and Their Impact on Organs at Risk (OAR)

Aim: Dosimetric analysis of three different Radiotherapy techniques in patients with Breast Cancer and their impact on OAR’s. Materials and Methods: 12 patients of Carcinoma Breast who received breast radiotherapy were selected for analysis. Computed tomography (CT) simulation image data sets were retrieved. Planning target Volume (PTV), heart and ipsilateral lung were contoured for planning and analysis of doses. Three different plans using conventional bi-tangential fields were prepared, Plan 1 with SAD full beam with wedge (SAD-FBW), Plan 2 with SSD half beam with wedge (SSD-HBW) and plan 3 with SSD half beam without wedge techniques (SSD-HBO) in CMS Xio TPS. Statistical analysis was done using SPSS version 16.0. Results: The PTV coverage was significantly better in SAD-FBW techniques when compared with the other two techniques i.e. SSD-HBW (mean = 92.33, SD = 4.69, p = 0.005) and SSD-HBO (mean = 75.05, SD = 11.92, p = 0.002). The mean heart doses were significantly better in SAD-FBW compared to SSD-HBW (mean = 3.75, SD = 2.27, p = 0.017) but in SSD-HBO technique mean heart doses were better than SAD-FBW technique (mean = 3.27, SD = 1.94, p = 0.004). Similarly, the left lung V20 values were significantly better in SSD-HBO technique than SAD-FBW technique (mean = 11.75, SD = 4.34, p = 0.004) but there was statistically insignificant difference between the SAD-FBW and SSD-HBW techniques. The treatment monitor units were significantly less in SAD-FBW compared to SSD-HBW but SSD-HBO has less MU compared to SAD-FBW technique. Conclusion: SAD Full Beam with wedge technique is practically better than SSD Half Beam technique with or without wedge without compromising PTV coverage considering other dosimetric parameters. We also recommend that centers treating patient with half beam SSD techniques should shift immediately to SAD techniques.

Dosimetric study of field junction in adjacent beams using asymmetric collimators and MLC

Adjacent treatment fields are commonly employed in external beam radiation therapy, such as the mantle and inverted-Y fields for the treatment of Hodgkin's disease. In some cases, the adjacent fields are orthogonal, such as the craniospinal fields used in the treatment of medulloblastoma. Another example is the irradiation of head and neck tumors when the lateral neck fields are placed adjacent to the anterior supraclavicular field. In each of these situations, there is a possibility of introducing very large dosage errors across the junction. Consequently, this region is at risk for tumor recurrence if it is underdosed or severe complications if it is overdosed. Four millimeter overlap and gap resulted in an unacceptable dose in homogeneity in the junction. As a result of this study, the magnitudes of hot and cold spots might be clinically acceptable for 3 mm gap between photon fields.

An experimental inter-comparison of radiotherapic dosimetric delivery to assess X-Ray linear accelerator output characteristics

The dosimetric inter-comparison studies carry pertinent significance to ensure uniform radiation dose delivery for clinical trials. This paper investigates the comparative performance analysis of an X-ray high power linear accelerator per- formed by the International Dosimetry Survey Mission and Institute of Nuclear Medicine ＆ Oncology （INMOL）, Lahore. The measurements were made using cylindrical ionization chambers based on the International Atomic Energy Agency （IAEA） TRS-398 protocol for absorbed dose-to-water dosimetric standards, and the percentage deviation was found to be between 0.5 % - 1%. The dosimetric analysis concerning linear X-ray accelerator output performed by INMOL, Lahore was found to be in good agreement with the results of IAEA Dosimtery Survey Mission.

Investigation of Target Minimum and Maximum Dosimetric Criteria for the Evaluation of Standardized Radiotherapy Plan <br/>—Target Minimum and Maximum Evaluation

Purpose: Standardization of tumor dosimetric coverage is essential for the evaluation of radiotherapy treatment plan quality. National clinical trials network RTOG protocols include tumor target dosimetric criteria that specify the prescription dose and minimum and maximum dose (Dmin and Dmax) coverages. This study investigated the impact of various minimum and maximum dose definitions using tumor control probability (TCP) models. Methods and Materials: Three disease sites (head and neck, lung, and prostate) were studied using target volume dosimetric criteria from the RTOG 0920, 1308, and 0938 protocols. Simulated target dose-volume histograms (DVHs) of Dmin and Dmax were modeled using the protocol specifications. Published TCP models for the three disease sites were applied to the DVH curves. The effects of various dose definitions on TCP were studied. Results: While the prescription dose coverage was maintained, a -3.7% TCP difference was observed for head and neck cancer when the target doses varied by 3.5% of the tumor volume from the point dose. For prostate and lung cancers, -3.3% and -2.2% TCP differences were observed, respectively. The TCPs for head and neck and prostate cancers were more negatively affected by deviations in the Dmin than the TCP for lung cancer. The lung TCP increased to a greater extent with a change in the Dmax compared with the head and neck and prostate TCPs. Conclusions: These results can be used to evaluate plan quality when the target dose only slightly deviates from the dosimetric criteria. When the overall target prescription dose coverage is maintained, the Dmax is recommended to be within 3% of the target volume: 98% (for head and neck and prostate) and 97% (for lung) of the target volume, satisfying the Dmin needed to maintain TCP variations at less than 2.1%. Using 0.03 cc instead of a point dose for Dmin and Dmax criteria minimally impacts TCPs.

Dosimetric Comparison: Volumetric Modulated Arc Therapy (VMAT) and 3D Conformal Radiotherapy (3D-CRT) in High Grade Glioma Cancer—Experience of Casablanca Cancer Center at the Cheikh Khalifa International University Hospital

Background: Intensity Modulated Radiation Therapy (IMRT) is currently employed as a major arm of treatment in multiforme glioblastoma (GBM). The present study aimed to compare 3D-CRT with IMRT to assess tumor volume coverage and OAR sparing for the treatment of malignant gliomas. Materials and methods: We assessed 22 anonymized patients datasets with High Grade Glioblastoma who had undergone post-operative Intensity Modulated Radiotherapy (IMRT) and 3D Conformal Radiotherapy (3D-CRT), This study will compare and contrast treatment plans Rapidarc and 3D-CRT to determine which technology improves significantly dosimetric parameters. Results: Plans will be assessed by reviewing the coverage of the PTV using mean, maximum and minimum doses while the OAR doses will be compared using the maximal doses for each, as set out in the QUANTEC dose limits. Conclusion: The use of IMRT seems a superior technique as compared to 3D-CRT for the treatment of malignant gliomas having the potential to increase the dose to the PTV while sparing OARs optimally.