Planning and dosimetric evaluation of three total body irradiation techniques: Standard SSD VMAT, Extended SSD VMAT and Extended SSD Field-in-Field

The aim of this study was to dosimetrically compare three total body irradiation (TBI) techniques which can be delivered by a standard linear accelerator, and to deduce which one is preferable. Specifically, Extended Source to Surface Distance (SSD) Field-in-Field (FiF), Extended SSD Volumetric Modulated Arc Therapy (VMAT), and Standard SSD VMAT TBI techniques were dosimetrically evaluated. Percent depth dose and dose profile measurements were made under treatment conditions for each specified technique. After having generated treatment plans with a treatment planning system (TPS), dose homogeneity and critical organ doses were investigated on a Rando phantom using radiochromic films and optically stimulated luminescence dosimeters (OSLDs). TBI dose of 12 Gy in six fractions was prescribed for each technique. The gamma index (5%/5 mm) was used for the analysis of radiochromic films. Passing rates for Extended SSD FiF, Extended SSD VMAT and Standard SSD VMAT techniques were found to be 90%, 87% and 94%, respectively. OSLD measurements were within ± 5% agreement with TPS calculations for the first two techniques whereas the agreement was found to be within ± 3% for the Standard SSD VMAT technique. TPS calculations demonstrated that mean lung doses in the first two techniques were around 8.5 Gy while it was kept around 7 Gy in Standard SSD VMAT. It is concluded that Standard SSD VMAT is superior in sparing the lung tissue while all three TBI techniques are feasible in clinical practice with acceptable dose homogeneity. In the absence of VMAT-based treatment planning, Extended SSD FiF would be a reasonable choice compared to other conventional techniques.

Post-induction lymph node delineation in nasopharyngeal cancer: A single-center experience

BACKGROUND

We routinely delineate the gross tumor volume (GTV) for the lymph nodes (LN) based on post-induction chemotherapy (IC) MRI in nasopharyngeal carcinoma (NPC). Herein, we investigated the sufficiency of this method, particularly in high-risk LNs.

METHODS

Eighty-one LNs with a high-risk of clinical extranodal extension and/or ≥3-cm diameter in 58 patients were evaluated. A new GTV covering the pre-IC LN volume was delineated for each LN.

RESULTS

The median volume reduction was 72.5% for the GTV and 53.1% for the planning target volume. After a median 43 months, the overall LN local control rate was 97.5%. The 2- and 5-year LN recurrence-free survival, overall survival, and disease-free survival rate was 88.3% and 84.4%, 92.5% and 85.1%, and 86.8% and 79.2%, respectively.

CONCLUSION

IC yields a significant reduction in nodal target volumes, and post-IC nodal volume-based radiotherapy provides excellent LC in NPC, even in high-risk LNs.

Transit dosimetry of stereotactic body radiotherapy treatments with electronic portal dosimetry device in patient with spinal implant

In recent years, the use of the Electronic Portal Imaging Device (EPID) as an in vivo dosimeter has become widespread. However, reports of EPID for stereotactic body radiotherapy (SBRT) applications is scarce. There is no data on this topic especially when there are high-density materials in the radiation field. In this study, we aimed to investigate the dose distributions of SBRT treatment plans in patients with spinal implants by transit EPID dosimetry. Implants were inserted in phantoms that mimic the vertebrae, and VMAT plans were created on the phantoms to deliver 16 Gy radiation doses to the target in 1 fraction. Transit EPID measurements were performed for each irradiation. The results were compared with the treatment planning system using the gamma analysis method. According to the gamma analysis results, while the non-implant model met the acceptance criteria with a rate of 95.4%, the implanted models did not pass the test with results between the rates of 70% to 73%. In addition, while the dose difference in the isocenter was 1.3% for the non-implanted model, this difference was observed to be between 7 and 8% in the implanted models. Our study revealed that EPID can be used as transit dosimetry for the VMAT-SBRT applications. However, unacceptable dose differences were obtained by transit EPID dosimetry in the VMAT-SBRT applications of patients with an implant. In the treatment of such patients, alternative treatment methods should be preferred in which the interaction of the implants with radiation can be prevented.

Predicting acute and late toxicity in prostate cancer stereotactic ablative radiotherapy: the role of dosimetric parameters and prostate volume

PURPOSE

Our objective was to identify the dosimetric parameters and prostate volume that most accurately predict the incidence of acute and late gastrointestinal (GI) and genitourinary (GU) toxicity in prostate cancer stereotactic ablative radiotherapy (SABR) treatments.

