RESUMEN

Intensity modulated radiation therapy (IMRT) is one of the most used techniques for cancer treatment. Using a linear accelerator, it delivers radiation directly at the cancerogenic cells in the tumour, reducing the impact of the radiation on the organs surrounding the tumour. The complexity of the IMRT problem forces researchers to subdivide it into three sub-problems that are addressed sequentially. Using this sequential approach, we first need to find a beam angle configuration that will be the set of irradiation points (beam angles) over which the tumour radiation is delivered. This first problem is called the Beam Angle Optimisation (BAO) problem. Then, we must optimise the radiation intensity delivered from each angle to the tumour. This second problem is called the Fluence Map Optimisation (FMO) problem. Finally, we need to generate a set of apertures for each beam angle, making the intensities computed in the previous step deliverable. This third problem is called the Sequencing problem. Solving these three sub-problems sequentially allows clinicians to obtain a treatment plan that can be delivered from a physical point of view. However, the obtained treatment plans generally have too many apertures, resulting in long delivery times. One strategy to avoid this problem is the Direct Aperture Optimisation (DAO) problem. In the DAO problem, the idea is to merge the FMO and the Sequencing problem. Hence, optimising the radiation's intensities considers the physical constraints of the delivery process. The DAO problem is usually modelled as a Mixed-Integer optimisation problem and aims to determine the aperture shapes and their corresponding radiation intensities, considering the physical constraints imposed by the Multi-Leaf Collimator device. In solving the DAO problem, generating clinically acceptable treatments without additional sequencing steps to deliver to the patients is possible. In this work, we propose to solve the DAO problem using the well-known Particle Swarm Optimisation (PSO) algorithm. Our approach integrates the use of mathematical programming to optimise the intensities and utilizes PSO to optimise the aperture shapes. Additionally, we introduce a reparation heuristic to enhance aperture shapes with minimal impact on the treatment plan. We apply our proposed algorithm to prostate cancer cases and compare our results with those obtained in the sequential approach. Results show that the PSO obtains competitive results compared to the sequential approach, receiving less radiation time (beam on time) and using the available apertures with major efficiency.

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Background and objectives: The standard treatment for locally advanced cervical cancer (CC) is chemoradiotherapy (CTRT) followed by high-dose-rate brachytherapy (HDRBT). The ideal scenario would be under novel intensity-modulated radiation therapy (IMRT) volumetric-modulated arc therapy (VMAT) radiation techniques over three-dimensional (3D) radiation therapy. However, radiotherapy (RT) centres in low- and middle-income countries have limited equipment for teletherapy services like HDRBT. This is why the 3D modality is still in use. The objective of this study was to analyse costs in a comparison of 3D versus IMRT versus VMAT based on clinical staging. Materials and methods: From 02/01/2022 to 05/01/2023 a prospective registry of the costs for oncological management was carried out for patients with locally advanced CC who received CTRT ± HDRBT. This included the administration of radiation with chemotherapy. The cost associated with patient and family transfers and hours in the hospital was also identified. These expenses were used to project the direct and indirect costs of 3D versus IMRT versus VMAT. Results: The treatment regimens for stage IIIC2, including 3D and novel techniques, are those with the highest costs. The administration of 3D RT for IIIC2 and novel IMRT or VMAT techniques, is $3,881.69, $3,374.76, and $2,862.80, respectively. The indirect cost from stage IIB to IIIC1 in descending order is IMRT, 3D and VMAT, but in IIIC2 the novel technique regimens reduce by up to 33.99% compared to 3D. Conclusion: In RT centres with an available supply of RT equipment, VMAT should be preferred over IMRT/3D since it reduces costs and toxicity. However, in RT centres where demand exceeds supply in the VMAT technique planning systems, the use of 3D teletherapy over IMRT/VMAT could continue to be used in patients with stage IIB to IIIC1.

RESUMEN

Craniospinal irradiation (CSI) is a complex radiation technique employed to treat patients with primitive neuroectodermal tumors such as medulloblastoma or germinative brain tumors with the risk of leptomeningeal spread. In adults, this technique poses a technically challenging planning process because of the complex shape and length of the target volume. Thus, it requires multiple fields and different isocenters to guarantee the primary-tumor dose delivery. Recently, some authors have proposed the use IMRT technique for this planning with the possibility of overlapping adjacent fields. The high-dose delivery complexity demands three-dimensional dosimetry (3DD) to verify this irradiation procedure and motivated this study. We used an optical CT and a radiochromic Fricke-xylenol-orange gel with the addition of formaldehyde (FXO-f) to evaluate the doses delivered at the field junction region of this treatment. We found 96.91% as the mean passing rate using the gamma analysis with 3%/2 mm criteria at the junction region. However, the concentration of fail points in a determined region called attention to this evaluation, indicating the advantages of employing a 3DD technique in complex dose-distribution verifications.

