Bilateral kidney preservation by volumetric-modulated arc therapy (RapidArc) compared to conventional radiation therapy (3D-CRT) in pancreatic and bile duct malignancies

Radiation therapy of pancreatic cancers

We present the update of the recommendations of the French society of oncological radiotherapy on radiotherapy of pancreatic tumors. Currently, the use of radiation therapy for patients with pancreatic cancer is subject to discussion. In the adjuvant setting, the standard treatment is six months of chemotherapy with 5-fluorouracile, irinotecan and oxaliplatin. Chemoradiation may improve the survival of patients with incompletely resected tumours (R1). This remains to be confirmed by a prospective trial. Neoadjuvant chemoradiation is a promising treatment especially for patients with borderline resectable tumours. For patients with locally advanced tumours, there is no standard. An induction chemotherapy followed by chemoradiation for non progressive patients reduces the rate of local relapse. Whereas in the first trials of chemoradiation large fields were used, the treated volumes have been reduced to improve tolerance. Tumour movements induced by breathing should be taken in account. Intensity modulated radiation therapy allows a reduction of doses to the organs at risk. Whereas widely used, this technique has poor evidence-based recommendation. Stereotactic body radiation therapy is also being studied, as a neoadjuvant or exclusive treatment.

Elective nodal irradiation with simultaneous integrated boost stereotactic body radiotherapy for pancreatic cancer: Analyses of planning feasibility and geometrically driven DVH prediction model

PURPOSE

We evaluate the feasibility of the elective nodal irradiation strategy in stereotactic body radiotherapy (SBRT) for pancreatic cancer.

METHODS

Three simultaneous integrated boost (SIB)-SBRT plans (Boost1, Boost2, and Boost3) were retrospectively generated for each of 20 different patients. Boost1 delivered 33 and 25 Gy to PTV1 and PTV2, respectively. Boost2 delivered 40, 33, and 25 Gy to boostCTV, PTV1, and PTV2, respectively. Boost3 delivered 33 and 25 Gy to PTV1 and PTV3, respectively. PTV1 covered the initial standard SBRT plan (InitPlan) gross tumor volume (GTV). PTV2 covered CTVgeom which was created by a 10-mm expansion (15 mm posterior) of GTV. PTV3 covered CTVprop which included elective nodal regions. The boostCTV included GTV as well as involved vasculature. The planning feasibility in each scenario and dose-volume histograms (DVHs) were analyzed and compared with the InitPlan (delivered 33 Gy only to PTV1) by paired t-test. Next, a novel DVH prediction model was developed and its performance was evaluated according to the prediction accuracy (AC) of planning violations. Then, the model was used to simulate the impacts of GTV-to-organs at risk (OAR) distance and gastrointestinal (GI) OAR volume variations on planning feasibility.

RESULTS

Significant dose increases were observed in GI-OARs in SIB-SBRT plans when compared with InitPlan. All dose constraints were met in 63% of cases in InitPlan, Boost1, and Boost2, whereas Boost3 developed DVH violations in all cases. Utilizing previous patient anatomy, the novel DVH prediction model achieved a high AC in the prediction of violations for GI-OARs; the positive predictive value, negative predictive value, and AC were 66%, 90%, and 84%, respectively. Experiments with the model demonstrated that the larger proximity volume of GI-OAR at the shorter distance substantially impacted on planning violations.

CONCLUSIONS

SIB-SBRT plan with geometrically defined prophylactic areas can be dosimetrically feasible, but including all nodal areas with 25 Gy in five fractions appears to be unrealistic.

Dosimetric analysis of stereotactic rotational versus static intensity-modulated radiation therapy for pancreatic cancer

PURPOSE

Stereotactic body radiation therapy is a promising treatment modality for locally advanced pancreatic cancer. To determine the optimal radiation treatment, we compared the plan characteristics of volumetric-modulated arc therapy and intensity-modulated radiation therapy when administered with stereotactic body radiation therapy to treat pancreatic cancer.

PATIENTS AND METHODS

Fifteen patients with locally advanced pancreatic cancer were treated by stereotactic body radiation therapy at a dose of 24-32Gy in four fractions with marker-guided gated volumetric-modulated arc therapy. Four dimensional-computed tomography scans were used to assess the target and surrounding normal organs. The same images, contours, and dose constraints were used for dual-arc volumetric-modulated arc therapy and 9-field intensity-modulated radiation therapy planning. Plans were compared using dosimetric parameters and treatment performance.