METHODS

We conducted a retrospective analysis of 122 patients who received SABR for prostate cancer at our clinic between March 2018 and September 2022 using a five-fraction SABR regimen. The existing plans of these patients were re-evaluated according to our institutional protocols (Hacettepe University [HU-1] and HU-2) as well as PACE‑B, RTOG 0938, and NRG GU005 dose-volume constraints. Univariate and multivariate logistic regression analyses were performed using SPSS version 23.0 (IBM, Armonk, NY, USA).

RESULTS

The median follow-up was 24.7 months (0.8-94.4 months). For acute GU toxicity, moderate-dose regions were predictive for grade 1-2 toxicity, while high-dose regions were more associated with grade 3-4 toxicity. For late GU toxicity, moderate-high-dose regions were predictive. For GI toxicity, moderate-dose regions were important for both acute and late toxicity. The HU protocol encompassed all significant dosimetric factors influencing toxicity outcomes. A prostate volume threshold of 60 cc was predictive of acute grade 3-4 GU toxicity.

CONCLUSION

Our study highlighted the critical role of moderate-dose regions for acute and late GI and GU toxicity. Prostate treatment plans should be rigorously evaluated, and moderate doses should be minimized. The HU protocol is an eligible choice for five-fraction SABR plans.

SU-E-T-208: The Secondary Malignancy Risk Estimation Due to the Neutron Contamination in 3D-CRT and IMRT Treatment Techniques by Using Bubble Detectors

PURPOSE

In this study, the neutron measurements were performed in free in air and RW3 solid water phantom to estimate the secondary malignancy risk for three dimensional conformal radiotherapy (3D-CRT) and intensity modulated radiotherapy (IMRT) techniques in prostate cancer treatment.

METHODS

Neutron dose were measured in 18 MV Elekta Synergy Platform and Varian Clinac linear accelerators by using bubble detector for personal neutron dosimetry (BD-PND). To determine the neutron equivalent dose in different depths and different distance from the edge of treatment field RW3 solid water phantom was used and organs location was defined in Alderson Rando phantom with respect to target (prostate) position in the treatment field. By using these data, we determined the neutron equivalent dose and effective dose for the standard prostate cancer patient treated with 3D-CRT and IMRT with 18 MV photon energy. The total dose was 70 Gy in 3D-CRT and 76 Gy in IMRT treatment in the current study. For both of these treatment techniques, we estimated the risk of secondary malignancies due to the neutron contamination by using the International Commission on Radiological Protection (ICRP) report 103.

RESULTS

The equivalent dose and effective dose due the neutron contamination were considerably high in 18 MV IMRT technique. The secondary malignancy risk estimation for 3D-CRT and IMRT were found to be 0.44% and 1.15% for Elekta Synergy Platform linear accelerator, 0.92% and 2.38% for the Varian Clinac DHX High Performance linear accelerator, respectively.

CONCLUSIONS

Therefore, one should take care of the secondary malignancy risk in case of using 18 MV in IMRT applications.

Robotic stereotactic radiosurgery in patients with nasal cavity and paranasal sinus tumors

The aim of this retrospective study is to evaluate our therapeutic results in patients with paranasal sinus (PNS) or nasal cavity (NC) malignancies treated with robotic stereotactic radiosurgery (SRS). Between August 2007 and October 2008, 27 patients with PNS or NC tumors were treated in our department using SRS. Median age was 53 years (range, 27-84 years). Eleven patients were female and sixteen were male. Most common histopathology was SCC (44%). The disease involved the maxillary sinus in 15 patients (55%). SRS was applied to 6 patients (22%) for reirradiation, while the others received it as a primary treatment. Seven patients had SRS as a boost dose to external beam radiotherapy. SRS was delivered with cyberknife (Accuray Incorporated, Sunnyvale, CA, USA). The median dose to the tumor was 31 Gy (range, 15-37.5 Gy) in median 5 fractions (range, 3-5 fractions). After a median follow-up of 21.4 months (range, 3-59 months), 76% of the patients were free of local relapse. Three patients showed local progression and 3 developed distant metastases. One- and two-year survival rates for the entire group were 95.2% (SEM = 0.046) and 77.1% (SEM = 0.102), respectively. We observed brain necrosis in 2 patients, visual disorder in 2 patients, bone necrosis in 2 patients and trismus in 1 patient as a SRS related late toxicity. Robotic SRS seems to be a feasible treatment strategy for patients with PNS tumors. Further prospective studies with longer follow up times should be performed.