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PURPOSE: To report preliminary outcomes of high dose image-guided intensity modulated radiotherapy (IG-IMRT) in the treatment of chordomas of the sacrum, mobile spine and skull base. METHODS: Retrospective analysis of chordoma patients treated with surgery and/or radiotherapy (RT) in a single tertiary cancer center. Initial treatment was categorized as (A) Adjuvant or definitive high-dose RT (78 Gy/39fx or 24 Gy/1fx) vs (B) surgery-only or low dose RT. The primary endpoint was the cumulative incidence of local failure. RESULTS: A total of 31 patients were treated from 2010 through 2020. Median age was 55 years, tumor location was 64% sacrum, 13% lumbar, 16% cervical and 6% clivus. Median tumor volume was 148 cc (8.3 cm in largest diameter), 42% of patients received curative-intent surgery and 65% received primary RT (adjuvant or definitive). 5-year cumulative incidence of local failure was 48% in group A vs 83% in group B (p = 0.041). Tumor size > 330 cc was associated with local failure (SHR 2.2, 95% CI 1.12 to 7.45; p = 0.028). Eight patients developed distant metastases, with a median metastases-free survival of 56.1 months. 5-year survival for patients that received high dose RT was 72% vs 76% in patients that received no or low dose RT (p = 0.63). CONCLUSION: Our study suggests high-dose photon IG-IMRT improves local control in the initial management of chordomas. Health systems should promote reference centers with clinical expertise and technical capabilities to improve outcomes for this complex disease.

Asunto(s)

Cordoma , Radioterapia de Intensidad Modulada , Cordoma/diagnóstico por imagen , Cordoma/patología , Cordoma/radioterapia , Humanos , Persona de Mediana Edad , Radioterapia de Intensidad Modulada/efectos adversos , Estudios Retrospectivos , Sacro/patología , Base del Cráneo , Resultado del Tratamiento

RESUMEN

PURPOSE: This study sought to discern the clinical outcomes of intensity-modulated radiation therapy (IMRT) administered to the spine in patients who had undergone previous radiotherapy. METHODS: A total of 81 sites of 74 patients who underwent previous radiotherapy administered to the spine or peri-spine and subsequently received IMRT for the spine were analyzed in this study. The prescribed dose of 80 Gy in a biologically effective dose (BED) of α/ß = 10 (BED10) was set as the planning target volume. The constraint for the spinal cord and cauda equine was D0.1 cc ≤ 100 Gy and ≤ 150 Gy of BED for re-irradiation alone and the total irradiation dose, respectively. RESULTS: The median follow-up period was 10.1 (0.9-92.1) months after re-irradiation, while the median interval from the last day of the previous radiotherapy to the time of re-irradiation was 15.6 (0.4-210.1) months. Separately, the median prescript dose of re-irradiation was 78.0 (28.0-104.9) of BED10. The median survival time in this study was 13.9 months, with 1-, 3-, and 5-year overall survival rates of 53.7%, 29.3%, and 26.6%, respectively. The 1-, 3-, and 5-year local control rates were 90.8%, 84.0%, and 84.0%, respectively. Neurotoxicity was observed in two of 72 treatments (2.8%) assessed after re-irradiation. CONCLUSION: Re-irradiation for the spine using IMRT seems well-tolerated. Definitive re-irradiation can be a feasible treatment option in patients with the potential for a good prognosis.

Asunto(s)

Radioterapia de Intensidad Modulada , Reirradiación/métodos , Neoplasias de la Columna Vertebral/radioterapia , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Análisis de Varianza , Cauda Equina/efectos de la radiación , Niño , Femenino , Humanos , Masculino , Persona de Mediana Edad , Órganos en Riesgo/efectos de la radiación , Tolerancia a Radiación , Dosificación Radioterapéutica , Radioterapia de Intensidad Modulada/efectos adversos , Reirradiación/efectos adversos , Efectividad Biológica Relativa , Estudios Retrospectivos , Médula Espinal/efectos de la radiación , Neoplasias de la Columna Vertebral/diagnóstico por imagen , Neoplasias de la Columna Vertebral/mortalidad , Tasa de Supervivencia , Factores de Tiempo , Adulto Joven

