Impact of pelvic nodal irradiation with intensity-modulated radiotherapy on treatment of prostate cancer

A contouring strategy and reference atlases for the full abdominopelvic bowel bag on treatment planning and cone beam computed tomography images

Purpose

Methods and Materials

Results

Conclusions

[Clinical to planning target volume margins in prostate cancer radiotherapy]

The knowledge of inter- and intrafraction motion and deformations of the intrapelvic target volumes (prostate, seminal vesicles, prostatectomy bed and lymph nodes) as well as the main organs at risk (bladder and rectum) allow to define rational clinical to planning target volume margins, depending on the different radiotherapy techniques and their uncertainties. In case of image-guided radiotherapy, prostate margins and seminal vesicles margins can be between 5 and 10mm. The margins around the prostatectomy bed vary from 10 to 15mm and those around the lymph node clinical target volume between 7 and 10mm. Stereotactic body radiotherapy allows lower margins, which are 3 to 5mm around the prostate. Image-guided and stereotactic body radiotherapy with adequate margins allow finally moderate or extreme hypofractionation.

Dosimetric consequences of prostate-based couch shifts on the precision of dose delivery during simultaneous IMRT irradiation of the prostate, seminal vesicles and pelvic lymph nodes

INTRODUCTION

To evaluate the impact interfraction prostate (CTV1) motion corrections on doses delivered to seminal vesicles (CTV2) and lymph nodes (CTV3), and to determine ideal planning target volume (PTV) margins for these targets with prostate-based position verification.

MATERIAL AND METHODS

Retrospective analysis based on 253 cone beam computed tomography (CBCT) studies of 28 patients. The isocenter-shift method was used to estimate the interfraction prostate and bony shift effects on the original plan coverage. Friedman's test was used to assess statistical significance between dose-volume histogram (DVH) parameters which were calculated for prostate-based sum plans, bony-based sum plans and original treatment plans. The van Herk formula was used to determine the set-up margin size for prostate-based verification.

RESULTS

The tracked shifts influenced the minimum, maximum and mean CTV2 and CTV3 doses, with a range differential of 0.17%-2.63% (prostate shifts) and 0.13%-1.92% (bony shifts) compared to the corresponding original parameters. Friedman's test revealed significant differences in the minimum doses to the CTV3 and maximum doses to both the CTV2 and CTV3. The calculated set-up margins of 1.22 cm (vertical), 0.19 cm (longitudinal) and 0.39 cm (lateral) should be added to CTV3 while performing prostate-based positioning.

CONCLUSION

To avoid geographical miss during simultaneous irradiation of independently moving targets (CTV1-3) appropriate margins should be used in accordance with the position verification method used. Based on our findings the following margin sizes should be used: 0.7 cm for the CTV1, 0.8-0.9 cm for the CTV2 , and asymmetric 1.0 cm (vertically) and 0.5 cm (other axes) for the CTV3.

Does Helical Tomotherapy Improve Dose Conformity and Normal Tissue Sparing Compared to Conventional IMRT? A Dosimetric Comparison in High Risk Prostate Cancer

The study was designed to compare Helical Tomotherapy (HT) based IMRT and conventional sliding window (SW IMRT) in patients with high risk prostate cancer. Complementary plans with HT and SWIMRT were compared using DVH parameters. The PTV Prostate was prescribed 74 Gy in 37 fractions and the nodal PTV received 55 Gy in 37 fractions by simultaneous integrated boost. Conformity Index, Homogeneity Index and dose-volume parameters were compared. The conformity index (CI) of HT (0.77, SD = 0.54) plans tended to be better (p = 0.069) compared to SWIMRT (0.70, SD = 0.01) for prostate PTV. CI for nodal PTV was similar. Helical tomotherapy plans were more homogeneous, with homogeneity index (HI) of 0.04 compared to 0.06 in SWIMRT (p = 0.018) for PTV prostate and HI of 0.06 and 0.15 (p = 0.025) for PTV nodes respectively. Median dose to bladder (p = 0.025) and rectum (p = 0.012) were less with HT. However, HT delivered a higher D10Gy and D1Gy to rectum and bladder overlap volumes as a consequence of achieving better homogeneity. Femoral heads were better spared with HT plans (p = 0.012). HT improves dose homogeneity, target coverage and conformity as compared to SWIMRT, with overall improvement in critical organ sparing.

