Dosimetric comparison of left-sided whole-breast irradiation with 3DCRT, forward-planned IMRT, inverse-planned IMRT, helical tomotherapy, and volumetric arc therapy.

PURPOSE: This study evaluated the dose distribution and homogeneity of four different types of intensity-modulated radiotherapy (IMRT) in comparison with standard wedged tangential-beam three-dimensional conformal radiotherapy (3DCRT) of the left breast in patients who had undergone lumpectomy. MATERIALS AND METHODS: Five radiotherapy treatment plans, including 3DCRT, forward-planned IMRT (for-IMRT), inverse IMRT (inv-IMRT), helical tomotherapy (HT) and volumetric-modulated arc therapy (VMAT), were created for 15 consecutive patients. RESULTS: All modalities presented similar target coverage. Target max doses were reduced with for-IMRT compared to 3DCRT, and these doses were further reduced with inv-IMRT and HT. HT resulted in the lowest max doses delivered to the heart, left anterior descending artery (LAD), and ipsilateral lung, but had higher mean, max, and low doses delivered to contralateral breast. HT resulted in increased low doses to a large volume of healthy tissue. Compared to other techniques, all inverse-planned modalities significantly improved conformity number; however, VMAT had worse homogeneity. The for-IMRT plan significantly lowered monitor unit (MU) compared to the inverse-planned techniques. CONCLUSION: All modalities evaluated provide adequate coverage of the whole breast. For-IMRT improves target homogeneity compared with 3DCRT, but to a lesser degree than the inverse-planned inv-IMRT and HT. HT decreases the ipsilateral OAR volumes receiving higher and mean doses with an increase in the volumes receiving low doses, which is known to lead to an increased rate of radiation-induced secondary malignancies.

Critical appraisal of RapidArc radiosurgery with flattening filter free photon beams for benign brain lesions in comparison to GammaKnife: a treatment planning study.

BACKGROUND: To evaluate the role of RapidArc (RA) for stereotactic radiosurgery (SRS) of benign brain lesions in comparison to GammaKnife (GK) based technique. METHODS: Twelve patients with vestibular schwannoma (VS, n = 6) or cavernous sinus meningioma (CSM, n = 6) were planned for both SRS using volumetric modulated arc therapy (VMAT) by RA. 104 MV flattening filter free photon beams with a maximum dose rate of 2400 MU/min were selected. Data were compared against plans optimised for GK. A single dose of 12.5 Gy was prescribed. The primary objective was to assess treatment plan quality. Secondary aim was to appraise treatment efficiency. RESULTS: For VS, comparing best GK vs. RA plans, homogeneity was 51.7 ± 3.5 vs. 6.4 ± 1.5%; Paddick conformity Index (PCI) resulted 0.81 ± 0.03 vs. 0.84 ± 0.04. Gradient index (PGI) was 2.7 ± 0.2 vs. 3.8 ± 0.6. Mean target dose was 17.1 ± 0.9 vs. 12.9 ± 0.1 Gy. For the brain stem, D(1cm3) was 5.1 ± 2.0 Gy vs 4.8 ± 1.6 Gy. For the ipsilateral cochlea, D(0.1cm3) was 1.7 ± 1.0 Gy vs. 1.8 ± 0.5 Gy. For CSM, homogeneity was 52.3 ± 2.4 vs. 12.4 ± 0.6; PCI: 0.86 ± 0.05 vs. 0.88 ± 0.05; PGI: 2.6 ± 0.1 vs. 3.8 ± 0.5; D(1cm3) to brain stem was 5.4 ± 2.8 Gy vs. 5.2 ± 2.8 Gy; D(0.1cm3) to ipsi-lateral optic nerve was 4.2 ± 2.1 vs. 2.1 ± 1.5 Gy; D(0.1cm3) to optic chiasm was 5.9 ± 3.1 vs. 4.5 ± 2.1 Gy. Treatment time was 53.7 ± 5.8 (64.9 ± 24.3) minutes for GK and 4.8 ± 1.3 (5.0 ± 0.7) minutes for RA for schwannomas (meningiomas). CONCLUSIONS: SRS with RA and FFF beams revealed to be adequate and comparable to GK in terms of target coverage, homogeneity, organs at risk sparing with some gain in terms of treatment efficiency.

Dosimetric performance of Strut-Adjusted Volume Implant: a new single-entry multicatheter breast brachytherapy applicator.

