3D-Conformal versus intensity-modulated postoperative radiotherapy of vaginal vault: A dosimetric comparison

A novel X-Ray and γ-Ray combination strategy for potential dose escalation in patients with locally advanced pancreatic cancer

BACKGROUND

Treatment of locally advanced pancreatic cancer (LAPC) has long been calling for advances in technology of radiotherapy. Patients who received radiotherapy still had high risks of local recurrence, while suffering from gastrointestinal side effects. Based on the inherent characteristics of the x-ray and γ-Ray radiation techniques, here we proposed and investigated an unexplored radiation therapy.

PURPOSE

To investigate the potential clinical benefit of a novel x-ray and γ-Ray combination radiation technique in patients with LAPC.

METHODS

Retrospective intensity-modulated radiotherapy (IMRT) treatment plans of 10 LAPC patients were randomly selected to compare with dual-modality plans. The prescribed dose to PGTV was 60.2 Gy. The PGTV dose was further escalated in dual-modality plan while maintaining clinically tolerable dose to organs at risk (OARs). Dosimetric comparisons were made and analyzed for three treatment plans (tomotherapy, standard dual-modality plan, escalated dual-modality plan) to assess the ability to increase dose to target volume while minimizing dose in adjacent OARs. Finally, radiobiological models were utilized for comparison.

RESULTS

All strategies resulted in dosimetrically acceptable plans. Dual-modality plans were present with similar conformity index (CI) and significantly lower gradient index (GI) compared with tomotherapy (3.64 ± 0.37 vs. 4.14 ± 0.61, p = 0.002; 3.64 ± 0.42 vs. 4.14 ± 0.61, p = 0.003). D_mean of PGTV (65.46 ± 3.13 vs. 61.56 ± 1.00, p = 0.009; 77.98 ± 5.86 vs. 61.56 ± 1.00, p < 0.001) and PCTV (55.04 ± 2.14 vs. 53.93 ± 1.67, p = 0.016; 58.24 ± 3.24 vs. 53.93 ± 1.67, p = 0.001) were significantly higher, while D_mean of the stomach was reduced in both dual-modality plans (17.98 ± 10.23 vs. 19.34 ± 9.75, p = 0.024; 17.62 ± 9.92 vs. 19.34 ± 9.75, p = 0.040). The lower V_30Gy in the liver (4.83 ± 5.87 vs. 6.23 ± 6.68, p = 0.015; 4.90 ± 5.93 vs. 6.23 ± 6.68, p = 0.016) and lower V_45Gy of the small intestine (3.35 ± 3.30 vs. 4.06 ± 3.87, p = 0.052) were found in dual-modality plans. Meanwhile, radiobiological models demonstrated higher probability of tumor control (29.27% ± 9.61% vs. 18.34% ± 4.70%, p < 0.001; 44.67% ± 18.16% vs. 18.34% ± 4.70%, p = 0.001) and lower probability of small intestine complication (2.16% ± 2.30% vs. 1.25% ± 2.72%, p = 0.048) in favor of dual-modality strategy.

CONCLUSIONS

A novel dual-modality strategy of x-ray and γ-Ray combination radiation appears reliable for target dose escalation and normal tissue dose reduction. This strategy might be beneficial for local tumor control and the protection of normal organs in patients with LAPC.

Dosimetric comparison of vaginal vault brachytherapy vs applicator-guided stereotactic body radiotherapy with volumetric modulated arc therapy and helical tomotherapy for endometrium cancer patients

We performed this dosimetric study to compare a nonstandard volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT) techniques with high-dose rate (HDR) brachytherapy (BRT) plan of vaginal vault in patients with postoperative endometrial cancer (EC). Twelve postoperative patients with early stage EC were included in this study. Three plans were performed for each patient; dosimetric and radiobiological comparisons were made using dose-volume histograms and equivalent dose for determining the planning target volume (PTV) coverages in brachytherapy and external beam radiotherapy, and organs-at-risk (OARs) doses between three different delivery techniques. All the plans achieved adequate dose coverage for PTV; however, the VMAT plan yielded better dose conformity, and the HT plan showed better homogeneity for target volume. With respect to the OARs, the bladder D_2cc was significantly lower in the BRT plan than in the VMAT and HT plans, with the highest bladder D_2cc value being observed in the HT plan. However, no difference was observed in the rectum D_2cc of the three plans. Other major advantages of the BRT plan over the VMAT and HT plans were the relatively lower body integral doses and femoral head doses as well as the fact that the integral doses were significantly lower in the BRT plan than in the VMAT and HT plans. This is the first dosimetric comparison of vaginal vault treatment for EC with BRT, VMAT, and HT plans. Our analyses showed the feasibility of stereotactic body radiotherapy technique as an alternative to HDR-BRT for postoperative management of EC patients.