RESUMEN

Resumen Introducción: En 2018 el cáncer de próstata presentó el segundo lugar en incidencia a nivel mundial. Con el avance en la tecnología y la aparición de la radioterapia de intensidad modulada (IMRT), se ha logrado disminuir dosis a tejido sano sin reducir la cobertura del volumen objetivo, permitiendo menor morbilidad asociada por la radioterapia y la posibilidad de escalar la dosis del tratamiento. El objetivo del estudio fue mostrar los resultados en supervivencia global y supervivencia libre de recaída bioquímica en el Instituto Nacional de Cancerología de Colombia (INC) en los paciente diagnosticados con cáncer de próstata tratados con radioterapia de intensidad modulada (IMRT). Materiales y métodos: La revisión retrospectiva incluyó 98 pacientes, mayores de 40 años con cáncer de próstata, sin evidencia de enfermedad metastásica, tratados con IMRT entre 2008 - 2015, independiente de la supresión androgénica. La dosis administrada de radioterapia varió según su riesgo basado en la clasificación D´Amico. Hallazgos: La mediana de edad fue de 68,5 años, dentro de los cuales 16 pacientes (16%) se catalogaron de bajo riesgo, 33 (34 %) de riesgo intermedio y 49 (50 %) de riesgo alto. La dosis media de radioterapia recibida fue de 75,8 Gy. La supervivencia libre de recaída bioquímica a 5 años fue del 78,6 % y la supervivencia global fue 98 %. Conclusión: En pacientes con cáncer de próstata de alto riesgo, la IMRT es una alternativa efectiva y segura, con una supervivencia global a 5 años del 98% y con un adecuado perfil dosimétrico a los órganos a riesgo.

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Abstract Background: In 2018, prostate cancer ranked second in incidence worldwide. Advances in technology and the appearance of intensity-modulated radiotherapy, have made it possible to reduce doses to healthy tissue without reducing the coverage of the target volume, thus allowing lower morbidity associated with adiotherapy and the possibility of scaling the treatment dose. The aim of the study was to present the results in overall survival and biochemical relapse-free survival at the Colombian National Cancer Institute (INC) in patients diagnosed with non-metastatic prostate cáncer treated with intensity-modulated radiotherapy (IMRT). Material and methods: The retrospective review included 98 patients over 40 years of age with prostate cancer, without evidence of metastatic disease, treated with IMRT between 2008 and 2015 irrespective of androgenic suppression. The administered dose of radiotherapy varied according to their risk based on the D'Amico classification. Results: The median age was 68.5 years, and of the total of 98 patients, 16 (16%) were classified as low risk, 33 (33%) as intermediate risk, and 49 (50%) as high risk. The mean dose of radiation therapy received was 75.8 Gy. Biochemical relapse-free survival at 5 years was 78.6%, and overall survival was 98%. Conclusions: In patients with high-risk prostate cancer, IMRT is an effective and safe alternative, with an overall 5-year survival of 98%, and an adequate dosimetric profile for at-risk organs.

Asunto(s)

Humanos , Masculino , Neoplasias de la Próstata , Radioterapia , Radioterapia de Intensidad Modulada , Supervivencia , Recurrencia , Terapéutica

RESUMEN

AIM: Describe characteristics and outcomes of three patients treated with pelvic radiation therapy after kidney transplant. BACKGROUND: The incidence of pelvic cancers in kidney transplant (KT) recipients is rising. Currently it is the leading cause of death. Moreover, treatment is challenging because anatomical variants, comorbidities, and associated treatments, which raises the concern of using radiotherapy (RT). RT has been discouraged due to the increased risk of urethral/ureteral stricture and KT dysfunction. MATERIALS AND METHODS: We reviewed the electronic health records and digital planning system of patients treated with pelvic RT between December 2013 and December 2018 to identify patients with previous KT. CASES DESCRIPTION: We describe three successful cases of KT patients in which modern techniques allowed full standard RT for pelvic malignances (2 prostate and 1 vaginal cancer) with or without elective pelvic nodal RT, without allograft toxicity at short and long follow-up (up to 60 months). CONCLUSION: When needed, RT modern techniques remain a valid option with excellent oncologic results and acceptable toxicity. Physicians should give special considerations to accomplish all OAR dose constraints in the patient's specific setting. Recent publications recommend KT mean dose <4 Gy, but graft proximity to CTV makes this unfeasible. We present 2 cases where dose constraint was not achieved, and to a short follow-up of 20 months renal toxicity has not been documented. We recommend the lowest possible mean dose to the KT, but never compromising the CTV coverage, since morbimortality from recurrent or progressive cancer disease outweighs the risk of graft injury.