RESULTS

Volumetric-modulated arc therapy required significantly lower monitor units (1726 vs. 4188; P<0.001) and shorter treatment delivery time in comparison with intensity-modulated radiation therapy (22.5min vs. 52.4min; P<0.001). Regarding target volume coverage, both modalities demonstrated comparable results (V_95%, 99.3% vs. 99.4%; P=0.796). Both modalities satisfied the dosimetric determinants for duodenal toxicity and the maximum and mean doses administered to normal organ were also statistically similar.

CONCLUSION

In comparison with 9-field intensity-modulated radiation therapy, volumetric-modulated arc therapy significantly reduces the number of monitoring units and treatment delivery times while administering similar dosimetric quality. Based on these results, volumetric-modulated arc therapy might be an appropriate treatment for locally advanced pancreatic cancer when combined with stereotactic body radiation therapy.

Should functional renal scans be obtained prior to upper abdominal IMRT for pancreatic cancer?

BACKGROUND

Upper abdominal irradiation for pancreatic cancer is administered in close proximity to the radiation-sensitive kidneys. There is difficulty in defining dose-volume parameters to predict late renal toxicity after partial kidney irradiation. Less than 10% of the general population is estimated to have asymmetrical kidney function; however, there are no studies that examine this in patients with pancreatic cancer. The primary purpose of this study was to determine the prevalence of asymmetrical kidney function in patients with pancreatic cancer. A secondary aim was to determine if asymmetrical kidney function was associated with abnormal laboratory values or kidney size on computed tomography scans. Finally, we aimed to develop recommendations for when a functional renal scan in patients with pancreatic cancer should be ordered.

METHODS AND MATERIALS

We performed a retrospective review of patients with resectable, borderline resectable, and locally advanced pancreatic cancer who received abdominal radiation therapy and had preradiation functional renal scans between 2009 and 2015. Asymmetrical kidney function was defined as a difference between the 2 kidneys that was ≥60%/40% on a functional renal scan. Serum studies (blood urea nitrogen [BUN], creatinine [Cr], and glomerular filtration rate [GFR]) and abdominal computed tomography scans were routinely obtained before simulation.

RESULTS

Of the 204 patients examined, 23 (11.2%) had asymmetrical kidney function that was identified on preradiation functional renal scans. Elevated Cr or BUN, a GFR <60, or a medical history that suggested abnormal renal function were not significantly associated with asymmetrical kidney function. Only 6 of 23 patients (26%) with asymmetrical kidney function had a notable difference in kidney size.

CONCLUSIONS

In our series, approximately 11% of patients with pancreatic cancer have asymmetrical kidney function that was not identified by kidney size, serum BUN, Cr, GFR, or a significant medical history. These data suggest that in cases in which renal radiation doses exceed a V18 of 20% to 30% or there is concern about baseline renal function, a functional renal scan should be considered.

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.

Image-guided volumetric arc radiotherapy of pancreatic cancer with simultaneous integrated boost: Optimization strategies and dosimetric results

PURPOSE

To introduce volumetric modulated arc therapy treatments (VMAT) with simultaneous integrated boost (SIB) for pancreatic cancer and describe dosimetric results on a large patient series.

METHODS AND MATERIALS

45 patients with pancreatic malignancies were treated with 18 MV single-arc VMAT. Image guidance was performed with daily online kilo-volt cone-beam computed tomography (CBCT). The conformity index (CI) and homogeneity index (HI) to the target volumes, PTV45Gy and PTV54Gy, and dose-volume indices to OARs from the QUANTEC task group were reported. The risk of clinical nephritis was evaluated using normal tissue complication probability (NTCP). Treatments were verified in-phantom with the Delta4 system.