Dosimetric and clinical toxicity comparison of critical organ preservation with three-dimensional conformal radiotherapy, intensity-modulated radiotherapy, and RapidArc for the treatment of locally advanced cancer of the pancreatic head

PURPOSE

We compared dosimetry and clinical toxicity for 3-dimensional conformal radiotherapy (3D-crt), intensity-modulated radiotherapy (imrt), and RapidArc (Varian Medical Systems, Palo Alto, CA, U.S.A.) in locally advanced pancreatic cancer (lapcc). We hypothesized that the technique with better sparing of organs at risk (oars) and better target dose distributions could lead to decreased clinical toxicity.

METHODS

The study analyzed 280 patients with lapcc who had undergone radiotherapy. The dosimetry comparison was performed using 20 of those patients. Dose-volume histograms for the target volume and the oars were compared. The clinical toxicity comparison used the 280 patients who received radiation with 3D-crt, imrt, or RapidArc.

RESULTS

Compared with 3D-crt, RapidArc and imrt both achieved a better conformal index, homogeneity index, V95%, and V110%. Compared with 3D-crt or imrt, RapidArc reduced the V10, V20, and mean dose to duodenum, the V20 of the right kidney, and the liver mean dose. Compared with 3D-crt, RapidArc reduced the V35, and V45 of duodenum, the mean dose to small bowel, and the V15 of right kidney. The incidences of grades 3 and 4 diarrhea (p = 0.037) and anorexia (p = 0.042) were lower with RapidArc than with 3D-crt, and the incidences of grades 3 and 4 diarrhea (p = 0.027) were lower with RapidArc than with imrt.

CONCLUSIONS

Compared with 3D-crt or imrt, RapidArc showed better sparing of oars, especially duodenum, small bowel, and right kidney. Also, fewer acute grades 3 and 4 gastrointestinal toxicities were seen with RapidArc than with 3D-crt or imrt. A technique with better sparing of oars and better target dose distributions could result in decreased clinical toxicities during radiation treatment for lapcc.

A comparison of liver protection among 3-D conformal radiotherapy, intensity-modulated radiotherapy and RapidArc for hepatocellular carcinoma

Purpose

The analysis was designed to compare dosimetric parameters among 3-D conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT) and RapidArc (RA) to identify which can achieve the lowest risk of radiation-induced liver disease (RILD) for hepatocellular carcinoma (HCC).

Methods

Twenty patients with HCC were enrolled in this study. Dosimetric values for 3DCRT, IMRT, and RA were calculated for total dose of 50 Gy/25f. The percentage of the normal liver volume receiving >40, >30, >20, >10, and >5 Gy (V₄₀, V₃₀, V₂₀, V₁₀ and V₅) were evaluated to determine liver toxicity. V₅, V₁₀, V₂₀, V₃₀ and D_mean of liver were compared as predicting parameters for RILD. Other parameters included the conformal index (CI), homogeneity index (HI), and hot spot (V_110%) for the planned target volume (PTV) as well as the monitor units (MUs) for plan efficiency, the mean dose (D_mean) for the organs at risk (OARs) and the maximal dose at 1% volume (D_1%) for the spinal cord.

Results

The D_mean of IMRT was higher than 3DCRT (p = 0.045). For V₅, there was a significant difference: RA > IMRT >3DCRT (p <0.05). 3DCRT had a lower V₁₀ and higher V₂₀, V₃₀ values for liver than RA (p <0.05). RA and IMRT achieved significantly better CI and lower V_110% values than 3DCRT (p <0.05). RA had better HI, lower MUs and shorter delivery time than 3DCRT or IMRT (p <0.05).

Conclusion

For right lobe tumors, RapidArc may have the lowest risk of RILD with the lowest V₂₀ and V₃₀ compared with 3DCRT or IMRT. For diameters of tumors >8 cm in our study, the value of D_mean for 3DCRT was lower than IMRT or RapidArc. This may indicate that 3DCRT is more suitable for larger tumors.

