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Static versus dynamic intensity-modulated radiotherapy: Profile of integral dose in carcinoma of the nasopharynx.

Jothybasu KS, Bahl A, Subramani V, Rath GK, Sharma DN, Julka PK - J Med Phys (2009)

Bottom Line: Integral dose, volume receiving 5 Gy, number of monitor units (MU) is compared against DMLC.The mean difference in the integral dose with 5, 10 and 15 L compared to DMLC was -2.96% (P < 0.001), -2.67% (P = 0.016) and -0.39% (P = 0.430), respectively.However, the difference in low-dose volume (V5Gy) was statistically insignificant with mean difference of 0.60% (P = 0.23), 1.18% (P = 0.017) and 1.70% (P = 0.078), respectively for 5, 10 and 15 L compared to DMLC.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiation Oncology, All India Institute of Medical Sciences, New Delhi-110 029, India.

ABSTRACT
This study is aimed to evaluate the impact of static and dynamic intensity modulated radiotherapy (IMRT) delivery techniques planned with Eclipse TPS on the integral dose to the healthy normal tissue surrounding the tumor-bearing area and to the volume receiving doses < 5 Gy in patients with carcinoma nasopharynx treated with Simultaneous Integrated Boost IMRT (SIB-IMRT). Ten patients with carcinoma nasopharynx were chosen for this dosimetric study. IMRT plans were generated with 6X using dynamic multileaf collimator (DMLC) and static multileaf collimator (SMLC) with 5, 10 and 15 intensity levels (L). Integral dose, volume receiving 5 Gy, number of monitor units (MU) is compared against DMLC. The mean difference in the MU delivered per fraction between 5, 10 and 15 L SMLC and DMLC was -13.25% (P < 0.001, with paired t test), -11.82% (P < 0.001) and -10.81% (P < 0.001), respectively. The mean difference in the integral dose with 5, 10 and 15 L compared to DMLC was -2.96% (P < 0.001), -2.67% (P = 0.016) and -0.39% (P = 0.430), respectively. However, the difference in low-dose volume (V5Gy) was statistically insignificant with mean difference of 0.60% (P = 0.23), 1.18% (P = 0.017) and 1.70% (P = 0.078), respectively for 5, 10 and 15 L compared to DMLC. Our results show that while choosing the IMRT delivery technique using conventional MLC the concerns about integral dose and volume receiving very low doses such as 5 Gy can be ignored.

No MeSH data available.


Related in: MedlinePlus

(a) DVH for PTV in DMLC and SMLC, (b) DVH for Normal healthy tissue in DMLC and SMLC
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Figure 0003: (a) DVH for PTV in DMLC and SMLC, (b) DVH for Normal healthy tissue in DMLC and SMLC

Mentions: The dosimetric results were almost similar for the DMLC and SMLC plans with 10 and 15 L. The SMLC plan with 5 L slightly deviated from the prescribed dose-volume constraints. Figures 2 and 3 present DVH for a typical patient plan with regard to PTV, brainstem, spinal cord, parotid and NHT along with the dose statistics. The mean difference in the MU delivered per fraction between 5 L SMLC and DMLC delivery was −13.25% (P < 0.001, with paired t test).The difference with other intensity levels varied very less compared to 5 L, with a difference of −11.82% (P < 0.001) for 10 L and −10.81% (P < 0.001) for 15 L. The difference between the SMLC delivery with 10 and 15 L compared with 5 L was 1.65% (P < 0.001) and 2.81% (P < 0.001), which may not increase the transmission and leakage dose significantly. However, 5 L SMLC delivery slightly degraded the PTV dose uniformity (DVH for a sample patient is given in Figure 3a) while reducing the high dose volume in the spinal cord. All other critical structure doses were within the tolerance limits for all the delivery techniques. The number of MU required to delivering the same dose varied between DMLC and SMLC, but the difference between SMLC with different intensity levels varied less. The mean difference between the DMLC and 5 L SMLC was −13.25% (P < 0.001). The mean difference in the integral dose observed with 5, 10 and 15 L compared to DMLC was −2.96% (P < 0.001), −2.67% (P = 0.016) and −0.39% (P = 0.430), respectively. However, the difference in the low dose volume (V5 Gy) was statistically insignificant with a mean difference of 0.60% (P = 0.23), 1.18% (P = 0.017) and 1.70% (P = 0.078), respectively for 5, 10 and 15 L compared to DMLC; Table 2). The error bars are given in Figures 4 and 5 for V5, integral dose and monitoring units.