PURPOSE: To evaluate the dosimetric performance and clinical utility of the Strut-Adjusted Volume Implant (SAVI) (Cianna Medical, Aliso Viejo, CA) applicator when used as the sole method of radiation therapy for patients with early breast carcinoma. METHODS AND MATERIALS: The dosimetric performance of a Phase II clinical trial has been reported using the SAVI applicator for patients with early breast carcinoma. Cavity volume, planning target volume, dose homogeneity, and dose for organs at risk had been calculated. As a result, the D(90) and D(100) averages had been presented especially on the distances to the skin and the chest wall because these are critical parameters using the MammoSite (Cytyc Corp., Marlborough, MA) technique. RESULTS: D(90) and D(100) averages were 95.8% and 91.2%, respectively. The average dose homogeneity index was 55.9%. Average minimum distances to the skin and chest wall were 15.1 and 23.4mm, respectively. The average D(max) values to the skin and ribs were 249 and 199 cGy/fraction, respectively. The mean V(20) for the lungs was 17.9 cc. The average V(150) and V(200) were 30.80 and 14.91 cc, respectively. CONCLUSIONS: With this study, we have been able to optimize dose distribution to obtain clinically acceptable dose plans, while minimizing doses to healthy tissues. The dose sculpting versatility of SAVI in the clinical setting makes the SAVI applicator a useful addition to the tools available for accelerated partial breast irradiation.

Effect of bladder distension on dose distribution of intracavitary brachytherapy for cervical cancer: three-dimensional computed tomography plan evaluation.

PURPOSE: To quantify the effect of bladder volume on the dose distribution during intracavitary brachytherapy for cervical cancer. METHODS AND PATIENTS: The study was performed on 10 women with cervical cancer who underwent brachytherapy treatment. After insertion of the brachytherapy applicator, the patients were transferred to the computed tomography unit. Two sets of computed tomography slices were taken, including the pelvis, one with an empty bladder and one after the bladder was filled with saline. The target and critical organs were delineated by the radiation oncologist and checked by the expert radiologist. The radiotherapy plan was run on the Plato planning system, version 14.1, to determine the dose distributions, dose-volume histograms, and maximal dose points. The doses and organ volumes were compared with the Wilcoxon signed ranks test on a personal computer using the Statistical Package for Social Sciences, version 11.0, statistical program. RESULTS: No significant difference regarding the dose distribution and target volumes between an empty or full bladder was observed. Bladder fullness significantly affected the dose to the small intestine, rectum, and bladder. The median of maximal doses to the small intestine was significantly greater with an empty bladder (493 vs. 284 cGy). Although dosimetry revealed lower doses for larger volumes of bladder, the median maximal dose to the bladder was significantly greater with a full bladder (993 vs. 925 cGy). The rectal doses were also affected by bladder distension. The median maximal dose was significantly lower in the distended bladder (481vs. 628 cGy). CONCLUSIONS: Bladder fullness changed the dose distributions to the bladder, rectum, and small intestine. The clinical importance of these changes is not known and an increase in the use of three-dimensional brachytherapy planning will highlight the answer to this question.

Spinal implants and radiation therapy: the effect of various configurations of titanium implant systems in a single-level vertebral metastasis model.

BACKGROUND: The combination of surgery and radiation therapy is a common clinical practice in the treatment of spinal tumors. Although it is known that metallic implants disturb radiation therapy beams, it is not known what kind of dose distributions appear with spinal irradiation in the presence of a spinal implant. The aim of the present study was to investigate the effect of various spinal implant constructs on the dose of radiation delivered to the spinal canal in a single-level metastasis model. METHODS: We performed four spinal implant reconstructions on standard sawbones spine models: posterior instrumentation without anterior column reconstruction, posterior instrumentation with anterior column reconstruction with use of a titanium cage, anterior instrumentation with anterior column reconstruction with use of a titanium cage, and anterior instrumentation with anterior column reconstruction with use of chest tubes filled with bone cement. Irradiation with two different radiation therapy units (a cobalt-60 teletherapy unit and a linear accelerator) was performed twice for each model in a posterior-to-anterior direction, and thermoluminescent dosimeters were used to measure the dose changes in the anterior, middle, and posterior portions of the spinal canal. RESULTS: Compared with the sawbones-only model, the posterior instrumentation reconstructions resulted in a 5% to 7% decrease in the radiation dose delivered to the spinal canal with both radiation therapy units, whereas the anterior instrumentation reconstructions resulted in a 1% decrease in the dose delivered with the linear accelerator unit and a < or = 2% increase in the dose delivered with the cobalt-60 teletherapy unit. When thermoluminescent dosimeters in the middle of the spinal canal were evaluated individually, anterior instrumentation with anterior column reconstruction with use of bone cement-filled chest tubes resulted in a 5.5% increase in the radiation dose delivered with the cobalt-60 teletherapy unit, whereas all of the other instrumentation models resulted in a <1% disturbance in the radiation dose delivered with both radiation therapy units. CONCLUSIONS: The posterior instrumentation systems did not result in the delivery of an increased dose of radiation to the spinal cord, suggesting that current radiation therapy regimens may be performed without additional harm. The anterior instrumentation systems also appeared to be relatively safe when irradiation was performed with the linear accelerator unit. However, when irradiation was performed with use of the cobalt-60 teletherapy unit, there was an increase in the dose of radiation delivered to the spinal canal in the presence of the anterior instrumentation systems, particularly the anterior column reconstruction with use of bone cement-filled chest tubes. These dose-perturbation characteristics might be important to consider during the calculation of radiation therapy protocols for patients who are going to receive high doses or recurrent treatments that would reach the tolerance limits of the spinal cord.