A dose-response analysis for classical Kaposi's sarcoma management by radiotherapy

OBJECTIVE

To evaluate the dose-response relationship in classical Kaposi's sarcoma (CKS) patients treated with external beam radiotherapy.

METHODS

Between 1993 and 2004, patients with CKS treated at the Department of Radiation Oncology, Gulhane Military Medical School, Ankara, Turkey were evaluated in this retrospective study. The median age at initial presentation was 60 years. First, we analyzed the overall response rates for normalized total dose 2Gy (NTD2Gy) of <20 Gy, 20 Gy, and >20 Gy. Secondly, we searched for whether better response rates could be obtained with the NTD2Gy of > or =20 Gy compared to the NTD2Gy of <20 Gy.

RESULTS

There were 109 evaluable lesions in 18 patients. The median follow-up was 4 years. The overall response rates at the post-radiotherapy twelfth month were 88% for NTD2Gy of <20 Gy, 97% for 20 Gy, and 96% for NTD2Gy>20 Gy, which were not statistically different. The complete and partial response rates at 12 months were 93.2%, and 3.4% for NTD2Gy of > or =20Gy, and 64% and 24% for NTD2Gy of <20 Gy and these were statistically different (p=0.001). Late side effects of radiation therapy were acceptable in all but 4 patients with fibrosis and edema.

CONCLUSION

This retrospective analysis showed that radiotherapy schedules with an NTD2Gy of 20 Gy and above by using local irradiation fields are effective in terms of complete response rates in the management of CKS compared to NTD2Gy of <20 Gy.

Analysis of patients with parotid recurrence after parotid-sparing IMRT for nasopharyngeal carcinoma: case series and review of the literature

PURPOSE

Intensity-modulated radiotherapy (IMRT) is the standard treatment approach for nasopharyngeal cancer (NPC). IMRT enables effective sparing of the parotid glands and reduces the risk of xerostomia, a common complication of head and neck irradiation. Nevertheless, it is essential to determine whether the parotid-sparing IMRT (ps-IMRT) technique yields increased intra-/periparotid recurrence rates, which constitutes the main purpose of this study.

METHODS

Patients with a diagnosis of NPC that received definitive chemoradiotherapy/radiotherapy (CRT/RT) between 1991 and 2021 were evaluated retrospectively. Patients with intra-/periparotid recurrence were detected and prognostic factors for recurrence were sought.

RESULTS

A total of 746 patients were evaluated. Two-dimensional (2D)-RT was applied to 541, 3D conformal RT (3D-CRT) to 10, and ps-IMRT to 195 patients. After a median 85-month follow-up, one (0.18%) patient who received 2D-RT and four (2%) patients who received ps-IMRT experienced an intra-/periparotid recurrence. The median time to intra-/periparotid recurrence was 11.9 months. All patients had been diagnosed with a metastatic lymph node > 2 cm at level II of the ipsilateral neck. In addition, all recurrences occurred on the same side as the positive neck at the time of diagnosis. The 3‑year overall survival, locoregional recurrence-free survival, and distant metastasis-free survival rates were 80%, 40%, and 60%, respectively.

CONCLUSION

Intra-/periparotid recurrence is extremely rare in NPC. However, it is still possible to identify and characterize particular risk factors, which include a metastatic lymph node at level II, particularly > 2 cm, and multinodal disease at the time of diagnosis.

Preclinical Dosimetry for Small Animal Radiation Research in Proton Therapy: A Feasibility Study

PURPOSE

To evaluate the feasibility of the three-dimensional (3D) printed small animal phantoms in dosimetric verification of proton therapy for small animal radiation research.

MATERIALS AND METHODS

Two different phantoms were modeled using the computed-tomography dataset of real rat and tumor-bearing mouse, retrospectively. Rat phantoms were designed to accommodate both EBT3 film and ionization chamber. A subcutaneous tumor-bearing mouse phantom was only modified to accommodate film dosimetry. All phantoms were printed using polylactic-acid (PLA) filament. Optimal printing parameters were set to create tissue-equivalent material. Then, proton therapy plans for different anatomical targets, including whole brain and total lung irradiation in the rat phantom and the subcutaneous tumor model in the mouse phantom, were created using the pencil-beam scanning technique. Point dose and film dosimetry measurements were performed using 3D-printed phantoms. In addition, all phantoms were analyzed in terms of printing accuracy and uniformity.