RESUMEN

BACKGROUND: Worsening voice and speech quality was frequently reported in head-and-neck patients after radiotherapy to the neck; omitting the lower neck and sparing the glottic larynx in node-negative nasopharyngeal carcinoma (NPC) patients might be safe and feasible, and improve voice and speech outcomes. METHODS: From January 2009 to January 2013, 71 patients were analyzed. All patients received bilateral neck irradiation. Upper group (UG) patients spared the glottic larynx while lower group (LG) patients did not. Voice and speech quality were evaluated at two time-points (T1 and T2) using the Communication Domain of the Head and Neck Quality of Life (HNQOL) instrument and the Speech question of the University of Washington Quality of Life instrument. RESULTS: At a median follow-up time of 32 months (T1),71.6% of patients reported worsened voice and speech quality. UG patients resulted in significant decreases in glottic larynx dose. With a median follow-up time of 71 months (T2), no patients experienced out-of-field nodal recurrence;there was no difference in the 5-year overall survival and nodal recurrence-free survival between two groups (P = 0.235 and 0.750, respectively). At T1, in patients who without concurrent chemotherapy (CCT), UG patients showed significantly better patient-reported voice quality, (P = 0.022). UG patients without CCT also showed higher scores in the HNQOL communication domain and pain domain (P = 0.012 and P = 0.019). CONCLUSIONS: For node-negative NPC patients, omitting the lower neck and sparing the glottic larynx was safe and feasible, and better voice outcomes were achieved in patients without CCT. Further prospective longitudinal studies to investigate whether this approach would be beneficial to node-negative patients are warranted.

Asunto(s)

Quimioradioterapia/efectos adversos , Glotis , Neoplasias Nasofaríngeas/terapia , Cuello , Tratamientos Conservadores del Órgano/mortalidad , Calidad de Vida , Trastornos de la Voz/prevención & control , Adolescente , Adulto , Anciano , Carcinoma de Células Escamosas/patología , Carcinoma de Células Escamosas/terapia , Estudios de Factibilidad , Femenino , Estudios de Seguimiento , Humanos , Ganglios Linfáticos/patología , Masculino , Persona de Mediana Edad , Neoplasias Nasofaríngeas/patología , Medición de Resultados Informados por el Paciente , Pronóstico , Tasa de Supervivencia , Trastornos de la Voz/etiología , Calidad de la Voz , Adulto Joven

RESUMEN

AIM: To evaluate whether hypofractionation with integrated boost to the tumour bed using intensity-modulated radiation therapy is an acceptable option and to determine whether this treatment compromises local control, toxicity and cosmesis. BACKGROUND: Retrospective studies have demonstrated that patients who are treated with HF and integrated boost experience adequate local control, a dosimetric benefit, decreased toxicity and acceptable cosmesis compared with conventional fractionation. MATERIALS AND METHODS: A retrospective, observational and longitudinal study was conducted from January 2008 to June 2015 and included 34 patients with breast cancer (stage 0-II) who were undergoing conservative surgery.The prescribed doses were 45 Gy in 20 fractions (2.25 Gy/fraction) to the breast and 56 Gy in 20 fractions (2.8 Gy/fraction) to the tumour bed. RESULTS: Thirty-four patients were included. The mean follow-up was 49.29 months, and the mean age was 52 years. The mean percentage of PTV from the mammary region that received 100% of the prescribed dose was 97.89% (range 95-100), and the mean PTV percentage of the tumour bed that received 100% of the dose was 98% (95-100).The local control and the overall survival were 100%, and the cosmesis was good in 82% of the patients. Grade 1 acute toxicity was present in 16 patients (47%), and grade 1 chronic toxicity occurred in 6 cases (18%). CONCLUSION: The results of the present study demonstrate that hypofractionation with integrated boost using intensity-modulated radiation therapy is an acceptable option that provides excellent local control and low toxicity.