Static versus dynamic intensity-modulated radiotherapy: Profile of integral dose in carcinoma of the nasopharynx.

Jothybasu KS, Bahl A, Subramani V, Rath GK, Sharma DN, Julka PK - J Med Phys (2009)

(a) DVH for PTV in DMLC and SMLC, (b) DVH for Normal healthy tissue in DMLC and SMLC
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2805892&req=5

Figure 0003: (a) DVH for PTV in DMLC and SMLC, (b) DVH for Normal healthy tissue in DMLC and SMLC
Mentions: The dosimetric results were almost similar for the DMLC and SMLC plans with 10 and 15 L. The SMLC plan with 5 L slightly deviated from the prescribed dose-volume constraints. Figures 2 and 3 present DVH for a typical patient plan with regard to PTV, brainstem, spinal cord, parotid and NHT along with the dose statistics. The mean difference in the MU delivered per fraction between 5 L SMLC and DMLC delivery was −13.25% (P < 0.001, with paired t test).The difference with other intensity levels varied very less compared to 5 L, with a difference of −11.82% (P < 0.001) for 10 L and −10.81% (P < 0.001) for 15 L. The difference between the SMLC delivery with 10 and 15 L compared with 5 L was 1.65% (P < 0.001) and 2.81% (P < 0.001), which may not increase the transmission and leakage dose significantly. However, 5 L SMLC delivery slightly degraded the PTV dose uniformity (DVH for a sample patient is given in Figure 3a) while reducing the high dose volume in the spinal cord. All other critical structure doses were within the tolerance limits for all the delivery techniques. The number of MU required to delivering the same dose varied between DMLC and SMLC, but the difference between SMLC with different intensity levels varied less. The mean difference between the DMLC and 5 L SMLC was −13.25% (P < 0.001). The mean difference in the integral dose observed with 5, 10 and 15 L compared to DMLC was −2.96% (P < 0.001), −2.67% (P = 0.016) and −0.39% (P = 0.430), respectively. However, the difference in the low dose volume (V5 Gy) was statistically insignificant with a mean difference of 0.60% (P = 0.23), 1.18% (P = 0.017) and 1.70% (P = 0.078), respectively for 5, 10 and 15 L compared to DMLC; Table 2). The error bars are given in Figures 4 and 5 for V5, integral dose and monitoring units.

Bottom Line: Integral dose, volume receiving 5 Gy, number of monitor units (MU) is compared against DMLC.The mean difference in the integral dose with 5, 10 and 15 L compared to DMLC was -2.96% (P < 0.001), -2.67% (P = 0.016) and -0.39% (P = 0.430), respectively.However, the difference in low-dose volume (V5Gy) was statistically insignificant with mean difference of 0.60% (P = 0.23), 1.18% (P = 0.017) and 1.70% (P = 0.078), respectively for 5, 10 and 15 L compared to DMLC.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiation Oncology, All India Institute of Medical Sciences, New Delhi-110 029, India.

ABSTRACT
This study is aimed to evaluate the impact of static and dynamic intensity modulated radiotherapy (IMRT) delivery techniques planned with Eclipse TPS on the integral dose to the healthy normal tissue surrounding the tumor-bearing area and to the volume receiving doses < 5 Gy in patients with carcinoma nasopharynx treated with Simultaneous Integrated Boost IMRT (SIB-IMRT). Ten patients with carcinoma nasopharynx were chosen for this dosimetric study. IMRT plans were generated with 6X using dynamic multileaf collimator (DMLC) and static multileaf collimator (SMLC) with 5, 10 and 15 intensity levels (L). Integral dose, volume receiving 5 Gy, number of monitor units (MU) is compared against DMLC. The mean difference in the MU delivered per fraction between 5, 10 and 15 L SMLC and DMLC was -13.25% (P < 0.001, with paired t test), -11.82% (P < 0.001) and -10.81% (P < 0.001), respectively. The mean difference in the integral dose with 5, 10 and 15 L compared to DMLC was -2.96% (P < 0.001), -2.67% (P = 0.016) and -0.39% (P = 0.430), respectively. However, the difference in low-dose volume (V5Gy) was statistically insignificant with mean difference of 0.60% (P = 0.23), 1.18% (P = 0.017) and 1.70% (P = 0.078), respectively for 5, 10 and 15 L compared to DMLC. Our results show that while choosing the IMRT delivery technique using conventional MLC the concerns about integral dose and volume receiving very low doses such as 5 Gy can be ignored.

No MeSH data available.


Related in: MedlinePlus