Using digitally reconstructed radiographs from MRI (MRI-DRR) to localize pelvic lymph nodes on 2D X-ray simulator-based brachytherapy treatment planning

Purpose: Many of the available brachytherapy treatment planning systems in developing countries are not equipped with CT [or MRI] simulator; therefore, 3D treatment planning cannot be performed. In this project a new procedure has been introduced for utilizing the 2D digitally reconstructed radiograph from MRI images in brachytherapy treatment planning. This procedure enables us to localize the tumor volume and delineate the extent of critical structures in vicinity of tumor volume. Methods: Pelvic lymph node chain position was delineated from transverse MRI images, and transferred into Digitally Reconstructed Radiograph [DRR] and then onto the X-ray images obtained from conventional simulator unit. These images were then imported to Brachytherapy treatment planning system to evaluate the dose to be applied to these organs in cervix Brachytherapy. The accuracy of the matching process was evaluated by phantom study, having known 3D geometric information and landmark assertion. Results: The statistical variations obtained from distance mismatch in phantom and patient studies were in the range of clinically applicable error of registration [< 2mm]. The results showed a large variation of the nodal dose when dose calculation is performed based on point B dose which is the geometrical reference point for calculating the dose to the pelvic lymphatic system. The result also shows that the dose to point B is usually underestimated to represent external iliac maximum dose, and overestimated for representation of external iliac minimum dose. Conclusion: The results indicated that the DRR images can produce comparable accuracies in tumor localization reported in 3D MRI or CT based treatment planning procedures. Therefore, this technique could be used as a feasible approach where a 3D treatment planning is not available

Chemoradiation in nasopharyngeal carcinoma: a 6-year experience in Tehran cancer institute

To determine the addition of value of neoadjuvant, concurrent and adjuvant chemotherapy to radiation in the treatment of nasopharyngeal carcinoma with regard to the overall survival [OS] and disease free survival [DPS] within a six year period in Tehran cancer institute. Files of all patients with nasopharyngeal carcinoma treated by radiotherapy with or without concurrent chemotherapy in a curative setting in Tehran cancer institute during the period of 1999-2005 were retrospectively reviewed. A total of 103 patients with nasopharyngeal carcinoma had been treated during the study period with radiotherapy or chemoradiotherapy in our institute. There were 29 [28.2%] females and 74 [71.8%] males. The median age at the time of radiotherapy was 47 years old [range 9-75 years]. The patients were followed 2 to 76 months with a median follow-up of 14 months. Time of first recurrence after treatment was 3-44 months with a median of 10 months. Survival in 2 groups of patients treated with radiotherapy alone or chemoradiation did not have a significant difference [P>0.1]. Two-year survival in patients treated with or without adjuvant chemotherapy and had local recurrence after treatment did not have significant difference [P>0.1]. Two-year survival in patients with or without local recurrence after treatment did not have significant difference [P>0.1]. A beneficial effect or a survival benefit of adjuvant/neoadjuvant chemotherapy and concurrent chemoradiation was not observed in Iranian patients

[Verification of the accuracy of the delivered dose in pelvic and breast cancer radiotherapy by in-vivo semi-conductor dosimetry]

Delivering maximum dose to tumor and minimum dose to normal tissues is the most important goal in radiotherapy. According to ICRU, the maximum acceptable uncertainty in the delivered dose compared to the prescribed dose should be lower than 5% and this is because of the relationship between absorbed dose, tumor control and normal tissue damage. Absorbed dose accuracy is investigated by an in vivo dosimetry method. In this paper, we compared absorbed dose in the tumors of the breast and pelvic region against the calculated dose. The amount of deviations and the factors that cause this deviation in dose delivery to patients and some methods for decreasing them were evaluated. The entrance and exit doses of 36 pelvi-region cancer patients and 38 breast cancer patients who were treated by cobalt-60 teletherapy were measured using p-type diodes. It should be noted that the transmission method was used to assess the dose at isocenter. Two ionization chambers [0.6cc and 0.3cc] were used for calibration and determination of the correction coefficients in water and slab phantoms. Deviations between calculated and measured doses of entrance, exit and midline point were calculated and the results were shown using histograms. The average and standard deviation for entrance, exit and midline points for pelvis cancer were assessed to be about 0.10%, -1.86% and -1.35% for mean deviation an d5.03%, 7.32% and 5.86% for standard deviation, respectively. The corresponding data for breast cancer were 0.78%, 5.29% and 3.59% for mean deviation and 5.97%, 10.23% and 9.86%, respectively. There was not significant difference between the calculated and measured doses [p>0.1], except exit dose in breast cancer [p<0.05]. The temperature and angle of incidence correction factors were neglected due to their less than 1% deviations. Some error sources are patient setup error, patient motion and dose calculation algorithm error [due to ignoring in homogeneity and patient curvature]. As no significant deviations were found in midline dose, the method used has an acceptable accuracy. In vivo dosminetry can perform a basic role in the quality control of radiotherapy departments