Reduced lung dose during radiotherapy for thoracic esophageal carcinoma: VMAT combined with active breathing control for moderate DIBH

Background

Lung radiation injury is a critical complication of radiotherapy (RT) for thoracic esophageal carcinoma (EC). Therefore, the goal of this study was to investigate the feasibility and dosimetric effects of reducing the lung tissue irradiation dose during RT for thoracic EC by applying volumetric modulated arc radiotherapy (VMAT) combined with active breathing control (ABC) for moderate deep inspiration breath-hold (mDIBH).

Methods

Fifteen patients with thoracic EC were randomly selected to undergo two series of computed tomography (CT) simulation scans with ABC used to achieve mDIBH (representing 80% of peak DIBH value) versus free breathing (FB). Gross tumor volumes were contoured on different CT images, and planning target volumes (PTVs) were obtained using different margins. For PTV_-FB, intensity-modulated radiotherapy (IMRT) was designed with seven fields, and VMAT included two whole arcs. For PTV_-DIBH, VMAT with three 135° arcs was applied, and the corresponding plans were named: IMRT_-FB, VMAT_-FB, and VMAT_-DIBH, respectively. Dosimetric differences between the different plans were compared.

Results

The heart volumes decreased by 19.85%, while total lung volume increased by 52.54% in mDIBH, compared to FB (p < 0.05). The mean conformality index values and homogeneity index values for VMAT_-DIBH (0.86, 1.07) were slightly worse than those for IMRT_-FB (0.90, 1.05) and VMAT_-FB (0.90, 1.06) (p > 0.05). Furthermore, compared to IMRT_-FB and VMAT_-FB, VMAT_-DIBH reduced the mean total lung dose by 18.64% and 17.84%, respectively (p < 0.05); moreover, the V₅, V₁₀, V₂₀, and V₃₀ values for IMRT_-FB and VMAT_-FB were reduced by 10.84% and 10.65% (p > 0.05), 12.5% and 20% (p < 0.05), 30.77% and 33.33% (p < 0.05), and 50.33% and 49.15% (p < 0.05), respectively. However, the heart dose-volume indices were similar between VMAT_-DIBH and VMAT_-FB which were lower than IMRT_-FB without being statistically significant (p > 0.05). The monitor units and treatment time of VMAT_-DIBH were also the lowest (p < 0.05).

Conclusions

VMAT combined with ABC to achieve mDIBH is a feasible approach for RT of thoracic EC. Furthermore, this method has the potential to effectively reduce lung dose in a shorter treatment time and with better targeting accuracy.

Dosimetric differences among volumetric modulated arc radiotherapy (RapidArc) plans based on different target volumes in radiotherapy of hepatocellular carcinoma

We investigated the dosimetric differences among volumetric-modulated arc radiotherapy (RapidArc, RA) plans designed for various target volumes in hepatocellular carcinoma (HCC). Ten HCC patients underwent 3D-CT scanning at free breathing (FB), 3D-CT at end inspiration hold (EIH) assisted by an Active Breathing Coordinator (ABC), and 4D-CT scanning. Gross tumor volumes (GTVs) were manually contoured on CT images. The individualized internal gross target volume (IGTV(1)) was obtained from 10 GTVs from 4D-CT images. Tumor individual margins were measured from GTV(FB) to IGTV(1). The IGTV(2) was obtained from GTV(FB) by applying individual margins. Four planning target volumes (PTV(1-4)) were obtained from IGTV(1), IGTV(2), GTV(FB), and GTV(EIH), respectively. An RA plan was designed for each of the PTVs (RA(1-4)). One 358° arc was used for PTVs(1-3), while three 135° arcs were used for PTV(4). It was found that PTV(2) and PTV(3) were larger than PTV(1) and PTV(4). The mean values of PTV(3)/PTV(1) and PTV(3)/PTV(4) were 2.5 and 1.9, respectively. The individual margins in the X, Y and Z axial directions varied greatly among these patients. There were no significant differences in the conformal index or homogeneity index among the four RA plans. RA(1) and RA(4) significantly reduced the radiation dose of normal liver tissue compared with RA(2) and RA(3) (P < 0.01). There were no significant differences between the radiation doses of the stomach and duodenum. RapidArc combined with 4D-CT or ABC technology is a promising method in radiotherapy of HCC, and accurately targeted the tumor volume while sparing more normal liver tissue.

RapidArc combined with the active breathing coordinator provides an effective and accurate approach for the radiotherapy of hepatocellular carcinoma

PURPOSE

The goal of this research was to investigate the feasibility of volumetric modulated arc therapy, RapidArc (RA), in association with the active breathing coordinator (ABC) for the treatment of hepatocellular carcinoma (HCC) with radiotherapy.