RESUMEN

BACKGROUND: Diarrhea is the primary symptom of concern in acute post-operative radiation-induced enteritis in gynecologic cancer. We retrospectively studied the correlation between the volume of irradiated small bowel and the development of acute diarrhea in these patients. MATERIALS AND METHODS: A total of 100 post-operative gynecologic cancer patients were analyzed. Pelvic computed tomography was performed to calculate the volume of irradiated small bowel. A dose-volume histogram was calculated from 5 to 40 Gy at 5 Gy intervals. Patients receiving conventional whole pelvic radiation therapy (RT) were assigned to Group I, and those who received intensity-modulated RT (IMRT) were assigned to Group II. A total dose of 40-50 Gy was delivered at 1.8-2.0 Gy per fraction daily. Acute diarrhea during treatment was scored. All data were expressed as a mean ± standard deviation. Different dose-volume parameters for small bowel in Grades 0-1 and Grades 2-3 diarrhea were calculated by the independent t-test. Univariate analysis of diarrhea risk factors was performed with the independent t-test or Chi-square/Fisher exact test. RESULTS: Of the 77 patients who received conventional RT, 44 (57.14%) experienced Grades 2-3 toxicities. Of the 23 patients who received IMRT, 9 (39.13%) experienced Grades 2-3 toxicities. Concurrent chemotherapy was slightly associated with a higher damage score in both groups (p = 0.028). None of the patient factors (weight, percentage depth dosage, dose fraction, distance from skin to tumor, lymph node metastasis, chemotherapy, block, brachytherapy, hypertension, or diabetes) were correlated with diarrhea in the two groups. The volumes of irradiated small bowel in patients who experienced Grades 2-3 diarrhea were significantly larger than those in patients who experienced Grades 0-1 diarrhea at all dose levels in Group I. V20 (372.19 ± 133.26 cm3, p = 0.004) was an independent factor for developing Grades 2-3 diarrhea in Group I. V25 (290.35 ± 130.22 cm3, p = 0.001) was an independent risk factor for all patients who developed higher score diarrhea. CONCLUSIONS: The volume of irradiated small bowel was an independent risk factor for all patients who developed diarrhea, especially those undergoing conventional RT.

Asunto(s)

Diarrea/etiología , Enteritis/etiología , Neoplasias de los Genitales Femeninos/radioterapia , Traumatismos por Radiación/epidemiología , Enfermedad Aguda , Antineoplásicos/administración & dosificación , Antineoplásicos/efectos adversos , Diarrea/epidemiología , Enteritis/epidemiología , Femenino , Humanos , Intestino Delgado/patología , Metástasis Linfática , Persona de Mediana Edad , Dosis de Radiación , Radioterapia de Intensidad Modulada/efectos adversos , Radioterapia de Intensidad Modulada/métodos , Estudios Retrospectivos , Factores de Riesgo , Tomografía Computarizada por Rayos X

RESUMEN

Resumen En la radioterapia de cabeza y cuello las glándulas salivales suelen recibir una dosis elevada de radiación, lo que provoca una disminución progresiva y, a partir de determinada dosis, irreversible de la secreción salival, entre otros efectos. La xerostomía o sensación de boca seca es el efecto secundario más frecuente tras la radioterapia de cabeza y cuello, el cual disminuye la calidad de vida de los pacientes al dificultar funciones como la fonación y la deglución. Dada la complejidad y la temprana aparición de este síntoma, su prevención es la solución más eficaz. Los avances de las últimas décadas tienen un papel imprescindible: la radioterapia de intensidad modulada, la administración de sustancias citoprotectoras y el autotransplante de glándula submandibular parecen limitar en cierta medida el efecto de la radiación y disminuir así la sensación de sequedad bucal.

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Abstract Radiation therapy is a key component in the multidisciplinary treatment of head-and-neck malignancies. In these cases, salivary glands are irradiated with high-level doses, which, among other side effects, results in a progressive and irreversible decrease in the salivary output. Radiation-induced xerostomia is the most common side effect of the head and neck region after radiotherapy treatment, and highly impairs the patients' long-term quality of life, threatening physiological functions, essentially speaking and swallowing. Given the complexity and early appearance of this symptom, its prevention is the most effective solution. In the past decades, the development of new radiation delivery techniques, such as intensity-modulated radiotherapy (IMRT), along with the administration of radioprotective drugs and autologous submandibular gland transplantation, seem to reduce the dose reaching the salivary glands, which in turn improves the patients' perception of dry mouth.

Asunto(s)

Humanos , Xerostomía , Radioterapia de Intensidad Modulada , Radiación , Radioterapia , Terapéutica , Métodos , Cabeza , Boca , Cuello

RESUMEN

This study assessed the prophylactic bethanechol use to prevent salivary gland dysfunction during radiotherapy. A total of 97 head and neck cancer patients were allocated into two groups: Bethanechol or Placebo. Bethanechol group presented significantly improve of salivary parameters. Bethanechol was effective in decreasing the salivary gland damage.