Dose-volume relationships for acute bowel toxicity in patients treated with pelvic nodal irradiation for prostate cancer

PURPOSE

To find correlation between dose-volume histograms (DVHs) of the intestinal cavity (IC) and moderate-severe acute bowel toxicity in men with prostate cancer treated with pelvic nodal irradiation.

METHODS AND MATERIALS

The study group consisted of 191 patients with localized prostate cancer who underwent whole-pelvis radiotherapy with radical or adjuvant/salvage intent during January 2004 to November 2007. Complete planning/clinical data were available in 175 of these men, 91 of whom were treated with a conventional four-field technique (50.4 Gy, 1.8 Gy/fraction) and 84 of whom were treated with IMRT using conventional Linac (n = 26, 50.4 Gy, 1.8 Gy/fraction) or Helical TomoTherapy (n = 58, 50-54 Gy, 1.8-2 Gy/fraction). The IC outside the planning target volume (PTV) was contoured and the DVH for the first 6 weeks of treatment was recovered in all patients. The correlation between a number of clinical and DVH (V10-V55) variables and toxicity was investigated in univariate and multivariate analyses. The correlation between DVHs for the IC outside the PTV and DVHs for the whole IC was also assessed.

RESULTS

Twenty-two patients experienced toxicity (3/22 in the IMRT/tomotherapy group). Univariate analyses showed a significant correlation between V20-V50 and toxicity (p = 0.0002-0.001), with a higher predictive value observed for V40-V50. Previous prostatectomy (p = 0.066) and abdominal/pelvic surgery (p = 0.12) also correlated with toxicity. Multivariate analysis that included V45, abdominal/pelvic surgery, and prostatectomy showed that the most predictive parameters were V45 (p = 0.002) and abdominal/pelvic surgery (p = 0.05, HR = 2.4)

CONCLUSIONS

Our avoidance IMRT approach drastically reduces the incidence of acute bowel toxicity. V40-V50 of IC and, secondarily, previous abdominal/pelvic surgery were the main predictors of acute bowel toxicity.

Significant reduction of acute toxicity following pelvic irradiation with Helical Tomotherapy in patients with localized prostate cancer

PURPOSE

To assess and quantify the possible benefit deriving from IMRT with Helical Tomotherapy (HTT) delivery to the pelvic nodal area in patients with prostate cancer in terms of reduction of acute and late toxicities.

METHODS AND MATERIALS

Thirty-five patients candidate to radical or postoperative RT on whole pelvis (WPRT) were treated with HTT, while receiving a concomitant boost to the prostate or the prostatic bed (median 74.2 and 72 Gy, respectively) within a moderately hypofractionated (28-33 fractions; median HTT duration 44 days) regimen. Median and mean doses to whole pelvis were 52 and 54 Gy, respectively. One of the major goals of planning optimisation was to minimize the dose received by the intestinal cavity (IC) outside the nodal PTV.

RESULTS

HTT resulted to be very efficient in sparing the IC even at dose levels below 30-35 Gy and guaranteed a significant sparing of bladder and rectum even at intermediate-low doses (V20-V40). No acute Grade 3 RTOG toxicity was recorded. Eighteen G1 and two G2 GU acute toxicities, 13 G1 upper GI acute toxicities, 8 G1 and 1 G2 acute proctitis were observed; no patient experienced G2 upper GI toxicity. After a median FU of 11.5 months (>10 in 18 patients) one case of late G3 GU toxicity was reported in one post-prostatectomy treated patient; no G2 late rectal bleeding or other GI toxicity was recorded.

CONCLUSIONS

WPRT with HTT resulted in a very low incidence of acute Grade 2 and in the disappearance of acute Grade 3 toxicities.

Conformity index: a review

We present a critical analysis of the conformity indices described in the literature and an evaluation of their field of application. Three-dimensional conformal radiotherapy, with or without intensity modulation, is based on medical imaging techniques, three-dimensional dosimetry software, compression accessories, and verification procedures. It consists of delineating target volumes and critical healthy tissues to select the best combination of beams. This approach allows better adaptation of the isodose to the tumor volume, while limiting irradiation of healthy tissues. Tools must be developed to evaluate the quality of proposed treatment plans. Dosimetry software provides the dose distribution in each CT section and dose-volume histograms without really indicating the degree of conformity. The conformity index is a complementary tool that attributes a score to a treatment plan or that can compare several treatment plans for the same patient. The future of conformal index in everyday practice therefore remains unclear.