PATIENTS AND MATERIALS

A total of 12 patients with HCC, after receiving transcatheter arterial chemoembolization (TACE) treatment, underwent three-dimensional computer tomography (3D-CT) scanning associated with ABC using end inspiration hold (EIH), end expiration hold (EEH), and free breathing (FB) techniques. The three-dimensional conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT), and RA plans (three 135° arcs) were designed on different CT images, respectively. The liver volume, gross tumor volume (GTV), and planning target volume (PTV) of the three breath status and the dosimetric differences of the different plans were compared.

RESULTS

There were no significant differences in the volumes of live and GTV between the three breathing techniques (p > 0.05); the PTV in FB was greater than in the EEH and EIH (p < 0.05). The overall conformality index (CI) and homogeneity index (HI) for RA (CI 0.92, HI 0.90) were better than IMRT (CI 0.90, HI 0.89) and 3D-CRT (CI 0.70, HI 0.84) for the three breathing techniques (p< 0.05). The RA and IMRT significantly reduced the mean dose, V(20), V(30), and V(40) of normal liver compared to 3D-CRT, while the V(5) and V(10) in RA were higher than in IMRT. The mean values in mean dose, V(10), V(20), V(30), and V(40) of the normal liver were reduced from 13.12 Gy, 46%, 24%, 13%, and 8% in RA(FB) to 10.23 Gy, 35%, 16%, 8%, and 5% in RA(EEH) and 9.23 Gy, 32%, 16%, 8%, and 5% in RA(EIH ), respectively. In addition, the treatment time of RA was equal to 3D-CRT, which was significantly shorter than IMRT.

CONCLUSION

RA in conjunction with ABC for the treatment of HCC with radiotherapy can achieve better dose delivery and ensure the accuracy of the target volume, which spares more organs at risk, uses fewer monitor units, and shortens treatment time.

Statistical analysis of IMRT dosimetry quality assurance measurements for local delivery guideline

Purpose

To establish our institutional guideline for IMRT delivery, we statistically evaluated the results of dosimetry quality assurance (DQA) measurements and derived local confidence limits using the concept confidence limit of |mean|+1.96σ.

Materials and methods

From June 2006 to March 2009, 206 patients with head and neck cancer, prostate cancer, liver cancer, or brain tumor were treated using LINAC-based IMRT technique. In order to determine site specific DQA tolerances at a later stage, a hybrid plan with the same fluence maps as in the treatment plan was generated on CT images of a cylindrical phantom of acryl. Points of measurement using a 0.125 cm³ ion-chamber were typically located in the region of high and uniform doses. The planar dose distributions perpendicular to the central axis were measured by using a diode array in solid water with all fields delivered, and assessed using gamma criteria of 3%/3 mm. The mean values and standard deviations were used to develop the local confidence and tolerance limits. The dose differences and gamma pass rates for the different treatment sites were also evaluated in terms of total monitor uints (MU), MU/cGy, and the number of PTV's pieces.

Results

The mean values and standard deviations of ion-chamber dosimetry differences between calculated and measured doses were -1.6 ± 1.2% for H&N cancer, -0.4 ± 1.2% for prostate and abdominal cancer, and -0.6 ± 1.5% for brain tumor. Most of measured doses (92.2%) agreed with the calculated doses within a tolerance limit of ±3% recommended in the literature. However, we found some systematic under-dosage for all treatment sites. The percentage of points passing the gamma criteria, averaged over all treatment sites was 97.3 ± 3.7%. The gamma pass rate and the agreement of ion-chamber dosimetry generally decreased with increasing the number of PTV's pieces, the degree of modulation (MU/cGy), and the total MU beyond 700. Our local confidence limits were comparable to those of AAPM TG 119 and ESTRO guidelines that were provided as a practical baseline for center-to-center commissioning comparison. Thus, our institutional confidence and action limits for IMRT delivery were set into the same levels of those guidelines.

Discussion and Conclusions

The systematic under-dosage were corrected by tuning up the MLC-related factors (dosimetric gap and transmission) in treatment planning system (TPS) and further by incorporating the tongue-and groove effect into TPS. Institutions that have performed IMRT DQA measurements over a certain period of time need to analyze their accrued DQA data. We confirmed the overall integrity of our IMRT system and established the IMRT delivery guideline during this procedure. Dosimetric corrections for the treatment plans outside of the action level can be suggested only with such rigorous DQA and statistical analysis.