Asunto(s)

Betanecol/uso terapéutico , Neoplasias de Cabeza y Cuello/radioterapia , Glándulas Salivales/fisiopatología , Xerostomía/prevención & control , Xerostomía/fisiopatología , Adulto , Anciano , Relación Dosis-Respuesta en la Radiación , Método Doble Ciego , Femenino , Humanos , Masculino , Persona de Mediana Edad , Estudios Prospectivos , Radioterapia/efectos adversos

RESUMEN

A small decrease in testosterone level has been documented after prostate irradiation, possibly owing to the incidental dose to the testes. Testicular doses from prostate external beam radiation plans with either intensity-modulated radiation therapy (IMRT) or volumetric-modulated arc therapy (VMAT) were calculated to investigate any difference. Testicles were contoured for 16 patients being treated for localized prostate cancer. For each patient, 2 plans were created: 1 with IMRT and 1 with VMAT. No specific attempt was made to reduce testicular dose. Minimum, maximum, and mean doses to the testicles were recorded for each plan. Of the 16 patients, 4 received a total dose of 7800 cGy to the prostate alone, 7 received 8000 cGy to the prostate alone, and 5 received 8000 cGy to the prostate and pelvic lymph nodes. The mean (range) of testicular dose with an IMRT plan was 54.7 cGy (21.1 to 91.9) and 59.0 cGy (25.1 to 93.4) with a VMAT plan. In 12 cases, the mean VMAT dose was higher than the mean IMRT dose, with a mean difference of 4.3 cGy (p = 0.019). There was a small but statistically significant increase in mean testicular dose delivered by VMAT compared with IMRT. Despite this, it unlikely that there is a clinically meaningful difference in testicular doses from either modality.

Asunto(s)

Neoplasias de la Próstata/radioterapia , Dosificación Radioterapéutica , Planificación de la Radioterapia Asistida por Computador/métodos , Radioterapia de Intensidad Modulada/métodos , Testículo/efectos de la radiación , Absorción de Radiación , Humanos , Masculino , Tratamientos Conservadores del Órgano/métodos , Exposición a la Radiación/análisis , Protección Radiológica/métodos , Resultado del Tratamiento

RESUMEN

Secondary brain tumor (SBT) is a devastating complication of cranial irradiation (CI). We reviewed the literature to determine the incidence of SBT as related to specific radiation therapy (RT) treatment modalities. The relative risk of radiation-associated SBT after conventional and conformal RT is well established and ranges from 5.65 to 10.9; latent time to develop second tumor ranges from 5.8 to 22.4 years, depending on radiation dose and primary disease. Theories and dosimetric models suggest that intensity-modulated radiation therapy may result in an increased risk of SBT, but clinical evidence is limited. The incidence of stereotactic radiosurgery-related SBT is low. Initial data suggest that no increased risk from proton therapy and dosimetric models predict a lower incidence of SBT compared with photons. In conclusion, the incidence of SBT related to CI is low. Longer follow-up is needed to clarify the impact of intensity-modulated radiation therapy, proton therapy and other developing technologies.

Asunto(s)

Neoplasias Encefálicas/etiología , Irradiación Craneana/efectos adversos , Neoplasias Inducidas por Radiación/patología , Animales , Neoplasias Encefálicas/epidemiología , Neoplasias Encefálicas/patología , Irradiación Craneana/métodos , Humanos , Incidencia , Terapia de Protones/efectos adversos , Terapia de Protones/métodos , Dosis de Radiación , Radiocirugia/efectos adversos , Radiocirugia/métodos , Radioterapia Conformacional/efectos adversos , Radioterapia Conformacional/métodos , Factores de Tiempo

RESUMEN

PURPOSE: One of the most widely used IMRT QA devices (MatriXX) is an array of ionization chambers which are periodically read during plan delivery. Although the ionization chambers are not expected to exhibit strong angular dependence, the measured dose distribution is often found to significantly differ from the planned dose distribution. We identify the origin of all factors that affect the measurement accuracy of the MatriXX and develop a per-frame post-processing strategy that reduces their impact on the passing rate of IMRT and VMAT plans. METHODS: We developed software that reads the dose frame sequence recorded by the MatriXX and applies a number of correction factors to each frame. Angular correction factors are computed as ratios of measured dose at the isocenter of the phantom and planned dose at the same location for all clinically used photon energies. For every clinical case, the recorded movie file is read and the dose for every frame is corrected according to the angle of the beam. In addition, the background evolution is tracked in the 'beam-off' frames which are subsequently subtracted from the 'beam-on' frames according to a predictive model. Machine output correction is also implemented, which significantly improves the absolute dose measurements. The IMRT effective plane of measurement of the MatriXX was identified and found not to coincide with the isocentric plane. RESULTS: The clinical passing rates are significantly improved when the per-frame analysis software was introduced in our IMRT QA procedure. For a group of 800 patients with no corrections the average passing rate was 93.6%, while for the first 300 cases with per frame corrections the average passing rate was 97.3%. CONCLUSIONS: We identify all factors that impact the measurement accuracy of the MatriXX (angular effects, background evolution, machine output, plane of measurement) and propose a strategy for their elimination.