RESULTS

Average CI was 1.06 with 95% confidence intervals (95% CI) of 0.97-1.22 for PTV45Gy and 1.17 (0.66-1.61) for PTV54Gy. HI of PTV54Gy was 1.06 (1.04-1.10). OAR constraints were achieved in all patients, except for kidneys V12Gy of 48 (35.4-72.3)%. NTCP of the kidneys was 0.98 (0.6-1.7)%. Kidneys V12Gy and V20Gy were inversely related to PTV54Gy CI and maximum dose. All in-phantom tests had gamma pass rates exceeding 95% with global 3% dose difference and 3 mm distance to agreement. Patient shifts measured with CBCT had 95% CI of -0.8, +0.8 in the RL, -0.7, +0.8 in the SI, and -0.8, +0.7 cm in the AP directions.

CONCLUSIONS

Dosimetric results of VMAT were excellent on PTVs and organs at risk. The kidneys represent the dose-limiting organ at risk for this technique. NTCP indicates that this technique is safe from radiation-induced side effects to the kidneys.

Feasibility of accelerated partial breast irradiation with volumetric-modulated arc therapy in elderly and frail patients

Background

Accelerated partial breast irradiation (APBI) is an option for adjuvant radiotherapy according to ASTRO and ESTRO recommendations. Among the available techniques, volumetric-modulated arc therapy (VMAT) is attractive but has not been extensively studied for APBI. This study assessed its feasibility, tolerance and early oncological outcomes.

Methods

We analysed the data of nine patients (median age 74 years) with ten lesions (one bilateral cancer) treated from May 2011 to July 2012 with APBI using VMAT. The radiation oncologist delineated the surgical tumour bed, and added an 18 mm isotropic margin to obtain the planning target volume (PTV). The dose was 40 Gy prescribed in 4 Gy fractions given twice a day over five days. Patients were regularly followed for toxicities and oncological outcomes.

Results

Mean PTV was 100.0 cm³ and 95 % of the PTV received a mean dose of 99.7 % of the prescribed dose. Hot spots represented 0.3 % of the PTV. 6.2 %, 1.6 % and 0.3 % of the ipsilateral lung volume received 5 Gy (V_5Gy), 10 Gy (V_10Gy) and 20 Gy (V_20Gy), respectively. Regarding the contralateral lung, V_5Gy was 0.3 %, and V_10Gy and V_20Gy were nil. V_5Gy accounted for 3.1 % of the heart. An average 580 monitor units were delivered. No acute or late grade ≥ 2 toxicities were observed. With a median follow-up of 26 months, no relapses occurred.

Conclusion

In our study, VMAT allowed optimal dosimetry with consequential high therapeutic ratio in elderly and frail patients.

Ipsilateral kidney sparing in treatment of pancreatic malignancies using volumetric-modulated arc therapy avoidance sectors

Recent research has shown treating pancreatic cancer with volumetric-modulated arc therapy (VMAT) to be superior to either intensity-modulated radiation therapy or 3-dimensional conformal radiotherapy (3D-CRT), with respect to reducing normal tissue toxicity, monitor units, and treatment time. Furthermore, using avoidance sectors with RapidArc planning can further reduce normal tissue dose while maintaining target conformity. This study looks at the methods in reducing dose to the ipsilateral kidney, in pancreatic head cases, while observing dose received by other critical organs using avoidance sectors. Overall, 10 patients were retrospectively analyzed. Each patient had preoperative/unresectable pancreatic tumor and were selected based on the location of the right kidney being situated within the traditional 3D-CRT treatment field. The target planning target volume (286.97 ± 85.17 cm(3)) was prescribed to 50.4 Gy using avoidance sectors of 30°, 40°, and 50° and then compared with VMAT as well as 3D-CRT. Analysis of the data shows that the mean dose to the right kidney was reduced by 11.6%, 15.5%, and 21.9% for avoidance angles of 30°, 40°, and 50°, respectively, over VMAT. The mean dose to the total kidney also decreased by 6.5%, 8.5%, and 11.0% for the same increasing angles. Spinal cord maximum dose, however, increased as a function of angle by 3.7%, 4.8%, and 6.1% compared with VMAT. Employing avoidance sector angles as a complement to VMAT planning can significantly reduce high dose to the ipsilateral kidney while not greatly overdosing other critical organs.

Dosimetric impact of inter-observer variability for 3D conformal radiotherapy and volumetric modulated arc therapy: the rectal tumor target definition case

Background

To assess the dosimetric effect induced by inter-observer variability in target definition for 3D-conformal RT (3DCRT) and volumetric modulated arc therapy by RapidArc (RA) techniques for rectal cancer treatment.