RESULTS

Three-dimensionally printed phantoms had excellent uniformity over the external body, and printing accuracy was within 0.5 mm. According to our findings, two-dimensional dosimetry with EBT3 showed acceptable levels of γ passing rate for all measurements except for whole brain irradiation (γ passing rate, 89.8%). In terms of point dose analysis, a good agreement (<0.1%) was found between the measured and calculated point doses for all anatomical targets.

CONCLUSION

Three-dimensionally printed small animal phantoms show great potential for dosimetric verifications of clinical proton therapy for small animal radiation research.

Stereotactic radiotherapy for head and neck paragangliomas: How long should we wait for treatment response?

BACKGROUND AND PURPOSE

Stereotactic radiotherapy (SRT) is an effective treatment for head & neck (H&N) paragangliomas. Nevertheless, the timeline for achieving a tumor-volume-reduction (TVR) remains unclear.

MATERIALS AND METHODS

Sixty-three cases with H&N paragangliomas received definitive SRT and were evaluated retrospectively. Statistical Package for the Social Sciences (SPSS) v23.0 (IBM, Armonk, NY, USA) was used for statistics.

RESULTS

Sixty-eight lesions were irradiated, with glomus jugulotympanicum being the most common location (44 %). Median tumor diameter and volume were 3 cm (range, 1-7.6 cm) and 15.4 cm3 (range,1-185 cm3), respectively. Median dose was 25 Gy (range, 12-37.5 Gy) in 5 fractions (range, 1-5 fractions). Median follow-up was 40 months (range, 3-184 months). Treatment response, evaluated at a median 4.6 months post-SRT (range: 3-11 months), revealed TVR in 26 cases (41 %). During follow-up, 13 additional cases showed TVR, resulting in an overall TVR rate of 62 %. The median duration for attaining TVR was 9 months (range, 3-36 months) after SRT, and TVR occurred ≥ 12 months in 42 % of cases. Patients without prior surgery (p = 0.03) and with a longer follow-up (p = 0.04) demonstrated a higher rate of TVR. The likelihood of TVR tends to increase as the SRT dose increases (p = 0.06). Overall local control (LC) rate was 100 %. No ≥ grade 3 acute or late toxicities were observed.

CONCLUSION

While SRT demonstrates an excellent LC rate for H&N paragangliomas, it's important to note that the response to treatment may require time. TVR may last beyond the initial year of treatment in a substantial proportion of patients.

Translation, Cross-Cultural Adaptation, and Psychometric Validation of the Turkish Version of the "Expanded Prostate Cancer Index Composite (EPIC)" in Prostate Cancer Patients

PURPOSE

The Expanded Prostate Cancer Index Composite (EPIC) is a symptom scale that measures health-related quality of life (HRQoL) in prostate cancer (PCa) patients. This scale is translated into different languages and used in daily practice. This study aimed to translate the EPIC scale into Turkish and provide Turkish validation by conducting validity and reliability analyses.

METHODS

Patients with biopsy-proven PCa who received definitive or postoperative radiotherapy (RT) at our department were included. All participants were evaluated using the Turkish EPIC, The European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC-QLQ) C30, and EORTC-QLQ PR25 questionnaires at five different time points. First, the original English version of the EPIC was translated into Turkish, and then, two reliability and five validity analyses were performed.

RESULTS

One hundred-five patients were included in the study. In the reliability analyses, Cronbach's alpha values of the whole scale were measured at 0.866, and the main scales' Cronbach's alpha values were measured between 0.654 and 0.969. In the test-retest analysis, the correlation values of the main scales were measured between 0.413 and 0.861. The pilot study with 20 patients was completed, thus providing face validity. Sensitivity to change analysis, interscale correlation, criterion validity, and explanatory factor analyses were performed, and results proving the scale's validity were obtained in all analyses.

CONCLUSION

The Turkish EPIC scale is applicable for patients in the Turkish population diagnosed with PCa who received either definitive or postoperative RT.

Testicular metastasis in prostate cancer: A rare case of testicular metastasis diagnosed with 68Ga-PSMA and review of the literature

Objective:

Testicular metastasis in prostate cancer is a rare entity. We aimed to report the case where this rare condition was diagnosed with Gallium prostate-specific membrane antigen–positron emission tomography/computed tomography (68Ga-PSMA-PET/CT).

Subjects/patients and methods:

A 68-year-old male with a prostate adenocarcinoma presented with testicular metastasis. The patient was diagnosed with 68Ga-PSMA-PET/CT, and bilateral inguinal orchiectomy was performed. Herein, our case is presented, and a short review of the literature is carried out.

Conclusion:

68Ga-PSMA-PET/CT is an effective imaging method for detecting rare metastases.

Level of evidence:

4