RESUMEN

PURPOSE: The implementation of an accurate beam model is an integral part of the commissioning of any planning system. This process is especially challenging in the case of IMRT beam models owing to the complexity of small field sizes and MLC leaf-end and tongue-and-groove effects. The question of how to judge the quality of an IMRT beam model in comparison with other versions of the same model is central to this work. METHODS: We make an important distinction between evaluation of the beam model and evaluation of the optimization routine that is a part of any IMRT planning system. The H-shaped target used in this work has several important features: it can only be covered by segments with small field size, for which all leaf design effects are important, and it has the overall dimensions of a common IMRT target. The procedure for inter-comparison of two IMRT beam models (old and new) involves the generation of two plans optimized with each beam model using identical IMRT prescriptions. Both plans are subsequently delivered on a solid water phantom with film located in two parallel planes with a small-volume ionization chamber inserted in the center. RESULTS: Four dose calculations are performed, such that each plan is calculated with either of the two beam models. The four dose distributions are subsequently compared with the two film measurements using gamma analysis. In addition, the absolute dose measured in the center of the dose distribution is compared with the calculated value. A score is assigned to each beam model based on the results. CONCLUSIONS: Using the procedure outlined in this presentation, different versions of an IMRT beam model can be compared and scored for quality. Adoption of a unified strategy for beam model inter-comparison can greatly facilitate the evaluation and commissioning of IMRT beam models.

RESUMEN

PURPOSE: Radiotherapy planning for iliac pelvic nodes can be challenging due to the close proximity of sensitive healthy tissues such as the bowel and rectum. Modern treatment techniques like photon intensity-modulated radiotherapy (IMRT) and intensity-modulated proton therapy (IMPT) offer improved healthy tissue sparing for similar target coverage. In this study we compare IMRT and IMPT plans for six post-cystectomy patients. METHODS: A dose of 50.4 Gy was prescribed to the planning target volume (PTV), which for IMRT is the clinical target volume (CTV) plus a 5 mm expansion for geometric uncertainties due to CTV and patient positioning errors, and for proton beams is the CTV plus the lateral 5 mm margin plus an additional longitudinal margin to allow for the proton range uncertainty. The optimization objectives are: 98% of the PTV receive at least 95% of the prescription, target maximum dose = 107% of prescription, rectum V[40Gy] < 30% and max = 105%, and bowel V[45Gy] < 125 cc and max = 107%. All IMRT and IMPT plans are made to achieve the target coverage objective. RESULTS: Using IMPT, the rectum would receive a mean dose of 9.0 Gy with an average (over the six patients) maximum dose of 38.1 Gy. Using IMRT, the rectum would receive a mean dose of 13.0 Gy and an average maximum dose of 37.6 Gy. The IMPT plans give a mean dose of 17.9 Gy and a maximum dose of 53.4 Gy for the bowel, whereas the IMRT plans give a mean dose of 23.8 Gy and a maximum dose of 53.2 Gy. Both the rectum and bowel show slightly lower mean doses for IMPT. CONCLUSIONS: Our results indicate that IMPT plans improve normal tissue sparing as compared to IMRT plans and provide adequate dose coverage of the target volume.

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PURPOSE: Modulated electron radiation therapy (MERT) can offer significant advantages for breast treatments over conventional radiotherapy in terms of sparing distal critical structures. While intensity modulated radiation therapy (IMRT) has the advantage of achieving better dose homogeneity inside the target combining both MERT and IMRT will be the ideal scenario. The Aim of the present study is to investigate the possibility of further improving breast radiation therapy using combined MERT/IMRT treatment technique. METHODS: Accurate modeling of a prototype motorized electron multileaf collimator was verified in a separate study. In this work treatment planning was performed by an in house Monte Carlo based inverse planning system. Dose deposition coefficients were calculated using MCPLAN and utilizing real patients CTs. Optimization is then conducted based on an equivalent uniform dose objective function. MERT and IMRT plans were created for different patients. RESULTS: The clinical beneficial outcome for MERT either alone or combined with IMRT was investigated based on isodose distributions and dose volume histograms. It is shown that MERT can give similar dose distributions as IMRT in some cases. For some cases, MERT could be advantageous whenever more skin dose was required. In some cases MERT can be identified as the best option. It was found that MERT compared to IMRT could introduce hot spots inside the target. However this was resolved in combined MERT/IMRT treatment. Dose uniformity can be restored with a reduction in the maximum lung and heart received dose. CONCLUSION: MERT can improve treatment plan quality for many breast patients. In some cases better results can be obtained with a combined MERT/IMRT treatment, where a homogeneous dose in the target can be achieved with an improvement in the DVH of critical structures. This work has been supported by a UICC American Cancer Society Beginning Investigators Fellowship funded by the American Cancer Society.