Methods

Ten patients with rectal cancer subjected to neo-adjuvant RT were randomly selected from the internal database. Four radiation oncologists independently contoured the clinical target volume (CTV) in blind mode. Planning target volume (PTV) was defined as CTV + 7 mm in the three directions. Afterwards, shared guidelines between radiation oncologists were introduced to give general criteria for the contouring of rectal target and the four radiation oncologists defined new CTV following the guidelines. For each patient, six intersections (I) and unions (U) volumes were calculated coupling the contours of the various oncologists. This was repeated for the contours drawn after the guidelines. Agreement Index (AI = I/U) was calculated pre and post guidelines. Two RT plans (one with 3DCRT technique using 3–4 fields and one with RA using a single modulated arc) were optimized on each radiation oncologist’s PTV. For each plan the PTV volume receiving at least 95% of the prescribed dose (PTV V95%) was calculated for both target and non-target PTVs.

Results

The inter-operator AI pre-guidelines was 0.57 and was increased up to 0.69 post-guidelines. The maximum volume difference between the various CTV couples, drawn for each patient, passed from 380 ± 147 cm³ to 137 ± 83 cm³ after the introduction of guidelines. The mean percentage for the non-target PTV V95% was 93.7 ± 9.2% before and 96.6 ± 4.9%after the introduction of guidelines for the 3DCRT, for RA the increase was more relevant, passing from 86.5 ± 13.8% (pre) to 94.5 ± 7.5% (post). The OARs were maximally spared with VMAT technique while the variability between pre and post guidelines was not relevant in both techniques.

Conclusions

The contouring inter-observer variability has dosimetric effects in the PTV coverage. The introduction of guidelines increases the dosimetric consistency for both techniques, with greater improvements for RA technique.

Stereotactic body radiation therapy planning with duodenal sparing using volumetric-modulated arc therapy vs intensity-modulated radiation therapy in locally advanced pancreatic cancer: a dosimetric analysis

Stereotactic body radiation therapy (SBRT) achieves excellent local control for locally advanced pancreatic cancer (LAPC), but may increase late duodenal toxicity. Volumetric-modulated arc therapy (VMAT) delivers intensity-modulated radiation therapy (IMRT) with a rotating gantry rather than multiple fixed beams. This study dosimetrically evaluates the feasibility of implementing duodenal constraints for SBRT using VMAT vs IMRT. Non-duodenal sparing (NS) and duodenal-sparing (DS) VMAT and IMRT plans delivering 25Gy in 1 fraction were generated for 15 patients with LAPC. DS plans were constrained to duodenal Dmax of<30Gy at any point. VMAT used 1 360° coplanar arc with 4° spacing between control points, whereas IMRT used 9 coplanar beams with fixed gantry positions at 40° angles. Dosimetric parameters for target volumes and organs at risk were compared for DS planning vs NS planning and VMAT vs IMRT using paired-sample Wilcoxon signed rank tests. Both DS VMAT and DS IMRT achieved significantly reduced duodenal Dmean, Dmax, D1cc, D4%, and V20Gy compared with NS plans (all p≤0.002). DS constraints compromised target coverage for IMRT as demonstrated by reduced V95% (p = 0.01) and Dmean (p = 0.02), but not for VMAT. DS constraints resulted in increased dose to right kidney, spinal cord, stomach, and liver for VMAT. Direct comparison of DS VMAT and DS IMRT revealed that VMAT was superior in sparing the left kidney (p<0.001) and the spinal cord (p<0.001), whereas IMRT was superior in sparing the stomach (p = 0.05) and the liver (p = 0.003). DS VMAT required 21% fewer monitor units (p<0.001) and delivered treatment 2.4 minutes faster (p<0.001) than DS IMRT. Implementing DS constraints during SBRT planning for LAPC can significantly reduce duodenal point or volumetric dose parameters for both VMAT and IMRT. The primary consequence of implementing DS constraints for VMAT is increased dose to other organs at risk, whereas for IMRT it is compromised target coverage. These findings suggest clinical situations where each technique may be most useful if DS constraints are to be employed.