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PURPOSE: A three-dimensional conformal radiotherapy (3DCRT) has been recently introduced to helical tomotherapy, allowing the user to plan and treat patients that do not require sophisticated IMRT planning and delivery. This study aims to test treatment planning on this modality and evaluate its performance by comparing to conventional LINAC-based 3DCRT planning. METHODS: Four clinical cases (whole brain, extremity, lung, and partial breast irradiation) were retrospectively selected from a Pinnacle planning system (Philips Medical System, Fitchburg, WI) and planned on Tomotherapy (Accuray Inc., Sunnyvale, CA). Computed tomography (CT) images together with contours of target and critical structures were exported from Pinnacle to the Tomotherapy planning station. The same prescription and fractionation scheme was adopted. The pitch factor for all clinical cases was set to 0.287. A 2.5 cm jaw was employed except in the lung case the field size was set to 1.0 cm for better dose conformity. The dose grid size was chosen to be half of that of the planning CT images. On Pinnacle 100% prescription dose was delivered to the treatment isocenter while onTomotherapy it was stipulated that at least 95% of the target volume received the prescribed dose. Comparison between two planning strategies was performed, in terms of dose volume histograms (DVH), dosimetric and radiobiological parameters, for plan quality assessment. RESULTS: Comparison of DVHs reveals that up to 25% healthy tissue sparing in volume can be accomplished with Tomotherapy 3DCRT while the same target coverage is ensured. Dosimetric and radiobiological indices between Tomotherapy and Pinnacle planning agree to within 3.0%. Additional beam modifiers and non-coplanar beams associated with LINAC-based 3DCRT are not needed on Tomotherapy, making it more favorable. CONCLUSIONS: Tomotherapy 3DCRT has similar dosimetric performance when compared to conventional LINAC-based 3DCRT while it is substantially easier to use.

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PURPOSE: Pulsed low dose-rate radiotherapy (PLDR) re-irradiation has the potential to reduce late normal tissue toxicity while still providing significant tumor control for recurrent cancers. In contrast to conventional treatments delivered at dose-rates of 400-600cGy/min, PLDR treatments deliver 20cGy pulses separated by 3-minute intervals to achieve an effective-dose-rate of 6.7cGy/min. This work aims to investigate the planning strategy and delivery quality of PLDR treatment using IMRT and RapidArc techniques. METHODS: Twenty cases (10 treated with PLDR IMRT, 10 for evaluation purposes) were recruited in this study including prostate, pancreas, lung, head-and-neck, breast and pelvis. IMRT and the RapidArc treatment plans were generated using the Eclipse TPS. For IMRT treatment, each plan consisted of 10 fields to achieve a daily dose of 200cGy. The breast IMRT and the RapidArc plans consisted of two fields/arcs, respectively (40cGy/plan) and were delivered 5 times. The dose contribution from each field to the planning target volume (PTV) was analyzed to evaluate the feasibility for PLDR treatment. Machine-operation- dose-rate and plan quality was also investigated. Dose delivery accuracy was assessed using a cylindrical diode array. RESULTS: Throughout the six treatment sites, the mean PTV dose ranged from 16.1 to 26.1cGy/arc for RapidArc plans and 10.3 to 36.7cGy/field for IMRT plans. For IMRT, the PTV dose contribution from each field strongly depends on the beam arrangement and optimization parameters. With very low dose for a full rotation (∼ 20cGy/arc), the machine-operation-dose-rate of RapidArc plans significantly affects plan quality and deliverability. A machine-operation-dose-rate of 100 MU/min results in superior delivery accuracy (>97.7% gamma-passing-rate for 3%/3mm criteria) for both IMRT and RapidArc plans. CONCLUSIONS: PLDR radiotherapy using IMRT and RapidArc techniques Result in both dosimetric and radiobiological benefits, which may have great potential for those previously-irradiated patients who have historically done poorly.